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Dirac point plays a crucial role in regulating electronic properties of topological semimetals. In two dimensions, the manipulation of Dirac points can spur a transition from Dirac semimetal through semi-Dirac phase to a gapped phase. Across such a so-called Lifshitz transition, we find that the quantum interference corrections to the conductivity $\ensuremath{\delta}{\ensuremath{\sigma}}_{xx}$ and $\ensuremath{\delta}{\ensuremath{\sigma}}_{yy}$ are always negative, giving rise to a weak localization behavior. The ratio $\ensuremath{\delta}{\ensuremath{\sigma}}_{xx}/\ensuremath{\delta}{\ensuremath{\sigma}}_{yy}$ undergoes a transition from linear to parabolic dependence on the merging parameter across the Lifshitz transition, which leads to a crossover of the temperature dependence of the inverse inelastic scattering time $1/{\ensuremath{\tau}}_{\ensuremath{\varepsilon}}$ from $\ensuremath{\sim}T$ to $\ensuremath{\sim}Tln({T}_{0}/T)$. This fingerprint behavior can be readily tested experimentally through merging Dirac points in two-dimensional lattices. This work presents an alternative perspective to understand weak localization through Lifshitz transition.

The complex behavior of magnetoconductance of Bi films grown epitaxially on Si(111) with a thickness of 20--100 bilayers (BL) was measured at $T$= 9 K in magnetic fields up to $B=4\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, oriented in-plane parallel and perpendicular to the electric dc current $I$. Contributions to magnetoconductance (MC) by diffuse scattering, by weak localization (WL) as well as by weak antilocalization (WAL) were identified. All these components to MC turned out to be isotropic in two dimensions, i.e., no dependence on angle between $B$ and $I$ within the surface plane was found. Only for $B\phantom{\rule{0.16em}{0ex}}\ensuremath{\perp}\phantom{\rule{0.16em}{0ex}}I$ an increase of MC was detected that is, to first approximation, $\ensuremath{\propto}{B}^{2}$. It is ascribed to ballistic scattering between the Rashba-split interfaces that allow Umklapp scattering without spin flip. While MC within the surface states, dominant at small thicknesses, $d$, shows negligible diffuse scattering under the chosen geometry, their quantum corrections are characterized by WAL with $\ensuremath{\alpha}=\ensuremath{-}0.3$ and a coupling strength that decays $\ensuremath{\propto}1/d$ with layer thickness. The admixing of quantized bulk states, which dominates MC above 50 BL, not only increases diffuse scattering, it introduces WL in combination with WAL. Presumably due to hybridization with the surface states, it also modifies strongly the WAL component for $dg60$ BL. Thus our findings suggest an intriguing interplay in magnetotransport between 2D and quantized 3D states at the Fermi surface of ultrathin bismuth quantum films and provide further deep insight into the electronic transport in quantized and partly spin split bands.

$\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Ru}}_{4}{\mathrm{O}}_{12}$ (CCRO) is considered a $d$-electron-based heavy-fermion metallic system with intriguing electronic properties. The magnetotransport measurements on metallic CCRO thin films reveal weak antilocalization (WAL) effects; however, it is not straightforward to infer whether the same originates from $e\text{\ensuremath{-}}e$ Coulomb interaction (EEI), spin-orbit interaction (SOI), or both present in CCRO. By evaluating quantum correction to sheet conductance for CCRO metallic thin films in the two-dimensional limit, it is observed that SOI gives rise to a dominant contribution to negative magnetoconductance (MC) in the weak-field regime. Based on weak localization (WL) and WAL analysis, SOI and inelastic scattering lengths (${l}_{so}$ and ${l}_{\ensuremath{\phi}}$) are obtained to be 30 and 74 nm, respectively, which indicates that WAL $({l}_{so}l{l}_{\ensuremath{\phi}})$ remains at play. The anisotropic effect of SOI is reflected in the field-direction-dependent in-plane and out-of-plane MC measurements. The presence of the EEI contribution is evidenced from (i) the linear increment (positive slope) of sheet conductance with $ln(T)$ in the quantum interference regime [only the WAL effect should otherwise show a negative slope with $ln(T)]$ and (ii) $ln(T)$ dependence of the Hall coefficient with a negative slope. Further, in the high-magnetic-field regime where WL or WAL is not valid, MC follows $ln(B)$-type behavior, indicating the presence of EEI. These findings have implications for the basic understanding of quantum magnetotransport properties in the presence of SOI and EEI in CCRO.

The electrical transport in the half-Heusler phases LuNiSb and YPdSb was measured in a temperature range 2--300 K. For both compounds, the electrical resistivity was found to decrease with increasing temperature, showing a linear-in-$T$ behavior over an extended temperature interval. In order to interpret the experimental data, a two-channel conductivity model was applied, which revealed that not only the semiconducting-like transport but also the metallic-like one exhibit negative temperature coefficients. The unusual behavior in the metallic channel was described within the Cote-Meisel formalism based on the diffraction model of strongly disordered metals. In addition, a weak localization scenario was considered including spin-orbit scattering and Coulomb interaction between conducting electrons. The electron-electron interaction was found most important at the lowest temperatures, where the semiconducting channel becomes ineffective, reminiscent of charge transport confined to a narrow yet finite-size metallic band located inside the semiconducting energy gap. The low-temperature resistivity of YPdSb appeared fully describable in terms of the Altshuler-Aronov quantum correction due to interacting electrons. In turn, the electronic transport in LuNiSb was found affected by the Kondo effect associated with a small amount of paramagnetic impurities present in the specimen investigated. The approach developed for LuNiSb and YPdSb can be applied to other half-Heusler compounds that exhibit atom disorder in their crystal structures.

Zr-Te compounds are an ideal platform to investigate novel electrical transport properties. Here we report the Kondo effect in single-crystalline ${\mathrm{ZrTe}}_{2}$. When $Tl8$ K, ${\mathrm{ZrTe}}_{2}$ exhibits a $\mathrm{log}T$ dependence of resistivity, which may derive from three different mechanisms, including electron-electron interaction, weak localization, and Kondo effect. By measuring transport properties with magnetic field along different directions, the former two mechanisms were excluded. Isotropic negative magnetoresistance was extracted by subtracting different quadratic background signals caused by Lorentz force, which reveals the existence of a weak Kondo effect in this material.

Because of the one-dimensional confinement of electron momentum in narrow semiconductor wires, spin relaxation is suppressed irrespective of the presence of spin-orbit (SO) interaction. In quantum transport, weak localization corrections to conductivity are reflected as suppressed spin relaxation, which makes quantification of the SO strength difficult because quantum correction theory requires weak antilocalization when evaluating SO coefficients. Narrow wires with strong SO interaction are potential platform for Majorana particles and parafermions for topological electronics and quantum computation, so revealing the SO strength in semiconductor wire structures is beneficial. Herein, we present quantification of the full SO coefficient under weak localization in InGaAs-based narrow wires. Using anisotropic weak localization observed under an in-plane external magnetic field with various orientations, one can ascertain the relative ratio between Rashba ($\ensuremath{\alpha}$) and linear Dresselhaus (${\ensuremath{\beta}}_{1}$) SO coefficients with no fitting. Furthermore, we find that widely tuning the potential profile of the quantum well through the top gate can expose a Rashba-predominant region in magnetoconductance, where the $\ensuremath{\alpha}$ value can be extracted reliably from two-dimensional quantum correction theory. Finally, we quantify the full SO coefficients including Rashba, linear Dresselhaus, and cubic Dresselhaus terms in the wire.

We report electron transport studies in an encapsulated few-layer $\mathrm{W}{\mathrm{Te}}_{2}$ at low temperatures and high magnetic fields. The magnetoconductance reveals a temperature-induced crossover between weak antilocalization and weak localization in the quantum diffusive regime. We show that the crossover clearly manifests coexistence and competition among several characteristic lengths, including the dephasing length, the spin-flip length, and the mean free path. In addition, low-temperature conductance increases logarithmically with the increase of temperature indicating an interplay of electron-electron interaction (EEI) and spin-orbit coupling (SOC). We demonstrate the existence and quantify the strengths of EEI and SOC which are considered to be responsible for gap opening in the quantum spin Hall state in $\mathrm{W}{\mathrm{Te}}_{2}$ at the monolayer limit.

Electron-electron interactions (EEIs) in 2D van der Waals (vdW) nanostructures is a topic of high current interest, with implications in both fundamental physics and nanoelectronics. In this Rapid Communication, we report the observation of a negative parabolic magnetoresistance (MR) in the multilayer 2D semiconductor InSe beyond the low-field weak localization/antilocalization regime, and provide evidence for the EEI origin of this MR behavior. Further, we analyze this negative parabolic MR and other observed quantum transport signatures of EEIs (temperature-dependent conductance and Hall coefficient) within the framework of Fermi-liquid theory and extract the gate voltage tunable Fermi-liquid parameter ${F}_{0}^{\ensuremath{\sigma}}$ which quantifies the electron spin-exchange interaction strength. This work opens up different directions for investigations of EEI effects in the electron transport of 2D vdW nanostructures.

We report an investigation of the combined structural and electronic properties of the bronze ${\mathrm{Na}}_{1.5}{({\mathrm{PO}}_{2})}_{4}{({\mathrm{WO}}_{3})}_{20}$. Its low-dimensional structure and possible large reconstruction of the Fermi surface due to charge density wave instability make this bulk material a natural superlattice with a reduced number of carriers and Fermi energy. Signatures of multilayered two-dimensional (2D) electron weak localization are consequently reported, with an enhanced influence of quantum oscillations. A crossover between these two antagonistic entities, previously observed only in genuine low-dimensional materials and devices, is shown to occur in a bulk crystal due to its hidden 2D nature.

We have studied the electrical transport in the charge-density wave material $1T\ensuremath{-}\mathrm{TiS}{\mathrm{e}}_{2}$ microflakes. In the low temperatures, the logarithmic temperature-dependent resistivity corrections were observed. In particular, the negative magnetoresistances in low magnetic fields were further measured and well described by the Hikami-Larkin-Nagaoka theory. All the experimental results demonstrate the weak localization effect in the $1T\ensuremath{-}\mathrm{TiS}{\mathrm{e}}_{2}$ microflakes. Furthermore, the power-law dependence of the extracted phase coherence length on temperature is $\ensuremath{\sim}{T}^{\ensuremath{-}0.6}$, indicating the presence of the two-dimensional electron-electron interaction in the $1T\ensuremath{-}\mathrm{TiS}{\mathrm{e}}_{2}$ microflakes.

We exploit the high-symmetry spin state obtained for equal Rashba and linear Dresselhaus interactions to derive a closed-form expression for the weak localization magnetoconductivity -- the paradigmatic signature of spin-orbit coupling in quantum transport. The small parameter of the theory is the deviation from the symmetry state introduced by the mismatch of the linear terms and by the cubic Dresselhaus term. In this regime, we perform quantum transport experiments in GaAs quantum wells. Top and back gates allow independent tuning of the Rashba and Dresselhaus terms in order to explore the broken-symmetry regime where the formula applies. We present a reliable two-step method to extract all parameters from fits to the new expression, obtaining excellent agreement with recent experiments. This provides experimental confirmation of the new theory, and advances spin-orbit coupling towards a powerful resource in emerging quantum technologies., 13 pages, 6 figures, supplementary included on arXiv

Three-dimensional (3D) Dirac and Weyl semimetals are quantum states that have emerged in physics recently. But their intrinsic transport properties are quite elusive because of either the coexistence of Schr\"odinger fermions or the deviation of linear dispersion at Fermi level in previously proposed Dirac and Weyl semimetals. Here, we provide the theoretical and experimental evidences of an intrinsic Dirac state in the quaternary chalcogenide $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$ that has bared linear dispersions in conduction bands. Scanning tunneling spectroscopy reveals the quadratic energy-dependent density of states within an extremely large energy range $(\ensuremath{\sim}400\phantom{\rule{0.16em}{0ex}}\mathrm{meV})$ on conduction bands of $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$, which is self-consistent with linear dispersion detected by angle-resolved photoemission spectroscopy. In electron-doped $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$, positive magnetoresistance at low magnetic field $B(l2.5\phantom{\rule{0.16em}{0ex}}\mathrm{T})$ and negative magnetoresistance under high $B$ are observed, which is attributed to the chiral anomaly effect. However, conventional negative magnetoresistance is observed in hole-doped $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$, which is attributed to weak localization broken by $B$. Remarkably, the carrier mobility has a ${10}^{5}$-fold decrease when the Fermi level is adjusted from conduction to valence bands. Our results suggest that $\mathrm{C}{\mathrm{u}}_{2}\mathrm{HgSnS}{\mathrm{e}}_{4}$ not only provides a playground for exploring intrinsic properties of 3D Dirac fermions but also is promising for developing high-speed, low-dissipation electronic devices.

Early experiments on alkali-doped graphene demonstrated that the dopant adatoms modify the conductivity of graphene significantly, as extra carriers enhance conductivity while Coulomb scattering off the adatoms suppresses it. However, conductivity probes the overall scattering rate, so a dominant channel associated with long-range Coulomb scattering will mask weaker short-range channels. We present weak localization measurements of epitaxial graphene with lithium adatoms that separately quantify intra- and intervalley scattering rates, then compare the measurements to tight-binding calculations of expected rates for this system. The intravalley rate is strongly enhanced by Li deposition, consistent with Coulomb scattering off the Li adatoms. A simultaneous enhancement of intervalley scattering is partially explained by extra carriers in the graphene interacting with residual disorder. But differences between measured and calculated rates at high Li coverage may indicate adatom-induced modifications to the band structure that go beyond the applied model. Similar adatom-induced modifications of the graphene bands have recently been observed in angle-resolved photoemission spectroscopy, but a full theoretical understanding of these effects is still in development.

Bilayer MoS2 is a centrosymmetric semiconductor with degenerate spin states in the six valleys at the corners of the Brillouin zone. It has been proposed that breaking of this inversion symmetry by an out-of-plane electric field breaks this degeneracy, allowing for spin and valley lifetimes to be manipulated electrically in bilayer MoS2 with an electric field. In this work, we report phase-coherent transport properties of double-gated mono-, bi-, and tri-layer MoS2. We observe a similar crossover from weak localization to weak anti-localization, from which we extract the spin relaxation time as a function of both electric field and temperature. We find that the spin relaxation time is inversely proportional to momentum relaxation time, indicating that D'yakonov-Perel mechanism is dominant in all devices despite its centrosymmetry. Further, we found no evidence of electric-field induced changes in spin-orbit coupling strength. This suggests that the interlayer coupling is sufficiently weak and that electron-doped dichalcogenide multilayers behave electrically as decoupled monolayers., Comment: 21 pages, 7 figures

The so called phase-coherence length ${l}_{\ensuremath{\varphi}}$ and its relation to the geometrical dimensions of a sample determine the electronic transport regime. Different approaches are established for extracting ${l}_{\ensuremath{\varphi}}$ from magnetotransport data of mesoscopic systems and need to be cross-checked by using experimental data on the same model system in order to ensure an overall consistent theoretical description. Suitable model systems for testing this consistency are single GaN:Ge nanowires. Their magnetoconductance at low temperatures exhibits universal conductance fluctuations as well as weak localization effects. We find that the values of ${l}_{\ensuremath{\varphi}}$ obtained from the established analysis of the magnitude of the conductance fluctuations rms($\mathrm{\ensuremath{\Delta}}G$) decrease with increasing measurement current, whereas the corresponding values of ${l}_{\ensuremath{\varphi}}$ determined by the analyses of the correlation field ${B}_{\text{C}}$ and the weak localization effect yield the same value for ${l}_{\ensuremath{\varphi}}$ independent of the measurement current used. We apply and modify the existing theoretical framework for bias-dependent differential conductance fluctuations, in order to explain the decrease of the conductance fluctuations rms($\mathrm{\ensuremath{\Delta}}G$) with increasing current density in our dc measurements. This leads to the same values of ${l}_{\ensuremath{\varphi}}$ independent of the analysis approach applied to the same set of data.

We investigate the magnetic, thermal, and electrical transport properties on the single-crystalline compound ${\mathrm{EuBiTe}}_{3}$. The magnetization measurements reveal the antiferromagnetic transition at 7 K along the $ab$ plane with a stable ${\mathrm{Eu}}^{2+}$ ion. A short-range ferromagnetic interaction along the $c$ axis is inferred from magnetic susceptibility and heat capacity measurements, which we associate with the presence of magnetic polarons. The magnetic polaron gives rise to unconventional negative magnetoresistance such as the weak antilocalization (WAL) and weak localization crossover. The WAL of the angle-resolved magnetoconductivity is well described by the Al'tshuler and Aronov model along the longitudinal magnetoconductivity. The magnetic polaron is widely observed above N\'eel temperature up to 50 K, which is supported by the Majumdar-Littlewood model in a scaled magnetoresistance. Even though ${\mathrm{EuBiTe}}_{3}$ should have one hole per formula unit, the electrical conductivity $\ensuremath{\sigma}(T)$ exhibits strong localized insulating behavior. The transport mechanism of $\ensuremath{\sigma}(T)$ is distinguished by two different mechanism: Efros-Shklovskii-type variable range hopping (VRH) transport in the high-temperature range ($T\phantom{\rule{0.16em}{0ex}}\ensuremath{\ge}\phantom{\rule{0.16em}{0ex}}52$ K) and three-dimensional VRH transport in the low-temperature regime ($T\ensuremath{\le}$ 50 K). The VRH transport suggests that the insulating behavior of $\ensuremath{\sigma}(T)$ on the compound can originate from a Mott-type insulator with strong Coulomb interaction.

Using the Feynman diagram techniques, we theoretically obtain the quantum conductivity correction for a two-dimensional pseudospin-1 electron system in the presence of long-range diagonal disorder. Theoretical results clearly reveal that the quantum correction depends on the sublattice correlation properties of disorder potential. The sublattice correlated disorder gives rise to normal weak localization, while the sublattice uncorrelated impurity potential leads to the absence of logarithmic term in quantum conductivity correction. Remarkably, those results cannot be understood by conventional symmetry classification. An additional symmetry operator involving internal sublattice degrees of freedom, analogous with the time reversal symmetry operator, enables us to clarify our findings from symmetry consideration.

We present measurements of weak localization on hexagonal boron nitride encapsulated bilayer ${\mathrm{MoS}}_{2}$. From the analysis we obtain information regarding the phase coherence and the spin diffusion of the electrons. We find that the encapsulation with boron nitride provides higher mobilities in the samples, and the phase coherence shows improvement, while the spin relaxation does not exhibit any significant enhancement compared to nonencapsulated ${\mathrm{MoS}}_{2}$. The spin relaxation time is in the order of a few picoseconds, indicating a fast intravalley spin-flip rate. Lastly, the spin-flip rate is found to be independent from electron density in the current range, which can be explained through counteracting spin-flip scattering processes based on electron-electron Coulomb scattering and extrinsic Bychkov-Rashba spin-orbit coupling.

First-principles transport modeling of disordered nanostructures commonly resorts to certain effective medium theory constructed with single-site methods. These methods are essentially approximations that account for the diffusive aspect of the problem, but missing the interference-induced long-range effects such as localization, which also plays an important role in the mesoscopic regime. In this work, we report a real-space implementation of the dual-fermion method in the nonequilibrium Keldysh formalism for correcting the transport coefficients given by single-site methods. A mapping between the Keldysh Green's function and its dual counterpart is established, and a diagrammatic perturbation technique is used in the dual space, whereby the long-range Cooperon is taken into account. When treated at the zeroth order, this theory reproduces the nonequilibrium coherent potential approximation. We require self-consistency on two aspects: the dual Green's function is solved consistently with its self-energy, and the medium Green's function must have its real-space diagonal equal to that of the local impurity. The method is applied to a quasi-one-dimensional hopping lattice which mimics a disordered transport structure. The numerically computed transmission coefficient shows quantitative agreement with the exact solution in the weak-localization regime, significantly correcting the single-site results. In addition, we find that the dual-fermion method leads to a power-law dependency of resistance on the channel length, instead of the classical Ohm's law, and the exponent is insensitive to disorder strengths. We also show that the negative magnetoresistance effect, a phenomenon associated with weak localization, is obtained by our numerical model when a perpendicular magnetic field is introduced. The method presented here paves the way for an ab initio atomistic implementation to simulate disordered quantum transport in real nanostructures.

The two-dimensional (2D) hole gas at the surface of transfer-doped diamond shows quantum-mechanical interference effects in magnetoresistance in the form of weak localization and weak antilocalization (WAL) at temperatures below about 5 K. Here we use the quenching of the WAL by an additional magnetic field applied parallel to the 2D plane to extract the magnitude of the in-plane $g$-factor of the holes and fluctuations in the well width as a function of carrier density. Carrier densities are varied between 1.71 and $4.35\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ by gating a Hall bar device with an ionic liquid. Over this range, calculated values of $|g|$ vary between 1.6 and 2.3 and the extracted well-width variation drops from 3 to 1.3 nm rms over the phase coherence length of 33 nm for a fixed geometrical surface roughness of about 1 nm as measured by atomic force microscopy. Possible mechanisms for the extracted variations in the presence of the ionic liquid are discussed.

The two-dimensional conducting interfaces in ${\mathrm{SrTiO}}_{3}$-based systems are known to show a variety of coexisting and competing phenomena in a complex phase space. Magnetoresistance measurements, which are typically used to extract information about the various interactions in these systems, must be interpreted with care, since multiple interactions can contribute to the resistivity in a given range of magnetic field and temperature. Here we review all the phenomena that can contribute to transport in ${\mathrm{SrTiO}}_{3}$-based conducting interfaces at low temperatures. We apply this understanding to the perpendicular magnetoresistance data of the high-mobility system of (111) oriented $({\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7})({\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}){\mathrm{O}}_{3}/\mathrm{STO}$ heterostructures, and find an excess negative magnetoresistance contribution which cannot be explained by weak localization alone. We argue that contributions from magnetic scattering as well as electron-electron interactions, combined with weak localization/antilocalization, can provide a possible explanation for the observed magnetoresistance.

Since the discovery of graphene, the localization physics has been studied extensively, and both weak antilocalization (WAL) and weak localization (WL) have been observed. A graphene superlattice (GSL) with multiple Dirac cones has emerged as a focus point in condensed-matter physics in recent years. However, the localization physics at multiple Dirac cones has not been studied to date. Here, we study the magnetoconductance in hexagonal boron nitride-graphene moir\'e-superlattice devices. Our magnetoconductance results show a clear signature of WL at the cloned Dirac cone (CDC) over one decade of variation of both carrier concentration and temperature in the two devices. In contrast, the WAL becomes stronger at the primary Dirac cone (PDC) with increasing temperature and lower carrier concentration in one device, in agreement with previous studies, whereas the other device shows stronger WAL for both lower temperature and carrier concentration. Since the observation of WAL at PDC is expected in a cleaner device due to the $\ensuremath{\pi}$ Berry phase, it is natural to ask whether the observation of WL at CDC in our GSL devices has any connection to Berry phase change or not. In order to address this issue we measure the Shubnikov--de Haas (SdH) resistance oscillations, which show a shift of the Berry phase by $\ensuremath{\pi}$ from PDC to CDC, indicating the role of the Berry phase for observing WL at CDC. We further corroborate our results with realistic electronic band structure calculations, which suggest a change in the Fermi surface topology from that with a small Fermi pocket enclosing a single PDC in each valley to a large Fermi surface shared by all the CDCs, in accordance with the change in oscillation frequency from PDC to CDC in the SdH measurements.

The persistent spin helix (PSH) state in III--V semiconductor quantum wells (QWs) is a promising candidate for spin-based applications because the PSH state realizes controllable spin orientation with long spin lifetime. Although the cubic Dresselhaus spin-orbit (SO) interaction is known for breaking the PSH state in both (001)-oriented and (110)-oriented QWs, it is not well understood how the distinct symmetry of cubic Dresselhaus terms ${\ensuremath{\beta}}_{3}$ between (001) and (110) QWs affects the robustness of the PSH state. Here we investigate robustness of the PSH state between (001) and (110) QWs under various strengths of cubic Dresselhaus SO interaction based on numerical Monte Carlo approach and magnetoconductance simulation, respectively, representing optical spin excitation/detection and weak localization/weak antilocalization in magnetotransport. For electron spins initialized along $z\ensuremath{\parallel}[001]$ in a (001) QW and $x\ensuremath{\parallel}[001]\phantom{\rule{4pt}{0ex}}\mathrm{and}\phantom{\rule{4pt}{0ex}}y\ensuremath{\parallel}[1\overline{1}0]$ in a (110) QW, where the spin distribution is developed with the helical spin mode, a (001) QW shows a more robust PSH state against the increase of ${\ensuremath{\beta}}_{3}$ than does a (110) QW. This phenomenon is contrary to numerically computed magnetoconductance, where weak localization is maintained on the variation of ${\ensuremath{\beta}}_{3}$ in a (110) QW, whereas weak antilocalization appears in a (001) QW. By deriving the spin lifetime of the PSH state in a (110) QW from a diffusion equation using a random-walk approach, we demonstrate that such a difference arises directly from the magnitude and orientation of third angular harmonics in cubic Dresselhaus fields for (001) and (110) QWs.

Indium selenide (InSe) has attracted tremendous research interest due to its high mobility and potential applications in next-generation electronics. However, the underlying transport mechanism of carriers in thin InSe at low temperatures remains unknown. Here we report the gate voltage and temperature-dependent magnetotransport properties of $\ensuremath{\gamma}$-InSe transistor devices with Hall mobility up to $2455\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at the temperature of 1.7 K. We observe a gate-tunable weak antilocalization behavior at lower magnetic field $B$, which shows a transition to weak localization at higher $B$ region. We find that the magnetotransport data agree well with the Hikami-Larkin-Nagaoka theory. The conductivity and temperature dependence of phase-coherence length reveal that the electron-electron ($e\text{\ensuremath{-}}e$) interactions are dominated dephasing mechanism for electronic transport in $\ensuremath{\gamma}$-InSe at low temperatures. The maximum phase-coherence length is found to be 320 nm at 1.7 K, larger than that of monolayer $\mathrm{Mo}{\mathrm{S}}_{2}$ and few-layer black phosphorus. These results enrich the fundamental understanding of electronic transport properties of InSe.

The out-of-plane magnetoresistance of a $\mathrm{LaAl}{\mathrm{O}}_{3}$/$\mathrm{SrTi}{\mathrm{O}}_{3}$ interface is commonly positive due to significant orbital effect. In this paper, a large negative magnetoresistance is observed at a $\mathrm{LaAl}{\mathrm{O}}_{3}$ and Fe-doped $\mathrm{SrTi}{\mathrm{O}}_{3}$ interface upon the application of an out-of-plane magnetic field. Such large negative magnetoresistance is attributed to enhanced two-dimensional weak localization and Kondo effect. We think that these two effects are mainly the consequences of intentional Fe dopants in the substrate, which introduce holes, disorders, and spin scattering centers into the electronically conducting interface, directly modifying the spin-orbit coupling, orbital effect, scale of electrons motion, and local magnetic moments at the $\mathrm{LaAl}{\mathrm{O}}_{3}$/$\mathrm{SrTi}{\mathrm{O}}_{3}$ interface. The ${\mathrm{LaAlO}}_{3}\text{/Fe-doped}\phantom{\rule{0.28em}{0ex}}{\mathrm{SrTiO}}_{3}$ interfacial system provides a prospective platform for studying quantum interference between strongly correlated electrons. The substrate doping method may facilitate the application of $\mathrm{LaAl}{\mathrm{O}}_{3}$/$\mathrm{SrTi}{\mathrm{O}}_{3}$ interfaces in versatile electronic devices.

Two-dimensional conducting interfaces in ${\mathrm{SrTiO}}_{3}$-based heterostructures display a variety of coexisting and competing physical phenomena, which can be tuned by the application of a gate voltage. (111) oriented heterostructures have recently gained attention due to the possibility of finding exotic physics in these systems due to their hexagonal surface crystal symmetry. In this work, we use magnetoresistance to study the evolution of spin-orbit interaction and magnetism in (111) oriented (${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7})({\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}){\mathrm{O}}_{3}/{\mathrm{SrTiO}}_{3}$. At more positive values of the gate voltage, which correspond to high carrier densities, we find that transport is multiband, and dominated by high-mobility carriers with a tendency toward weak localization. At more negative gate voltages, the carrier density is reduced, the high-mobility bands are depopulated, and weak antilocalization effects begin to dominate, indicating that spin-orbit interaction becomes stronger. At millikelvin temperatures, at gate voltages corresponding to the strong spin-orbit regime, we observe hysteresis in magnetoresistance, indicative of ferromagnetism in the system. Our results suggest that in the (111) (${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7})({\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}){\mathrm{O}}_{3}/{\mathrm{SrTiO}}_{3}$ system, low-mobility carriers that experience strong spin-orbit interactions participate in creating magnetic order in the system.

We demonstrate the inplane anisotropy of longitudinal thermal conductivities and the weak localization of magnons in a disordered screw-type spiral magnet on a square lattice. We consider a disordered spin system, described by a spin Hamiltonian for the antiferromagnetic Heisenberg interaction and the Dzyaloshinsky-Moriya interaction with the mean-field type potential of impurities. We derive longitudinal thermal conductivities for the disordered screw-type spiral magnet in the weak-localization regime by using the linear-response theory with the linear-spin-wave approximation and performing perturbation calculations. We show that the inplane longitudinal thermal conductivities are anisotropic due to the Dzyaloshinsky-Moriya interaction. This anisotropy may be useful for experimentally estimating the magnitude of a ratio of the Dzyaloshinsky-Moriya interaction to the Heisenberg interaction. We also show that the main correction term gives a logarithmic suppression with the length scale due to the critical back scattering. This suggests that the weak localization of magnons is ubiquitous for the disordered two-dimensional magnets having global time-reversal symmetry. We finally discuss several implications for further research., 16 pages, 4 figures; published version

We report an approach for examining electron properties using information about the shape and size of a nanostructure as a measurement reference. This approach quantifies the spin precession angles per unit length directly by considering the time-reversal interferences on chaotic return trajectories within mesoscopic ring arrays (MRAs). Experimentally, we fabricated MRAs using nanolithography in InGaAs quantum wells which had a gate-controllable spin-orbit interaction (SOI). As a result, we observed an Onsager symmetry related to relativistic magnetic fields, which provided us with indispensable information for the semiclassical billiard ball simulation. Our simulations, developed based on the real-space formalism of the weak localization/antilocalization effect including the degree of freedom for electronic spin, reproduced the experimental magnetoconductivity (MC) curves with high fidelity. The values of five distinct electron parameters (Fermi wavelength, spin precession angles per unit length for two different SOIs, impurity scattering length, and phase coherence length) were thereby extracted from a single MC curve. The methodology developed here is applicable to wide ranges of nanomaterials and devices, providing a diagnostic tool for exotic properties of two-dimensional electron systems.

The charge-density waves (CDW) in the framework Landau theory are visualized to manifest in complex $R\mathrm{Ni}{\mathrm{O}}_{3}$ ($R$ = rare-earth) nickelates in which the structure controls the incipient charge order in the weak localization limit. Any consequent effect demonstrating these nickelates in the rare category of CDW conductors with controlled charge-lattice interactions has been elusive so far. Employing terahertz time-domain spectroscopy along selective crystal axes, we present evidence of the CDW in epitaxial strain-modulated crystal structures of prototypical $\mathrm{NdNi}{\mathrm{O}}_{3}$. A finite peak structure at 5 meV in the terahertz conductivity displays all the characteristics of a CDW condensate in (110)- and (111)-oriented $\mathrm{NdNi}{\mathrm{O}}_{3}$ thin films. Contrasting charge dynamics of collective CDW mode and Drude conductivity emerging across dissimilar orientations helps disentangle charge ordering from the metal-insulator transition and establish a structure-property cause-effect relationship which may propose novel attributes in emerging oxide electronics.

Two-dimensional Lorentz gases formed by obstacles in the shape of circles, squares, and retroreflectors are reported to show a pronounced linear negative magnetoresistance at small magnetic fields. For circular obstacles at low number densities, our results agree with the predictions of a model based on classical retroreflection. In extension to the existing theoretical models, we find that the normalized magnetoresistance slope depends on the obstacle shape and increases as the number density of the obstacles is increased. The peaks are furthermore suppressed by in-plane magnetic fields as well as by elevated temperatures. These results suggest that classical retroreflection can form a significant contribution to the magnetoresistivity of two-dimensional Lorentz gases, while contributions from weak localization cannot be excluded, in particular for large obstacle densities.

Epitaxial $\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) films have been grown on $\mathrm{SrTi}{\mathrm{O}}_{3}$ (001) substrates via pulsed laser deposition. In a 22-nm-thick LSMO film with a low residual resistivity of ${\ensuremath{\rho}}_{0}\ensuremath{\approx}59\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$, we found a zero-field dip in the magnetoresistance (MR) below 10 K, manifesting the weak antilocalization (WAL) effect due to strong spin-orbit coupling (SOC). We have analyzed the MR data by including the D'yakonov-Perel' spin-relaxation mechanism in the WAL theory. We explain that the delocalized spin-down electron sub-band states play a crucial role for facilitating marked SOC in clean LSMO. Moreover, we find that the SOC strength and gate voltage tunability are similar to those in a two-dimensional electron gas at the $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ interface, indicating the presence of an internal electric field near the LSMO/$\mathrm{SrTi}{\mathrm{O}}_{3}$ interface. In a control measurement on a 5-nm-thick high resistivity $({\ensuremath{\rho}}_{0}\ensuremath{\approx}280\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})$ LSMO film, we observe only a small zero-field peak in MR from weak localization effect, indicating negligible SOC.

Transport measurements on the two dimensional electron system in Al2O3 SrTiO3 heterostructures indicate significant noncrystalline anisotropic behavior below T = 30 K. Lattice dislocations in SrTiO3 and interfacial steps are suggested to be the main sources for electronic anisotropy. Anisotropic defect scattering likewise alters magnetoresistance at low temperature remarkably and influences spin-orbit coupling significantly by the Elliot Yafet mechanism of spin relaxation resulting in anisotropic weak localization. Applying a magnetic field parallel to the interface results in an additional field induced anisotropy of the conductance, which can be attributed to Rashba spin orbit interaction. Compared to LaAlO3 SrTiO3, Rashba coupling seems to be reduced indicating a weaker polarity in Al2O3 SrTiO3 heterostructures.

Transition-metal dichalcogenides are unique semiconductors because of their exclusive coupling between the spin and the valley degrees of freedom. The spin flip simultaneously requires a large amount of the crystal momentum variation; hence most of the carrier scattering is expected to be the spin-conserving intravalley scattering. Analysis of the quantum interference effects on the magnetoconductivity in ${\mathrm{WSe}}_{2},{\mathrm{MoSe}}_{2}$, and ${\mathrm{MoS}}_{2}$ reveals that the spin-relaxation time is orders of magnitude longer than the carrier momentum scattering time, indicating that the valley-spin coupling robustly protects the spin polarization from carrier scatterings. In addition, the electron-spin-relaxation time of ${\mathrm{MoSe}}_{2}$ is found to be anomalously short compared to other members, which is likely the origin of the ultrafast valley scattering of excitons in ${\mathrm{MoSe}}_{2}$.

In this Rapid Communication we report a phenomenon in a disordered interacting electron system. The measurements of structural, magnetic, and transport properties of $\mathrm{FeA}{\mathrm{l}}_{2\ensuremath{-}x}\mathrm{G}{\mathrm{a}}_{x}$ ($0\ensuremath{\le}x\ensuremath{\le}0.5$) show that antiferromagnetic transition in these intermetallic compounds occurs concomitantly with a disorder-induced weak localization of electrons; the temperatures ${T}_{N}$ and ${T}_{m}$, at which antiferromagnetic transition and the weak localization respectively occur, closely track each other as the Ga concentration is varied. The antiferromagnetic transition is confirmed from the magnetic and specific heat measurements, and the occurrence of weak localization is confirmed from the temperature variation of resistivity and magnetoresistance measurements. With increasing Ga concentration, substitutional disorder in the system increases, and the consequent disorder-enhanced magnetic exchange interaction and disorder-induced fluctuations simultaneously drive antiferromagnetic transition and weak localization, respectively, to higher temperatures.

Electron transport in thin metallic wires and films is strongly influenced by the quality of their surface. Weak localization and magnetoconductivity are also sensitive to the electron scattering at the edges of the sample. We study weak localization effects in a two-dimensional electron gas patterned in the form of a narrow quasi-one-dimensional channel in transverse magnetic field. The most general boundary conditions interpolating between the limits of mirror and diffuse edge scattering are assumed. We calculate magnetoconductivity for an arbitrary width of the sample including the cases of diffusive and ballistic lateral transport as well as the crossover between them. We find that in a broad range of parameters, the electron mobility is limited by the boundary roughness while the magnetotransport is only weakly influenced by the quality of the edges. In addition, we calculate magnetoconductivity for a metallic cylinder in the transverse field and a quasi-two-dimensional metallic film in the parallel field., Comment: 18 pages, 11 figures

Individual dopants in semiconductors are attracting considerable attention due to the prospect of using them in a wide range of applications. In particular, phosphorus donors in silicon have attracted significant interest owing to their weak interaction with the host crystal. However, harnessing their attributes toward the construction of scalable circuitry will require low resistive interconnects at a comparable scale as the dopant atoms. In this Rapid Communication, the authors investigate the transition from quantum coherent to the semiclassical diffusive transport in a 4.6-nm quasi-one-dimensional Si:P metal wire. Analyzing the temperature dependence of universal conductance fluctuations (UCF) the authors show that electron transport evolves from a quantum coherent to a semiclassical regime at temperatures as low as ~4 K and confirm that concepts of UCF and weak localization remain valid in metallic conductors at the atomic-scale.

Spin-flip scattering of charge carriers in metals with magnetic defects leads to the low-temperature saturation of the decoherence time ${\ensuremath{\tau}}_{\ensuremath{\varphi}}$ of electrons at a value comparable to their spin relaxation time ${\ensuremath{\tau}}_{s}$. In two-dimensional (2D) conductors such a saturation can be lifted by an in-plane magnetic field ${B}_{\ensuremath{\parallel}}$, which polarizes spins of scatterers without affecting the orbital motion of free carriers. Here, we show that in 2D conductors with substantially different values of the $g$ factors of electrons (${g}_{e}$) and magnetic defects (${g}_{i}$), the decoherence time ${\ensuremath{\tau}}_{\ensuremath{\varphi}}({B}_{\ensuremath{\parallel}})$ (reflected by the curvature of magnetoconductance) displays an anomaly: It first gets shorter, decaying on the scale ${B}_{\ensuremath{\parallel}}\ensuremath{\sim}\ensuremath{\hbar}/|{g}_{i}\ensuremath{-}{g}_{e}|{\ensuremath{\mu}}_{B}{\ensuremath{\tau}}_{s}$, before becoming longer at higher values of ${B}_{\ensuremath{\parallel}}$.

The Hikami-Larkin-Nagaoka (HLN) formula [S. Hikami, A. I. Larkin, and Y. Nagaoka, Prog. Theor. Phys. 63, 707 (1980)] describes the quantum corrections to the magnetoconductivity of a quasi-2D electron gas (quasi-2DEG) with parabolic dispersion. It predicts a crossover from weak localization to antilocalization as a function of the strength of scattering off spin-orbit impurities. Here, we derive the conductivity correction for massless Dirac fermions in 3D topological insulators (TIs) in the presence of spin-orbit impurities. We show that this correction is always positive and therefore we predict weak antilocalization for every value of the spin-orbit disorder. Furthermore, the correction to the diffusion constant is surprisingly linear in the strength of the impurity spin-orbit. Our results call for a reinterpretation of experimental fits for the magnetoconductivity of 3D TIs, which have so far used the standard HLN formula.

The influence of GaN nanowires on the optical and electrical properties of graphene deposited on them was studied using Raman spectroscopy and microwave induced electron transport method. It was found that interaction with the nanowires induces spectral changes as well as large enhancement of Raman scattering intensity. Surprisingly, the smallest enhancement (about 30-fold) was observed for the defect induced D' process and the highest intensity increase (over 50-fold) was found for the 2D transition. The observed energy shifts of the G and 2D bands allowed to determine carrier concentration fluctuations induced by GaN nanowires. Comparison of Raman scattering spatial intensity maps and the images obtained using scanning electron microscope led to conclusion that vertically aligned GaN nanowires induce a homogenous strain, substantial spatial modulation of carrier concentration in graphene and unexpected homogenous distribution of defects created by interaction with nanowires. The analysis of the D and D' peak intensity ratio showed that interaction with nanowires also changes the probability of scattering on different types of defects. The Raman studies were correlated with weak localization effect measured using microwave induced contactless electron transport. Temperature dependence of weak localization signal showed electron-electron scattering as a main decoherence mechanism with additional, temperature independent scattering reducing coherence length. We attributed it to the interaction of electrons in graphene with charges present on the top of nanowires due to spontaneous and piezoelectric polarization of GaN. Thus, nanowires act as antennas and generate enhanced near field which can explain the observed large enhancement of Raman scattering intensity.

The two-dimensional electron system (2DES) in $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ (LAO/STO) heterostructures, showing superconductivity below 200 mK at ambient pressure, displays incipient localization under hydrostatic pressure $p$. Even small $p$ significantly affects the transport properties for $10\phantom{\rule{0.16em}{0ex}}\mathrm{K}lTl100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ where impurity scattering dominates. The distinct $T$ dependence of impurity scattering results in a minimum of the sheet resistance ${R}_{\mathrm{s}}(T)$, which has been often attributed to Kondo scattering. We show that the strong suppression of the dielectric permittivity $\ensuremath{\varepsilon}(p)$ of STO enhances impurity scattering via the loss of screening and leads to incipient localization of charge carriers with increasing hydrostatic pressure. For $Tl10\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ negative logarithmic corrections to the conductance are attributed to electron-electron interaction. Weak localization and antilocalization, if present, are dominated by the pivotal role of impurity scattering by, e.g., oxygen vacancies, for the transport properties of the 2DES in LAO/STO heterostructures. This interpretation is favorited by exploiting the strong dependence of the dielectric permittivity of STO on pressure. Measurements of the magnetoresistance corroborate this interpretation.

We study the quantum correction to conductivity on the surface of cubic topological Kondo insulators with multiple Dirac bands. We consider the model of time-reversal invariant disorder which induces the scattering of the electrons within the Dirac bands as well as between the bands. When only intraband scattering is present we find three long-range diffusion modes which lead to weak antilocalization correction to conductivity, which remains independent of the microscopic details such as Fermi velocities and relaxation times. Interband scattering gaps out two diffusion modes leaving only one long-range mode. We find that depending on the value of the phase coherence time, either three or only one long-range diffusion modes contribute to weak localization correction rendering the quantum correction to conductivity non-universal. We provide an interpretation for the results of the recent transport experiments on samarium hexaboride where weak antilocalization has been observed., Comment: 15 pages, 7 figures

The effect of disorder on magnonic transport in low-dimensional magnetic materials is studied in the framework of a classical spin model. Numerical investigations give insight into scattering properties of the systems and show the existence of Anderson localization in 1D and weak localization in 2D, potentially affecting the functionality of magnonic devices., 5 pages, 3 figures; v2: references added, published version

Enhancement of the spin-orbit coupling in graphene may lead to various topological phenomena and also find applications in spintronics. Adatom adsorption has been proposed as an effective way to achieve the goal. In particular, great hope has been held for indium in strengthening the spin-orbit coupling and realizing the quantum spin Hall effect. To search for evidence of the spin-orbit coupling in graphene adsorbed with indium adatoms, we carry out extensive transport measurements. It is found that indium adatoms dope graphene and introduce significant Coulomb scattering. No signature of the spin-orbit coupling is observed in the weak localization magnetoconductance and nonlocal spin Hall effect. Possible explanations are discussed.

The radial confining potential in a semiconductor nanowire plays a key role in determining its quantum transport properties. Previous reports have shown that an axial magnetic field induces flux-periodic conductance oscillations when the electronic states are confined to a shell. This effect is due to the coupling of orbital angular momentum to the magnetic flux. Here, we perform calculations of the energy level structure, and consequently the conductance, for more general cases ranging from a flat potential to strong surface band bending. The transverse states are not confined to a shell, but are distributed across the nanowire. It is found that, in general, the subband energy spectrum is aperiodic as a function of both gate voltage and magnetic field. In principle, this allows for precise identification of the occupied subbands from the magnetoconductance patterns of quasi-ballistic devices. The aperiodicity becomes more apparent as the potential flattens. A quantitative method is introduced for matching features in the conductance data to the subband structure resulting from a particular radial potential, where a functional form for the potential is used that depends on two free parameters. Finally, a short-channel InAs nanowire FET device is measured at low temperature in search of conductance features that reveal the subband structure. Features are identified and shown to be consistent with three specific subbands. The experiment is analyzed in the context of the weak localization regime, however, we find that the subband effects predicted for ballistic transport should remain visible when back scattering dominates over interband scattering, as is expected for this device., 8 pages, 3 figures; revised version (Nov. 2014)

Temperature dependent transport measurements on ultrathin antiferromagnetic Mn films reveal a heretofore unknown non-universal weak localization correction to the conductivity which extends to disorder strengths greater than 100 k$\Omega$ per square. The inelastic scattering of electrons off of gapped antiferromagnetic spin waves gives rise to an inelastic scattering length which is short enough to place the system in the 3d regime. The extracted fitting parameters provide estimates of the energy gap ($\Delta = 16$ K) and exchange energy ($\bar{J} = 320$ K).

Using field effect devices with side gates, we modulate the 2-dimensional electron gas hosted at the ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ interface to study the temperature and doping evolution of the magnetotransport. The analysis of the data reveals different transport regimes depending on the interplay between the different (elastic, inelastic, and spin-orbit) scattering times and their temperature dependencies. We find that the spin-orbit interaction strongly affects the low-temperature transport in the normal state in a very large region of the phase diagram, extending beyond the superconducting dome.

We put forward a theory of the weak localization in two dimensional graphene layers which explains experimentally observable transition between positive and negative magnetoresistance. Calculations are performed for the whole range of classically weak magnetic field with account on intervalley transitions. Contribution to the quantum correction which stems from closed trajectories with few scatterers is carefully taken into account. We show that intervalley transitions lead not only to the transition from weak antilocalization to the weak localization, but also to the non-monotonous dependence of the conductivity on the magnetic field.

We investigate ramifications of the persistent spin helix symmetry in two-dimensional hole gases in the conductance of disordered mesoscopic systems. To this end we extend previous models by going beyond the axial approximation for III-V semiconductors. For heavy-hole subbands we identify an exact spin-preserving symmetry analogous to the electronic case by analyzing the crossover from weak antilocalization to weak localization and spin transmission as a function of extrinsic spin-orbit interaction strength., Comment: 7 pages, 3 figures; reference added

Theory of weak localization is developed for electrons in semiconductor quantum wells grown along [110] and [111] crystallographic axes. Anomalous conductivity correction caused by weak localization is calculated for symmetrically doped quantum wells. The theory is valid for both ballistic and diffusion regimes of weak localization in the whole range of classically weak magnetic fields. We demonstrate that in the presence of bulk inversion asymmetry the magnetoresistance is negative: The linear in the electron momentum spin-orbit interaction has no effect on the conductivity while the cubic in momentum coupling suppresses weak localization without a change of the correction sign. Random positions of impurities in the doping layers in symmetrically doped quantum wells produce electric fields which result in position-dependent Rashba coupling. This random spin-orbit interaction leads to spin relaxation which changes the sign of the anomalous magnetoconductivity. The obtained expressions allow determination of electron spin relaxation times in (110) and (111) quantum wells from transport measurements., 10 pages, 4 figures

International audience; We present the magnetoresistance (MR) of highly doped monolayer graphene layers grown by chemical vapor deposition on 6H-SiC. The magnetotransport studies are performed on a large temperature range, from T=1.7 K up to room temperature. The MR exhibits a maximum in the temperature range 120–240 K. The maximum is observed at intermediate magnetic fields (B=2–6 T), in between the weak localization and the Shubnikov-de Haas regimes. It results from the competition of two mechanisms. First, the low-field magnetoresistance increases continuously with T and has a purely classical origin. This positive MR is induced by thermal averaging and finds its physical origin in the energy dependence of the mobility around the Fermi energy. Second, the high-field negative MR originates from the electron-electron interaction (EEI). The transition from the diffusive to the ballistic regime is observed. The amplitude of the EEI correction points towards the coexistence of both long- and short-range disorder in these samples.