Search

Gallium nitride nanowire and nanorod substrates are prospective platforms allowing to control the local strain distribution in graphene films on top of them, resulting in an induction of pseudomagnetic fields. AFM measurements performed in a HybriD mode complemented by SEM allow for a detailed visualization of the strain distribution on graphene surface. Graphene in direct contact with supporting regions is tensile strained, while graphene located in-between is characterized by lower strain. Characteristic tensile strained wrinkles also appear in the areas between the supporting regions. A positive correlation between strain gradient and distances between borders of supporting regions is observed. These results are confirmed by analysis of the Raman D’ band intensity, which is affected by an enhancement of intravalley scattering. Furthermore, scanning tunneling spectroscopy shows a local modification of the density of states near the graphene wrinkle and weak localization measurements indicate the enhancement of pseudomagnetic field-induced scattering. Therefore, we show that nanowire and nanorod substrates provide strain engineering and induction of pseudomagnetic fields in graphene. The control of graphene morphology by modification of distances between supporting regions is promising for both further fundamental research and the exploration of innovative ways to fabricate pseudomagnetic field-based devices like sensors or filters.

The magnetoresistance of bulk specimens of graphite nanoplatelets obtained by different methods is studied in magnetic fields up to 2.2 T. It has been established that magnetoresistance is negative for graphite nanoplatelets prepared by chemical treatment of source graphite with a solution of potassium permanganate in sulfuric acid. This negative magnetoresistance can be explained in terms of the model of charge carrier's weak localization in a system with imperfect structure. It has been established that the magnetoresistance is positive and independent of temperature for graphite nanoplatelets produced by sonication method. Moreover, magnetoresistance is linear relative to a magnetic field in fields above ∼0.7 T. It is shown that linear magnetoresistance can be explained in the terms of the Abrikosov's model of quantum linear magnetoresistance.

Two-dimensional layered carbon materials such as graphene constructed by sp2 hybridization have raised considerable interest due to their large, non-saturating magnetoresistance. As a new sp-sp2 hybridization structure layered carbon material, the transport performance of graphdiyne has been founded comparable with graphene, while the magnetoresistance remains to be clarified. In this work, we developed a modified non-transferred graphdiyne film synthesized method and studied its magnetoresistance effect. We observed an unexpected temperature-dependent crossover between positive and negative magnetoresistance in graphdiyne film. The film shows negative magnetoresistance at 5–19 K, the maximum intensity of the negative magnetoresistance was about 150% at 5 K under 3 T magnetic field. It presents positive magnetoresistance at 19–21 K under 3 T magnetic field, the magnetoresistance value reached 150% at 20 K. The mechanism of crossover positive and negative magnetoresistance originates from a superposition of the magnetic polaron model and weak localization.

Structural and magneto-electrical transport properties of double-layered La1.6-xPrxCa1.4-xBaxMn2O7 (x = 0.2 and 0.4) manganite compounds were studied. X-ray diffraction patterns refinement shows that the samples crystallize in a tetragonal I4/mmm structure, whereas a rhombohedral structure phase with $$R\stackrel{-}{3}c$$ space group is detected as a secondary phase. The electrical resistivity under 0 and 1 T exhibited a metal–insulator transition at TMI. It is found that the ρ(T) decreases with increasing Pr-Ba contents. Magnetoresistance (MR%) curves displayed a maximum value of ∼51.69% at 63 K for the x = 0.2 sample and decreases with increasing Pr-Ba concentrations to ∼33.44% at 64 K for x = 0.4 under 1 T. The obtained values of the temperature coefficient of resistivity for both samples have similar trend as TMI. Below $$T_{{MI}}$$ , $$~\rho \left( T \right) = \rho ~_{0} - \rho _{{0.5}} T^{{0.5}} + \rho _{2} T^{2} + \rho _{5} T^{5}$$ model fits well the resistivity curves which reflect a combination of the grain boundary effects, weak localization, electron–electron, and electron–phonon scattering to the electrical resistivity. Above TMI, the non-adiabatic small polaron hopping model describes the electrical resistivity behavior in $$T > ~\theta _{D} /2$$ region. The Mott’s 3D variable range hopping mechanism (3D-VRH) was found to be the most suitable mechanism for describing the high-temperature resistivity behavior between TMI and θD/2. The density of states near the Fermi level $$N(E_{F} )$$ , mean hopping distance, $$(R_{h} )$$ and mean hopping energy $$(E_{h} )$$ of the charge carriers have been calculated from the experimental curves using Mott’s 3D-VRH model. The experimental and fitting curves of the resistivity and the related results are discussed in detail.

Anderson localization (AL), a major topic in condensed matter physics, has been extensively studied. Since the discovery of graphene, its unique AL in Dirac materials, particularly weak localization (WL), has been studied intensively. Strong localization (SL) has also been investigated in graphene with intentionally introduced defects. The precise control of spacing/strength of defects using conventional methods is challenging; thus, He-ion-irradiation is a promising technology. However, magnetotransport, a sensitive tool to probe AL, has not yet been studied for He-ion-irradiated graphene. Herein, we systematically investigate the magnetotransport of He-ion-irradiated graphene. We observe negative magnetoresistance (MR) due to SL-dominated hopping transport. By systematically tuning the device parameters, negative MR at room temperature is first revealed for graphene field-effect transistor devices. Our study reveals carrier localization via searching in the multidimensional parameter space of Dirac materials, contributing to the development of fundamental AL physics and magnetoelectronic device applications.

Although the amorphous two-dimensional electron gas (a-2DEG) of oxides provides new opportunities to explore nanoelectronic as well as quantum devices, the intrinsic effect of rare earth (Re = La, Pr, Nd, Sm, Gd, and Tm) elements at ReAlO3/SrTiO3 heterointerfaces is still largely unknown and needs to be addressed systematically. Herein, we first propose that the ionization potential of Re elements is a critical factor for the 2DEG fabricated by chemical spin coating. Furthermore, the photoresponsive properties of heterointerfaces are investigated comprehensively with the ionization potential ranging from 35.79 to 41.69 eV. The results show that the sheet resistances significantly increase with increasing the ionization potential, and a resistance upturn phenomenon is observed at TmAlO3/SrTiO3 heterointerfaces, which can be attributed to the weak localization effect theoretically. The most important observation is the dramatic transition from negative (-178.3%, Re = La) to positive (+89.9%, Re = Gd) photoresponse at ReAlO3/SrTiO3 heterointerfaces under the irradiation of 405 nm light at 50 K. More remarkably, a unique recovery behavior of transient-persistent photoconductivity coexistence at low temperatures is discovered at the TmAlO3/SrTiO3 heterointerface. This work reveals an effective approach to tune the transport and photoresponsive properties by changing Re elements and paves the way for the application of all-oxide devices.

Charge transport and thermoelectric conversion mechanisms in doped semicrystalline polymer films are key issues in the field of wearable electronics, whereas the complex film structure consisting of crystalline domains and non-crystalline boundaries prevents sufficient understanding of them. In this study, we fully clarify the roles of the domains and the boundaries in a typical semicrystalline polymer on macroscopic charge transport under continuous electrochemical doping. In the crystalline domains, a multi-step transformation of the transport properties from effectively metallic behavior to weak localization (WL) to variable-range hopping (VRH) is found with decreasing temperature and doping level. On the other hand, at the domain boundaries, the effectively metallic conduction changes directly to VRH. Based on these results, the extremely complicated phase diagram, including the coexistence of the WL and VRH processes, is well explained. The proposed transport mechanism further explains the thermoelectric properties of the film. Polymer films are flexible, conductive materials with an expected application to a range of electronic devices, but the complexity of the underlying transport mechanisms inhibit improvements in performance. Here, the authors investigate the transport properties of doped semicrystalline polymer films and determine the role of crystalline domains and boundaries, finding evidence of weak localisation and variable range hopping, which vary with doping level.

On the basis of the theory of weak localization, taking into account the mechanism of spin-orbit scattering, the laws of the magnetoresistance of the PbSnAgTe films are considered. The dependences of the magnetoresistance of PbSnAgTe films on the composition and thickness in a magnetic field perpendicular to the film surface are investigated. It is shown that for polycrystalline films on mica-muscovite substrates, the time of spin-orbital interaction depends on the composition and may change the sign of the magnetoresistance. With increasing thickness, the intensity of spin-orbital scattering decreases due to decrease of the surface impact.

We report the deposition of epitaxial SrHfO3 thin films on a SrTiO3 (001) substrate in different substrate temperatures by using a pulsed laser deposition (PLD) method. We carried out X-ray diffraction (XRD), X-ray reflectivity (XRR), reciprocal space mapping (RSM), atomic force microscopy (AFM), resistivity, and Hall measurements to examine the crystallinity, morphology and electrical properties of these films. All films showed smooth and uniform morphology with small root mean square (RMS) roughness. While the SrHfO3 sample grown at 750 °C is metallic, the films deposited at 600 °C, 650 °C, and 700 °C show an upturn at low temperatures. The temperature dependence of the metallic parts was analyzed based on the parallel resistor model that includes resistivity saturation. On the other hand, the low-temperature upturn was found to be well described by a weak localization mechanism. We also observed the possible emergence of non-Fermi liquid behavior when the upturn disappeared. All SrHfO3 films have p-type charge carriers.

The unusual observation of the Kondo effect in the two-dimensional electron gas (2DEG) of magnetically undoped AlGaN/GaN heterostructures is reported. The temperature-dependent zero-field resistivity data exhibits an upturn below 120 K, while the standard low-temperature weak localization and then weak antilocalization behaviour is revealed at T → 0. Magnetic transport investigations of the system are performed in the temperature range of 0.1–300 K and at magnetic fields up to 8 T, applied perpendicularly to the 2DEG plane. The experimental data are analyzed in terms of the multichannel Kondo model for d0 magnetic materials and weak localization theory taking into account the spin-orbit interaction.

Lead halide perovskites have attracted increasing interest for their exciting potential in diverse optoelectronic devices. However, their charge transport properties remain elusive, plagued by the issues of excessive contact resistance and large hysteresis in ambient conditions. Here we report a van der Waals integration approach for creating high-performance contacts on monocrystalline halide perovskite thin films with minimum interfacial damage and an atomically clean interface. Compared to the deposited contacts, our van der Waals contacts exhibit two to three orders of magnitude lower contact resistance, enabling systematic transport studies in a wide temperature range. We report a Hall mobility exceeding 2,000 cm2 V–1 s–1 at around 80 K, an ultralow bimolecular recombination coefficient of 3.5 × 10–15 cm3 s–1 and a photocurrent gain >106 in the perovskite thin films. Furthermore, magnetotransport studies reveal a quantum-interference-induced weak localization behaviour with a phase coherence length up to 49 nm at 3.5 K. Our results lay the foundation for exploring new physics in this class of ‘soft-lattice’ materials. The realization of high-quality van der Waals contacts on monocrystalline halide perovskite thin films enables the probing of their long-range carrier and photocarrier transport properties.

The crystalline samples of La0.67Ca0.33Mn1-xNixO3 (x = 0, 0.05, and 0.1) manganites were prepared by conventional solid-state reaction method. The analysis of X-ray diffraction spectra revealed that all the prepared samples are single phased in nature and have acquired orthorhombic structure with space group Pbnm. Temperature-dependent dc resistivity measurements infer metallic nature of the samples in the lower temperature region (T > 50 K) where metal to insulator transition (TMI) occurs at temperature 238 K, 204 K, and 187 K for x = 0, 0.05, and 0.1, respectively. For the temperature below 50 K, a kind of transition from paramagnetic insulator to the ferromagnetic metallic phase was observed in all the materials. The application of magnetic field of 8 T indicates the shift of TMI toward the higher temperature region with high reduction in resistivity due to suppression of any thermal agitations present. The resistivity data analysis for conduction mechanism above 50 K infers that the grain/domain boundary scattering processes play a dominant role in the the metallic region. However, the analysis of the region below 50 K infers that weak localization effect is the responsible factor in conduction phenomena. Isothermal at 300 K for magnetoresistance study conveys that the pristine La0.67Ca0.33MnO3 manganite exhibits larger MR effect with rise in magnetic field compared to doped ones.

The microstructural, magnetic, and electrical properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCFO) nanofibers prepared by electrospinning and calcination were systematically investigated. It was found that the as-prepared nanofibers manifested ferromagnetism at low temperatures. Moreover, the resistance and magnetoresistance (MR) data conformed to the one-dimensional variable range hopping (1D VRH) model and revealed that LSCFO nanofibers had different electronic conduction behavior at different temperatures and magnetic fields. LSCFO nanofibers had small negative MR at low temperatures and large positive MR at high temperatures, and the transition temperature ranged between 240 and 260 K. The negative MR and the positive MR of LSCFO nanofibers manifested a fit to the 1D weak localization model and the 1D VRH model, respectively. Therefore, the proposed work can provide an important reference to the design of solid oxide fuel cells (SOFCs) based on the LSCFO cathode.

The resistivity and magnetoresistance of multi-walled carbon nanotubes with different degrees of structural perfection in the temperature interval from 4.2 K to 293 K and in the magnetic field up t...

The Bi2Se3 whisker temperature dependencies of resistance with palladium doping concentration of (1 ÷ 2)×1019 cm−3 were studied in the range of 1.5 ÷ 77 K. At the temperature of 5.3 K there was fou...

Using dc transport and wide-band spectroscopic ellipsometry techniques, we study localization effects in the disordered metallic Ta interlayer of different thickness in the multilayer films (MLFs) (Ta - FeNi)_N grown by rf sputtering deposition. In the grown MLFs, the FeNi layer was 0.52 nm thick, while the Ta layer thickness varied between 1.2 and 4.6 nm. The Ta layer dielectric function was extracted from the Drude-Lorentz simulation. The dc transport study of the MLFs implies non-metallic (dr/dT, 11 pages, 4 figures

Temperature-dependent electrical and magneto-transport measurements have been performed on devices composed of few layer (4L) graphene grown directly on SiO2/Si substrates using the CVD method. An intrinsic energy band-gap of 4.6 meV in 4L graphene is observed, which primarily dictates the current transport at T 50 K, which can be explained in the framework of the defect scattering of relativistic charge carriers. Magneto-transport measurements reveal a weak localization effect sustainable till T >200 K. The coexistence of phonon mediated carrier mobility and defect induced weak localization effects in measuring devices suggests low disorder and impurity scattering.

The discovery of magnetically doped topological insulators (TIs) provides a strong platform for investigating the correlation between long-range ferromagnetic/antiferromagnetic (FM/AFM) ordering and low temperature electron interference phenomena like weak anti-localization (WAL) or weak localization (WL). One such TI material Bi1−xSbx, which has recently been realised as a potential topological material for spintronics, has been studied in the present work. Influence of magnetic doping such as cobalt (Co) and manganese (Mn) in structural, morphological and magneto-transport properties on Bi0.94Sb0.06 nanoparticles has been investigated. The focus was on studying the correlation between magnetic ordering and WAL/WL. In undoped sample for temperatures up to 5K, field dependent magneto resistance (MR) shows a prominent WAL dip around zero field demonstrating the presence of surface states. In both the Co- and Mn-doped samples, the WAL feature is destroyed indicating the absence of time reversal symmetry (TRS) in the system on doping. Interestingly, in the case of 49% manganese (Mn) doping, a clear crossover from WAL to WL has been observed in the MR alongside magnetic ordering and is evident from magnetic force microscopy as well.

Solution-processed graphene inks that use ethyl cellulose as a polymer stabilizer are blade-coated into large-area thin films. Following blade-coating, the graphene thin films are cured to pyrolyze the cellulosic polymer, leaving behind an sp(2)-rich amorphous carbon residue that serves as a binder in addition to facilitating charge transport between graphene flakes. Systematic charge transport measurements, including temperature-dependent Hall effect and non-contact microwave resonant cavity characterization, reveal that the resulting electrically percolating graphene thin films possess high mobility (≈ 160 cm(2) V(−1) s(−1)), low energy gap, and thermally activated charge transport, which develop weak localization behavior at cryogenic temperatures.

Sb2-xCoxTe3 (x = 0, 0.05, 0.3) nanostructures have been synthesized using microwave-assisted solvothermal synthesis technique. The x = 0 and x = 0.05 samples show a semiconducting-like resistivity with an upturn in the low temperature (T

The use of graphene in electronics requires both an experimental study of the formation of high-quality low-resistance contacts and a deeper understanding of the mechanisms of electron carrier transport in graphene sheets and in the vicinity of metal / graphene interface. In this work, we studied the charge carrier transport in twisted CVD graphene, which was decorated with electrochemically deposited Co particles forming an ohmic contact with the graphene sheet. The temperature and magnetic field dependences of the sheet resistance R ‘ ( T , B ) in the pristine and decorated twisted graphene on silicon oxide substrate are compared. The coexistence of the negative (at magnetic fields with induction B below 1 T) and positive ( B higher than 1 T) contributions to the magnetoresistive effect in both types of samples is shown. The R ‘ ( T , B ) dependences are analyzed in fraimwork of the theory of two-dimensional interference quantum corrections to Drude conductivity, taking into account the competition of the contribution from the hopping conduction mechanism. It has been shown that in the studied temperatures range (2-300 K) and magnetic fields (up to 8 T), when describing the transport of charge carriers in the studied samples, it is necessary to take into account at least three interference contributions to the conductivity: from weak localization, intervalley scattering, and breaking of pseudospin chirality, as well as warping of graphene due to thermal fluctuations.

Discovery of ferromagnetism with simultaneous bandgap opening in graphene[ 1 ] provides an attractive platform towards multifunctional spintronic devices. However, device integration of graphene and reduced graphene oxide (rGO) is hindered by scalability and high temperature required for reducing GO. In this paper, we present a nonequilibrium approach for direct laser writing heavily reduced GO films by melting amorphous carbon in ambient conditions. Nanosecond laser irradiation melts carbon, which regrows into rGO in low undercooling conditions. These rGO films exhibit room-temperature ferromagnetism with a high saturation magnetization of 7.0 emu/g and 40 Oe coercivity. The intrinsic ferromagnetic ordering triggers a broad negative magnetoresistance (MR) cusp from 20 to 50 K. An anomalous crossover from weak localization (WL) to weak antilocalization (WAL) is observed below 5 K, suggesting a substantial enhancement in spin-orbit coupling strength, opening a new route to access topological states in rGO. The rGO films exhibit 12.6 cm2/Vs electron mobility with n-type carrier concentration of 1.2 × 1021/cc. Raman spectroscopy and temperature-dependent transport investigations in rGO suggest low-disorder, following 2D Mott variable range hopping (VRH) mechanism with a bandgap of ∼0.22 eV and 3 nm localization length. These findings open a definitive pathway for tuning electrical and magnetic properties in graphene-based materials with laser-writing.

Experimental studies of the temperature dependence of the resistance and magnetoresistance of the composite metal-carbon samples C(Co), which show the effect of weak localization, have been carried out. The magnetoresistance at a temperature T = 2.2 K is alternating, which is explained by the spin-orbit interaction. Analysis of the magnetoresistance curves made it possible to calculate the values of the parameters characterizing the phase loss time in inelastic scattering and the spin-orbit interaction time. For the parameter characterizing the elastic scattering time, the minimum value was estimated.

Silicon nanowires (SiNWs) are formed by metal-assisted chemical etching of crystalline p-type silicon, in a mixture of aqueous HF and AgNO3 chemical solutions. The magnetic field effects on the current of Ag/SiNWs/Si/Al structures have been studied. At room temperature, magnetoresistance (MR) measurements revealed positive and negative MR depending on the etching time and on the applied voltage. Huge positive MR of about 1200% has been observed at the low field. The negative MR is attributed to the weak localization effect, while the positive one is related to the ohmic regime, where holes control the current. The MR effect depends on the applied voltage and on the SiNWs length. The huge MR effect on SiNWs can be exploited in magnetic-field sensor devices.

A series of Cr-doped In2-xCrxO3 (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 104% at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s-d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In2O3-based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.

The measurements of the magnetoresistance for p-type poly-Si with concentration 2.4 × 1018 cm−3 were carried out in the low temperature range 4.2–20 K and in the magnetic field up to 14 T. The results showed the presence of a negative magnetoresistance in polycrystalline silicon films in SemOI-structures. The low-temperature transport of charge carriers in p-type polycrystalline silicon films was considered within the framework of hopping conductivity and can be described by the spin–orbital interaction in the theory of weak localization. The calculated values of the coherence phase length 3–4 nm and the spin–orbit coherence length 30–50 nm at low temperatures 4.2–30 K correlate with parameters of hopping conductance and grain size, respectively, which show a contribution of Rashba spin–orbit interaction with energy ΔSO = 1.6 meV in the conductance not only inside the grains, but also its surface and between grain boundaries of polycrystalline silicon in SemOI structures.

The spin density distribution of itinerant electrons, neg, and their effect on pairwise correlations of localized spins S(t2g) of Mn4+ ions in cubic Sr1 − xLaxMnO3 antiferromagnet (x = 0.02, TN = 230 K, G type magnetic structure) is studied experimentally by nuclear magnetic resonance on 17O nuclei. The regions with neg > x, in which the local spin susceptibility of pairs of Mn atoms follows the dependence χ ∼ (T − Θ)−1 with Θ = 20(5) K, indicating the growth of ferromagnetic spin correlations of neighboring magnetic ions in these domains, are found in the paramagnetic phase. The fraction of Mn-O-Mn bonds (neg > x) increases with the decrease in the temperature. The interpenetrating meshes of Mn-O-Mn bonds with different densities of itinerant eg electrons form an antiferromagnetic metal phase below TN. The role of weak localization effects is discussed as the main origin of the magnetic inhomogeneity of the antiferromagnetic metal phase in Sr0.98La0.02MnO3.

The addition of nitrogen as a dopant in monolayer graphene is a flexible approach to tune the electronic properties of graphene as required for applications. Here, we investigate the impact of the doping process that adds N dopants and defects on the key electronic properties, such as the mobility, the effective mass, the Berry phase, and the scattering times of the charge carriers. Measurements at low temperatures and magnetic fields up to 9 T show a decrease of the mobility with increasing defect density due to elastic, short-range scattering. At low magnetic fields weak localization indicates an inelastic contribution depending on both defects and dopants. Analysis of the effective mass shows that the N dopants decrease the slope of the linear bands, which are characteristic for the band structure of graphene around the Dirac point. The Berry phase, however, remains unaffected by the modifications induced through defects and dopants, showing that the overall band structure of the samples is still exhibiting the key properties as expected for Dirac fermions in graphene.

This paper reports a comprehensive study of electrical and thermal transport properties of a series of face-centered cubic structured high-entropy alloys by alloying Mn, Cr, and Pd elements in NiCo, NiFe, and NiCoFe alloys. X-ray diffraction revealed a single-phase Cu-type cubic structure, and scanning electron microscopy displayed elongated grained microstructures in all alloys. Like NiCo, NiFe, and NiCoFe alloys, the alloys containing Cr/Mn/Pd exhibit metallic behavior; however, their electrical transport properties, such as residual resistivity, residual resistivity ratio, and temperature coefficient of resistivity, vary significantly due to the increase of chemical disorder and defects. The analysis of resistivity of these alloys further showed different scattering mechanisms at low temperatures. Interestingly, the electrical resistivity of NiCoCr, NiCoFeCr, and NiCoFeMn alloys is nearly linear at low temperatures, most likely related to the Mott-Ioffe-Regel limit. Additionally, the NiCoMnCr and NiCoFeMnCr alloys exhibit a minimum in resistivity at low temperatures, which can be explained by the weak localization effect. The Seebeck coefficient measurements reveal that the charge carrier for thermoelectric transport in NiCo, NiFe, and NiCoFe is changed from electrons to holes with Mn alloying. In contrast, a sign reversal of the charge carriers observed in the Cr-containing alloys is connected to the compensation of electron and hole carriers. Furthermore, the NiCoCr, NiCoFeCr, NiCoMnCr, and NiCoFeMnCr alloys show a negative phonon drag effect at low temperatures due to electron-phonon interaction. The measured thermal conductivity behaves similarly in all alloys, except for a considerable reduction in magnitude in Cr/Mn/Pd-containing alloys. This is attributed to a significant decrease of electronic thermal conductivity due to an increased electron scattering by disorders and lattice distortions and a substantial modification of band structure. There is almost an equal contribution of electronic and lattice to the total thermal conductivity in Cr/Mn/Pd-containing alloys, suggesting a semimetallic nature. The temperature dependence of lattice thermal conductivity of these alloys is described by different phonon scattering mechanisms.

We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26K≤T≤300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities.

Disordered optical media are an emerging class of materials that can strongly scatter light. These materials are useful to investigate light transport phenomena and for applications in imaging, sensing and energy storage. While coherent light can be generated using such materials, its directional emission is typically hampered by their strong scattering nature. Here, the authors directly image Rayleigh scattering, photoluminescence and weakly localized Raman light from a random network of silicon nanowires via real‐space microscopy and Fourier imaging. Direct imaging enables us to gain insight on the light transport mechanisms in the random material, to visualize its weak localization length and to demonstrate out‐of‐plane beaming of the scattered coherent Raman light. The direct visualization of coherent light beaming in such random networks of silicon nanowires offers novel opportunities for fundamental studies of light propagation in disordered media. It also opens venues for the development of next generation optical devices based on disordered structures, such as sensors, light sources, and optical switches., Coherent light arising from complex optical media is typically nondirectional due to random scattering events. Here, beaming of directional coherent light from a network of random structures is demonstrated and visualized. Generating directional coherent light in random media is a significant step forward toward their integration in next generation optical devices.

A combination of out-of-plane and in-plane magnetoconductance (MC) study in topological insulators (TI) is often used as an experimental technique to probe weak anti-localization (WAL) response of the topological surface states (TSSs). However, in addition to the above WAL response, weak localization (WL) contribution from conducting bulk states are also known to coexist and contribute to the overall MC; a study that has so far received limited attention. In this article, we accurately extract the above WL contribution by systematically analyzing the temperature and magnetic field dependency of conductivity in Bi$_2$Se$_3$ films. For accurate analysis, we quantify the contribution of electron-electron interactions to the measured MC which is often ignored in recent WAL studies. Moreover, we show that the WAL effect arising from the TSSs with finite penetration depth, for out-of-plane and in-plane magnetic field can together explain the anisotropic magnetoconductance (AMC) and, thus, the investigated AMC study can serve as a useful technique to probe the parameters like phase coherence length and penetration depth that characterise the TSSs in 3D TIs. We also demonstrate that increase in bulk-disorder, achieved by growing the films on amorphous SiO$_2$ substrate rather than on crystalline Al$_2$O$_3$(0001), can lead to stronger decoupling between the top and bottom surface states of the film.

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.

Van der Waals heterostructures composed of multiple few layer crystals allow the engineering of novel materials with predefined properties. As an example, coupling graphene weakly to materials with large spin–orbit coupling (SOC) allows to engineer a sizeable SOC in graphene via proximity effects. The strength of the proximity effect depends on the overlap of the atomic orbitals, therefore, changing the interlayer distance via hydrostatic pressure can be utilized to enhance the interlayer coupling between the layers. In this work, we report measurements on a graphene/WSe2 heterostructure exposed to increasing hydrostatic pressure. A clear transition from weak localization to weak antilocalization is visible as the pressure increases, demonstrating the increase of induced SOC in graphene.

Despite the low energy topological surface bands attracting main interest gapped bulk bands of rhombohedral graphite are also peculiar. Here we report on three-dimensional transport properties bulk electrons in high quality thin film devices of rhombohedral graphite, a nodal line system in bulk limit. We show that bulk electrons show a thickness dependent cross-over from three dimensional weak anti-localization to weak localization as well as a quadratic negative magnetoresistance resembling chiral anomaly.

Spin-orbit coupling (SOC) can provide essential tools to manipulate electron spins in two-dimensional materials like graphene, which is of great interest for both fundamental physics and spintronics application. In this paper, we report the low-field magnetotransport of in situ hydrogenated graphene where hydrogen atoms are attached to the graphene surface in continuous low temperature and vacuum environment. Transition from weak localization to weak antilocalization with increasing hydrogen adatom density is observed, indicating enhancing Bychkov-Rashba-type SOC in a mirror symmetry broken system. From the low-temperature saturation of phase breaking scattering rate, the existence of spin-flip scattering is identified, which corroborates the existence of magnetic moments in hydrogenated graphene.

Understanding and tuning of metal–insulator transition (MIT) in oxide systems is an interesting and active research topics of condensed matter physics. We report thickness dependent MIT in Ga-doped ZnO (Ga:ZnO) thin films grown by pulsed laser deposition technique. From the electrical transport measurements, we find that while the thinnest film (6 nm) exhibits a resistivity of 0.05 Ω cm, lying in the insulating regime, the thickest (51 nm) has resistivity of 6.6 × 10−4 Ω cm which shows metallic type of conduction. Our analysis reveals that the Mott’s variable range hopping model governs the insulating behavior in the 6 nm film whereas the 2D weak localization (WL) phenomena is appropriate to explain the electron transport in the thicker Ga:ZnO films. Magnetoresistance study further confirms the presence of strong localization in 6 nm film while WL is observed in 20 nm and above thicker films. From the density functional calculations, it is found that due to surface reconstruction and Ga doping, strong crystalline disorder sets in very thin films to introduce localized states and thereby, restricts the donor electron mobility.

The electrical and magnetotransport properties of nanocrystalline tin dioxide films were studied in the temperature range of 4&ndash, 300 K and in magnetic fields up to 8 T. SnO2&minus, &delta, films were fabricated by reactive direct current (DC) magnetron sputtering of a tin target with following 2 stage temperature annealing of synthesized samples. The nanocrystalline rutile structure of films was confirmed by X-ray diffraction analysis. The temperature dependences of the resistance R(T) and the negative magnetoresistance (MR) were explained within the frame of a model, taking into account quantum corrections to the classical Drude conductivity. Extracted from the R(T) and R(B) dependences electron dephasing length values indicate the 3D character of the weak localization (WL) in our samples.

We report an investigation of Metal Insulator Transition (MIT) using conductivity and magnetoconductance (MC) measurements down to 0.3 K in Nd_{0.7}La_{0.3}NiO_{3} films grown on crystalline substrates of LaAlO_{3} (LAO), SrTiO_{3} (STO), and NdGaO_{3}(NGO) by pulsed laser deposition. The film grown on LAO experiences a compressive strain and shows metallic behavior with the onset of a weak resistivity upturn below 2 K which is linked to the onset of weak localization contribution. Films grown on STO and NGO show a crossover from a Positive Temperature Coefficient (PTC) resistance regime to Negative Temperature Coefficient (NTC) resistance regime at definite temperatures. We establish that a cross-over from PTC to NTC on cooling does not necessarily constitute a MIT because the extrapolated conductivity at zero temperature \sigma_{0} though small (, Comment: 24 pages

Transverse magnetoresistance in p-type conductivity Si whiskers with different impurity concentration that correspond to the dielectric side of metal-insulator transition were studied in magnetic fields 0–8 T at low temperatures 1.6 to 50 K. The presence of negative magnetoresistance in Si whiskers with concentration 2 × 1018 cm−3 was observed and associated with weak localization. The obtained parameters of phase coherence length lφ and spin-orbit coherence length lso comprise approximately 45 nm and 750 nm, respectively, at 4.2 K. The parameters obtained for Si whisker indicate the presence of hopping conductivity, orders of magnitude stronger than the parameters obtained for Si whisker with variable-range conductance, which indicates substantial impact of Ni impurities on the whisker magnetoresistance.

The anomalous magnetoresistance caused by the weak antilocalization (WAL) effects in 200-nm HgTe films is experimentally studied. This system is a high quality 3D topological insulator that has much stronger spatial separation of surface states compare to previously studied thinner HgTe structures. However, in contrast to that films, the system under study is characterized by a reduced strain resulting in an almost zero bulk energy gap. It has been shown that at all positions of the Fermi level the system exhibits a positive conductivity correction superimposed on classical parabolic magnetoresistance. Since high mobility of carriers, the analysis of the obtained results was performed using a ballistic WAL theory. The maximum of the WAL conductivity correction amplitude was found at a Fermi level position near the bulk energy gap indicating to full decoupling of the surface carriers in these conditions. The WAL amplitude monotonously decreases when the density of either bulk electrons or holes increases that is caused by the increasing coupling between surface and bulk carriers.

We investigate the ion gel gating of wide bandgap oxide, La-doped SrSnO3 films grown using radical-based molecular beam epitaxy. An applied positive bias resulted in a reversible electrostatic control of sheet resistance over 3 orders of magnitude at low temperature driving sample from Mott variable range hopping to a weakly localized transport. Analysis of low temperature transport behavior revealed electron-electron interaction and weak localization effects to be the dominant scattering mechanisms. A large voltage window (-4 V ≤ Vg ≤ +4 V) was obtained for reversible electrostatic doping of SrSnO3 films showing robustness of stannate with regards to redox chemistry with electrolyte gating irrespective of the bias type.

We report the crystal growth as well as transport properties of Co added Bi2Se3 (Co0.1Bi2Se3) single crystals. The values of the lattice parameters for pure and Co added sample were nearly the same. The Raman spectroscopy displayed slightly higher Raman shift of corresponding A1g1, Eg2, and A1g2 vibrational modes for Co0.1Bi2Se3, and the resistivity curves with and without applied magnetic field show a metallic behavior. Both the crystals were subjected to magneto-resistance (MR) measurements under applied fields of 14 T. The value of MR is found to decrease from about 380% (5 K, 14 T) for Bi2Se3 to 200% for Co0.1Bi2Se3. To elaborate the transport properties of pure and Co added Bi2Se3 crystals, the magneto-conductivity is fitted to the HLN (Hikami-Larkin-Nagaoka) equation, and it is found that the charge conduction is mainly dominated by surface-driven WAL (weak anti-localization) with negligible bulk WL (weak localization) contribution in both crystals alike. The MH curves of Co0.1Bi2Se3 crystal at different temperatures displayed a combination of both ferromagnetic and diamagnetic behavior. On the other hand, the electron paramagnetic resonance (EPR) revealed that pure Bi2Se3 is diamagnetic, whereas Co orders ferromagnetically with resonating field around 3422 Oe at room temperature. The calculated value of Lande “g” factor is around 2.04 ± 0.05. Summarily, the short letter discusses the interesting magneto-conductivity and complex magnetism of Co in Co0.1Bi2Se3.

Highly stable ultrathin films of large unsaturated room-temperature magnetoresistance (MR) are essential for the next-generation real-time magnetoelectric devices. A large-area, transfer-free, highly crystalline, and phase-engineered ultrathin film of Td-Mo0.27W0.71Te2.02 or 2H- & Td-Mo0.22W0.89Te1.89 on a hexagonal boron nitride (h-BN) substrate was synthesized using an atmospheric-pressure chemical vapor deposition (APCVD) method. The Td-Mo0.27W0.71Te2.02 with average mobility of 725 cm2 V−1 s−1 possesses non-saturating MR of 18% at 5 K and 11% at room temperature. Quantum correction to the magnetotransport study suggests the existence of a weak anti-localization effect dominated by the electron–electron interaction to render the non-saturating linear MR in a wide temperature range. Moreover, the spin–orbit interaction in Td-Mo0.27W0.71Te2.02 was found valid till an applied field of 0.05 T with an interaction length of 18 nm at 300 K. In this alloy system, the weak localization effect was evidenced unprecedentedly by the Te-deficient 2H- & Td-Mo0.22W0.89Te1.89 thin film with unusual co-existence of two crystal phases, which exhibit a suppressed MR caused by the recurring inelastic scattering with a reduced phase coherence length. This work explores the production of phase-engineered large-area Weyl semi-metallic 2D materials for the realization of magnetoelectrics in the near future.

Topological insulator bismuth selenide (Bi2Se3) thin films with a thickness of 6.0 quintuple layers (QL) to 23 QL are deposited using pulsed laser deposition (PLD). The arithmetical mean deviation of the roughness (Ra) of these films is less than 0.5 nm, and the root square mean deviation of the roughness (Rq) of these films is less than 0.6 nm. Two-dimensional localization and weak antilocalization are observed in the Bi2Se3 thin films approaching 6.0 nm, and the origin of weak localization should be a 2D electron gas resulting from the split bulk state. Localization introduced by electron–electron interaction (EEI) is revealed by the temperature dependence of the conductivity. The enhanced contribution of three-dimensional EEI and electron–phonon interaction in the electron dephasing process is found by increasing the thickness. Considering the advantage of stoichiometric transfer in PLD, it is believed that the high quality Bi2Se3 thin films might provide more paths for doping and multilayered devices.

We study theoretically weak localization of excitons in atomically-thin transition metal dichalcogenides. The constructive interference of excitonic de Broglie waves on the trajectories forming closed loops results in a decrease of the exciton diffusion coefficient. We calculate the interference contribution to the diffusion coefficient for the experimentally relevant situation of exciton scattering by acoustic phonons and static disorder. For the acoustic phonon scattering, the quantum interference becomes more and more important with increasing the temperature. Our estimates show that the quantum contribution to the diffusion coefficient is considerable for the state-of-the-art monolayer and bilayer transition metal dichalcogenides., Comment: 6 pages, 3 figures

Pulsed electron beam deposition (PED) was used to grow indium oxide thin films on c-cut sapphire single crystalline substrates between room temperature and 500 °C under oxygen gas. A slight difference in oxygen pressure during the PED growth (from 2 × 10−2 to 1.3 × 10−2 mbar) has strong effects on the electrical and optical film properties. The indium oxide thin films grown in these conditions changed from a non-degenerate semiconducting behaviour (at 2 × 10−2 mbar) to a degenerate semiconductor one (at 1.3 × 10−2 mbar), with a metal-insulator transition at 149 K. This crossover from strong to weak localization, evidenced in the temperature dependent resistivity curves, may be due to the effects of a structural disorder in such films. The direct optical band gap was estimated from transmission spectra taking into account non-degenerate/degenerate behaviour.

It is shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons. In weak magnetic fields and at low temperatures, a negative magnetoresistance is observed due to weak localization. A crossover in the magnetoresistance from weak localization to weak antilocalization (the latter is the manifestation of the isospin in graphene) is observed for the first time in samples of this kind at elevated temperatures. A pronounced pattern of Shubnikov–de Haas oscillations is observed in strong magnetic fields (up to 30 T). This pattern demonstrated fourfold carrier spectrum degeneracy due to the double spin and double valley degeneracies. Also, the manifestation of the Berry phase is observed. The effective electron mass is estimated to be m* = 0.08m0, which is characteristic of graphene with a high carrier concentration.