Search

We characterize the effect of ferromagnetic nickel nanoparticles (size ∼6nm) on the magnetotransport properties of chemical-vapor-deposited (CVD) graphene. The nanoparticles were formed by thermal annealing of a thin Ni film evaporated on top of a graphene ribbon. The magnetoresistance was measured while sweeping the magnetic field at different temperatures, and compared against measurements performed on pristine graphene. Our results show that, in the presence of Ni nanoparticles, the usually observed zero-field peak of resistivity produced by weak localization is widely suppressed (by a factor of ∼3), most likely due to the reduction of the dephasing time as a consequence of the increase in magnetic scattering. On the other hand, the high-field magnetoresistance is amplified by the contribution of a large effective interaction field. The results are discussed in terms of a local exchange coupling, J∼6meV, between the graphene π electrons and the 3d magnetic moment of nickel. Interestingly, this magnetic coupling does not affect the intrinsic transport parameters of graphene, such as the mobility and transport scattering rate, which remain the same with and without Ni nanoparticles, indicating that the changes in the magnetotransport properties have a purely magnetic origin.

Sr2FeMoO6-δ (SFMO) double perovskite is a promising candidate for room-temperature spintronic applications, since it possesses a half-metallic character (with theoretically 100% spin polarization), a high Curie temperature of about 415 K and a low-field magnetoresistance (LFMR). The magnetic, resistive and catalytic properties of the double perovskite SFMO are excellent for spintronic (non-volatile memory), sensing, fuel cell and microwave absorber applications. However, due to different synthesis conditions of ceramics and thin films, different mechanisms of electrical conductivity and magnetoresistance prevail. In this work, we consider the occurrence of a weak localization effect in SFMO commonly obtained in disordered metallic or semiconducting systems at very low temperatures due to quantum interference of backscattered electrons. We calculate the quantum corrections to conductivity and the contribution of electron scattering to the resistivity of SFMO. We attribute the temperature dependence of SFMO ceramic resistivity in the absence of a magnetic field to the fluctuation-induced tunneling model. We also attribute the decreasing resistivity in the temperature range from 409 K to 590 K to adiabatic small polaron hopping and not to localization effects. Neither fluctuation-induced tunneling nor adiabatic small polaron hopping favors quantum interference. Additionally, we demonstrate that the resistivity upturn behavior of SFMO cannot be explained by weak localization. Here, the fitted model parameters have no physically meaningful values, i.e., the fitted weak localization coefficient (B′) was three orders of magnitude lower than the theoretical coefficient, while the fitted exponent (n) of the electron–electron interaction term (CnTn) could not be assigned to a specific electron-scattering mechanism. Consequently, to the best of our knowledge, there is still no convincing evidence for the presence of weak localization in SFMO.

Sr2FeMoO6-δ (SFMO) double perovskite is a promising candidate for room-temperature spintronic applications, since it possesses a half-metallic character (with theoretically 100% spin polarization), a high Curie temperature of about 415 K and a low-field magnetoresistance (LFMR). The magnetic, resistive and catalytic properties of the double perovskite SFMO are excellent for spintronic (non-volatile memory), sensing, fuel cell and microwave absorber applications. However, due to different synthesis conditions of ceramics and thin films, different mechanisms of electrical conductivity and magnetoresistance prevail. In this work, we consider the occurrence of a weak localization effect in SFMO commonly obtained in disordered metallic or semiconducting systems at very low temperatures due to quantum interference of backscattered electrons. We calculate the quantum corrections to conductivity and the contribution of electron scattering to the resistivity of SFMO. We attribute the temperature dependence of SFMO ceramic resistivity in the absence of a magnetic field to the fluctuation-induced tunneling model. We also attribute the decreasing resistivity in the temperature range from 409 K to 590 K to adiabatic small polaron hopping and not to localization effects. Neither fluctuation-induced tunneling nor adiabatic small polaron hopping favors quantum interference. Additionally, we demonstrate that the resistivity upturn behavior of SFMO cannot be explained by weak localization. Here, the fitted model parameters have no physically meaningful values, i.e., the fitted weak localization coefficient (B′) was three orders of magnitude lower than the theoretical coefficient, while the fitted exponent (n) of the electron–electron interaction term (CnTn) could not be assigned to a specific electron-scattering mechanism. Consequently, to the best of our knowledge, there is still no convincing evidence for the presence of weak localization in SFMO.

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 impact of bismuth incorporation into the epitaxial layer of a (Ga,Mn)As dilute ferromagnetic semiconductor on its magnetic and electromagnetic properties is studied in very thin layers of quaternary (Ga,Mn)(Bi,As) compound grown on a GaAs substrate under a compressive misfit strain. An addition of a small atomic fraction of 1% Bi atoms, substituting As atoms in the layer, predominantly enhances the spin–orbit coupling strength in its valence band. The presence of bismuth results in a small decrease in the ferromagnetic Curie temperature and a distinct increase in the coercive fields. On the other hand, the Bi incorporation into the layer strongly enhances the magnitude of negative magnetoresistance without affecting the hole concentration in the layer. The negative magnetoresistance is interpreted in terms of the suppression of weak localization in a magnetic field. Application of the weak-localization theory for two-dimensional ferromagnets by Dugaev et al. to the experimental magnetoresistance results indicates that the decrease in spin–orbit scattering length accounts for the enhanced magnetoresistance in (Ga,Mn)(Bi,As).

Graphene and related 2D material (GRM) thin films consist of 3D assembly of billions of 2D nanosheets randomly distributed and interacting via van der Waals forces. Their complexity and the multiscale nature yield a wide variety of electrical characteristics ranging from doped semiconductor to glassy metals depending on the crystalline quality of the nanosheets, their specific structural organization ant the operating temperature. Here, the charge transport (CT) mechanisms are studied that are occurring in GRM thin films near the metal-insulator transition (MIT) highlighting the role of defect density and local arrangement of the nanosheets. Two prototypical nanosheet types are compared, i.e., 2D reduced graphene oxide and few-layer-thick electrochemically exfoliated graphene flakes, forming thin films with comparable composition, morphology and room temperature conductivity, but different defect density and crystallinity. By investigating their structure, morphology, and the dependence of their electrical conductivity on temperature, noise and magnetic-field, a general model is developed describing the multiscale nature of CT in GRM thin films in terms of hopping among mesoscopic bricks, i.e., grains. The results suggest a general approach to describe disordered van der Waals thin films.

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.

This paper presents low-temperature measurements of magnetoresistivity in heavily doped n-type GaN grown by basic GaN growth technologies: molecular beam epitaxy, metal-organic vapor phase epitaxy, halide vapor phase epitaxy and ammonothermal. Additionally, GaN crystallized by High Nitrogen Pressure Solution method was also examined. It was found that all the samples under study exhibited negative magnetoresistivity at a low temperature (10 K < T < 50 K) and for some samples this effect was observed up to 100 K. This negative magnetoresistivity effect is analyzed in the frame of the weak localization phenomena in the case of three-dimensional electron gas in a highly doped semiconductor. This analysis allows for determining the phasing coherence time τφ for heavily doped n-type GaN. The obtained τφ value is proportional to T−1.34, indicating that the electron–electron interaction is the main dephasing mechanism for the free carriers.

Although previous studies have reported the Raman and weak localization properties of graphene separately, very few studies have examined the correlation between the Raman and weak localization characterizations of graphene. Here, we report a Raman spectroscopy and low-magnetic-field electronic transport study of graphene devices with a controlled amount of defects introduced into the graphene by exposure to electron-beam irradiation and oxygen plasma etching. The relationship between the defect correlation length (LD), calculated from the Raman “D” peak, and the characteristic scattering lengths, Lϕ, Li and L*, computed from the weak localization effects measured in magneto-transport was investigated. Furthermore, the effect on the mean free path length due to the increasing amounts of irradiation incident on the graphene device was examined. Both parameters—including LD and Lϕ—decreased with the increase of irradiation, which was shown to be related to the increase of disorder through the concomitant decrease in the mean free path length, l. Although these are similar trends that have been observed separately in previous reports, this work revealed a novel nonlinear relationship between LD and Lϕ, particularly at lower levels of disorder. These findings are valuable for understanding the correlation between disorder in graphene and the phase coherence and scattering lengths of its charge carriers.

We use the bond fluctuation model to study the contraction process of two polymer loops with $N$ segments that are connected each to the bottom and top parts of a Feringa engine. The change in the size of the molecules as well as the folding of the two strands follows approximately scaling predictions that are derived by assuming that the strands are confined inside an effective tube. Conformation data can be overlapped when plotting it as a function of ${W}_{\text{n}}{N}^{\ensuremath{-}1/4}$, where ${W}_{\text{n}}$ is the winding number of the two strands that is proportional to the number of blobs inside the ``knotted'' region of the molecule and $N$ is the degree of polymerization of the strands. Our data support a weak localization of the knots along the contour of flexible cyclic athermal polymers with a localization exponent $t\ensuremath{\approx}0.78$.

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.

A quantitative version of strong localization of the Kobayashi, Azukawa and Sibony metrics, as well as of the squeezing function, near a plurisubharmonic peak boundary point of a domain in $${\mathbb {C}}^n$$ is given. As an application, the behavior of these metrics near a strictly pseudoconvex boundary point is studied. A weak localization of the three metrics and the squeezing function is also given near a plurisubharmonic antipeak boundary point.

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.

The weak localization or enhanced backscattering phenomenon has received a lot of attention in the literature. The enhanced backscattering cone refers to the situation that the wave backscattered by a random medium exhibits an enhanced intensity in a narrow cone around the incoming wave direction. This phenomenon can be analyzed by a formal path integral approach. Here a mathematical derivation of this result is given based on a system of equations that describes the second-order moments of the reflected wave. This system derives from a multiscale stochastic analysis of the wave field in the situation with high-frequency waves and propagation through a lossy medium with fine scale random microstructure. The theory identifies a duality relation between the spreading of the wave and the enhanced backscattering cone. It shows how the cone, its regularity and width relate to the statistical structure of the random medium. We discuss how this information in particular can be used to estimate the internal structure of the random medium based on observations of the reflected wave.

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.

Hydrogen-terminated diamond possesses an intriguing p-type surface conductivity which is induced via thermodynamically driven electron transfer from the diamond surface into surface acceptors such as atmospheric adsorbates, a process called surface transfer doping. High electron affinity transition metal oxides (TMOs) including MoO3 and V2O5 have been shown to be highly effective solid-state surface acceptors for diamond, giving rise to a sub-surface two-dimensional (2D) hole layer with metallic conduction. In this work, low temperature magnetotransport is used as a tool to show the presence of a Rashba-type spin-orbit interaction with a high spin-orbit coupling of 19.9 meV for MoO3 doping and 22.9 meV for V2O5 doping, respectively, through the observation of a transition in the phase-coherent backscattering transport from weak localization to weak antilocalization at low temperature. Surface transfer doping of diamond with TMOs provides a 2D hole system with spin-orbit coupling that is over two times larger than that reported for diamond surfaces with atmospheric acceptors, opening up possibilities to study and engineer spin transport in a carbon material system.

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...

The differential conductance of graphene is shown to exhibit a zero-bias anomaly at low temperatures, arising from a suppression of the quantum corrections due to weak localization and electron interactions. A simple rescaling of these data, free of any adjustable parameters, shows that this anomaly exhibits a universal, temperature- (T) independent form. According to this, the differential conductance is approximately constant at small voltages (V kBT/e), while at larger voltages it increases logarithmically with the applied bias. For theoretical insight into the origins of this behaviour, which is inconsistent with electron heating, we formulate a model for weak-localization in the presence of nonequilibrium transport. According to this model, the applied voltage causes unavoidable dispersion decoherence, which arises as diffusing electron partial waves, with a spread of energies defined by the value of the applied voltage, gradually decohere with one another as they diffuse through the system. The decoherence yields a universal scaling of the conductance as a function of eV/kBT, with a logarithmic variation for eV/kBT > 1, variations in accordance with the results of experiment. Our theoretical description of nonequilibrium transport in the presence of this source of decoherence exhibits strong similarities with the results of experiment, including the aforementioned rescaling of the conductance and its logarithmic variation as a function of the applied voltage.

The effects of quantum corrections on electron conductivity in bilayer graphene have been studied under various temperatures and gate voltages to seek the origin of the restrictions in electron conductions. Although previous studies suggested the enhanced intervalley scattering effect to be the major reason behind the restriction on electron transport, tested samples in this work exhibited the weak localization effect due to much weaker intervalley scattering rates. The enhancement of inelastic scattering near Dirac point are further tested to show the reason behind the inconsistency. It is successfully shown that the amount of electron-hole puddles, and thus, screening effects could enhance intervalley scattering near Dirac point.

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.

The brilliant white appearance of ultrathin scattering media with low refractive index contrast and the underlying radiative transport phenomena fascinate scientists for more than a decade. Examples of such systems are the scales of beetles of the genus Cyphochilus, photonic network structures or disordered Bragg stacks (DBS). While previous studies relate the highly efficient scattering in the scales to the anisotropy of the intra-scale network and diffusive light transport, the coherent radiation propagation dynamics remains unaccounted for. Here, the identification of different coherent light transport regimes using time and spatially resolved coherent light scattering spectroscopy is shown. At least 20% of the collected scattered light originates from weakly localized random photonic modes, in contrast to solely diffusive light transport assumed to date. The identification of this significant role of weak localization in ultrathin brilliant scattering media establishes a new design paradigm for efficient scattering optical materials.

The brilliant white appearance of ultrathin scattering media with low refractive index contrast and the underlying radiative transport phenomena fascinate scientists for more than a decade. Examples of such systems are the scales of beetles of the genus Cyphochilus, photonic network structures or disordered Bragg stacks (DBS). While previous studies relate the highly efficient scattering in the scales to the anisotropy of the intra-scale network and diffusive light transport, the coherent radiation propagation dynamics remains unaccounted for. Here, the identification of different coherent light transport regimes using time and spatially resolved coherent light scattering spectroscopy is shown. At least 20% of the collected scattered light originates from weakly localized random photonic modes, in contrast to solely diffusive light transport assumed to date. The identification of this significant role of weak localization in ultrathin brilliant scattering media establishes a new design paradigm for efficient scattering optical materials.

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.

We theoretically explore the possibility to detect weak localization of light in a hot atomic vapor, where one usually expects the fast thermal motion of the atoms to destroy any interference in multiple scattering. To this end, we compute the coherent backscattering peak, assuming high temperature and taking into account the quantum level structure of the atomic scatterers. It is found that the decoherence due to thermal motion can be partially counterbalanced by working at large laser detuning and using small atomic cells with an elongated geometry. Under these conditions, our estimates suggest that weak localization in a hot vapor should be within reach of experimental detection., Comment: 11 pages, 5 figures

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.

We consider quantum spin ice in a temperature regime in which its response is dominated by the coherent motion of a dilute gas of monopoles. The hopping amplitude of a monopole is sensitive to the configuration of its surrounding spins, taken to be quasi-static on the relevant timescales. This leads to well-known blocked directions in the monopole motion; we find that these are sufficient to reduce the coherent propagation of monopoles to quantum diffusion. This result is robust against disorder, as a direct consequence of the ground-state degeneracy, which disrupts the quantum interference processes needed for weak localization. Moreover, recent work [Tomasello et al., Phys. Rev. Lett. 123, 067204 (2019)] has shown that the monopole hopping amplitudes are roughly bimodal: for $\approx 1/3$ of the flippable spins surrounding a monopole, these amplitudes are extremely small. We exploit this structure to construct a theory of quantum monopole motion in spin ice. In the limit where the slow hopping terms are set to zero, the monopole wavefunctions appear to be fractal; we explain this observation via a mapping to quantum percolation on trees. The fractal, non-ergodic nature of monopole wavefunctions manifests itself in the low-frequency behavior of monopole spectral functions, and is consistent with experimental observations., Comment: 12 pages, 11 figures

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.

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.

The exciton transfer between light-harvesting complex 1(LH1) and photosynthetic reaction center dimer is investigated theoretically. We assume a ring shape structure of the LH1 complex with dimer in the ring centre. The kinetic equations which describe the energy transfer between the antenna complex and reaction center dimer were derived. It was shown that the dimer does not act as a photon trap. There is a weak localization of the exciton on the dimer and there is relatively rapid back exciton transfer from dimer to antenna complex which depends on the number of the pigment molecules in the antenna ring. The relation between the rates of the exciton transfer from the antenna complex to dimer and back transfer from dimer to antenna complex has been derived.

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.

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.

This study explores the nonlinear dynamics of helical compression valve springs. To this end, the spring is mathematically modeled as a finite nonhomogenous one-dimensional mass–spring–damper discrete chain. Periodic displacement, which mimics the actual camshaft profile, is assumed at the upper end of the chain, while the other end is fixed. For the linear dynamics, the amplitudes of the periodic response are determined directly; they decrease toward the fixed end of the spring. Then, in order to meet more realistic conditions, the displacement of the upper mass is assumed to be nonnegative. This condition is realized by introducing an appropriate impact constraint. We assume that the impact is described by Newton impact law with restitution coefficient less than unity. For the case of one impact per period (1IPP) of excitation, exact periodic solutions are derived. The interplay between the nonhomogenous structure, multi-frequency excitation and nonlinearity leads to two qualitatively different states of the periodic responses; we refer to them as propagating states and edge states. The propagating states are characterized by weak localization, and the edge states—by strong localization at the forced edge. The stability of the system is analyzed using Floquet theory. Generic pitchfork and Neimark–Sacker bifurcations are observed. Analytical solutions conform to numerical simulations and experimental tests conducted on real valve springs.

Thin films of solid solutions based on the three-dimensional Dirac semimetal Cd3As2 with the addition of manganese are investigated. Cd3 –xMnxAs2 films (x = 0, 0.05, and 0.1) 50–70 nm in thickness are formed on a glassceramic substrate using vacuum-thermal deposition from cadmium arsenide ingots doped by Mn and fabricated by direct alloying elements by the vacuum-cell method. The temperature and magnetic-field dependences of the resistance are measured and the transport parameters of the films under study are determined. Positive magnetoresistance of the characteristic shape corresponding to the contribution of the weak antilocalization effect is observed for films with x = 0 and 0.05. The contribution from the weak localization effect is observed at a higher Mn content (x = 0.1). This change in the quantum correction type as applied to topological semimetals points to reconstruction of the band structure and transition from the Dirac semimetal state into a trivial semiconductor phase, which corresponds to the critical Mn content xc ~ 0.07 in this case.

Quantum effects in p-type Si0.2Ge0.8/Ge/Si0.2Ge0.8 heterostructure with an extremely high mobility of charge carriers μH = 1367000 cm2/(V ⋅ s) have been comprehensively studied. An analysis of Shubnikov–de Haas oscillations yielded effective mass of charge carriers, which proved to be very low, m* = 0.062m0, and the value of fluctuations of hole density along the channel δp = 3.5 ⋅ 109 cm–2. The fractional Hall effect (filling numbers 8/3, 7/3, 5/3, 4/3) observed at temperatures up to 5 K has been discovered in strong magnetic fields. The studies of quantum interference effects related to weak localization and electron-electron interaction between charge carriers, which have been conducted in such a high-mobility system for the first time, enabled calculation of spin splitting Δ = 1.07 meV and the Fermi-liquid coupling constant F 0 σ = − 0.12, which agree with results obtained earlier.Quantum effects in p-type Si0.2Ge0.8/Ge/Si0.2Ge0.8 heterostructure with an extremely high mobility of charge carriers μH = 1367000 cm2/(V ⋅ s) have been comprehensively studied. An analysis of Shubnikov–de Haas oscillations yielded effective mass of charge carriers, which proved to be very low, m* = 0.062m0, and the value of fluctuations of hole density along the channel δp = 3.5 ⋅ 109 cm–2. The fractional Hall effect (filling numbers 8/3, 7/3, 5/3, 4/3) observed at temperatures up to 5 K has been discovered in strong magnetic fields. The studies of quantum interference effects related to weak localization and electron-electron interaction between charge carriers, which have been conducted in such a high-mobility system for the first time, enabled calculation of spin splitting Δ = 1.07 meV and the Fermi-liquid coupling constant F 0 σ = − 0.12, which agree with results obtained earlier.

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.