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In a recent paper [Cáceres MO, Comments on wave-like propagation with binary disorder. J. Stat. Phys. 2021;182(36):doi.org/10.1007/s10955-021-02699-0.], the evolution of a wave-like front perturbed by space-correlated disorder was studied. In addition, the generic solution of the field mean-value was presented as a series expansion in Terwiel's cumulants operators. This infinite series cuts due to the algebra of naked Terwiel's cumulants when these cumulants are associated to a space exponential-correlated symmetric binary disorder. We apply an equivalent approach to study the dispersion-relation for 1D surface gravity waves propagating on an irregular floor. The theory is based on the study of the mean-value of plane-wave-like Fourier modes for the propagation and damping of surface waves on a random bottom. [ABSTRACT FROM AUTHOR]

In recent years, few-layer or even monolayer ferromagnetic materials have drawn a great deal of attention due to the promising integration of two-dimensional (2D) magnets into next-generation spintronic devices. The SrRuO3 monolayer is a rare example of stable 2D magnetism under ambient conditions, but only weak ferromagnetism or antiferromagnetism has been found. The bi-atomic layer SrRuO3 as another environmentally inert 2D magnetic system has been paid less attention heretofore. Here we study both the bi-atomic layer and monolayer SrRuO3 in (SrRuO3)n/(SrTiO3)m (n = 1, 2) superlattices in which the SrTiO3 serves as a non-magnetic and insulating space layer. Although the monolayer exhibits arguably weak ferromagnetism, we find that the bi-atomic layer exhibits exceedingly strong ferromagnetism with a Tc of 125 K and a saturation magnetization of 1.2 µB/Ru, demonstrated by both superconducting quantum interference device (SQUID) magnetometry and element-specific X-ray circular dichroism. Moreover, in the bi-atomic layer SrRuO3, we demonstrate that random fluctuations and orbital reconstructions inevitably occurring in the 2D limit are critical to the electrical transport, but are much less critical to the ferromagnetism. Our study demonstrates that the bi-atomic layer SrRuO3 is an exceedingly strong 2D ferromagnetic oxide which has great potentials for applications of ultracompact spintronic devices. [Figure not available: see fulltext.].

The results of studies of magnetoresistance for GaAs filamentous crystals doped with tellurium admixture to a concentration of 2·1017 сm−3, in the temperature range 4.2–60 K and in the magnetic field ranges 0–14 T are presented. The GaAs filamentary crystal magnetoresistance has shown a sharp positive jump at a low magnetic field (up to 0.2 T) at a temperature near 4.2 K, while at higher magnetic field inductions linear behavior of magnetoresistance occurs. The low field magnetoresistance is discussed in the framework of weak localization of charge carriers due to their spin-orbit exchange interaction. The high-field linear magnetoresistance is connected with electron-electron interaction. [ABSTRACT FROM AUTHOR]

In this paper, the patterns of manifestation of weak localization and antilocalization in graphene with enhanced spin-orbit interaction, as well as in a topological insulator with a gap in surface states induced by magnetic impurities are studied. The parameters characterizing the manifestation of weak localization, antilocalization and crossover between them are established. Quantum corrections to the conductivity of graphene are determined in units of e2/h = 38.64 μS for various ratios between the characteristic dephasing time and spin-orbit scattering time. It has been established that with a relatively long spin-orbit scattering time, not less than 10–10 s, it does not affect the correction to conductivity and its value is determined by the dephasing time and the times of intervalley and intravalley scattering. The effect of the spin-orbit scattering is to suppress weak antilocalization. It leads to a spin flip of the conduction electron during elastic scattering, and the interference pattern of weak localization becomes more complicated due to the mixing of spin states. The sign of the quantum correction depends on which spin state contributes the most.

We characterize the effect of ferromagnetic nickel nanoparticles (size ∼ 6   n m ) 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 ∼ 6   m e V , 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The electronic and atomic structure and transport properties of black phosphorus single crystals prepared by high-pressure and gas-transport methods were studied by X-ray photoelectron spectroscopy and scanning probe microscopy (STM, AFM). The atomic resolution of the single crystal surface was obtained by scanning tunneling microscopy. After exposure of the clean surface under ambient conditions, the features in X-ray photoelectron spectroscopy spectra corresponding to the oxidized form of phosphorus were observed and detected using atomic force microscopy. Using low-temperature transport measurements, impurity activation energies were determined and negative magnetoresistance was detected. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

The magneto-quantum and quantum interference effects in a two-dimensional gas of p-type charge carriers are studied for three quantum wells made of practically pure germanium in a Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructure. The quantum well widths were 8 nm for sample I, 19.5 nm for sample II, and 25.6 nm for sample III. The dependences of resistance on the magnetic field for all samples exhibit Shubnikov–de Haas oscillations. Their analysis made it possible to calculate the kinetic characteristics of charge carriers for the cases of one (sample I) and two occupied subbands (samples II and III). In the region of weak magnetic fields (B < 0.1 T), the effect of weak localization of holes was revealed, which determines the negative magnetoresistance and the increase in resistance with decreasing temperature. The manifestation of the charge carriers interaction effect at various temperatures and magnetic fields is discovered and analyzed. A transition from the diffusion mode of manifestation of the quantum correction to the intermediate, and then to the ballistic mode is observed. In all regions, the behavior of the quantum correction due to the charge carriers interaction effect is in good agreement with modern theoretical predictions. The temperature dependences of the hole-phonon relaxation time are calculated. In weak magnetic fields, with an increase in the temperature of the 2D system, a transition from the "partial inelasticity" mode, characterized by the dependence τ h ph − 1 ∝ T 2 , to the small-angle scattering mode, described by the relation τ h ph − 1 ∝ T 5 , takes place. In stronger magnetic fields for samples with two occupied subbands, the dependence τ h ph − 1 ∝ T 3 was observed. Possible explanations for this dependence are presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Intercalation is a promising technique to modify the structural and electronic properties of 2D materials on the wafer scale for future electronic device applications. Yet, few reports to date demonstrate 2D intercalation as a viable technique on this scale. Spurred by recent demonstrations of mm-scale sensors, we use hydrogen intercalated quasi-freestanding bilayer graphene (hQBG) grown on 6H-SiC(0001), to understand the electronic properties of a large-area (16 mm 2 ) device. To do this, we first analyze Shubnikov-de Haas (SdH) oscillations and weak localization, permitting determination of the Fermi level, cyclotron effective mass, and quantum scattering time. Our transport results indicate that at low temperature, scattering in hQBG is dominated by charged impurities and electron-electron interactions. Using low- temperature scanning tunneling microscopy and spectroscopy (STS), we investigate the source of the charged impurities on the nm-scale via observation of Friedel oscillations. Comparison to theory suggests that the Friedel oscillations we observe are caused by hydrogen vacancies underneath the hQBG. Furthermore, STS measurements demonstrate that hydrogen vacancies in the hQBG have an extremely localized effect on the local density of states, such that the Fermi level of the hQBG is only affected directly above the location of the defect. Hence, we find that the calculated Fermi level from SdH oscillations on the millimeter scale agrees with the value measured locally on the nanometer scale with STS measurements.

In a 2D electron system (2DES) the breaking of the inversion, time-reversal and bulk crystal-field symmetries is interlaced with the effects of spin-orbit coupling (SOC) triggering exotic quantum phenomena. Here, epitaxial engineering is used to design and realize a 2DES characterized simultaneously by ferromagnetic order, large Rashba SOC and hexagonal band warping at the (111) interfaces between LaAlO 3 , EuTiO 3 , and SrTiO 3 insulators. The 2DES displays anomalous quantum corrections to the magneto-conductance driven by the time-reversal-symmetry breaking occurring below the magnetic transition temperature. The results are explained by the emergence of a non-trivial Berry phase and competing weak anti-localization/weak localization back-scattering of Dirac-like fermions, mimicking the phenomenology of gapped topological insulators. These findings open perspectives for the engineering of novel spin-polarized functional 2DES holding promises in spin-orbitronics and topological electronics., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

MXenes stand out from other 2D materials because they combine very good electrical conductivity with hydrophilicity, allowing cost-effective processing as thin films. Therefore, there is a high fundamental interest in unraveling the electronic transport mechanisms at stake in multilayers of the most conducting MXene, Ti 3 C 2 T x . Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti 3 C 2 T x thin films, there have been few attempts to model it quantitatively. In this work, the role of important structural parameters - thickness, interflake coupling, defects - on the dimensionality of the LT transport mechanisms in spin-coated Ti 3 C 2 T x thin films is investigated through LT and magnetic field dependent resistivity measurements. A dimensional crossover from 2D to 3D WL is clearly evidenced when the film thickness exceeds the dephasing length l ϕ , estimated here in the 50-100 nm range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than l ϕ , hence acting as parallel 2D conductors. Alternatively, l ϕ can be reduced down to the 10 nm range by defects. These results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thin films., (© 2024 Wiley‐VCH GmbH.)

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, few-layer or even monolayer ferromagnetic materials have drawn a great deal of attention due to the promising integration of two-dimensional (2D) magnets into next-generation spintronic devices. The SrRuO3 monolayer is a rare example of stable 2D magnetism under ambient conditions, but only weak ferromagnetism or antiferromagnetism has been found. The bi-atomic layer SrRuO3 as another environmentally inert 2D magnetic system has been paid less attention heretofore. Here we study both the bi-atomic layer and monolayer SrRuO3 in (SrRuO3)n/(SrTiO3)m (n = 1, 2) superlattices in which the SrTiO3 serves as a non-magnetic and insulating space layer. Although the monolayer exhibits arguably weak ferromagnetism, we find that the bi-atomic layer exhibits exceedingly strong ferromagnetism with a Tc of 125 K and a saturation magnetization of 1.2 µB/Ru, demonstrated by both superconducting quantum interference device (SQUID) magnetometry and element-specific X-ray circular dichroism. Moreover, in the bi-atomic layer SrRuO3, we demonstrate that random fluctuations and orbital reconstructions inevitably occurring in the 2D limit are critical to the electrical transport, but are much less critical to the ferromagnetism. Our study demonstrates that the bi-atomic layer SrRuO3 is an exceedingly strong 2D ferromagnetic oxide which has great potentials for applications of ultracompact spintronic devices. [ABSTRACT FROM AUTHOR]

The recent development of subwavelength photonic and phononic crystals shows the possibility of controlling wave propagation at deep subwavelength scales. Subwavelength bandgap phononic crystals are typically created using a periodic arrangement of subwavelength resonators, in our case small gas bubbles in a liquid. In this work, a waveguide is created by modifying the sizes of the bubbles along a line in a dilute two-dimensional bubbly crystal, thereby creating a line defect. Our aim is to prove that the line defect indeed acts as a waveguide; waves of certain frequencies will be localized to, and guided along, the line defect. The key result is an original formula for the frequencies of the defect modes. Moreover, these frequencies are numerically computed using the multipole method, which numerically illustrates our main results. [ABSTRACT FROM AUTHOR]

We characterize the effect of ferromagnetic nickel nanoparticles (size ∼6 nm) 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∼6 meV, 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.

We calculate the spectral statistics of the Kramersâ€"Weyl Hamiltonian H = v âˆ' α σ α  sin  p α + tσ 0âˆ' α cos  p α in a chaotic quantum dot. The Hamiltonian has symplectic time-reversal symmetry (H is invariant when spin σ α and momentum p α both change sign), and yet for small t the level spacing distribution P (s) ∝ s β follows the β = 1 orthogonal ensemble instead of the β = 4 symplectic ensemble. We identify a supercell symmetry of H that explains this finding. The supercell symmetry is broken by the spin-independent hopping energy ∝ t  cos  p, which induces a transition from β = 1 to β = 4 statistics that shows up in the conductance as a transition from weak localization to weak antilocalization. [ABSTRACT FROM AUTHOR]

The conductivity of single-crystal nanoplates of the Sb2Te3 topological insulator has been investigated. A sharp drop in resistance occurs in ultrathin Sb2Te3 nanoplates at a temperature of about 4 K, which is a manifestation of superconductivity. The results show that the presence of an optimal degree of disorder is a necessary condition for the onset of superconductivity. A superconductor-insulator transition, tunable by a magnetic field, is observed in these nanoplates. The temperature dependence of the magnetoresistance in fields below the critical value (B < BC) shows a successive transformation of a weak antilocalization anomaly into a superconducting transition. The value of the correlation length exponent ν = 0.75 ± 0.05 was obtained using the scaling theory. [ABSTRACT FROM AUTHOR]

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. [Display omitted] [ABSTRACT FROM AUTHOR]

Many current and proposed programs of satellite remote sensing of the Earth and other celestial bodies rely upon measurements of the intensity and polarization of light scattered by these bodies. These measurement data are interpreted by searching for the best fits to light-scattering characteristics precalculated with some theoretical models. For regolith-like surfaces, i.e., discrete densely packed random media, the light-scattering models are still under development and they work under different approaches. Here, to estimate the difference between the reflectance characteristics yielded by these procedures, we compare the results of simulations performed according to five frequently used approximate models of a semi-infinite particulate medium. Special attention is paid to taking into account the weak-localization effect. The models differ by the scattering matrixes of a volume element and the dependence of the imaginary part of the effective refractive index on the filling factor. The volume element is an individual spherical particle or a randomly oriented cluster of particles. The cases of modifying the scattering matrix by the static structure factor correction or by subtracting the contribution of the mean field are also considered. The values for the size parameter of particles or monomers in the clusters and the refractive index were assumed at 1.76 and 1.50 + i0.0001, respectively; and two values for the filling factor (defined as a volume fraction occupied by particles in the medium), 20 and 10%, were considered. Our analysis shows that the angular dependences of the intensity and the linear polarization degree obtained with the considered models are rather close to each other. Moreover, they agree with the corresponding characteristics for a large cloud of particles (N is equal to or exceeds 106) with the filling factor up to 20%, which were obtained by approximate methods but well follow the trends found in rigorous simulations for smaller ensembles of particles (Penttilä et al., J. Quant. Spectrosc. Radiat. Transfer, 2021, 262, 107524). Hence, these approximate models are equally acceptable to the interpretation of the results of observations.

The mutual interplay between electron transport and magnetism has attracted considerable attention in recent years, primarily motivated by strategies to manipulate magnetic degrees of freedom electrically, such as spin–orbit torques and domain wall motion. Within this field the topological Hall effect, which originates from scalar spin chirality, is an example of inter-band quantum coherence induced by real-space inhomogeneous magnetic textures, and its magnitude depends on the winding number and chiral spin features that establish the total topological charge of the system. Remarkably, in the two decades since its discovery, there has been no research on the quantum correction to the topological Hall effect. Here we will show that, unlike the ordinary Hall effect, the inhomogeneous magnetization arising from the spin texture will give additional scattering terms in the kinetic equation, which result in a quantum correction to the topological Hall resistivity. We focus on two-dimensional systems, where weak localization is strongest, and determine the complicated gradient corrections to the Cooperon and kinetic equation. Whereas the weak localization correction to the topological Hall effect is not large in currently known materials, we show that it is experimentally observable in dilute magnetic semiconductors. Our theoretical results will stimulate experiments on the topological Hall effect and fill the theoretical knowledge gap on weak localization corrections to transverse transport.

Two-dimensional layered carbon materials such as graphene constructed by sp 2 hybridization have raised considerable interest due to their large, non-saturating magnetoresistance. As a new sp - sp 2 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. [Display omitted] ● Developed a modified non-transferred graphdiyne film synthesis method grown on an arbitrary substrate. ● Crossover positive and negative magnetoresistance was observed in graphdiyne film. ● Graphdiyne film presents maximum value of 150% in positive magnetoresistance (PMR), and 150% in negative magnetoresistance. [ABSTRACT FROM AUTHOR]

The electrical conductivity of Sb2Te3 topological insulator nanoplates of different thickness, grown by vapor-phase deposition, has been studied. The characteristic properties of conductivity are revealed depending on the transverse magnetic field (0–9 T) and temperature (3–300 K). In a magnetic field, ultrathin 11 nm thick Sb2Te3 nanoplates demonstrate a giant anomaly of weak antilocalization, accompanied by the effect of weak localization. A continuous decrease in electrical resistance with decreasing temperature and its sharp drop at the temperature of ∼4 K is a sign of the superconducting transition. Ultrathin samples exhibit a magnetic-field tunable superconductor-insulator transition. [ABSTRACT FROM AUTHOR]

It was studied the electrical magnetoresistance of nickel-and boron-doped filamentary silicon crystals in which a metal-insulator transition is observed. A giant magnetoresistance reaches up to 280% in the Si whiskers with doping concentration of boron р300K = 5⋅1018 cm−3 in the magnetic fields with induction up to 14 T at temperature 4.2 K. Peculiarities of magnetoresistance at low temperatures were shown to be caused by "core-shell" structure of crystals. A giant magnetoresistance nature was considered within quantum magnetoresistance model. The analysis was performed to determine the critical field of transition from classical parabolic magnetoresistance to quantum magnetoresistance, realized in the near-surface region of the crystal. The silicon whiskers were used for design of magnetic field sensors. [ABSTRACT FROM AUTHOR]

Magnetic field and temperature dependence of the magneto‐conductance (MC) of thin films made of self‐p‐doped poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) having room temperature conductivity of ≈200 S cm−1 in the range of fields B = 0–14 T and temperatures T = 1.8–300 K are reported. At B = 0 and for current parallel to the film surface, the conductance follows a variable range hopping mechanism in two dimensions. It is shown that the finite Coulomb correlations, U, within the nano‐crystalline PEDOT islands dominates MC at low temperatures and high fields. At T = 1.8 K, the intra‐island Coulomb correlation spin polarization mechanism is already saturated for B > 10 T establishing a finite minimum of ≈2 meV for U. This small value of U is in line with the delocalized nature of the holes within the PEDOT islands and the relatively high conductivity that makes it essential in organic opto‐electronics. [ABSTRACT FROM AUTHOR]

Zero thermal coefficients of resistivity (ZTCR) materials exhibit minimal changes in resistance with temperature variations, making them essential in modern advanced technologies. The current ZTCR materials, which are based on the resistivity saturation effect of heavy metals, tend to function at elevated temperatures because the mean free path approaches the lower limit of the semiclassical Boltzmann theory when the temperature is sufficiently high. ZTCR materials working at low-temperatures are difficult to achieve due to electron-phonon scattering, which results in increased resistivity according to Bloch's theory. In this work, the ZTCR behavior at low-temperatures is realized in pre-microstrained Mn 3 NiN. The delicate balance between the resistivity contribution from electron-phonon scattering and spin-wave mediated weak localization is well revealed. A remarkable temperature coefficient of resistivity (TCR) value as low as 1.9 ppm K -1 (50 K ≤ T ≤ 200 K) is obtained, which is significantly superior to the threshold value of ZTCR behavior and the application standard of commercial ZTCR materials. The demonstration provides a unique paradigm in the design of ZTCR materials through the contraction effects of two opposite conductance mechanisms with positive and negative thermal coefficients of resistivity., (© 2024 Wiley‐VCH GmbH.)

The effect of a magnetic field on the current-voltage characteristics of MoRe-Si(W)-MoRe heterostructures formed by superconducting banks (molybdenum-rhenium alloy) and a hybrid semiconducting tunnelling barrier (nanoscale silicon layer with tungsten nanoclusters) is investigated experimentally. A growth of the resistive region in the corresponding curves is observed and it is shown that this effect is a consequence of a modification in the weak localization of electrons in the disordered barrier under the influence of the applied magnetic field. [ABSTRACT FROM AUTHOR]

We report the deposition of epitaxial SrHfO 3 thin films on a SrTiO 3 (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 SrHfO 3 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 SrHfO 3 films have p-type charge carriers. Image 1 • High quality SrHfO 3 thin films grown on a SrTiO 3 (001) using the pulsed laser deposition method. • All thin films have metallic behavior at high temperature and possess the p-type charge carrier. • SrHfO 3 thin films have resistivity upturns at low temperatures, which are accounted for by localization mechanism. [ABSTRACT FROM AUTHOR]

This work reports the first experimental study of graphene transferred on β‐Si3N4(0001)/Si(111). A comprehensive quantitative understanding of the physics of ultrathin Si3N4 as a gate dielectric for graphene‐based devices is provided. The Si3N4 film is grown on Si(111) under ultra‐high vacuum (UHV) conditions and investigated by scanning tunneling microscopy (STM). Subsequently, a graphene flake is deposited on top of it by a polymer‐based transfer technique, and a Hall bar device is fabricated from the graphene flake. STM is employed again to study the graphene flake under UHV conditions after device fabrication and shows that the surface quality is preserved. Electrical transport measurements, carried out at low temperature in magnetic field, reveal back gate modulation of carrier density in the graphene channel and show the occurrence of weak localization. Under these experimental conditions, no leakage current between back gate and graphene channel is detected. [ABSTRACT FROM AUTHOR]

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 to 2 T are investigated. The revealed anomalies of the temperature and field dependences of resistivity of multi-walled carbon nanotubes are analyzed in the terms of charge carrier's weak localization and interaction effects for two-dimensional systems. For carbon nanotubes with different degrees of structural perfection diffusion coefficient, charge carrier's interaction parameter and the value of the Fermi energy are estimated. It is shown that the anomalies found in the resistivity and magnetoresistance for the defective multi-walled carbon nanotubes are related with the manifestation of the weak localization effect, while for the multi-walled carbon nanotubes of the perfect structure these anomalies are explained by the charge carriers interaction effect. [ABSTRACT FROM AUTHOR]

The improved analysis of carrier transport in the single-layer graphene and hybrid structures like graphene/Co nanoparticles (NPs) and graphene/Co NPs/graphene has been conducted. The temperature and magnetic field dependences of the sheet resistance R Sq (T , B) and/or conductivity σ Sq (T, В) has shown the coexistence of negative (NMR) and positive (PMR) contributions in magnetoresistive effect in all the samples under study. The dependences of R Sq (T, B) and/or σ Sq (T, В) were analyzed in the framework of some combinations of 5 models relating to quantum corrections (QCs) to Drude conductivity theory and different hopping models for variable range hopping (VRH) regimes. It was shown, in particular, that in the region of NMR effect below 75 K and in fields B < (0.5–1) T , σ Sq (T, В) dependences obey the combination of QCs theory (at induction <100 mT) and conduction by coherent hopping over localized states in the VRH regime at T < 20 K. In this case, with the phase breaking time of the wave function it follows the power-like law τφ (Т) ∼ T - p with the exponent p ≈ 1. These dependences also allowed to estimate the values of electron concentration n (T) in the structures studied, which were close to the values in the undoped graphene near the neutrality point. In the region of the PMR effect, the electrical resistance of the structures studied increases linearly with increasing B without saturation. This behavior is often attributed to the presence of structural inhomogeneities in the samples (due to e.g. Co-based nanoparticles) under study, which leads to distortion of the current paths under the action of the Lorentz force arising in a perpendicular magnetic field. [Display omitted] • Sandwich graphene/Co nanoparticles/graphene reveal negative and positive contributions into the sheet magnetoresistance. • Negative contribution is due to low localization interference effects and hopping of coherent electrons over localized states. • Positive contribution increases with magnetic induction without saturation owing to inhomogeneities in sandwich structure. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

Highlights • Discovery of electron-diffuson scattering contribution to anomalous Hall effect (AHE). • Only in disordered ferromagnets (FMs) does the weak localization contribute to AHE. • Electron-electron interaction effects do not contribute to AHE in crystalline FMs. • A universal scaling holds between AHE and temperature-dependent part of resistivity. Abstract An exhaustive study of the influence of disorder on anomalous Hall (AH) resistivity ( ρ xy AH ), longitudinal resistivity ( ρ xx ), magnetoresistance and magnetization of Co 2 FeSi (CFS) Heusler alloy thin films of fixed (50 nm) thickness, deposited on Si (1 1 1) substrate, reveals the following. Regardless of the degree of disorder present, the side-jump mechanism gives a dominant contribution to ρ xy AH . A new and novel contribution to both ρ xx and ρ xy AH , characterized by the logarithmic temperature (- lnT) dependence at temperatures below the minimum (T < T min ), exclusive to the amorphous CFS films, originates from the scattering of conduction electrons from the diffusive hydrodynamic modes associated with the longitudinal component of magnetization, called 'diffusons'. The electron-diffuson, e - d , scattering and weak localization (WL) mechanisms compete with the inelastic electron-magnon, e - m , scattering to produce the minimum in ρ xx (T) , whereas the minimum in ρ xy AH (T) is caused by the competing contributions from the e - d and e - m scattering, as WL does not contribute to ρ xy AH . Another novel finding is that the e - d scattering contributions to ρ xy AH (T) and ρ xx (T) scale with each other. In sharp contrast, in crystalline films, enhanced electron-electron Coulomb interaction (EEI), which is basically responsible for the resistivity minimum, does not contribute to ρ xy AH with the result that no minimum in ρ xy AH (T) is observed. The conventional ρ xy AH = f (ρ xx) scaling breaks down completely in the present case. However, when ρ xy AH (T) is corrected for the e - d contribution and ρ xx (T) for both e - d and WL contributions (only EEI) in the amorphous (crystalline) films, the AH coefficient, R A (T) = ρ xy AH (T) / 4 π M s (T) , (calculated from the corrected ρ xy AH and spontaneous magnetization, M s ), perfectly scales with ρ xxT , the temperature-dependent part of the corrected ρ xx , for all the CFS thin films. [ABSTRACT FROM AUTHOR]

Grain boundaries (GBs) in polycrystalline graphene could significantly modulate the physicochemical properties of graphene films, and have attracted intense interest. However, fundamental magnetotransport mechanisms of GBs in bilayer graphene grown by chemical vapour deposition (CVD) are scarcely reported. In this work, we synthesize bilayer graphene bicrystals on polycrystalline Cu foils and measure the electronic properties of such grains as well as of individual graphene grain boundaries. Interestingly, the pronounced metallic character of GB is observed, which is dramatically different from individual grains. Large linear magnetoresistance in graphene bicrystals is observed, which attributes to inhomogeneous charge transport, decorated by quantum interference effects at low temperatures. The measurement data show that individual boundaries between coalesced grains impede electrical transport, suppress the magnetoresistance and enhance intervalley scattering, leading to degradation of electrical performance of CVD graphene. Nevertheless, GBs embedded in a perfect graphene sheet can tune its electronic structure at the nanoscale, act as quasi-one-dimensional metallic wires and can be used as good candidates for strong magnetic field sensors. This work is beneficial to the fundamental understanding of the role of GBs in CVD-grown graphene and opens a potential avenue of application for polycrystalline bilayer graphene in functional devices. The pronounced metallic character of grain boundary is observed in bilayer graphene bicrystals synthesized using the solid-state-source CVD method, which is dramatically different from individual grains. Electrical transport measurements show that individual boundaries between coalesced grains impede electrical transport, suppress the magnetoresistance and enhance intervalley scattering in graphene. Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract Experimental data transverse magnetoresistance of p-type Si whiskers for different temperatures (1.6–50K) and temperature variation of the phase coherence length (1) and spin-orbit coherence length (2) in p-type Si whiskers. Highlights • The influence of magnetic impurity in microcrystals of Si is studied. • Transport of a boron admixture is associated with a weak localization. • Evaluated the phase coherence length and spin-orbit coherence length. Abstract 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 l φ and spin-orbit coherence length l so 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 _B_ whisker with variable-range conductance, which indicates substantial impact of Ni impurities on the whisker magnetoresistance. [ABSTRACT FROM AUTHOR]

Abstract Topological and thermal disorder complicate the mobility characterization in poly(3,4-ethylenedioxythiophene) systems and presently leaves the exact transport mechanisms not fully understood. Here we show that ac -Hall measured by lock-in amplifier is able to resolve the Hall voltage in semimetallic polymers between room temperature and 32 K. These results are evaluated using an organic random phase model. This accounts for the role of tail states and, particularly, for thermal disorder of molecular semiconductors. We report band mobilities up to 3.7 cm2 V−1 s−1 in semimetallic polymers occurring in delocalized bands that originate from significant electron coherence across the polymer chains. Graphical abstract Image 1 Highlights • Moderate disorder inside semimetallic conducting polymers makes the band widths larger than the random disorder potentials fluctuations. • This effect is used to probe low, but stable Hall voltages in presence of dynamic disorder. • We present an organic phase model to derive temperature-dependent band mobilities. • We demonstrate band mobilities for 3 types of commonplace conducting poly(3,4-ethylene-dixoythiophenes). [ABSTRACT FROM AUTHOR]