Transverse Magnetoresistance Research Articles

Chiral anomaly induced negative magnetoresistance and weak anti-localization in Weyl semimetal Bi0.97Sb0.03 alloy

Experimental access to massless Weyl fermions through topological materials promises substantial technological ramifications. Here, we report magneto-transport properties of Bi1−x Sb x alloy near the quantum critical point x = 3% and 3.5%. The two compositions that are synthesized and studied are single crystals of Bi0.97Sb0.03 and Bi0.965Sb0.035. We observe a transition from semimetal to semiconductor with the application of magnetic field in both specimens. An extremely large transverse magnetoresistance (MR) 1.8 × 105% and 8.2 × 104% at 2.5 K and 6 T is observed in Bi0.97Sb0.03 and Bi0.965Sb0.035, respectively. Kohler scaling of transverse MR reveals the crossover from low field quadratic MR to a high field linear MR at low temperatures in both samples. A decrease in longitudinal MR is observed only in Bi0.97Sb0.03 that implies the presence of chiral anomaly associated with the Weyl state at the crossover point (x = 0.03) in Bi1−x Sb x system. The chiral anomaly is absent for the sample Bi0.965Sb0.035. A sharp increase in longitudinal resistivity for Bi0.97Sb0.03 close to zero magnetic fields indicates the weak anti-localization effect in Bi0.97Sb0.03. Extremely high carrier concentrations and high mobilities have been recorded for both the samples.

Detecting topological phase transitions in cadmium arsenide films via the transverse magnetoresistance

Topological protection against localization causes electrical transport phenomena in disordered topological materials to differ from those in topologically trivial systems. For example, a transition between a regime of weak localization to one of weak antilocalization can occur in systems such as topological insulators and topological semimetals when an external potential is applied across the system. Here, we report on the transverse magnetoresistance of thin films of cadmium arsenide, a topologically nontrivial, as we tune the electronic states and the Fermi level. We show that the appearance of weak localization and weak antilocalization sensitively reflects the relative contributions of multiple transport channels involving both gapless (massless) and gapped (massive) Dirac fermion states present in these films. The data are consistent with expectations of the different topological states of these films. Weak (anti-)localization phenomena can, therefore, serve as a probe of the types of Dirac fermions present in topological semimetals.

Peculiarity of the low temperature magnetoresistive effect in the Corbino disk with magnetic ordering

The transverse magnetoresistance (MR) hysteresis loops of a magnetically ordered Corbino disk have been studied in the temperature range 300–2 K in an external magnetic field with induction up to 1 T oriented in the plane of the disk (ϕ = 0°) and perpendicularly to its plane (ϕ = 90°). The Corbino disk is made of a thin permalloy film obtained on an insulating sitall substrate by ion-beam sputtering. Independently of the temperature and measurement geometry, the field dependences of MR in the range of weak magnetic fields up to the magnetisation saturation exhibit sharp peaks of the negative MR caused by the domain walls motion during the magnetisation reversal of the sample. The position of the peak in the magnetic field (Bp) is determined by the temperature as well as the angle between magnetic field direction and the disk plane. It was found that a temperature change in the range of T = 300–2 K leads to a change in its position in the range of 0.2–6.0 mT and 8–22 mT at ϕ = 0° and ϕ = 90°, respectively. The magnetic field direction reorientation from in-plane to out-of-pane at T = 2 K leads to the Bp change from 6 to 22 mT. In the range of strong magnetic fields above the magnetization saturation field at ϕ = 0° the positive MR component decreases with induction and has a linear non-saturable dependence down to T ≈ 40–50 K due to the magnon MR component dominance. The complete freezing of magnons at T = 2 K leads to the absence of high-field magnetoresistive effect. At ϕ = 90° in weak fields, the MR changes its sign from positive to negative due to the anisotropic MR component dominance because of the disk magnetisation reorientation perpendicular to the current lines. In a strong field it changes the slope due to the saturation of negative anisotropic MR component, as well as possible additional contribution of the positive geometric Lorentzian MR.

Evidence of weak Anderson localization revealed by the resistivity, transverse magnetoresistance and Hall effect measured on thin Cu films deposited on mica

We report the resistivity of 5 Cu films approximately 65 nm thick, measured between 5 and 290 K, and the transverse magnetoresistance and Hall effect measured at temperatures 5 K < T < 50 K. The mean grain diameters are D = (8.9, 9.8, 20.2, 31.5, 34.7) nm, respectively. The magnetoresistance signal is positive in samples where D > L/2 (where L = 39 nm is the electron mean free path in the bulk at room temperature), and negative in samples where D < L/2. The sample where D = 20.2 nm exhibits a negative magnetoresistance at B < 2 Tesla and a positive magnetoresistance at B > 3 Tesla. A negative magnetoresistance in Cu films has been considered evidence of charge transport involving weak Anderson localization. These experiments reveal that electron scattering by disordered grain boundaries found along L leads to weak Anderson localization, confirming the localization phenomenon predicted by the quantum theory of resistivity of nanometric metallic connectors. Anderson localization becomes a severe obstacle for the successful development of the circuit miniaturization effort pursued by the electronic industry, for it leads to a steep rise in the resistivity of nanometric metallic connectors with decreasing wire dimensions (D < L/2) employed in the design of Integrated Circuits.

Normal-state negative longitudinal magnetoresistance and Dirac-cone-like dispersion in PtPb4 single crystals: a potential Weyl-semimetal superconductor candidate

Magnetotransport measurements of PtPb4 single crystals with the T c of ∼2.80 K reveal pronounced exotic topological nature. An anomalous negative longitudinal magnetoresistance (MR) related to the chiral anomaly and a linear-like transverse MR examined within the framework of quantum MR theory were studied. Results indicate the presence of chiral-anomaly-induced quantum transport associated with the Weyl states and show a Dirac-cone-like band dispersion in PtPb4. This work reveals the drastic impact of the concept that the surface electrons in a Weyl fermion state may dominate the normal-state magnetotransport in PtPb4, leading to the conclusion that PtPb4 can be a Weyl-semimetal superconductor candidate.

Features in low-temperature electrical resistivity of amorphous Cd3As2 films due to hopping conductivity with changing activation energy

Amorphous Cd3As2 films were deposited on single-crystalline SrTiO3 substrate by high-frequency non-reactive magnetron sputtering. Electrical resistivity of the film, measured within 3-75 K range, increases at cooling. Below ∼70 K, negative transverse magnetoresistance observed. Features in electrical resistivity and magnertoresistance can be attributed to variable-range hopping conductivity of the Mott type with local activation energy, which is temperature-dependent. Two temperature ranges in the hopping conductivity observed. Appearing two ranges is in qualitative accordance with the Mott-Davis energy-band model developed for amorphous semiconductors. High temperature range of the hopping conductivity is attributed to electron hops between localized states, positioned inside band tails, whereas electron hops between localized states, positioned inside Fermi-peak, can be responsible for low-temperature range. At taking into account temperature dependences of local activation energy, universal expression for various mechanisms of the hopping conductivity could be successfully applied to analyze the experimental data.

Anomalous Thermoelectric Transport Properties of Fe‐Rich Magnetic FeTe

The interplay between magnetism and quantum effects has motivated several thermoelectric studies on iron‐telluride yet with little insight on the anomalous features in transport properties near magnetostructural transition temperature (≈70 K). A detailed investigation is carried out on Fe1.1Te by characterizing magnetic, heat capacity, galvanomagnetic, and thermoelectric transport properties to understand the electronic, magnetic, and structural origin of those anomalies. The magnetic susceptibility indicates a bicollinear stripe and short‐range ordering in the antiferromagnetic and paramagnetic domains, respectively. Hall conductivity and transverse magnetoresistance reveal a multicarrier transport impacted by spin fluctuations and magnons. Contributions from phonon‐drag and magnon‐drag are evaluated to understand the origin of the broad peak in antiferromagnetic thermopower. The peak at ≈50 K and the insignificant entropy contribution from the magnonic heat capacity support the phonon‐drag as the origin. The field‐dependent enhancement of thermal conductivity must be associated with field‐dependent spin‐phonon coupling modification. The field‐induced thermopower reduction can be attributed to the suppression of magnons or paramagnons, as evidenced by the magnetic susceptibility data. Above 70 K, the thermal conductivity drops sharply due to the structural change modifying phonon modes. Understanding these properties originated from the spin, and quantum effects are instrumental for designing high‐performance spin‐driven thermoelectrics.

Thermopower peculiarities and Umkehr effect in strained bismuth wires

Measurements of the transverse magnetothermopower and magnetoresistance in single bismuth wires are performed at 80 K. Manifestation of the asymmetry in the magnetothermopower defined as Umkher effect is observed. Investigations of the magnetotransport properties under uniaxial strain reveal a rearrangement of the electronic structure with subsequent changes in the anisotropy of the Fermi surface at high strain rates. A moderate applied strain leads to a decrease in the magnitude of the Umkehr effect in the thermopower up to the vanishing of the effect along the binary axis. The observed behavior of the Umkehr effect is attributed to a decrease in tilt angle φ of electronic ellipsoids under strain, which is consistent with the phenomenological analysis of transport phenomena in bismuth.

Anomalous anisotropic magnetoresistance in single-crystalline Co/SrTiO3(001) heterostructures* *Project supported by the National Natural Science Foundation of China (Grant Nos. 12174163 and 91963201), the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. IRT-16R35), and the 111 Project, China (Grant No. B20063).

The anisotropic magnetoresistances (AMRs) in single crystalline Co(6 nm)/SrTiO3(001) heterostructures from 5 K to 300 K with the current direction setting along either Co[100] or Co[110] are investigated in this work. The anomalous (normal) AMR is observed below (above) 100 K. With the current along Co[100] direction, the AMR shows negative longitudinal and positive transverse magnetoresistances at T < 100 K, while the AMR is inverse with the current along Co[110]. Meanwhile, the amplitude ratio between Co[110] and Co[100] is observed to be as large as 29 at 100 K. A crystal symmetry-adapted model of AMR demonstrates that interplay between the non-crystalline component and crossed AMR component results in the anomalous AMR. Our results may reveal more intriguing magneto-transport behaviors of film on SrTiO3 or other perovskite oxides.

Theoretical study of 3D quantum Hall effect in periodic electron system

The exsitance of three-dimensional Hall effect (3DQHE) due to spontaneous Fermi surface instabilities in magnetic field was proposed decades ago, and has stimulated recent progress in experiments. The reports in recent experiments show that the Hall plateaus and vanishing transverse magneto-resistivities (TMRs) (which are two main signatures of 3DQHE) are not easy to be observed in natural materials. And two main different explanations of the slow varying slope like Hall plateaus and non-vanishing TMRs (which can be called as quasi-quantized Hall effect (QQHE)) have been proposed. By studying the magneto-transport with a simple effective periodic 3D system, we show how 3DQHE can be achieved in certain parameter regimes at first. We find two new mechanisms that may give rise to QQHE. One mechanism is the low Fermi energy effect, and the other is the strong impurity effect. Our studies also proved that the artificial superlattice is an ideal platform for realizing 3DQHE with high layer barrier periodic potential.

Angular dependence of magnetoresistance and planar Hall effect in semimetals in strong magnetic fields

The semiclassical transport theory is especially powerful for investigating galvanomagnetic effects. Generally, the semiclassical theory is applicable only in weak fields because it does not consider Landau quantization. Herein, we extend the conventional semiclassical theory by considering Landau quantization through the field dependence of carrier density in semimetals. The extended semiclassical theory is applicable even in strong fields, where Landau quantization is noticeable. Using this new approach, we explain the qualitative change in the angular dependence of transverse magnetoresistance (TMR), anisotropic magnetoresistance (AMR), and planar Hall effect (PHE) in bismuth with an increase in the magnetic field. This unveils the puzzle of nontrivial field-induced changes in TMR, AMR, and PHE observed recently in semimetal bismuth.

Critical fields and features of electromagnetic transport of Bi2Se3 whiskers at low temperatures

The temperature dependences of resistance of n-type conductivity Bi2Se3 whiskers with doping concentration (1–2)⋅1019 cm−3 were studied in the temperature range 1.6–300 K. The sharp drop of the resistance was detected that is a result of a partial transition to the superconductive state at the critical temperature Tc = 5.3 K and probably due to the inclusion of β-PdBi2 phase in the studied samples. The transverse magnetoresistance of Bi2Se3 whiskers with various concentration of Pd doping impurity corresponding to the metal side of metal-insulator transition was studied in a magnetic field of 0–10 T. Superconductivity suppression effect by the magnetic field was found that permits to create the basic parameters such as the upper critical field Bc2 = 1.5 T, the coherence length of the superconductor ξ (0) = 15 nm and the superconducting gap Δ ≈ 0.8 meV. Studies of the n-type conductivity Bi2Se3 whiskers allow to create on their basis magnetic field sensors with a sensitivity of about 3.5% / T, capable in the temperature range of 4.2–77 K. The investigated crystals can also be used in the magnetic switch-control sensors magnetic switches due to the transition to the superconducting state at the critical temperature Tc, depending on a magnetic field induction.

Корреляция электрических, гальваномагнитных и магнитных характеристик нанокристаллических пленок железа, полученных методом ионно-ассистированного осаждения

Here we present the measurements of the temperature dependence of resistance, transverse and longitudinal magnetoresistance (MR) in nanocrystalline iron films in the temperature range 2-300 K and the sweep of the magnetic field up to 8 T. Thin nanocrystalline films of α- iron phase with 80 nm thickness were obtained by ion-beam assisted deposition on a silicon substrate. In addition to the shape anisotropy, the obtained iron films exhibited perpendicular magnetic anisotropy (PMA), which disappeared after annealing the films at a temperature of 450 oC in a vacuum. The effect of PMA on the sign and magnitude of the MR of iron films, as well as on the magnetic field dependences of the magnetoresistive effect, recorded at different orientations of the external magnetic field with respect to the film plane and current direction, is experimentally shown. The results obtained are discussed in the framework of modern views on the processes of charge transfer in a weakly disordered ferromagnetic films with different magnetic anisotropy and domain structure when a weak (less than the saturation field of magnetization) or strong (higher than the saturation field) external magnetic field is applied.

Tilted Dirac cone gapped due to spin-orbit coupling and transport properties of a 3D metallic system CaIr2Ge2

We present results of electrical transport (resistance, magnetoresistance, Hall effect) and heat capacity measurements performed on single crystals of the tetragonal compound, CaIr2Ge2. Their analysis is supported by the electronic structure data (band dispersion, density of states, Fermi surface), calculated for this three-dimensional (3D) system from first principles, using the full-potential local-orbital code. Interestingly, we have found the highly anisotropic Dirac cone at the Fermi level, in the bulk band structure, being gapped due to the strong p-d hybridization and spin-orbit coupling effects. However, this feature seems to have insignificant influence on the transport properties studied. The compound appears to be metallic-like with a rather low Sommerfeld coefficient (3.23 mJ mol−1 K−2) and non-superconducting even down to 0.1 K. In turn, the transverse magnetoresistance curves do not saturate with magnetic field up to 9 T revealing sub-quadratic scaling but relatively small values (up to 11 % in 2 K) as for Dirac semimetals. We may ascribe these properties to small values of the estimated relaxation time of charge carriers (~10−13 s) and, therefore, small electronic mobilities. Moreover, the angular magnetoresistance exhibits very small anisotropy (~ 1.7 %), in line with weakly anisotropic large 3D Fermi surface sheets, predicted by our calculations.

Magnetoresistance, Hall Effect, and Shubnikov–de Haas Effect in Antiferromagnetic Kondo Semimetal CeRu2Al10

To investigate the electronic state of CeRu2Al10, which exhibits an unusual antiferromagnetic order below TN = 27 K, we measured the electrical resistivity ρ, the transverse magnetoresistance (TMR)...

Effect of disorder on the transverse magnetoresistance of Weyl semimetals

We study the effect of random potential created by different types of impurities on the transverse magnetoresistance of Weyl semimetals. It is shown that the magnetic field and temperature dependence of magnetoresistance is strongly affected by the type of impurity potential. Two limiting cases are analyzed in detail: ($i$) the ultra-quantum limit, when the applied magnetic field is so high that only the zeroth and first Landau levels contribute to the magnetotransport, and ($ii$) the semiclassical situation, for which a large number of Landau levels comes into play. A formal diagrammatic approach allowed us to obtain expressions for the components of the electrical conductivity tensor in both limits. In contrast to the oversimplified case of the $\delta$-correlated disorder, the long-range impurity potential (including that of Coulomb impurities) introduces an additional length scale, which changes the geometry and physics of the problem. It is shown that the magnetoresistance can deviate from the linear behavior as a function of magnetic field for a certain class of impurity potentials.

Anomalous Hall effect and negative longitudinal magnetoresistance in half-Heusler topological semimetal candidates TbPtBi and HoPtBi

Half-Heusler compounds have attracted significant attention because of their topologically non-trivial electronic structure, which leads to unusual electron transport properties. We thoroughly investigated the magnetotransport properties of high-quality single crystals of two half-Heusler phases, TbPtBi and HoPtBi, in pursuit of the characteristic features of topologically non-trivial electronic states. Both studied compounds are characterized by the giant values of transverse magnetoresistance with no sign of saturation in a magnetic field up to 14 T. HoPtBi demonstrates the Shubnikov–de Haas effect with two principal frequencies, indicating a complex Fermi surface; the extracted values of carrier effective masses are rather small, 0.18 me and 0.27 me. The investigated compounds exhibit negative longitudinal magnetoresistance and anomalous Hall effect, which likely arise from a nonzero Berry curvature. Both compounds show strongly anisotropic magnetoresistance that in HoPtBi exhibits a butterfly-like behavior.

Two-Dimensional Surface Topological Nanolayers and Dirac Fermions in Single Crystals of the Diluted Magnetic Semiconductor (Cd1−x−yZnxMny)3As2 (x + y = 0.3)

Features in the transverse magnetoresistance of single-crystalline diluted magnetic semiconductors of a (Cd1−x−yZnxMny)3As2 system with x + y = 0.3 have been found and analyzed in detail. Two groups of samples have been examined. The samples of the first group were thermally annealed for a long time, whereas the samples of the second group were not thermally annealed. The Shubnikov–de Haas (SdH) oscillations were observed for both groups of the samples within a 4.2 ÷ 30 K temperature range and under transverse magnetic field sweeping from 0 up to 11 T. The value of a phase shift, according to the SdH oscillations, was found to be a characteristic of the Berry phase existing in all the samples, except the unannealed sample with y = 0.08. Thickness of 2D surface topological nanolayers for all the samples was estimated. The thickness substantially depended on Mn concentration. The experimental dependence of reduced cyclotron mass on the Fermi wave vector, extracted from the SdH oscillations for the samples with different doping levels, is in satisfactory agreement with the predicted theoretical linear dependence. The existence of the Dirac fermions in all the samples studied (except the unannealed sample with y = 0.08) can be concluded from this result.

LARGE VALUES OF THE TRANSVERSE M UES OF THE TRANSVERSE MAGNETIC RESISTANCEOF SINGLE CRYSTAL NICKEL FILMS

Background. The anisotropy of the transverse magnetoresistance of single-crystal nickel films was studied in this work. The measurements were carried out on samples whose surface plane coincided with the [001] plane. Studies of the magnetoresistance in a single-crystal nickel film have shown the effect of tensile stresses acting on it from the side of magnesium oxide. The modification of the anisotropy of magnetoreflection of a film on a substrate as compared to a free sample is apparently associated with a change in the shape of the Fermi surface of carriers.

Electron transport in Dirac nodal-line semimetal ZrSiS

We report a study of magnetization and transport properties such as electrical resistivity, thermal conductivity, and thermal Hall conductivity in high fields and at low temperatures for ZrSiS single crystals. Here, we find that the thermal conductivity (κxx/T) is strongly suppressed in applied fields, having a good correlation with the large positive transverse magnetoresistance (TMR). The thermal Hall conductivity (κxy/T) displays a sharp peak at extremely low field which reveals the high mobility of the electrons. In addition, the TMR displays clear Shubnikov de Haas (SdH) oscillation at low temperatures. Although the Zeeman splitting is obviously appeared in de Haas-van Alphen (dHvA) oscillation of the magnetization measurements and distinguished easily from the SdH oscillation. Negative longitudinal magnetoresistance (LMR) is also observed in ZrSiS which may be related to the chiral anomaly.