Nonlinear Hall Resistance Research Articles

Semimetallic electrical properties of rock salt-type LaBi thin films grown by solid-phase reaction of La/Bi multilayer precursors

Highly crystalline LaBi thin films, grown by solid-phase reaction of La/Bi multilayer precursors, showed metallic conduction and nonlinear Hall resistance, indicating the semimetallic nature with electron and hole carriers.

Multiple channel transport properties of topological surface states in SmB6 nanoribbons

SmB6, a topological Kondo insulator, possesses topologically protected surface states, in which carrier mobility is supposed to be high but is significantly varied in orders of magnitude dependent upon characterization methods. Herein, we performed magnetoresistance measurements on a Hall-bar device constructed on a highly uniform SmB6 nanoribbon with (001) surface grown by chemical vapor deposition. Unusual non-linear Hall resistance was observed at low temperature and explained with a two-carrier model. The two types of carriers were attributed to two types of Fermi pockets on the Brillouin zone of the SmB6 (001) surface. The Fermi pocket on Γ point provided high hole mobility up to 1.4×103 cm2/V s but low hole density at a temperature of 2.2 K. On the other hand, the Fermi pockets on X points supplied low electron mobility down to 1.8 cm2/V s but high electron density. The identification of the two types of pockets laid the foundation for the understanding of the transport via the topological surface states of the SmB6 (001) surface.

Low-temperature resistivity upturn and weak antilocalization in layered Ta1.04Ru0.78Te4 bulk single crystal

Quantum corrections to conductivity, which reflect charge carriers' quantum behavior, are a significant topic in condensed state physics and device design. A resistivity upturn at low temperature or weak antilocalization due to quantum corrections has been often observed experimentally. However, the coexistence of the low-temperature resistivity upturn and weak antilocalization from quantum corrections in bulk single crystals is seldom reported. Here, we report the transport properties of bulk Ta1.04Ru0.78Te4 single crystals. The samples showed a metallic behavior with a resistivity upturn below ∼8.6 K, which may be the result of quantum correction to the resistivity. The magnetic field enhances the upturn feature. The weakly nonlinear Hall resistivity with a positive slope suggests a p-type and multiband feature for bulk Ta1.04Ru0.78Te4; the electron and hole concentrations and mobilities of the samples are very close to each other and have the same order of magnitude. The Ta1.04Ru0.78Te4 single crystals displayed small and positive magnetoresistance, and the 3 K magnetoresistance at 9 T was about 15%. A lack of overlap of Kohler's plot curves at different temperature implies the violation of Kohler's rule. At low temperature, the dip-like magnetoresistance at low field strengths suggests a weak antilocalization in the Ta1.04Ru0.78Te4 single crystal. A small phase coherence length implies weakened screening and enhancing electron–electron interaction effects. These results reveal the quantum transport properties of Ta1.04Ru0.78Te4 single crystals, which can be considered in the future device design.

Carrier‐Modulated Anomalous Electron Transport in Electrolyte‐Gated SrTiO3

The anomalous transport phenomena and underlying mechanism of SrTiO3 have been long term concerned, including the Kondo physics and anomalous Hall effects to be discussed herein. Nevertheless, a clarification of the physical origins for these phenomena and their intertransitions upon varying carrier density remain to be an issue, due to the limited modulation of carrier density. Herein, the intriguing transport behaviors of electrolyte‐gated SrTiO3 in the field‐effect transistor geometry are investigated, which allows a relatively wide carrier density window. It is revealed that the remarkable Kondo‐like resistance upturn, identified at relatively low carrier density, becomes gradually disappeared and replaced by the emerging nonlinear Hall resistance with increasing gating voltage, indicating the interesting gating‐controlled transport behaviors. The detailed discussions on the underlying physics suggest that the gating‐controlled transport can be well described by the multiband transport model taking into account magnetic scattering in the channel layer, a comprehensive scenario for the emergent transport effects in carrier‐doped SrTiO3. The present work provides a promising platform for exploring novel quantum materials phenomena in SrTiO3 and analogous systems.

Dirac semimetal like transport features in high-quality Bi0.96Sb0.04 thin films

This work demonstrates that Dirac semimetal like transport properties can be observed in high quality, epitaxial Bi0.96Sb0.04 films grown by two-step growth method using molecular beam epitaxy. A large linear magnetoresistance (MR) of 825% (7 T, 1.8 K) and nonlinear Hall resistivity were observed, which indicate the presence of high mobility conducting layers that correspond to topological semimetallic layers. A field-induced semimetal-semiconductor transition appeared, which is a unique characteristic of Dirac semimetals. Large negative MR was also observed when the magnetic field was parallel to the current direction due to the chiral anomaly related to topological magnetoelectric effects. These transport phenomena are typical signatures of Dirac semimetals, which suggests that epitaxial Bi0.96Sb0.04 films can be regarded as Dirac semimetals.

Quantum oscillations and weak anisotropic resistivity in the chiral fermion semimetal PdGa

We perform a detailed analysis of the magnetotransport and de Haas-van Alphen (dHvA) oscillations in crystal PdGa which is predicted to be a typical chiral Fermion semimetal from CoSi family holding a large Chern number. The unsaturated quadratic magnetoresistance (MR) and nonlinear Hall resistivity indicate that PdGa is a multi-band system without electron-hole compensation. Angle-dependent resistivity in PdGa shows weak anisotropy with twofold or threefold symmetry when the magnetic field rotates within the (1$\bar{1}$0) or (111) plane perpendicular to the current. Nine or three frequencies are extracted after the fast Fourier-transform analysis (FFT) of the dHvA oscillations with B//[001] or B//[011], respectively, which is confirmed to be consistent with the Fermi surfaces (FSs) obtained from first-principles calculations with spin-orbit coupling (SOC) considered.

Observation of nonlinear planar Hall effect in magnetic-insulator–topological-insulator heterostructures

Interfacing topological insulators (TIs) with magnetic insulators (MIs) has been widely used to study the interaction between topological surface states and magnetism. Previous transport studies typically interpret the suppression of weak antilocalization or appearance of the anomalous Hall effect as signatures of magnetic proximity effect (MPE) imposed to TIs. Here, we report the observation of nonlinear planar Hall effect (NPHE) in Bi2Se3 films grown on MI thulium and yttrium iron garnet (TmIG and YIG) substrates, which is an order of magnitude larger than that in Bi2Se3 grown on nonmagnetic gadolinium gallium garnet (GGG) substrate. The nonlinear Hall resistance in TmIG/Bi2Se3 depends linearly on the external magnetic field, while that in YIG/Bi2Se3 exhibits an extra hysteresis loop around zero field. The magnitude of the NPHE is found to scale inversely with carrier density. We speculate the observed NPHE is related to the MPE-induced exchange gap opening and out-of-plane spin textures in the TI surface states, which may be used as an alternative transport signature of the MPE in MI/TI heterostructures.

GdV6Sn6: A Multi-carrier Metal with Non-magnetic 3d-electron Kagome Bands and 4f-electron Magnetism

Electronic properties of the single crystal of GdV6Sn6, where non-magnetic V-kagome layers are separated by magnetic Gd-triangular lattice, are investigated. GdV6Sn6 exhibits unique magnetotransport properties at low-temperature such as non-linear Hall resistivity and increase of resistance R in magnetic field H as R ~ H^0.75 up to 56 T with Shubnikov-De Haas oscillations. Investigation of the non-magnetic analogue YV6Sn6 and the first principles calculations reveal these properties are relevant to the bands arising from the V-kagome layer. A magnetic transition at 5 K in GdV6Sn6 modifies the transport properties, pointing to a coupling between Gd-spins on the triangular lattice and carriers in the V-kagome layer.

Impurity band conduction in Si-doped β -Ga2O3 films

By combining temperature-dependent resistivity and Hall effect measurements, we investigate donor state energy in Si-doped β-Ga2O3 films grown using metal-organic vapor phase epitaxy. High-magnetic field (H) Hall effect measurements (–90 kOe ≤ H ≤ +90 kOe) showed non-linear Hall resistance for T < 150 K, revealing two-band conduction. Further analyses revealed carrier freeze out characteristics in both bands yielding donor state energies of ∼33.7 and ∼45.6 meV. The former is consistent with the donor energy of Si in β-Ga2O3, whereas the latter suggests a residual donor state. This study provides critical insight into the impurity band conduction and the defect energy states in β-Ga2O3 using high-field magnetotransport measurements.

Nanometer-Thick Bismuth Nanocrystal Films for Sensoric Applications

The present article is concerned with investigations of the structural, surface morphological, and magnetotransport properties of DC magnetron-sputtered nanometer-thick Bi nanocrystal films on Si(111) substrates. Crystal structure and surface morphology were studied with X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, and atomic force microscopy. For the samples deposited at the melting point of Bi, 271 °C, equilibrium crystals formed and according to Wulff theorem acquire a specific shape determined by the surface tension. These crystals were investigated for different film thicknesses and deposition temperatures varying from 25 to 300 °C. Furthermore, magnetotransport characterization was carried out in steady and pulsed magnetic fields of up to 9 and 70 T, respectively. At low temperatures, clear weak antilocalization behavior is observed, attributed to 2D conduction channels. A nonlinear Hall resistance is also confirmed, ascribed to the coexistence of two types of carriers (p and n). This study contributes to the elucidation of the transport properties of the Bi thin films and opens new perspectives for their exploitation in modern applications such as sensorics.

One-dimensional antilocalization of electrons from spin disorder probed by nonlinear Hall effect

In recent years, nonreciprocal transport measurement has emerged as a probe of spin orbit interaction, spin texture, superconductivity, and other fundamental properties of materials. Here, we study the nonlinear Hall effect (NLHE) in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}/\mathrm{CoFeB}$ heterostructures measured by second harmonic voltage method. Magneto-optical Kerr effect measurements demonstrate the origin of the NLHE to be the asymmetric magnon scattering mechanism. Moreover, a linear relation between the nonlinear Hall resistance and the electron phase coherence length of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is observed between 5 and 50 K. We propose a phenomenological model that explains the enhancement of the NLHE below 50 K as a result of one-dimensional antilocalization of electrons from spin disorder, enabled by spin-momentum locking and conservation of angular momentum.

Nonsaturating Magnetoresistance and Nontrivial Band Topology of Type‐II Weyl Semimetal NbIrTe4

AbstractWeyl semimetals, characterized by nodal points in the bulk and Fermi arc states on the surface, have recently attracted extensive attention due to their potential application as materials for low‐energy‐consumption electronics. The thermodynamic and transport properties of a theoretically predicted Weyl semimetal NbIrTe4 is measured in high magnetic fields up to 35 T and low temperatures down to 0.4 K. Remarkably, NbIrTe4 exhibits a nonsaturating transverse magnetoresistance that follows a power‐law dependence in B. Low‐field Hall measurements reveal that hole‐like carriers dominate the transport for T > 80 K, while the significant enhancement of electron mobilities obtained by lowering T results in a non‐negligible contribution from electron‐like carriers, which is responsible for the observed nonlinear Hall resistivity at low T. The Shubnikov‐de Haas oscillations of the Hall resistivity under high B give the light effective masses of charge carriers and the nontrivial Berry phase associated with Weyl fermions. Further first‐principles calculations confirm the existence of 16 Weyl points located at kz = 0, ± 0.02, and ± 0.2 planes in the Brillouin zone.

Large nonlinear Hall effect in (FeCo)0.67Ge0.33/Ge heterojunctions

The large nonlinear Hall effect was found in (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions formed by sputtering amorphous [Formula: see text]-type (FeCo)[Formula: see text]Ge[Formula: see text] magnetic semiconductor films on near intrinsic n-type Ge substrate. It is very interesting that the mechanisms of the large nonlinear Hall effect in (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions are different at different temperature ranges. Below 10 K, the Hall resistance of (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions is almost the same as the anomalous Hall effect of (FeCo)[Formula: see text]Ge[Formula: see text] ferromagnetic films. While the temperature increased from 10 to 60 K, the nonlinear Hall resistance, longitudinal conductance, and magnetoresistance all increased quickly and reached the maximum at T[Formula: see text]=[Formula: see text]60 K. In this case, thermally excited conducting carriers can tunnel through the interfacial potential barrier in (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions. Thus, in the range of 10–60 K, the enhanced nonlinear Hall resistance can be attributed to the anomalous Hall effect which was further enhanced by interfacial Rashba spin–orbit coupling effect. When the temperature further increased from 60 to 250 K, the interfacial potential barrier weakened gradually, and the Hall resistance and magnetoresistance decreased due to the shunting of the Ge substrate. In this case, the nonlinear Hall effect of (FeCo)[Formula: see text]Ge[Formula: see text]/Ge heterojunctions can be explained very well by the two-band model of nonlinear Hall effect.

Shubnikov–de Haas and de Haas–van Alphen oscillations in the topological semimetal CaAl4

We report the magneto-transport properties of CaAl$_4$ single crystals with $C2/m$ structure at low temperature. CaAl$_4$ exhibits large unsaturated magnetoresistance $\sim$3000$\%$ at 2.5 K and 14 T. The nonlinear Hall resistivity is observed, which indicates the multi-band feature. The first-principles calculations show the electron-hole compensation and the complex Fermi surface in CaAl$_4$, to which the two-band model with over-simplified carrier mobility can't completely apply. Evident quantum oscillations have been observed with B//c and B//ab configurations, from which the nontrivial Berry phase is extracted by the multi-band Lifshitz-Kosevich formula fitting. An electron-type quasi-2D Fermi surface is found by the angle-dependent Shubnikov-de Haas oscillations, de Haas-van Alphen oscillations and the first-principles calculations. The calculations also elucidate that CaAl$_4$ owns a Dirac nodal line type band structure around the $\Gamma$ point in the $Z$-$\Gamma$-$L$ plane, which is protected by the mirror symmetry as well as the space inversion and time reversal symmetries. Once the spin-orbit coupling is included, the crossed nodal line opens a negligible gap (less than 3 meV). The open-orbit topology is also found in the electron-type Fermi surfaces, which is believed to help enhance the magnetoresistance observed.

Magnetotransport Properties of a Nodal Line Semimetal TiSi**Supported by the National Key Research Program of China under Grant Nos 2016YFA0401000 and 2016YFA0300604, the National Basic Research Program of China under Grant No 2015CB921303, the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB07020100, and the National Natural Science Foundation of China under Grant No 11874417.

We report the magnetoresistance (MR), de Haas-van Alphen (dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ(T) and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.

Linear positive and negative magnetoresistance in topological insulator Bi2Se3 flakes

The linear positive magnetoresistance (MR) and negative MR are emerging as intriguing phenomena in topological materials. Here, we report the magnetotransport properties of topological insulator Bi2Se3 flakes with different thicknesses grown by chemical vapor deposition. A non-saturating positive MR is observed in the perpendicular fields (B⊥I), while an evident negative MR is observed in the parallel fields (B//I). Both the positive MR and negative MR show a linear magnetic field dependence at high magnetic fields (B > 8 T). In addition, two types of carriers are extracted from the nonlinear Hall resistance measurements, which are attributed to the Bi2Se3 bulk electrons and the electron accumulation layer at the surface or Bi2Se3/SiO2 interface, respectively. The conductivity fluctuations in the accumulation layer are believed to be the origin for the observation of positive MR in the perpendicular fields and negative MR in the parallel fields with linear and non-saturating characteristics.

Dynamic evolution of photogenerated carriers at complex oxide heterointerfaces

Heterointerfaces between two insulators play a central role in the study of oxide electronics owing to a spectrum of emergent properties. Manipulating transport of the interface by light can result in significant modulation of the ground state and excite localized states. However, their dynamics and mechanisms of photogenerated carries remain unclear. Here, this study presents the dynamics of carrier density and mobility under and after light illumination by Hall effect over time. It is discovered that the density and mobility after light illumination obey a stretched exponential expression, further indicating that the variation of mobility caused by the electron-electron scattering plays an important role in the recovery process in addition to the reduction of carrier density. Meanwhile, a non-linear Hall resistance at the LaAlO3/SrTiO3 interface under the illumination of a 360 nm laser at low temperature is observed. Furthermore, the gating effect can tune the recovery process after light illumination and induce a disappearance of non-linear Hall resistance. The results provide the experimental support for detailed mechanisms of the nonequilibrium process and developing of all-oxide electronic devices based on heterointerfaces.

Dirac Cone Spin Polarization of Graphene by Magnetic Insulator Proximity Effect Probed with Outermost Surface Spin Spectroscopy

AbstractThe effects of the proximity contact with magnetic insulator on the spin‐dependent electronic structure of graphene are explored for the heterostructure of single‐layer graphene (SLG) and yttrium iron garnet Y3Fe5O12 (YIG) by means of outermost surface spin spectroscopy using a spin‐polarized metastable He atom beam. In the SLG/YIG heterostructure, the Dirac cone electrons of graphene are found to be negatively spin polarized in parallel to the minority spins of YIG with a large polarization degree, without giving rise to significant changes in the π band structure. Theoretical calculations reveal the electrostatic interfacial interactions providing a strong physical adhesion and the indirect exchange interaction causing the spin polarization of SLG at the interface with YIG. The Hall device of the SLG/YIG heterostructure exhibits a nonlinear Hall resistance attributable to the anomalous Hall effect, implying the extrinsic spin–orbit interactions as another manifestation of the proximity effect.

Crystal growth and magneto-transport properties of α-ZrSb2 and α-HfSb2

We report the synthesis of single crystals of α-ZrSb2/α-HfSb2 and their magneto-transport properties. Both of α-ZrSb2 and α-HfSb2 exhibit metallic behavior. The T3 behavior of zero-field resistivity for both compounds below 30 K indicates interband electron-phonon scattering. The magnetoresistance (MR) is found to obey Kohler's rule for ZrSb2 while the MR of HfSb2 deviates from this rule. A possible explanation for the results of Kohler's plot is considered, which is confirmed with the results of the Hall effect. The positive linear Hall resistivity of ZrSb2 suggests hole-type carriers and a mobility of , while the existence of two types of carriers in HfSb2 is confirmed from the nonlinear Hall resistivity.

Fermi surface reconstruction and anomalous low-temperature resistivity in electron-doped La2−xCexCuO4

We report $ab$-plane Hall-effect and magnetoresistivity measurements on $\mathrm{L}{\mathrm{a}}_{2\ensuremath{-}x}\mathrm{C}{\mathrm{e}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ thin films as a function of doping for magnetic fields up to 14 T and temperatures down to 1.8 K. A dramatic change in the low-temperature (1.8 K) normal-state Hall coefficient is found near a doping $\mathrm{Ce}=0.14$. This, along with a nonlinear Hall resistance as a function of magnetic field, suggests that the Fermi surface reconstructs at a critical doping of $\mathrm{Ce}=0.14$. A competing antiferromagnetic phase is the likely cause of this Fermi surface reconstruction. Low-temperature linear-in-$T$ resistivity is found at $\mathrm{Ce}=0.14$, but anomalously, also at higher doping. We compare our data with similar behavior found in hole-doped cuprates at a doping where the pseudogap ends.