Non-saturating Linear Magnetoresistance Research Articles

Nonsaturating Linear Magnetoresistance Manifesting Two-Dimensional Transport in Wet-Chemical Patternable Bi2O2Te Thin Films.

Two-dimensional (2D) materials with exotic transport behaviors have attracted extensive interest in microelectronics and condensed matter physics, while scaled-up 2D thin films compatible with the efficient wet-chemical etching process represent realistic advancement toward new-generation integrated functional devices. Here, thickness-controllable growth and chemical patterning of high-quality Bi2O2Te continuous films are demonstrated. Noticeably, except for an ultrahigh mobility (∼45074 cm2 V-1 s-1 at 2 K) and obvious Shubnikov-de Hass quantum oscillations, a 2D transport channel and large linear magnetoresistance are revealed in the patterned Bi2O2Te films. Investigation implies that the linear magnetoresistance correlates with the inhomogeneity described by P. B. Littlewood's theory and EMT-RRN theory developed recently. These results not only reveal the nonsaturating linear magnetoresistance in high-quality Bi2O2Te but shed light on understanding the corresponding physical origin of linear magnetoresistance in 2D high-mobility semiconductors and providing a pathway for the potential application in multifunctional electronic devices.

Large linear magnetoresistance and nontrivial band topology in In3Rh

While In3Rh has been predicted to be a three-dimensional Dirac semimetal, experimental studies of its physical properties are lacking. Here, we report the angular-dependent magnetoresistance (MR) measurements of In3Rh single crystals under high magnetic fields up to 32 T. The crystals show large, non-saturating linear MR, and remarkable quantum oscillations with multi-frequencies. Analysis of the quantum oscillations reveals that there are three bands hosting a nontrivial Berry phase, which is corroborated by first-principles calculations. Our work may provide a platform for exploring topological materials in indium-rich transition metal compounds.

Effect of thickness on the superconducting properties of the thin films of FeTe0.55Se0.45 deposited on YSZ substrates using Pulsed laser deposition (PLD) technique

We report the successful fabrication of thin films of thickness ∼26 nm, 59 nm, 76 nm, and 158 nm of the composition FeTe0.55Se0.45 on the (100)-oriented Yttria-stabilized zirconia (YSZ) substrate using the pulsed laser deposition (PLD) technique. The effect of thickness on the structure and superconducting properties of the thin films has been investigated. X-ray diffraction study reveals the growth of thin films along the c-axis. The temperature-dependent resistivity measurements confirm superconductivity in all the fabricated thin films, and the highest ∼ 16.2 K has been observed for the thin film of thickness ∼59 nm, which is higher than the corresponding value of the polycrystalline target sample. The superconducting parameters such as upper critical magnetic field coherence length thermally activated energy (TAE) U0, and vortex phase state have been measured by magnetotransport measurements near in the different applied magnetic fields up to 12 T. The TAE values determined from the conventional and modified thermally activated flux flow (TAFF) models are discussed and compared. A crossover from 2-dimensional (2D) vortex to 3-dimensional (3D) vortex behaviour has been observed. The vortex phase diagrams are used to observe the transition from the vortex liquid to the vortex glass state in the grown thin films. Moreover, magnetoresistance (MR) measurements show non-saturating linear magnetoresistance (LMR) in the high field region, indicating the presence of the possible topological state in the grown thin films. The values of magnetic field dependent transport critical current density, have been evaluated from the current-voltage (I-V) curves. Furthermore, the normalised pinning force density has been used to characterize the pinning processes using the Dew Hughes’ scaling rule which reveals that the grown thin films contain δl-surface pinning centers.

Disorder-controlled linear magnetoresistance in monolayer graphene

The nonsaturating linear magnetoresistance (MR) in graphene has been found for more than ten years, but its origin still lacks a quantitative study. Here, we report magneto-transport properties of monolayer graphene samples grown on silicon carbide. A positive parabolic MR is observed at low magnetic fields, and it is transformed into a large linear MR with increasing field. The observed linear MR is gradually suppressed either by increasing temperature or by increasing annealing time. The slope of the linear MR is proportional to the Hall mobility, and the crossover field, representing a transition from quadratic to linear field dependence, is proportional to the inverse of the Hall mobility. We therefore attribute the linear MR to a classical origin. This classical MR is considered to be controlled by the interaction between carrier and the low-mobility island, and the fraction of the low-mobility island is extracted. The extracted fraction is consistent with the calculated results when the absorbed acceptor is regarded as the main source of the disorder. Our data also can be explained by the effective-medium theory.

Single crystal growth and physical properties of layered compound SrCdBi2

We have grown the high quality single crystals of SrCdBi2 successfully and investigated the physical properties systematically through measurements of magnetoresistance (MR), Hall effect, magnetic susceptibility, and specific heat measurements. The compound is a nonmagnetic 112-type pnictide with a Bi square net layer, which is potential for hosting Dirac fermions. We found that it exhibited metallic behavior with an anomaly appearing at around 210 K. MR study reveal that the electronic structure of SrCdBi2 is quasi-two-dimensional. At low temperatures, we observed magnetic field induced metal-to-insulator-like transition and resistivity plateau, nonsaturating quasilinear MR, and high carrier mobility in magnetotransport measurements, which indicate the possible existence of nearly massless Dirac fermions in SrCdBi2. The anomaly at around 210 K can be observed in resistivity, Hall effect, and magnetic susceptibility, but cannot be detected in heat capacity. This implies the anomaly might be caused by domain formation or disorder. We found that the nonsaturating linear MR in SrCdBi2 is likely caused by both of the quantum linear dispersion and the classical disorder. Our findings suggest that SrCdBi2 is a natural experimental platform for realizing the topological properties of nonmagnetic 112-type pnictides.

Resistance anomaly and linear magnetoresistance in thin flakes of itinerant ferromagnet Fe3GeTe2

Research interests in recent years have expanded into quantum materials that display novel magnetism incorporating strong correlations, topological effects, and dimensional crossovers. Fe3GeTe2 represents such a two-dimensional van der Waals platform exhibiting itinerant ferromagnetism with many intriguing properties. Up to date, most electronic transport studies on Fe3GeTe2 have been limited to its anomalous Hall responses while the longitudinal counterpart (such as magnetoresistance) remains largely unexplored. Here, we report a few unusual transport behaviors on thin flakes of Fe3GeTe2. Upon cooling to the base temperature, the sample develops a resistivity upturn that shows a crossover from a marginally –ln T to a –T 1/2 dependence, followed by a lower-temperature deviation. Moreover, we observe a negative and non-saturating linear magnetoresistance when the magnetization is parallel or antiparallel to the external magnetic field. The slope of the linear magnetoresistance also shows a nonmonotonic temperature dependence. We deduce an anomalous contribution to the magnetoresistance at low temperatures with a scaling function proportional –HT 1/2, as well as a temperature-independent linear term. Possible mechanisms that could account for our observations are discussed.

Analytical formula describing the non-saturating linear magnetoresistance in inhomogeneous conductors

The effective-medium theory (EMT) has proved successful in modeling the non-saturating linear magnetoresistance induced by inhomogeneity. However, calculating magnetoresistance using the EMT usually involves solving coupled integral equations which have no analytical solutions, and therefore, it is still difficult to directly compare the predictions of EMT with experimental data. Here we demonstrate that the linear magnetoresistance predicted by the EMT can be either exactly formulated or well approximated by a simple analytical equation in a number of known situations. The relations between the EMT parameters and the phenomenological parameters k and a are evaluated. Our results provide a convenient and effective method for extracting the EMT parameters from experimental data.

Linear magnetoresistance induced by mobility fluctuations in iodine-intercalated tungsten ditelluride

We report a systematic study of the magnetoresistance, Hall effect, and the electronic structure in an iodine-intercalated tungsten ditelluride (${\mathrm{WTe}}_{2}\mathrm{I}$) single crystal, which crystallizes in a centrosymmetric structure. ${\mathrm{WTe}}_{2}\mathrm{I}$ presents significant anisotropic magnetotransport behavior with the magnetic field rotated in the $xz$ and $yz$ planes and violation of the Kohler's rule. Unexpectedly, nonsaturating linear magnetoresistance (LMR) was observed under the magnetic field parallel to the $z$ axis and the current along the $x$ axis. The analysis of the Hall effect reveals that the carrier mobility in ${\mathrm{WTe}}_{2}\mathrm{I}$ is notably lower than that of ${\mathrm{WTe}}_{2}$ and meets the picture of the Parrish and Littlewood model, suggesting that the LMR is likely caused by disorder effects. First-principles calculations show that the electronic structure undergoes a topological phase transition from a Weyl state to a Dirac state due to iodine intercalation. This finding provides a platform to search for physical phenomena related to ${\mathrm{WTe}}_{2}$ and study the topological phase transition.

Synthesis mechanism and magnetoresistance effect of millimeter-sized GeTe faceted crystals

GeTe materials have a wide range of applications in the fields of thermoelectrics, phase-change switching or storage, ferroelectrics, spintronics, and so on. In this paper, millimeter-sized GeTe faceted crystals are synthesized through heterogeneous chemical reactions without metal catalysts or transport agents. Most of the crystals have hexagonal surfaces, while a few crystals have rectangular surfaces, which are dominated by the closest packed (111) planes and the low-energy (100) planes, respectively. The 180° and 141°/39° ferroelectric domain walls are found on the (111) plane of hexagonal GeTe crystals by the chemical etching. By studying the products under different conditions, it's inferred that the GeTe faceted crystals are grown below the melting point by the reactions of preferentially deposited Ge motes and Te2/GeTe2 vapor phase, which are caused by the partial dissociation of polycrystalline GeTe. Hexagonal GeTe crystals with (111) plane exhibit non-saturating linear magnetoresistance (MR) of ∼25.9% under 9 T at 4.2 K, but the MR of rectangular crystals with (100) plane is just ∼9.5%. The MR effect of GeTe is likely related to the spin splitting on band structure due to the Rashba effect and the intrinsic inhomogeneity of telluride because of the heavily self-doped characteristic.

From Low-Field Sondheimer Oscillations to High-Field Very Large and Linear Magnetoresistance in a SrTiO3-Based Two-Dimensional Electron Gas.

Quantum materials harbor a cornucopia of exotic transport phenomena challenging our understanding of condensed matter. Among these, a giant, nonsaturating linear magnetoresistance (MR) has been reported in various systems, from Weyl semimetals to topological insulators. Its origin is often ascribed to unusual band structure effects, but it may also be caused by extrinsic sample disorder. Here, we report a very large linear MR in a SrTiO3 two-dimensional electron gas and, by combining transport measurements with electron spectromicroscopy, show that it is caused by nanoscale inhomogeneities that are self-organized during sample growth. Our data also reveal semiclassical Sondheimer oscillations arising from interferences between helicoidal electron trajectories, from which we determine the 2DEG thickness. Our results bring insight into the origin of linear MR in quantum materials, expand the range of functionalities of oxide 2DEGs, and suggest exciting routes to explore the interaction of linear MR with features like Rashba spin-orbit coupling.

Classical linear magnetoresistance in exfoliated NbTe2 nanoflakes

Recently, the transition metal dichalcogenide ${\mathrm{NbTe}}_{2}$ was predicted to be a candidate material of topological semimetal. Here we report the magnetotransport data measured in two devices fabricated from ${\mathrm{NbTe}}_{2}$ nanoflakes. A nonsaturating linear magnetoresistance was observed in both devices at various temperatures. A close analysis shows that the observed linear magnetoresistance is not consistent with the Abrikosov quantum theory; instead, it can be well explained in the framework of the effective-medium theory which describes the classical magnetoresistance of inhomogeneous systems. Our results indicate that the linear magnetoresistance of ${\mathrm{NbTe}}_{2}$ is most likely a classical magnetoresistance induced by disorders and inhomogeneities. This speculation is supported by the abundant domain structures observed in ${\mathrm{NbTe}}_{2}$ crystals in transmission electron microscopy measurements.

Magnetoresistance and scaling laws in type-II Weyl semimetal WP2

Topological materials with extremely large magnetoresistance exhibit a prognostic feature of resistivity turn-on behaviour. This occurs when the temperature dependence of resistivity ρ(T) changes from metallic to semiconducting characteristics on application of external magnetic field above a threshold value. Here, we study the magneto-transport properties of type-II Weyl Semimetal WP2. The zero field electrical resistivity in the low temperature region indicates the dominant electron-phonon scattering. The saturation in ρ(T) curves under all applied magnetic fields are observed at low temperatures. A minimum in resistivity at ~40K is revealed in the temperature derivative of resistivity curves, which implies onset of field induced turn-on effect. Furthermore, a non-saturating linear magnetoresistance (MR) is observed above ~ 5 T which is generally assigned to linear energy dispersion near the Weyl nodes. However, Kohler's scaling fits the data well with resistivity ρ~(B/ρ0)m that implicitly explains the turn-on behaviour and the resistivity minimum. Thus, semi-classical theories of magnetoresistance are consistent with our data without the need to invoke topological surface states. Our findings in this work provides an alternative basis to understand the temperature dependence of magnetoresistance in topological materials.

Extremely large linear magnetoresistance in antimony crystal

In this article, we report the observation of extremely large non-saturating linear magnetoresistance (MR) in antimony (Sb) crystal. An extremely large magnetoresistance of 43 000% at 2 K and large unsaturating MR ∼70% at room temperature is observed at the magnetic field of 9 T. Hall measurements reveal a very high mobility ∼3.8 × 104 cm2 V s−1 of charge carriers and strong temperature dependence of carrier concentration and mobility. The respective scaling of MR and crossover field (B c ) from quadratic to linear MR with mobility and inverse of mobility describes the classical origin of large linear MR in this crystal as suggested by Parish and Littlewood model for disordered systems.

Linear magnetoresistance with a universal energy scale in the strong-coupling superconductor Mo8Ga41 without quantum criticality

The recent discovery of a nonsaturating linear magnetoresistance in several correlated electron systems near a quantum critical point has revealed an interesting interplay between the linear magnetoresistance and the zero-field linear-in-temperature resistivity. These studies suggest a possible role of quantum criticality on the observed linear magnetoresistance. Here we report our discovery of a nonsaturating, linear magnetoresistance in ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$, a nearly isotropic strong electron-phonon coupling superconductor with a linear-in-temperature resistivity from the transition temperature to $\ensuremath{\sim}55$ K. The growth of the resistivity in field is comparable to that in temperature, provided that both quantities are measured in the energy unit. Our data sets are remarkably similar to magnetoresistance data of the optimally doped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$, despite the clearly different crystal and electronic structures, and the apparent absence of quantum critical physics in ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$. A new empirical scaling formula is developed, which is able to capture the key features of the low-temperature magnetoresistance data of ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$, as well as the data of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$.

Enhanced Mobility and Large Linear Nonsaturating Magnetoresistance in the Magnetically Ordered States of TmNiC_{2}.

We have studied the magnetic, magnetotransport, and galvanomagnetic properties of TmNiC_{2}. We find that the antiferromagnetic and field induced metamagnetic and ferromagnetic orderings do not suppress the charge density wave. The persistence of Fermi surface pockets, open as a result of imperfect nesting accompanying the Peierls transition, results in an electronic carriers mobility of the order of 4×10^{3} cm^{2} V^{-1} s^{-1} in ferromagnetic state, without any signatures for a significant deterioration of nesting properties. This is independently evidenced by high, nonsaturating linear magnetoresistance reaching 440% at T=2 K and an analysis of the Hall conductivity. We thus demonstrate that, the coexistence of charge density wave and magnetism provides an alternative route to maintain high electronic mobility in the magnetically ordered state.

Huge linear magnetoresistance due to open orbits in γ−PtBi2

Some single-crystalline materials present an electrical resistivity which decreases between room temperature and low temperatures at zero magnetic field as in a good metal and switches to a nearly semiconductinglike behavior at low temperatures with the application of a magnetic field. Often, this is accompanied by a huge and nonsaturating linear magnetoresistance which remains difficult to explain. Here we present a systematic study of the magnetoresistance in single-crystal $\gamma$-PtBi$_2$. We observe that the angle between the magnetic field and the crystalline $c$ axis fundamentally changes the magnetoresistance, going from a saturating to a nonsaturating magnetic field dependence. In between, there is one specific angle where the magnetoresistance is perfectly linear with the magnetic field. We show that the linear dependence of the nonsaturating magnetoresistance is due to the formation of open orbits in the Fermi surface of $\gamma$-PtBi$_2$.

Superconductivity and Fermi Surface Anisotropy in Transition Metal Dichalcogenide NbTe2**Supported by the National Basic Research Program of China under Grant Nos 2018YFA0305600 and 2017YFA0303302, the National Natural Science Foundation of China under Grant Nos 11888101, 11774008, 11704414 and 11427805, the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB28000000, and Beijing Natural Science Foundation (Z180010).

Transition metal dichalcogenides, featuring layered structures, have aroused enormous interest as a platform for novel physical phenomena and a wide range of potential applications. Among them, special interest has been placed upon WTe2 and MoTe2, which exhibit non-trivial topology both in single layer and bulk as well as pressure induced or enhanced superconductivity. We study another distorted 1T material NbTe2 through systematic electrical transport measurements. Intrinsic superconductivity with onset transition temperature () up to 0.72 K is detected where the upper critical field (Hc) shows unconventional quasi-linear behavior, indicating spin-orbit coupling induced p-wave paring. Furthermore, a general model is proposed to fit the angle-dependent magnetoresistance, which reveals the Fermi surface anisotropy of NbTe2. Finally, non-saturating linear magnetoresistance up to 50 T is observed and attributed to the quantum limit transport.

Quadratic to linear magnetoresistance tuning in TmB4

The change of a material's electrical resistance (R) in response to an external magnetic field (B) provides subtle information for the characterization of its electronic properties and has found applications in sensor and storage related technologies. In good metals, Boltzmann's theory predicts a quadratic growth in magnetoresistance (MR) at low B, and saturation at high fields. On the other hand, a number of nonmagnetic materials with weak electronic correlation and low carrier concentration for metallicity, such as inhomogeneous conductors, semimetals, narrow gap semiconductors and topological insulators, two-dimensional electron gas (2DEG) show positive, non-saturating linear magnetoresistance (LMR). However, observation of LMR in single crystals of a good metal is rare. Here we present low-temperature, angle dependent magnetotransport in single crystals of the antiferromagnetic metal, TmB4. We observe large, positive and anisotropic MR(B), which can be tuned from quadratic to linear by changing the direction of the applied field. In view of the fact that isotropic, single crystalline metals with large Fermi surface (FS) are not expected to exhibit LMR, we attribute our observations to the anisotropic FS topology of TmB4. Furthermore, the linear MR is found to be temperature-independent, suggestive of quantum mechanical origin.

Signatures of long-range-correlated disorder in the magnetotransport of ultrathin topological insulators

In an ultrathin topological insulator (TI) film, a hybridization gap opens in the TI surface states, and the system is expected to become either a trivial insulator or a quantum spin Hall insulator when the chemical potential is within the hybridization gap. Here we show, however, that these insulating states are destroyed by the presence of a large and long-range-correlated disorder potential, which converts the expected insulator into a metal. We perform transport measurements in ultrathin, dual-gated topological insulator films as a function of temperature, gate voltage, and magnetic field, and we observe a metallic-like, non-quantized conductivity, which exhibits a weak antilocalization-like cusp at the low magnetic field and gives way to a nonsaturating linear magnetoresistance at large field. We explain these results by considering the disordered network of electron- and hole-type puddles induced by charged impurities. We argue theoretically that such disorder can produce an insulator-to-metal transition as a function of increasing disorder strength, and we derive a condition on the band gap and the impurity concentration necessary to observe the insulating state. We also explain the linear magnetoresistance in terms of strong spatial fluctuations of the local conductivity, using both numerical simulations and a theoretical scaling argument.

Magnetoresistance of a three-dimensional Dirac gas

We study the transversal magnetoconductivity and magnetoresistance of a massive Dirac fermion gas. This can be used as a simple model for gapped Dirac materials. In the zero-mass limit, the case of gapless Dirac semimetals is also studied. In the case of Weyl semimetals, to reproduce the nonsaturating linear magnetoresistance seen in experiments, the use of screened charged impurities is inevitable. In this paper, these are included using the first Born approximation for the self-energy. The screening wave number is calculated using the random phase approximation with the polarization function taking into account the electron-electron interaction. The Hall conductivity is calculated analytically in the case of no impurities and is shown to be perfectly inversely proportional to the magnetic field. Thus the magnetic field dependence of the magnetoresistance is mainly determined by $\sigma_{xx}$. We show that in the extreme quantum limit at very high magnetic fields the gapped Dirac materials are expected to have $\sigma_{xx}\propto B^{-3}$ leading to $\varrho_{xx}\propto B^{-1}$, in contrast with the gapless case where $\sigma_{xx}\propto B^{-1}$ and $\varrho_{xx}\propto B$. At lower fields, we find that the effect of the mass term is negligible and in the region of the Shubnikov-de Haas oscillations the two systems behave almost identically. We suggest a phenomenological scattering rate that is able to reproduce the linear behavior at the oscillating region. We show that in the case of the scattering rate calculated using the Born approximation, the strength of the relative permittivity and the density of impurities affects the magnetic field dependence of the conductivity significantly.