Large Unsaturated Magnetoresistance Research Articles

Large magnetoresistance and nontrivial Fermi surface topology in quasi-one-dimensional Ta2PdSe6

We report the experimental investigation of quasi-one-dimensional (quasi-1D) Ta2PdSe6 single crystals by magnetotransport measurements under high magnetic fields up to 31 T. The crystals show large unsaturated magnetoresistance up to (1.8 × 105%) under 31 T at 1.6 K, accompanied by remarkable resistivity oscillations. The analysis of quantum oscillations reveals the existence of five Fermi pockets, consistent with theoretical calculations. Furthermore, our investigation suggested that band structure is modified by the electron correlations in Ta2PdSe6, which may provide a platform for exploring the interplay between electron effects and topological properties in quasi-1D materials.

The vertical longitudinal magnetoresistance in a van der Waals thin film of WTe2

We report the magneto-transport measurements of thin film devices of the topological Weyl semimetal WTe2 with the applied current along and vertical to the in-plane directions. The device is composed of a van der Waals thin film of WTe2 sandwiched between top and bottom Au electrodes. At low temperatures, we observe not only a large unsaturated magnetoresistance and Shubnikov–de Haas oscillations with current in the in-plane direction but also a saturated vertical longitudinal magnetoresistance and quantum oscillations with current in the out-of-plane direction in a thin film of WTe2. Our work provides insight into the origin of the unsaturated magnetoresistance in WTe2 and may inspire non-planar engineering to reach higher integration in spintronics.

Large unsaturated magnetoresistance and electronic structure studies of single-crystal GdBi

Single crystal of the binary equiatomic compound GdBi crystallizing in the rock-salt-type cubic crystal structure with the space group $Fm\overline{3}m$ has been grown by flux method. The electrical and magnetic measurements have been performed on well-oriented single crystals. The antiferromagnetic ordering of the Gd moments is confirmed at ${T}_{\mathrm{N}}=27.5$ K. The magnetization measurement performed at 2 K along the principal crystallographic direction [100] attained a value of $1.3\phantom{\rule{0.16em}{0ex}}{\textmu{}}_{B}$/Gd in a field of 7 T, which is about 5 times smaller than its saturation value of $7\phantom{\rule{0.16em}{0ex}}{\textmu{}}_{B}$. Zero-field electrical resistivity reveals a sudden drop at 27.5 K, suggesting a reduction in the spin disorder scattering due to the antiferromagnetic alignment of the Gd moments. The residual resistivity at 2 K is 390 $\mathrm{n}\mathrm{\ensuremath{\Omega}}\mathrm{cm}$, suggesting a good quality of the grown crystal. The magnetoresistance attains a value of ${10}^{4}%$ with no signature of saturation, in a field of 14 T at $T=2$ K. Shubnikov--de Hass oscillations have been observed in the high field range of the magnetoresistance with three fundamental frequencies corresponding to the extremal areas of the Fermi surface. Our results suggest that the extremely large unsaturated magnetoresistance in this compound is due to near compensation of the charge carriers. We also performed angle-resolved photoelectron spectroscopy measurements with different photon energies and compared our results with the calculated band structure of GdBi.

Large magnetoresistance and de Haas–van Alphen oscillations in the topological semimetal candidates BaX4 (X=Ga, In)

We report the magnetoresistance (MR), de Haas--van Alphen (dHvA) oscillations, and first-principles calculation studies on topological semimetal candidates ${\mathrm{Ba}X}_{4}$ $(X=\mathrm{Ga}, \mathrm{In})$. Large unsaturated MR that reaches $3\ifmmode\times\else\texttimes\fi{}{10}^{3}%$ in ${\mathrm{BaGa}}_{4}$ and $4\ifmmode\times\else\texttimes\fi{}{10}^{4}%$ in ${\mathrm{BaIn}}_{4}$ are observed, which is due to the carrier compensations and high mobility. Evident dHvA oscillations are detected with $B//[001]$ configuration, from which the quantum mobilities are extracted. The light cyclotron effective masses are extracted from the fitting of the thermal damping term in the LK formula. According to the first-principles calculations, ${\mathrm{Ba}X}_{4}$ possesses several Dirac points in the absence of spin-orbit coupling (SOC), some of which open negligible gaps when SOC is considered. The ${Z}_{2}$ invariants of ${\mathrm{Ba}X}_{4}$ are equal to 1, indicating the nontrivial topological properties.

Quantum Oscillations and Electronic Structure in the Large-Chern-Number Topological Chiral Semimetal PtGa*Supported by the National Key Research and Development Program of China (Grant Nos. 2019YFA0308602, 2018YFA0305700 and 2016YFA0300600), the National Natural Science Foundation of China (Grant Nos. 11874422 and 11574391), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant Nos. 19XNLG18

We report the magnetoresistance (MR), de Haas-van Alphen (dHvA) oscillations and the electronic structures of single-crystal PtGa. The large unsaturated MR is observed with the magnetic field B ∥ [111]. Evident dHvA oscillations with the B ∥ [001] configuration are observed, from which twelve fundamental frequencies are extracted and the spin-orbit coupling (SOC) induced band splitting is revealed. The light cyclotron effective masses are extracted from the fitting by the thermal damping term of the Lifshitz–Kosevich formula. Combining with the calculated frequencies from the first-principles calculations, the dHvA frequencies F1/F3 and F11/F12 are confirmed to originate from the electron pockets at Γ and R, respectively. The first-principles calculations also reveal the existence of spin-3/2 Rarita–Schwinger–Weyl fermions and time-reversal doubling of the spin-1 excitation at Γ and R with large Chern numbers of ± 4 when SOC is included.

Large magnetoresistance in topological insulator candidate TaSe3

Large unsaturated magnetoresistance (XMR) with magnitude ∼103% is observed in topological insulator candidate TaSe3 from our high field (up to 38 T) measurements. Two oscillation modes, associated with one hole pocket and two electron pockets in the bulk, respectively, are detected from our Shubnikov-de Hass measurements, consistent with our first-principles calculations. With the detailed Hall measurements performed, our two-band model analysis exhibits an imperfect density ratio nh/ne ≈ 0.9 at T < 20 K, which suggests that the carrier compensations account for the XMR in TaSe3.

Signature of Dirac semimetal states in gray arsenic studied by de Haas–van Alphen and Shubnikov–de Haas quantum oscillations

We report systematically studies of de Haas--van Alphen (dHvA) and Shubnikov--de Haas (SdH) quantum oscillations under high magnetic fields on gray arsenic, which has been suggested to be a topological insulator by first-principles calculations and angle-resolved photoemission spectroscopy. We observed large unsaturated magnetoresistance and pronounced quantum oscillations in two methods. By analysis of these quantum oscillation spectra, we obtained two major frequency branches around 3.8--18 and 153--162 T, and the light effective quasiparticle mass and nontrivial Berry phase. These results suggest that bulk crystals of gray arsenic may belong to the category of topological Dirac semimetals rather than topological insulators.

Quantum oscillations and electronic structure in the large–Chern number semimetal RhSn

We report the magnetoresistance, Hall effect, de Haas-van Alphen (dHvA) oscillations and the electronic structures of single crystal RhSn, which is a typical material of CoSi family holding a large Chern number. The large unsaturated magnetoresistance is observed with B//[001]. The Hall resistivity curve indicates that RhSn is a multi-band system with high mobility. Evident quantum oscillations have been observed, from which the light effective masses are extracted. Ten fundamental frequencies are extracted after the fast Fourier transform analysis of the dHvA oscillations with B//[001] configuration. The two low frequencies F$_1$ and F$_2$ do not change obviously and the two high frequencies F$_9$ and F$_{10}$ evolve into four when B rotates from B//[001] to B//[110], which is consistent with the band structure in the first-principles calculations with spin-orbit coupling (SOC). The extracted Berry phases of the relative pockets show a good agreement with the Chern number $\pm4$ (with SOC) in the first-principles calculations. Above all, our studies indicate that RhSn is an ideal platform to study the unconventional chiral fermions and the surface states.

Angle-dependent magnetoresistance and its implications for Lifshitz transition in W2As3

Lifshitz transition represents a sudden reconstruction of Fermi surface structure, giving rise to anomalies in electronic properties of materials. Such a transition does not necessarily rely on symmetry-breaking and thus is topological. It holds a key to understand the origin of many exotic quantum phenomena, for example, the mechanism of extremely large magnetoresistance (MR) in topological Dirac/Weyl semimetals. Here, we report studies of the angle-dependent MR (ADMR) and the thermoelectric effect in W2As3 single crystal. The compound shows a large unsaturated MR (of about 7000% at 4.2 K and 53 T). The most striking finding is that the ADMR significantly deforms from the horizontal dumbbell-like shape above 40 K to the vertical lotus-like pattern below 30 K. The window of 30–40 K also corresponds substantial changes in Hall effect, thermopower and Nernst coefficient, implying an abrupt change of Fermi surface topology. Such a temperature-induced Lifshitz transition results in a compensation of electron-hole transport and the large MR as well. We thus suggest that the similar method can be applicable in detecting a Fermi-surface change of a variety of quantum states when a direct Fermi-surface measurement is not possible.

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.

Magnetoresistance of semimetals: The case of antimony

Large unsaturated magnetoresistance has been recently reported in numerous semi-metals. Many of them have a topologically non-trivial band dispersion, such as Weyl nodes or lines. Here, we show that elemental antimony displays the largest high-field magnetoresistance among all known semi-metals. We present a detailed study of the angle-dependent magnetoresistance and use a semi-classical framework invoking an anisotropic mobility tensor to fit the data. A slight deviation from perfect compensation and a modest variation with magnetic field of the components of the mobility tensor are required to attain perfect fits at arbitrary strength and orientation of magnetic field in the entire temperature window of study. Our results demonstrate that large orbital magnetoresistance is an unavoidable consequence of low carrier concentration and the sub-quadratic magnetoresistance seen in many semi-metals can be attributed to field-dependent mobility, expected whenever the disorder length-scale exceeds the Fermi wavelength.

Extremely Large Magnetoresistance in a Topological Semimetal Candidate Pyrite PtBi_{2}.

While pyrite-type PtBi_{2} with a face-centered cubic structure has been predicted to be a three-dimensional (3D) Dirac semimetal, experimental study of its physical properties remains absent. Here we report the angular-dependent magnetoresistance measurements of a PtBi_{2} single crystal under high magnetic fields. We observed extremely large unsaturated magnetoresistance (XMR) up to (11.2×10^{6})% at T=1.8 K in a magnetic field of 33T, which is comparable to the previously reported Dirac materials, such as WTe_{2}, LaSb, and NbP. The crystals exhibit an ultrahigh mobility and significant Shubnikov-de Hass quantum oscillations with a nontrivial Berry phase. The analysis of Hall resistivity indicates that the XMR can be ascribed to the nearly compensated electron and hole. Our experimental results associated with the abinitio calculations suggest that pyrite PtBi_{2} is a topological semimetal candidate that might provide a platform for exploring topological materials with XMR in noble metal alloys.

Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride.

Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides.