De Haas Oscillations Research Articles

Extremely large magnetoresistance and Shubnikov–de Haas oscillations in the compensated semimetal W2As3

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Contactless Microwave Detection of Shubnikov–De Haas Oscillations in Three-Dimensional Dirac Semimetal ZrTe5**Supported by the National Key Research and Development Program of China under Grant No 2016YFA0401003, the National Natural Science Foundation of China under Grant Nos 11774353, 11574320, 11374302, 11804340, U1432251 and U1732274, the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology under Grant No

We report Shubnikov–de Haas (SdH) oscillations of a three-dimensional (3D) Dirac semimetal candidate of layered material ZrTe5 single crystals through contactless electron spin resonance (ESR) measurements with the magnetic field up to 1.4 T. The ESR signals manifest remarkably anisotropic characteristics with respect to the direction of the magnetic field, indicating an anisotropic Fermi surface in ZrTe5. Further experiments demonstrate that the ZrTe5 single crystals have the signature of massless Dirac fermions with nontrivial π Berry phase, key evidence for 3D Dirac/Weyl fermions. Moreover, the onset of quantum oscillation of our ZrTe5 crystals revealed by the ESR can be derived down to 0.2 T, much smaller than the onset of SdH oscillation determined by conventional magnetoresistance measurements. Therefore, ESR measurement is a powerful tool to study the topologically nontrivial electronic structure in Dirac/Weyl semimetals and other topological materials with low bulk carrier density.

Quantization in magnetoresistance of strained InSb whiskers

Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentration 6·1016–6·1017 сm–3 was studied in the temperature range 4.2–40 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were observed in the strained and unstrained samples in all range of doping concentrations and magnetic fields. The character of longitudinal magnetoresistance dependences was analyzed and compared with theoretical one. The whisker magnetoresistance alters its sign with increasing magnetic field. It is positive at weak magnetic fields and becomes negative at higher magnetic fields. Possible mechanism of the large value of negative magnetoresistance (NMR) was discussed in the InSb whiskers with doping concentration in the vicinity to metal–insulator transition. The origin of large NMR was explained by the existence of classical size effect and boundary scattering during conductance in subsurface whisker layers.

Strain-Induced Berry Phase in GaSb Microcrystals

The transverse and longitudinal magnetoresistances of GaSb microcrystals with tellurium doping concentration of 1.7 × 1017 cm−3 under the influence of uniaxial compression strain were studied in high magnetic fields of 0–14 T. Low-temperature Shubnikov–de Haas oscillations were observed for unstrained and strained n-type conductivity GaSb microcrystals in the whole range of the magnetic fields. The magnetoresistance oscillation amplitude decreases with the temperature increasing in the range of 4.2–30 K. The Shubnikov–de Haas oscillation period was changed due to the strain influence, and it was found to be 0.039 T−1. The emergence of the splitting at a magnetic field of about 7 T was revealed in the longitudinal magnetoresistance of GaSb microcrystals doped to a concentration in the vicinity of the metal–insulator transition. The value of the g-factor was found in the strained samples, and it has a value of 53. The strain influence on the effective mass of the electron mc and the Dingle temperature TD were also studied. The appearance of the Berry phase caused by the strain was revealed in GaSb microcrystals allowing their transition to the topological insulator state.

The Electron Structure of Metallic Layers in the Quasi-Two-Dimensional Dual-Layered Organic Metal (BETS)4HgBr4(C6H4Cl2)

We have studied the behavior of the Shubnikov–de Haas (SdH) oscillations in the quasi-two-dimensional dual-layered organic metal (BETS)4HgBr4(C6H4Cl2). It is established that the spectrum of SdH oscillations in this compound agrees well with theoretical calculations and qualitatively coincides with the analogous spectrum of (ET)4HgBr4(C6H4Cl2) isostructural organic metal. The fractional substitution of sulfur by selenium in the cationic layer strongly decreases the values of cyclotron masses. This decrease is most probably caused by weakening of the electron–phonon interaction.

The electron structure of Pb1–x–ySnxFeyTe alloys

A study of phase and elemental compositions, galvanomagnetic properties (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) and Shubnikov – de Haas oscillations (T = 4.2 K, B ≤ 6.5 T) in Pb1–x–ySnxFeyTe alloys with varying concentrations of tin and iron in single-crystal ingots synthesized using the Bridgman-Stockbarger method was performed. Scanning electron microscopy and X-ray fluorescence microanalysis revealed the presence of iron enriched microscopic inclusions, and the distribution of tin and iron along the ingots was determined. An increase in the concentration of holes with increasing concentrations of tin and iron, as well as anomalous temperature dependences of the Hall coefficient, which indicates a pinning of the Fermi level at the resonant level of iron, were detected. A model of electron structure rearrangement is proposed in order to explain the experimental dependences of the hole concentration and the Fermi energy relative to the valence band top as a function of tin concentration in the alloys. The model assumes that the iron level moves from the top to the depth of the valence band as the tin concentration increases. The compositional coefficient of iron level movement relative to the edges of the energy bands with increasing tin content in Pb1–x–ySnxFeyTe alloys is determined using the two-band Kane dispersion law.

Nontrivial topology of bulk HgSe from the study of cyclotron effective mass, electron mobility and phase shift of Shubnikov–de Haas oscillations

In this paper, the authors report the results of an experimental study of effective mass, electron mobility and phase shift of Shubnikov–de Haas oscillations of transverse magnetoresistance in an extended electron concentration region from 8.8 × 1015 cm−3 to 4.3 × 1018 cm−3 in single crystals of mercury selenide. The revealed features indicate that Weyl semimetal phase may exist in HgSe at low electron density. The most significant result is the discovery of an abrupt change of Berry phase at electron concentration 2 × 1018 cm−3, which we explain in terms of a manifestation of topological Lifshitz transition in HgSe that occurs by tuning Fermi energy via doping.

Электронная структура металлических слоев в двухслойном квазидвумерном органическом металле (BETS)-=SUB=-4-=/SUB=-HgBr-=SUB=-4-=/SUB=-(C-=SUB=-6-=/SUB=-H-=SUB=-4-=/SUB=-Cl-=SUB=-2-=/SUB=-)

AbstractWe have studied the behavior of the Shubnikov–de Haas (SdH) oscillations in the quasi-two-dimensional dual-layered organic metal (BETS)_4HgBr_4(C_6H_4Cl_2). It is established that the spectrum of SdH oscillations in this compound agrees well with theoretical calculations and qualitatively coincides with the analogous spectrum of (ET)_4HgBr_4(C_6H_4Cl_2) isostructural organic metal. The fractional substitution of sulfur by selenium in the cationic layer strongly decreases the values of cyclotron masses. This decrease is most probably caused by weakening of the electron–phonon interaction.

Investigation of semiconducting materials for magnetic field sensors in strong magnetic fields under cryogenic temperatures

Influence of strong magnetic fields B ˃ 3 T under cryogenic temperatures (1.5 ÷ 4.2) K on the signals of Hall sensors based on single-crystal whiskers (InSb, InAs) and nano-sized heterostructures (InSb/i-GaAs, InAs/i-GaAs) have been investigated. There are distinct Shubnikov – de Haas oscillations for whisker-based sensors, whereas heterostructures-based sensors demonstrate the linear field dependence of the output signal. This difference explained by the higher concentration of structure defects in the heterostructures. The derived results confirm the operability of Hall sensors based on indicated heterostructures for the magnetic fields diagnostics in the temperature and field conditions of modern particle accelerators and fusion reactors.

Evidence of Incoherent Carriers Associated with Resonant Impurity Levels and Their Influence on Superconductivity in the Anomalous Superconductor Pb_{1-x}Tl_{x}Te.

We present a combined experimental and theoretical study of the evolution of the Fermi surface of the anomalous superconductor Pb_{1-x}Tl_{x}Te as a function of thallium concentration, drawing on a combination of magnetotransport measurements (Shubnikov-de Haas oscillations and the Hall coefficient), angle resolved photoemission spectroscopy, and density functional theory calculations of the electronic structure. Our results indicate that for Tl concentrations beyond a critical value, the Fermi energy coincides with resonant impurity states in Pb_{1-x}Tl_{x}Te, and we rule out the presence of an additional valence band maximum at the Fermi energy. A comparison to nonsuperconducting Pb_{1-x}Na_{x}Te implies that the presence of these impurity states at the Fermi energy provides the enhanced pairing interaction and thus also the anomalously high temperature superconductivity in this material.

Transition between Electron Localization and Antilocalization and Manifestation of the Berry Phase in Graphene on a SiC Surface

It is shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons. In weak magnetic fields and at low temperatures, a negative magnetoresistance is observed due to weak localization. A crossover in the magnetoresistance from weak localization to weak antilocalization (the latter is the manifestation of the isospin in graphene) is observed for the first time in samples of this kind at elevated temperatures. A pronounced pattern of Shubnikov–de Haas oscillations is observed in strong magnetic fields (up to 30 T). This pattern demonstrated fourfold carrier spectrum degeneracy due to the double spin and double valley degeneracies. Also, the manifestation of the Berry phase is observed. The effective electron mass is estimated to be m* = 0.08m0, which is characteristic of graphene with a high carrier concentration.

Determination of Electron Temperature in DA-pHEMT Heterostructures by Shubnikov – de Haas Oscillation Method

The electron temperature of a two-dimensional electron gas heated by an electric field in DA-pHEMT heterostructures was determined by the Shubnikov – de Haas (SdH) oscillation method separately for each size-quantization subband. An analysis of the Fourier spectra of SdH oscillations showed that throughout the entire range of electron temperatures obtained, harmonics associated with different size-quantization subbands and transitions between the Landau levels of these subbands dominate in the spectra. To separate the SdH oscillations into individual harmonics, we used the approximation of the magnetic-field dependences of the oscillations by theoretical expressions using the ratio between the peak heights in the Fourier spectra. It is shown that this method allows one to determine the values of the electron temperature in case when the electron concentrations in the first and second subbands are close in magnitude. The obtained values of the electron temperature correspond to the literature data.

Berry phase in strained InSb whiskers

Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentrations 6·1016–6·10 17 сm–3 were studied at temperatures from 4.2 to 50 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were revealed in the strained and unstrained samples with all range doping concentration. Some peaks of the longitudinal magnetoresistance split as a doublet in the InSb whiskers with doping concentration in the vicinity to metal-insulator transition. Taking into account peak splitting giant g-factor from 30 to 60 was defined for strained and unstrained samples. The magnetoresistance oscillation period of the InSb whiskers doesn’t differ under strain for all doping concentration, but Fermi energy increases and electron effective mass mс decreases and consists 0.02 m0. Berry phase presence was also revealed in strained n-InSb whiskers that shows their transition under a strain to topological insulator phase.

Asymmetry and Parity Violation in Magnetoresistance of Magnetic Diluted Dirac–Weyl Semimetal (Cd0.6Zn0.36Mn0.04)3As2

Orientation dependences of magnetoresistance, ρ, of single crystal (Cd0.6Zn0.36Mn0.04)3As2 having tetragonal P42/nmc symmetry have been studied. Three orientations between electrical current, , flowing along crystal (100) plane and magnetic field, , have been used as follows: 1) is perpendicular to both and (100) plane; 2) is perpendicular to but parallel to (100) plane; 3) is parallel to both and (100) plane. Asymmetry in curves ρ is observed for all orientations. For orientation (2), crossover from negative to positive magnetoresistance is found as magnetic field changes its direction from one position corresponding to negative to opposite direction corresponding to positive . So magnetoresistance parity typical for numerous solids is violated for this orientation. The Shubnikov–de Haas (SdH) oscillations are observed for all orientations above ≈1.8 T and below ≈40 K. The effective mass of electrons extracted from SdH oscillations analysis is found to be orientation dependent. Smeared kinks correlated with the SdH oscillations are also observed in the Hall effect study for orientation (1). Magnetoresistance peculiarities can be related to specific properties of the Dirac semimetals and their evolution under magnetic field.

Deviation from the Kohler’s rule and Shubnikov–de Haas oscillations in type-II Weyl semimetal WTe2: High magnetic field study up to 56 T

We have measured magnetoresistance of type-II Weyl semimetal WTe2 in high magnetic fields of B//c up to B = 56 T using a high quality single crystal with the residual resistivity ratio 1330. A Kohler plot demonstrates the existence of a deviation from the B2 dependence. Significant deviation from Kohler’s rule appears with increasing temperature, indicating wave-vector k dependent anisotropic carrier scattering, which develops with increasing temperature. The fast-Fourier-transform spectra of the observed large-amplitude Shubnikov–de Haas oscillations confirm the existence of four fundamental and one additional (cyclotron frequency of 255 T) peaks. The amplitude of the latter one increases anomalously with increasing field, confirming this oscillation being due to magnetic breakdown (or magnetic breakthrough) between the two cyclotron orbits of the adjacent hole pockets.

Interference in spin-orbit coupled transverse magnetic focusing: Emergent phase due to in-plane magnetic fields

Spin-orbit (SO) interactions in two dimensional systems split the Fermi surface, and allow for the spatial separation of spin-states via transverse magnetic focusing (TMF). In this work, we consider the case of combined Rashba and Zeeman interactions, which leads to a Fermi surface without cylindrical symmetry. While the classical trajectories are effectively unchanged, we predict an additional contribution to the phase, linear in the applied in-plane magnetic field. We show that this term is unique to TMF, and vanishes for magnetic (Shubnikov de Haas) oscillations. Finally we propose some experimental signatures of this phase.

Shubnikov–de Haas oscillations in the anomalous Hall conductivity of Chern insulators

The Haldane model on a honeycomb lattice is a paradigmatic example of a system featuring quantized Hall conductivity in the absence of an external magnetic field, that is, a quantum anomalous Hall effect. Recent theoretical work predicted that the anomalous Hall conductivity of massive Dirac fermions can display Shubnikov-de Haas (SdH) oscillations, which could be observed in topological insulators and honeycomb layers with strong spin--orbit coupling. Here, we investigate the electronic transport properties of Chern insulators subject to high magnetic fields by means of accurate spectral expansions of lattice Green's functions. We find that the anomalous component of the Hall conductivity displays visible SdH oscillations at low temperature. \textcolor{black}{The effect is shown to result from the modulation of the next-nearest neighbour flux accumulation due to the Haldane term,} which removes the electron--hole symmetry from the Landau spectrum. To support our numerical findings, we derive a long-wavelength description beyond the linear ('Dirac cone') approximation. Finally, we discuss the dependence of the energy spectra shift for reversed magnetic fields with the topological gap and the lattice bandwidth.

Shubnikov–de Haas Oscillations in the Magnetoresistance of Layered Conductors in Proximity to the Topological Lifshitz Transition

The dependence of the resistance of a layered conductor with a quasi-two-dimensional charge carrier energy spectrum on the strength and orientation of a quantizing magnetic field is studied. The case of an organic conductor with a multisheet Fermi surface consisting of a weakly warped cylinder and two adjoining planar sheets is considered. By applying an external pressure to the conductor or doping it with impurity atoms, the gap between the cylinder and the planar sheets of the Fermi surface (FS) may be reduced so that electrons start wandering on the FS, tunneling between its different parts due to magnetic breakdown. If an electron can pass through all the different sheets of the FS several times during the mean free time, its motion in the plane orthogonal to the magnetic field becomes finite. This leads to Shubnikov–de Haas oscillations with a period determined by the area enclosed by the closed breakdown orbit of an electron in momentum space. However, even at a slight tilting of the field from the normal to the layers by an angle ϑ, the equidistance is broken and at certain angles ϑk the probability of the magnetic breakdown to one of the planar FS sheets may become so low that the electron cannot complete the magnetic-breakdown orbit and its motion over the other planar sheet and the cylindrical part of the FS becomes infinite. As a result, magnetic-breakdown quantum oscillations of magnetization and all kinetic properties vanish. This vanishing repeats periodically as a function of tan ϑ with changing the tilt angle. Possibilities for experimental observation and investigation of the influence of magnetic breakdown on quantum oscillation phenomena are discussed.

Galvanomagnetic properties of the putative type-II Dirac semimetal PtTe2

Platinum ditelluride has recently been characterized, based on angle-resolved photoemission spectroscopy data and electronic band structure calculations, as a possible representative of type-II Dirac semimetals. Here, we report on the magnetotransport behavior (electrical resistivity, Hall effect) in this compound, investigated on high-quality single-crystalline specimens. The magnetoresistance (MR) of PtTe2 is large (over 3000% at T = 1.8 K in B = 9 T) and unsaturated in strong fields in the entire temperature range studied. The MR isotherms obey a Kohler’s type scaling with the exponent m = 1.69, different from the case of ideal electron-hole compensation. In applied magnetic fields, the resistivity shows a low-temperature plateau, characteristic of topological semimetals. In strong fields, well-resolved Shubnikov – de Haas (SdH) oscillations with two principle frequencies were found, and their analysis yielded charge mobilities of the order of 103 cm2 V−1 s−1 and rather small effective masses of charge carriers, 0.11 me and 0.21 me. However, the extracted Berry phases point to trivial character of the electronic bands involved in the SdH oscillations. The Hall effect data corroborated a multi-band character of the electrical conductivity in PtTe2, with moderate charge compensation.

Electron heating induced by an ac-bias current in the regime of Shubnikov–de Haas oscillation in the high mobility GaAs/AlxGa1−xAs two-dimensional electron system

The magnetotransport properties of the high mobility GaAs/AlGaAs two-dimensional electron gas systems have been examined to determine the influence of the ac current bias on the carrier temperature. The changes in the line shape of Shubnikov–de Haas oscillations in the longitudinal magnetoresistance () were followed as a function of the ac current bias in the temperature range of in order to determine the carrier heating effect due to the ac bias. The lineshape analysis of these oscillations indicates that the carrier temperature of the two-dimensional electron system is linearly proportional to the ac bias current.