Cyclotron Effective Mass Research Articles

Magnetotransport properties of MoP2

We report magnetotransport and de Haas-van Alphen (dHvA) effect studies on MoP$_2$ single crystals, predicted to be type-2 Weyl semimetal with four pairs of robust Weyl points located below the Fermi level and long Fermi arcs. The temperature dependence of resistivity shows a peak before saturation, which does not move with magnetic field. Large nonsaturating magnetoresistance (MR) was observed, and the field dependence of MR exhibits a crossover from semicalssical weak-field $B^2$ dependence to the high-field linear-field dependence, indicating the presence of Dirac linear energy dispersion. In addition, systematic violation of Kohler's rule was observed, consistent with multiband electronic transport. Strong spin-orbit coupling (SOC) splitting has an effect on dHvA measurements whereas the angular-dependent dHvA orbit frequencies agree well with the calculated Fermi surface. The cyclotron effective mass $\sim$ 1.6$m_e$ indicates the bands might be trivial, possibly since the Weyl points are located below the Fermi level. Interestingly, quasi-two dimensional(2D) band structure is observed even though the crystal structure of MoP$_2$ is not layered.

2D massless Dirac Fermi gas model of superconductivity in the surface state of a topological insulator at high magnetic fields

The Nambu-Gorkov Green's function approach is applied to strongly type-II superconductivity in a 2D spin-momentum–locked (Weyl) Fermi gas model at high perpendicular magnetic fields. The resulting phase diagram can be mapped onto that derived for the standard, parabolic band-structure model, having the same Fermi surface parameters, EF and v, but with cyclotron effective mass . Significant deviations from the predicted mapping are found only for very small EF, when the Landau-Level filling factors are smaller than unity, and EF shrinks below the cutoff energy.

Large magnetoresistance in the type-II Weyl semimetal WP2

We report magnetotransport study on type-II Weyl semimetal WP$_2$ single crystals. Magnetoresistance (MR) exhibits a nonsaturating $H^{n}$ field dependence (14,300\% at 2 K and 9 T) whereas systematic violation of Kohler's rule was observed. Quantum oscillations reveal a complex multiband electronic structure. The cyclotron effective mass close to the mass of free electron m$_e$ was observed in quantum oscillations along $b$-axis, while reduced effective mass of about 0.5$m_e$ was observed in $a$-axis quantum oscillations, suggesting Fermi surface anisotropy. Temperature dependence of the resistivity shows a large upturn that cannot be explained by the multi-band magnetoresistance of conventional metals. Even though crystal structure of WP$_{2}$ is not layered as in transition metal dichalcogenides, quantum oscillations suggest partial two-dimensional character.

Magnetotransport properties of the triply degenerate node topological semimetal tungsten carbide

We report the magnetoresistance (MR), Hall effect, and de Haas-van Alphen (dHvA) effect studies of the single crystals of tungsten carbide, WC, which is predicted to be a new type of topological semimetal with triply degenerate nodes. With the magnetic field rotated in the plane perpendicular to the current, WC shows field induced metal to insulator like transition and large nonsaturating quadratic MR at low temperature. As the magnetic field parallel to the current, a pronounced negative longitudinal MR only can be observed when the current flows along the certain direction. Hall effect indicates WC is a perfect compensated semimetal, which may be related to the large nonsaturating quadratic MR. The analysis of dHvA oscillations reveals that WC is a multiband system with small cross-sectional areas of Fermi surface and light cyclotron effective masses. Our results indicate that WC is an ideal platform to study the recently proposed New Fermions with triply degenerate crossing points.

Fermi Surface and Magnetic Properties in Ferromagnet CoS2 and Paramagnet CoSe2 with the Pyrite-type Cubic Structure

We succeeded in growing high-quality single crystals of pyrite-type cubic compounds CoSe2 and CoS2 using a transport agent of CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and the de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2·mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature TC = 122 K and an ordered moment μs = 0.93 μB/Co. The γ value of 21 mJ/(K2·mol) in CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ value, is a characteristic feature in CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discussed on the basis of the results of energy band calculations, revealing a broken four-fold-symmetry in the angular dependence of the dHvA frequency.

Shubnikov–de Haas oscillations and electronic correlations in the layered organic metal κ-(BETS)2 Mn[N(CN)2

We present magnetoresistance studies of the quasi-two-dimensional organic conductor κ-(BETS)2Mn[N(CN)2]3, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. Under a moderate pressure of 1.4 kbar, required for stabilizing the metallic ground state, Shubnikov–de Haas oscillations, associated with a classical and a magnetic-breakdown cyclotron orbits on the cylindrical Fermi surface, have been found at fields above 10 T. The effective cyclotron masses evaluated from the temperature dependence of the oscillation amplitudes reveal strong renormalization due to many-body interactions. The analysis of the relative strength of the oscillations corresponding to the different orbits and of its dependence on magnetic field suggests an enhanced role of electron-electron interactions on flat parts of the Fermi surface.

Fermi surface evolution of Na-doped PbTe studied through density functional theory calculations and Shubnikov–de Haas measurements

We present a combined experimental and theoretical study of the evolution of the low-temperature Fermi surface of lead telluride, PbTe, when holes are introduced through sodium substitution on the lead site. Our Shubnikov-de-Haas measurements for samples with carrier concentrations up to $9.4\times10^{19}$cm$^{-3}$ (0.62 Na atomic $\%$) show the qualitative features of the Fermi surface evolution (topology and effective mass) predicted by our density functional (DFT) calculations within the generalized gradient approximation (GGA): we obtain perfect ellipsoidal L-pockets at low and intermediate carrier concentrations, evolution away from ideal ellipsoidicity for the highest doping studied, and cyclotron effective masses increasing monotonically with doping level, implying deviations from perfect parabolicity throughout the whole band. Our measurements show, however, that standard DFT calculations underestimate the energy difference between the L-point and $\Sigma$-line valence band maxima, since our data are consistent with occupation of a single Fermi surface pocket over the entire doping range studied, whereas the calculations predict an occupation of the $\Sigma$-pockets at higher doping. Our results for low and intermediate compositions are consistent with a non-parabolic Kane-model dispersion, in which the L-pockets are ellipsoids of fixed anisotropy throughout the band, but the effective masses depend strongly on Fermi energy.

Large Cyclotron Mass and Large Ordered Moment in Ferromagnet CoS2 Compared with Paramagnet CoSe2

We succeeded in growing high-quality single crystals of the pyrite-type cubic compounds CoSe2 and CoS2 using the transport agent CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2·mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature TC = 122 K and an ordered moment μs = 0.93 μB/Co. The γ of 21 mJ/(K2·mol) of CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ, is characteristic of CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discus...

Peculiarities of magnetoresistance in InSb whiskers at cryogenic temperatures

The study of the magnetoresistance in InSb whiskers with an impurity concentration in the vicinity to the metal-insulator phase transition, at low temperature range 4.2–77K, and in fields, with induction up to 14T, was conducted. The presence of Shubnikov-de Haas oscillations in both transverse and longitudinal magnetoresistance was observed. The following parameters of InSb whiskers were defined: period of oscillations 0.1Т−1, cyclotron effective mass of electrons mс≈0.14mо, concentration of charge carriers 2.3×1017сm−3, g-factor g*≈30 and Dingle temperature ТD=14.5K. To determine the nature of crystal defects, the electron scattering processes on the short-range potential, caused by interaction with polar and nonpolar optical phonons, piezoelectric and acoustic phonons, static strain centers and ionized impurities in n-InSb whiskers, with defect concentration 2.9×1017cm−3, are considered. The temperature dependences of electron mobility in the range 4.2–500K were calculated.

Probing the Fermi surface of three-dimensional Dirac semimetalCd3As2through the de Haas–van Alphen technique

We have observed Shubnikov-de Haas and de Haas-van Alphen effect in the single crystals of three dimensional Dirac semimetal Cd$_{3}$As$_{2}$ upto 50 K, traceable at field as low as 2 T and 1 T, respectively. The values of Fermi wave vector, Fermi velocity, and effective cyclotron mass of charge carrier, calculated from both the techniques, are close to each other and match well with the earlier reports. However, the de Haas-van Alphen effect clearly reflects the existence of two different Fermi surface cross-sections along certain direction and a non-trivial Berry's phase which is the signature of 3D Dirac Fermion in Cd$_{3}$As$_{2}$.

Enhancement of the cyclotron effective mass in U0.03Th0.97Ru2Si2

Electronic states of a dilute uranium alloy U0.03Th0.97Ru2Si2 have been investigated by using de Haas-van Alphen (dHvA) measurements on single crystal samples. Quantum oscillations were successfully observed for the field along the principal axes. The dHvA frequency of the observed branches roughly agrees with those of the reference compound ThRu2Si2, indicating the change of Fermi surface volume is not significant. On the other hand, the dHvA amplitude is strongly diminished compared to ThRu2Si2. Furthermore, cyclotron effective masses for corresponding branches are strongly enhanced. The latter effects are indicative of the strong scattering as well as the mass renormalization due to 5f moments.

Mass Enhancement of Nearly Trivalent Compound EuCo2Si2: Studied by the de Haas-van Alphen Experiments and Energy Band Calculations

We succeeded in growing single crystals of EuCo2Si2 by the Bridgman method, and carried out the de Haas-van Alphen (dHvA) experiments. EuCo2Si2 was previously studied from a viewpoint of the trivalent electronic state on the basis of the magnetic susceptibility and X-ray absorption experiments, whereas most of the other Eu compounds order magnetically, with the divalent electronic state. The detected dHvA branches in the present experiments are found to be explained by the results of the full potential linearized augmented plane wave energy band calculations on the basis of a local density approximation (LDA) for YCo2Si2 (LDA) and EuCo2Si2 (LDA + U), revealing the trivalent electronic state. The detected cyclotron effective masses are moderately large, ranging from 1.2 to 2.9 m0.

Shubnikov-de Haas Oscillation in the cubic Γ3-based heavy fermion superconductor PrV2Al20

PrV2Al20 is the cubic Γ3 doublet system that exhibits strong hybridization effects and heavy fermion superconductivity. We measured the magnetoresistance using a high quality single crystal of PrV2Al20 under the DC high magnetic field up to 35 T below ~ 0.4 K. We have succeeded in detecting the Shubnikov-de Haas (SdH) oscillation with a frequency of 250 T. Our analysis of this SdH oscillation yields the cyclotron effective mass (m*c/m0 ~ 5) and the mean-free path (l = 170 Å).

Large Cyclotron Effective Mass Detected by de Haas–van Alphen Effect in YbCu2Si2

De Haas–van Alphen experiments were performed on the valence fluctuation compound YbCu2Si2. For the field direction close to the c-axis in the tetragonal structure, a very large cyclotron effective mass of 43 m0 was detected on branch β, which corresponds to the nearly cylindrical Fermi surface. This mass is one of the largest cyclotron masses detected experimentally in Yb compounds.

De Haas-van Alphen Effect and Fermi Surface Properties in Ferromagnet LaCo2P2 and Related Compounds

We grew single crystals of a ferromagnet LaCo2P2 and an antiferromagnet CaCo2P2, and clarified the magnetic properties by measuring the electrical resistivity, specific heat, magnetic susceptibility, and magnetization. For LaCo2P2, we also carried out the de Haas-van Alphen (dHvA) experiment. Detected dHvA branches are well explained by the results of energy band calculations using a full-potential linearized augmented plane wave method within the local spin density approximation, where the ferromagnetic state is assumed. The cyclotron effective masses are (2–3)m0 (m0: rest mass of an electron). The present relatively large cyclotron masses in LaCo2P2 are due to ferromagnetic correlations of Co-3d conduction electrons, which are compared with much larger cyclotron masses of (3–7)m0 for a nearly ferromagnet SrCo2P2.

THz Magneto-Photoresponse Spectroscopy of Two-Dimensional Electrons in an InAs/InGaAs/InAlAs Inserted-Channel

We have used THz magneto-photoresponse/transmission to measure various electronic parameters of a two-dimensional electron gas (2DEG) located primarily within an InAs inserted-channel and the surrounding InGaAs well in an asymmetric InAs/InGaAs/InAlAs inserted-well heterostructure in magnetic fields up to 10 T. We have developed an analytical approach to the photoresponse based on resonant heating of the 2DEG by cyclotron resonance (CR) absorption. The analysis incorporates a resonant T-profile mimicking the CR absorption, combined with the theoretical expression for quantized resistance oscillations of a 2DEG. Fitting of an individual set of PR data vs. magnetic field can in principle, provide g-factor, cyclotron effective mass, SdH scattering time, CR scattering time and carrier density of the 2DEs. This is a temperature differential technique, which leads to enhanced sensitivity to harmonic content of the Shubnikov-deHaas (S-dH) oscillations and thus to clearer spin-splitting of the Landau levels at lower fields than is possible in direct S-dH measurements at the same bath temperature. Results show an enhanced g-factor for electrons and large g-factor anisotropy.

De Haas–van Alphen Effect and Fermi Surface Properties in Nearly Ferromagnet SrCo2P2

We grew high-quality single crystals of SrCo2P2 with the ThCr2Si2-type tetragonal structure, and clarified the Fermi surface properties by carrying out de Haas–van Alphen (dHvA) experiments and energy band calculations. SrCo2P2 is known to be a nearly ferromagnetic compound, where the magnetic susceptibility follows the Curie–Weiss law above 200 K, with the effective magnetic moment μeff = 1.72 μB/Co, but becomes almost constant below about 100 K. The electronic specific heat coefficient γ is thus relatively large, being γ = 40 mJ/(K2·mol). Detected dHvA branches possess the corresponding cyclotron effective masses \(m_{\text{c}}^{*}\), ranging from 0.87 to 7.2 m0 (m0: rest mass of an electron). The angular dependences of the dHvA frequencies are well explained by the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations, revealing a multiply-connected band 25th hole Fermi surface and a compensated nearly cylindrical band 26th electron Fermi surface. It is thus conclud...

Quantum oscillations of the two-dimensional hole gas at atomically flat diamond surfaces

Shubnikov--de Haas oscillations are observed in atomically flat hydrogen-terminated diamond surfaces with high-density hole carriers introduced by the electric field effect using an ionic liquid. The Shubnikov--de Haas oscillations depend only on the magnetic field component perpendicular to the diamond surface, thus providing evidence of two-dimensional Fermi surfaces. The effective masses estimated from the temperature dependence of the oscillations are close to the cyclotron effective masses of the valence band maxima in diamond. The estimated quantum scattering time is one order of magnitude longer than the transport scattering time and indicates that the carrier mobility is locally as high as several thousand cm${}^{2}$/V s at low temperature.

De Haas–van Alphen Effect and Fermi Surface Properties of EuPd3 with the Trivalent Electronic State

EuPd3, which is in the trivalent (Eu3+) electronic state, is a rare compound because most Eu compounds are in the divalent (Eu2+) electronic state and order magnetically. The electronic state of EuPd3 was previously studied by Mossbauer, magnetic susceptibility, and X-ray absorption experiments using polycrystalline samples. We succeeded in growing single crystals of EuPd3 by the Bridgeman method and carried out a de Haas–van Alphen (dHvA) experiment. The dHvA branches detected in EuPd3 are well explained by the results of the full potential linear augmented plane wave (FLAPW) energy band calculation based on a local density approximation (LDA) with additional treatments for EuPd3, revealing the trivalent electronic state. Conduction electrons are mainly Pd-4d electrons. The cyclotron effective masses are determined from the temperature dependence of the dHvA amplitude, ranging from 0.3 to 1.0m0 (m0: rest mass of an electron), which are also consistent with the corresponding band masses.

Surface states of charge carriers in epitaxial films of the topological insulator Bi2Te3

The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S(kF), the wave vector kF, and the surface concentration of charge carriers ns on the frequency of magnetoresistance oscillations in p-type Bi2Te3 heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi2Te3 films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.