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We have investigated the illumination effect on the magnetotransport properties of a two-dimensional electron system at the LaAlO3/SrTiO3 interface. The illumination significantly reduces the zero-field sheet resistance, eliminates the Kondo effect at low-temperature, and switches the negative magnetoresistance into the positive one. A large increase in the density of high-mobility carriers after illumination leads to quantum oscillations in the magnetoresistance originating from the Landau quantization. The carrier density (∼2 × 1012 cm−2) and effective mass (∼1.7m e) estimated from the oscillations suggest that the high-mobility electrons occupy the d xz/yz subbands of Ti:t2g orbital extending deep within the conducting sheet of SrTiO3. Our results demonstrate that the illumination which induces additional carriers at the interface can pave the way to control the Kondo-like scattering and study the quantum transport in the complex oxide heterostructures.

Compounds with the A15 structure have attracted extensive attention due to their superconductivity and nontrivial topological band structure. We have successfully grown Nb$_3$Sb single crystals with a A15 structure and systematically measured the longitudinal resistivity, Hall resistivity and quantum oscillations in magnetization. Similar to other topological trivial/nontrivial semimetals, Nb$_3$Sb, exhibits large magnetoresistance (MR) at low temperatures (717$\%$, 2 K and 9 T), unsaturating quadratic field dependence of MR and up-turn behavior in $\rho_{xx}$(\emph{T}) curves under magnetic field, which is considered to result from a perfect hole-electron compensation, as evidenced by the Hall resistivity measurements. The nonzero Berry phase obtained from the de-Hass van Alphen (dHvA) oscillations demonstrates that Nb$_3$Sb is topologically nontrivial. These results indicate that Nb$_{3}$Sb superconductor is also a semimetal with large MR and nontrivial Berry phase, indicating that Nb$_{3}$Sb may be another platform to search for Majorana zero-energy mode., Comment: 5 pages, 5 figures. arXiv admin note: text overlap with arXiv:2007.04814, arXiv:2104.03799

We have synthesized high-quality single crystals of SnxPb1-xTe and carried out detailed studies of the magnetotransport properties of one of the samples, Sn0.05Pb0.95Te. Longitudinal magnetoresistance increases almost linearly with increasing applied field (H) and reaches ∼310% atH= 13 T. At higher fields, both longitudinal and Hall resistance show clear Shubnikov de Haas oscillations. The oscillations are smooth and periodic, and there exists only one frequency,fα∼ 57 T. However, an additional frequency,fβ∼ 69 T, appears as the angle between the field direction and the normal to the sample surface (θ) is increased. Bothfαandfβexhibitθ-dependence;fαdecreases whereasfβincreases gradually with increasingθ. The presence of two frequencies in Sn0.05Pb0.95Te indicates that there exist two Fermi surface pockets (αandβpockets). We have constructed the Landau-level fan plot and determined the Berry phase (δ) for theαpocket to beδ∼ 0.1. Thisδvalue is very close to the expected value of 0 for a topologically trivial system.

In the search of topological superconductors, nailing down the Fermiology of the normal state is as crucial a prerequisite as unraveling the superconducting pairing symmetry. In particular, the number of time-reversal-invariant momenta (TRIM) in the Brillouin zone enclosed by Fermi surfaces is closely linked to the topological class of time-reversal-invariant systems, and can experimentally be investigated. We report here a detailed study of de Haas van Alphen quantum oscillations in single crystals of the topological semimetal CaSn3 with torque magnetometry in high magnetic fields up to 35 T. In conjunction with density functional theory based calculations, the observed quantum oscillations frequencies indicate that the Fermi surfaces of CaSn3 enclose an odd number of TRIM, satisfying one of the proposed criteria to realize topological superconductivity. Nonzero Berry phases extracted from the magnetic oscillations also support the nontrivial topological nature of CaSn3.

Comparing quantum oscillation measurements, dc magnetoresistance measurements, and Fermi surfaces obtained from LDA calculations, we argue that the metamagnetic transition of UPt3, which occurs at an applied field μ ◦ H M ∼ 20 T, coincides with a Lifshitz transition at which an open orbit on the band 2 hole-like Fermi surface becomes closed for one spin direction. At low field, proximity of the Fermi energy to this particular van Hove singularity may have implications for the superconducting pairing potential of UPt3. In our picture the magnetization comes from non-linear spin-splitting of the heavy fermion bands. In support of this, we show that the non-linear field dependence of a particular quantum oscillation frequency can be fitted by assuming that the corresponding extremal Fermi surface area is proportional to the magnetization. In addition, below H M , we find in our LDA calculations a new, non-central orbit on band 1, whose non-linear behaviour explains a field-dependent frequency recently observed in magnetoacoustic quantum oscillation measurements.

The layered transition-metal dichalcogenide PdTe2 has been discovered to possess bulk Dirac points as well as topological surface states. By measuring the magnetization (up to 7 T) and magnetic torque (up to 35 T) in single crystalline PdTe2, we observe distinct de Haas–van Alphen (dHvA) oscillations. Eight frequencies are identified with H||c, with two low frequencies (F α = 8 T and F β = 117 T) dominating the spectrum. The effective masses obtained by fitting the Lifshitz–Kosevich (LK) equation to the data are m α * = 0.059 m 0 and m β * = 0.067 m 0 where m 0 is the free electron mass. The corresponding Landau fan diagrams allow the determination of the Berry phase for these oscillations resulting in values of ∼0.67π for the 3D α band (hole-type) (down to the 1st Landau level) and ∼0.23π–0.73π for the 3D β band (electron-type) (down to the 3rd Landau level). By investigating the angular dependence of the dHvA oscillations, we find that the frequencies and the corresponding Berry phase (ΦB) vary with the field direction, with a ΦB ∼ 0 when H is 10°–30° away from the ab plane for both α and β bands. The multiple band nature of PdTe2 is further confirmed from Hall effect measurements.

We study the electronic heat capacity in doped graphene under magnetic fields. The partition function is calculated considering only the thermal excitations in the last occupied energy levels. Due to the large energy separation between the Landau levels (LLs) and the Zeeman splitting, at low temperatures the heat capacity is dominated by the spin excitations in the last occupied LL. Correspondingly the heat capacity oscillates with maximum amplitude at half filling of each LL. At higher temperatures the inter-LLs excitations dominate the heat capacity, with maximum amplitude at full filling factors. The oscillation amplitudes are compared with the phonon heat capacity C p. It is shown that the spin induced heat capacity oscillations have a maximum amplitude approaching 3% of C p, whereas for the inter-LLs excitations the maximum amplitude is only 0.1% of C p. These amplitudes decrease in the presence of impurities, although the effect is appreciable if the LLs broadening is bigger than the excitation energies. Fil: Escudero, Federico Nahuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Ardenghi, Juan Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Jasen, Paula Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina

Characterization of Fermi surface of the BaSn3 superconductor (T c ∼ 4.4 K) by de Haas–van Alphen (dHvA) effect measurement reveals its non-trivial topological properties. Analysis of non-zero Berry phase is supported by the ab initio calculations, which reveals a type-II Dirac point setting and tilting along the high symmetric K–H line of the Brillouin zone, about 0.13 eV above the Fermi level, and other two type-I Dirac points on the high symmetric Γ–A direction, but slightly far below the Fermi level. The results demonstrate BaSn3 as an excellent example hosting multiple Dirac fermions and an outstanding platform for studying the interplay between nontrivial topological states and superconductivity.

Angle-resolved photoemission spectroscopy (ARPES) and torque magnetometry (TM) measurements have been carried out to study the electronic structures of a correlated topological insulator (TI) candidate YbB6. We observed clear surface states on the [001] surface centered at the Γ ¯ and M ¯ points of the surface Brillouin zone. Interestingly, the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements. Moreover, the band structures we observed suggest that the band inversion in YbB6 happens between the Yb5d and B2p bands, instead of the Yb5d and Yb4f bands as suggested by previous theoretical investigation, which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.

We present a detailed magnetotransport study on HfB2, a possible topological nodal-line semimetal. HfB2 exhibits field-induced resistivity upturn and plateau behaviors at low temperature and high field, accompanying rather large magnetoresistance. The analysis of the field dependence of Hall and longitudinal resistivity shows that there are two kinds of carriers (electrons and holes) with almost same carrier concentrations and rather high mobilities in HfB2. Above field-induced phenomena can be well explained by using the two-band model with compensation condition. Even the carrier concentration is significantly high (∼1.8 [Formula: see text] 1021 cm-3) in HfB2, much larger than other known topological semimetals with discrete Dirac nodal points, the electron-type carriers still have relatively small effective masses. In contrast to ZrB2, the slightly increased effective mass in HfB2 manifests the effect of enhanced spin-orbit coupling due to the large atomic number of Hf.

Magneto-transport study has been performed in ZrTe5 single crystals. The observed Shubnikov–de Hass quantum oscillation at low temperature clearly demonstrates the existence of a nontrivial band with small effective mass in ZrTe5. Furthermore, we also revealed the highly anisotropic nature of high-field Landau level splitting in ZrTe5, suggesting the dominant role of orbital contribution to the splitting. Besides these, an abnormal large enhancement of magnetoresistance appears at high temperatures, which is believed to arise from the Lifshitz transition induced two-carrier transport in ZrTe5. Our study provides more understanding of the physical properties of ZrTe5 and sheds light on potential application of ZrTe5 in spintronics.

In this paper, we systematically investigate the transportation properties of the zigzag nano-ribbon graphene in a local potential barrier/well with electrons hopping between and beyond nearest neighbor. When the local potential is present, the conductance exhibits novel periodic oscillation plateaus around increasing quantized conductance. The oscillation plateau hops down with the quantized conductance until vanishes with increasing local potential barrier. Furthermore, when a small voltage is applied between the two terminals of the conductor, the local current presents periodic oscillation in the barrier region. In contrast, when a local potential well is applied, the conductance shows irregular oscillation, exhibiting incommensurate oscillations of local current inside and outside the well. Finally, similar phenomena persists when more local potentials are applied to the system. We expect our studies can facilitate the design of relevant electronic devices.

Neutrino production is the dominant cooling process in neutron stars. After the rapid cooling during the protoneutron star stage, the neutron star crust is formed. Neutrinos continue to be produced in the crust, which can escape from the surface. This neutrino production is an important process to the final cooling phase of the star. They are produced in the crystalline lattice formed by nuclei permeated by an electronic gas. Quantum oscillations of the electron density with respect to the lattice of nuclei generates plasmons, which decay in a pair of neutrinos. Many works have studied the plasma of the nucleus in the star, however, without incorporating the effect of the lattice in the crust of the neutron star. The objective of this work is to include the lattice in the calculation of the plasmon decay rate using quantum field theory at finite temperature. It is not common to find studies on the crystalline lattice of the star using quantum field theory and the calculations generally used for neutrino emissivity consider a homogeneous and isotropic medium, which can not be directly applied in the context of neutron star crust.

We have investigated the spatial distribution of the electron temperature generated in a two-dimensional electron system (2DES) subjected to a perpendicular magnetic field. We measure thermoelectric voltages between Ohmic contacts located at the end of the voltage-probe arms of a Hall bar fabricated from a GaAs/AlGaAs 2DES wafer, immersed in the mixing chamber of a dilution refrigerator held at 20 mK. Magneto-oscillations due to the Landau quantization are examined for the thermoelectric voltages between the contact pairs straddling the main bar (arrangement to measure the transverse component $V_{yx}$), and between the pairs located along the same side of the main bar (arrangement for the longitudinal component $V_{xx}$). For the former arrangement, the oscillation amplitude diminishes with the distance from the heater. For the latter arrangement, the pair on one side exhibits much larger amplitude than the pair on the opposite side, and the relation becomes reversed by inverting the magnetic field. The behaviours of the oscillation amplitude are qualitatively explained by the spatial distribution of the electron temperature numerically calculated taking into consideration the thermal diffusion into the voltage contacts and the electron-phonon interaction. For both arrangements, the oscillations are shown to derive predominantly from the transverse (Nernst) component, $S_{yx}$, of the thermopower tensor. The calculation also reveals that the voltage probes, introducing only minor disturbance at zero magnetic field, substantially reduce the temperature once a magnetic field is applied, and the thermoelectric voltages generated at the voltage arms account for a significant part of the measured voltages., Comment: 17 pages, 18 figures (including Supplementary data), minor corrections

We present a systematical study on single crystalline FeSb2 using electrical transport and magnetic torque measurements at low temperatures. Nonlinear magnetic field dependence of Hall resistivity demonstrates a multi-carrier transport instinct of the electronic transport. Current-controlled negative differential resistance (CC-NDR) observed in current–voltage characteristics below ~ 7 K is closely associated with the intrinsic transition ~ 5 K of FeSb2, which is, however, mediated by extrinsic current-induced Joule heating effect. The antimony crystallized in a preferred orientation within the FeSb2 lattice in the high-temperature synthesis process leaves its fingerprint in the de Haas-Van Alphen (dHvA) oscillations, and results in the regular angular dependence of the oscillating frequencies. Nevertheless, possible existence of intrinsic non-trivial states cannot be completely ruled out. Our findings call for further theoretical and experimental studies to explore novel physics on flux-free grown FeSb2 crystals.

An experimental study of a Fabry-Perot interferometer in the quantum Hall regime reveals Aharonov-Bohm-like (ABL) oscillations. Unlike the Aharonov-Bohm effect, which has a period of one flux quantum, Φ0, ABL oscillations possess a flux period of Φ0/f, where/is the integral value of fully filled Landau levels in the constrictions. The detection of ABL oscillations is limited to the low magnetic field side of the vc = 1, 2, 4, 6,..., integer quantum Hall plateaus. These oscillations can be understood within the Coulombdominated model of quantum Hall interferometers as forward tunneling and backscattering, respectively, through the center of the interferometer from the bulk and the edge states. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

The present density functional calculations propose the compounds CaSrX (X: Si, Ge, Sn, Pb) as strong topological insulators, with appreciable thermoelectric properties. Emergence of Dirac semi-metallic states has been observed in CaSrX (X: Si, Ge, Sn, Pb), which is induced by uni-axial strain along 'b' axis. CaSrSi and CaSrGe evolved as normal semiconductors with uni-axial strain. The trivial and non-trivial topological phases are evaluated by band inversion and Z 2 topological invariants. A comprehensive analysis of thermopower, electrical conductivity scaled by relaxation time at these Dirac semi-metallic states exposes the highly oscillating behaviour, which gives insight to quantum oscillations driven by uni-axial strain. Further the thermoelectric properties at strong topological insulating states and normal insulating states have been summarized, which reveals the potential thermoelectric properties of these materials.

The magnetoresistance (MR) in semimetals with Dirac (or Weyl) electrons and free holes is investigated on the basis of the Boltzmann theory. The MR is modified from the conventional results with free electrons and holes in a very complex way due to the correction of the Dirac dispersion. The obtained formula explicitly includes the magnetic field dependence, which is very useful for the analysis of experimental results. In order to verify the validity of our results, the results obtained by the Boltzmann approach are compared with those by the Kubo theory. It is revealed that, by taking into account the field dependence of carrier density, the MR obtained by the Boltzmann theory almost perfectly agrees with that based on the Kubo theory even in the high-field region (in the quantum limit) except for the quantum oscillations. It is also shown that the MR in semimetals increases linearly with respect to the field in the quantum limit due to the drastic change of the carrier density, which is a significant characteristic of semimetals.

In the present paper, we study effect of the long-range Coulomb interaction on the thermodynamic properties of graphene by renormalization group methods. Our calculations show that both the specific heat and the magnetic susceptibility of the material behave differently from the Landau Fermi liquid. More precisely, we find that these quantities are logarithmically suppressed with respect to its noninteracting counterpart when temperature is low.

In this paper, we first review fundamental aspects of magnetoresistance in multi-valley systems based on the semiclassical theory. Then we will review experimental evidence and theoretical understanding of magnetoresistance in an archetypal multi-valley system, where the electric conductivity is set by the sum of the contributions of different valleys. Bulk bismuth has three valleys with an extremely anisotropic effective mass. As a consequence, the magnetoconductivity in each valley is extremely sensitive to the orientation of the magnetic field. Therefore, a rotating magnetic field plays the role of a valley valve tuning the contribution of each valley to the total conductivity. In addition to this simple semi-classical effect, other phenomena arise in the high-field limit as a consequence of an intricate Landau spectrum. In the vicinity of the quantum limit, the orientation of magnetic field significantly affects the distribution of carriers in each valley, namely, the valley polarization is induced by the magnetic field. Moreover, experiment has found that well beyond the quantum limit, one or two valleys become totally empty. This is the only case in condensed-matter physics where a Fermi sea is completely dried up by a magnetic field without a metal-insulator transition. There have been two long-standing problems on bismuth near the quantum limit: the large anisotropic Zeeman splitting of holes, and the extra peaks in quantum oscillations, which cannot be assigned to any known Landau levels. These problems are solved by taking into account the interband effect due to the spin-orbit couplings for the former, and the contributions from the twinned crystal for the latter. Up to here, the whole spectrum can be interpreted within the one-particle theory. Finally, we will discuss transport and thermodynamic signatures of breaking of the valley symmetry in this system., A topic review for JPCM, 22 pages, 18 figures

The physical properties of a solid are determined by the electrons near the Fermi energy and their low-lying excitations. Thus, it is crucially important to obtain the band structure near the Fermi energy of a material to understand many novel phenomena that occur, such as high-T c superconductivity, density waves, and Dirac-type excitations. One important way to determine the Fermi surface topology of a material is from its quantum oscillations in an external magnetic field. In this article, we provide a brief introduction to the substation at the Synergetic Extreme Condition User Facility (SECUF), with a focus on quantum oscillation measurements, including our motivation, the structure of and the challenges in building the substation, and perspectives.

We present a systematic quantum oscillations study on a metallic, p-type Bi2Te3 topological single crystal in magnetic fields up to B = 7 T. The maxima/minima positions of oscillations measured at different tilt angles align to one another when plotted as a function of the normal component of magnetic field, confirming the presence of the 2D Fermi surface. Additionally, the Berry phase, β = 0.4 ± 0.05 obtained from the Landau level fan plot, is very close to the theoretical value of 0.5 for the Dirac particles, confirming the presence of topological surface states in the Bi2Te3 single crystal. Using the Lifshitz-Kosevich analyses, the Fermi energy is estimated to be [Formula: see text] meV, which is lower than that of other bismuth-based topological systems. The detection of surface states in the Bi2Te3 crystal can be explained by our previous hypothesis of the lower position of the Fermi surface that cuts the 'M'-shaped valence band maxima. As a result, the bulk state frequency is shifted to higher magnetic fields, which allows measurement of the surface states signal at low magnetic fields.

The thermostatistic problems of a q-deformed ideal Fermi gas in any dimensional space and with a general energy spectrum are studied, based on the q-deformed Fermi?Dirac distribution. The effects of the deformation parameter q on the properties of the system are revealed. It is shown that q-deformation results in some novel characteristics different from those of an ordinary system. Besides, it is found that the effects of the q-deformation on the properties of the Fermi systems are very different for different dimensional spaces and different energy spectrums.

The unlimited energy growth (Fermi acceleration) of a classical particle moving in a billiard with a parameter-dependent boundary oscillating in time is numerically studied. The shape of the boundary is controlled by a parameter and the billiard can change from a focusing one to a billiard with dispersing pieces of the boundary. The complete and simplified versions of the model are considered in the investigation of the conjecture that Fermi acceleration will appear in the time-dependent case when the dynamics is chaotic for the static boundary. Although this conjecture holds for the simplified version, we have not found evidence of Fermi acceleration for the complete model with a breathing boundary. When the breathing symmetry is broken, Fermi acceleration appears in the complete model.

With a two-channel model, we study the influence of temperature, external voltage and magnetic flux on the line shape of the Fano resonance, and show that in the Luttinger liquid case, the background transmittance and the asymmetric parameter depend strongly on the temperature and external voltage, while for the Landau Fermi liquid case they are nearly independent of these parameters in the low energy region. Moreover, we demonstrate that the asymmetric parameter changes periodically with an external magnetic flux, which is consistent with the recent experimental data.

In this paper the analytical expression of free energy expressed by small parameter r of a weakly interacting Fermi gas trapped in weak magnetic field is derived by using `the maximum approximation' method and the ensemble theory. Based on the derived expression, the exact instability conditions of a weakly interacting Fermi gas trapped in weak magnetic field at both high and low temperatures are given. From the instability conditions we get the following two results. (1) At the whole low-temperature extent, whether the interactions are repulsive or attractive with (αn+4eF/3) (n and eF denote the particle-number density and the Fermi energy respectively, α = 4πa2/m, and a is s-wave scattering length) positive, there is a lower-limit magnetic field of instability; in addition, there is an upper-limit magnetic field for the system of attractive interactions with (αn+4eF/3) negative. (2) At the whole high-temperature extent, the system with repulsive interactions is always stable, but for the system with attractive interactions, the greater the scattering length of attractive interactions |a| is, the stronger the magnetic field is and the larger the particle-number density is, the bigger the possibility of instability in the system will be.

A simplified version of a time-dependent annular billiard is studied. The dynamics is described using nonlinear maps and we consider two different configurations for the billiard, namely (i) concentric and (ii) eccentric cases. For the concentric case and for a null angular momentum, we confirm that the results for the Fermi–Ulam model are recovered and the particle does not experience the phenomenon of Fermi acceleration. However, on the eccentric case the particle demonstrates unlimited energy gain and Fermi acceleration is therefore observed.

The Fermi surface topology of Na0.5CoO2 is studied using the hybrid density functional theory. We first study a single (CoO2)0.5− layer model with the percentage of the nonlocal Hartree–Fock exchange changing from 0% to 20%. The results show that only when the mixed nonlocal Hartree–Fock exchange is between 1% and 5%, the Fermi surface topology is similar to the experimental one. With 3% HF exchange in the hybrid density functional, considering the effects of Na ions in the Na0.5CoO2 system, we find that the Fermi surface is split to double holes and small gaps open near the intersections between the Brillouin zone and the Fermi surface. Our results show that both the amounts of the nonlocal Hartree–Fock exchange in the hybrid density functional and the Na ions have much influence on the Fermi surface topology.

Recent experiments observed coherent quantum oscillations for a system of Josephson phase qubits and critical-current fluctuators, which demonstrated the ability to measure two-qubit interactions. Here we propose a new scheme of manipulations with a system consisting of coupled qubits and fluctuators. In such a scheme one can, on the one hand, observe quantum coherent Rabi-like oscillations. On the other hand, the scheme permits us to distinguish responses from qubits with different eigenvalues. Also, it will be useful for testing the system and extracting its parameters.

We have studied the Fermi surface of copper by angle-resolved photoemission for photon energies between 95.37 and 259.6 eV. Fermi surface images were obtained by scanning the polar emission angle as well as the photon energy while monitoring the photoemission intensity at the Fermi level. Such images are distorted because of the non-conservation of the perpendicular k component in photoemission. However, if the scans are performed such that the k steps parallel to the surface are identical for all photon energies, the distortion can be corrected for using appropriate final states, for example free-electron final states. We find reasonable agreement between our results and the well-known Fermi surface of copper.

Relativistic energy band calculations have been carried out for CeIrIn5, CeCoIn5, UFeGa5, UCoGa5 and URhGa5 under the assumption that f electrons are itinerant. The main Fermi surface sheet of CeIrIn5 is quite similar to that of CeCoIn5, which is a quasi-two-dimensional Fermi surface. The Fermi surface sheets of UCoGa5 are quite similar to those of URhGa5, which are all small in size and closed in topology. UFeGa5 has a quasi-two-dimensional Fermi surface and a lattice-structure-like Fermi surface.

We fabricated nanodevices from MoxW1−xTe2 (x = 0, 0.07, 0.35), and conducted a systematic comparative study of their electrical transport. Magnetoresistance measurements show that Mo doping can significantly suppress mobility and magnetoresistance. The results for the analysis of the two band model show that doping with Mo does not break the carrier balance. Through analysis of Shubnikov–de Haas oscillations, we found that Mo doping also has a strong suppressive effect on the quantum oscillation of the sample, and the higher the ratio of Mo, the fewer pockets were observed in our experiments. Furthermore, the effective mass of electron and hole increases gradually with increasing Mo ratio, while the corresponding quantum mobility decreases rapidly.

We discuss a conductivity of a three-dimensional gas of Dirac electrons in the direction of magnetic field in high magnetic fields. Analytical expressions for the zero temperature conductivity are calculated in the linear response theory using the basis of relativistic Landau levels. The impurity scattering is treated in the self-consistent Born approximation which gives Landau level broadening increasing linearly in magnetic field. We demonstrate that in the special case of zero-gap Dirac semimetal this leads to the magnetic field and temperature independent conductivity in high magnetic field limit.

The Hall effect and the Shubnikov–de Haas (SdH) effect have been investigated in magnetic fields up to 54 T in p-(Bi1−xSbx)2Te3 (0 ≤ x ≤ 1.0) Sn doped single crystals. Doping of (Bi1−xSbx)2Te3 with tin has shown that Sn exhibits acceptor properties in all crystals. We discuss the valence band structure of (Bi1−xSbx)2Te3 with the upper valence band (light hole band (LHB)), the lower valence band (heavy hole band (HHB)) and Sn-induced impurity band (IB). The Hall resistivity ρH as a function of magnetic field shows quantization in the form of plateaus. The calculated Landau levels of the LHB with the best-fit parameters are in agreement with the experiment. The oscillation of ρH is due to the presence of the carrier reservoir. The impurity resonant band with a high density of states or the HHB with a higher hole effective mass serve as the reservoir.

Explicit analytic expressions are obtained for the density of states D(E) and Fermi energy E-F of a two-dimensional electron gas in the presence of a weak and periodic unidirectional electric or magnetic modulation and of a uniform perpendicular magnetic field B. The Landau levels broaden into bands and their width, proportional to the modulation strength, oscillates with B and gives rise to Weiss oscillations in D(E), E-F and the transport coefficients. When both electric and magnetic modulations are present the position of the resulting oscillations depends on the ratio delta between the two modulation strengths. When the modulations are out of phase there is no shift in the position of the oscillations when delta varies and for a particular value of delta the oscillations are suppressed.

The attenuation and the velocity shift of surface acoustic waves (SAWs) in a GaAs–Al0.3Ga0.7As asymmetric double quantum well structure are investigated under nonequilibrium conditions. When the electron density is in the vicinity of the occupation threshold of the second subband, the SAW transmission in the quantum Hall regime is suppressed over the entire magnetic field range with a large magnitude. The suppression is quenched in the presence of a dc current whenever the Fermi level lies just above the Landau gaps associated with the first subband, resulting in marked oscillations in the SAW transmission.

We report preparation of nanoribbons (crossection ~ 250*25 nm2) by focused ion beam etching of single-crystalline Bi2Se3 and detailed measurements of their magnetoresistance at temperatures down to 4.2 K, magnetic field up to 9 T. In a magnetic field parallel to the axis of nanowire the magnetoresistance shows up oscillations. Surprisingly, the Fourier analysis shows the presence not only of oscillations with a period corresponding to the flux quantum (Φ0 = hc/e), but also oscillations with a period of 2Φ0 and 4Φ0. Possible mechanisms of the observed effect are discussed.

Quantum phase transition in topological insulators has drawn heightened attention in condensed matter physics and future device applications. Here we report the magnetotransport properties of single crystalline (Bi0.92In0.08)2Se3. The average mobility of is obtained from the Lorentz law at the low field () up to 50 K. The quantum oscillations rise at a field of , revealing a high mobility of at 2 K. The Dirac surface state is evident by the nontrivial Berry phase in the Landau–Fan diagram. The properties make the (Bi0.92In0.08)2Se3 a promising platform for the investigation of quantum phase transition in topological insulators.

Single crystals of topological Dirac semimetal Cd3As2 were synthesized using a modified vapour transport technique. The magnetization of Cd3As2 single crystals was measured in the temperature range from 4.2-300 K and magnetic field up to 5 T along [001] and [100] directions. In the low temperature region we observed the de Haas van Alphen (dHvA) oscillations which allow us to characterize the three dimensional Fermi surface by extracting its relevant parameters. The dHvA oscillations show the existence of two different Fermi surface cross sections and nontrivial Berry's phase, which is the signature of Dirac fermion in Cd3As2.

The Weyl semimetal NbP exhibits an extremely large magnetoresistance (MR) and an ultra-high mobility. The large MR originates from a combination of the nearly perfect compensation between electron- and hole-type charge carriers and the high mobility, which is relevant to the topological band structure. In this work we report on temperature- and field-dependent thermopower and thermal conductivity experiments on NbP. Additionally, we carried out complementary heat capacity, magnetization, and electrical resistivity measurements. We found a giant adiabatic magnetothermopower with a maximum of 800 $\mu$V/K at 50 K in a field of 9 T. Such large effects have been observed rarely in bulk materials. We suggest that the origin of this effect might be related to the high charge-carrier mobility. We further observe pronounced quantum oscillations in both thermal conductivity and thermopower. The obtained frequencies compare well with our heat capacity and magnetization data., Comment: 6 pages, 3 figures

We report on the development of a sensitive dilatometer based upon an atomic force microscope piezocantilever. This dilatometer is designed to measure the elastic properties of bulk materials in extreme conditions, such as temperatures down to 25 mK and magnetic fields up to 16 T. The layered heavy fermion superconductor and its non-magnetic analog are measured to demonstrate their use in detecting phase transitions and quantum oscillations. In addition, using this dilatometer, a simultaneous multi-axis dilation measurement is performed. This compact dilatometer has many advantages, such as its ability to measure very small samples with sub-mm lengths at low temperature and small field dependence, and its ability to rotate, while it works well irrespective of whether it is in a changing liquid or gas environment (i.e. within a flow cryostat or mixing chamber).