Shubnikov-de Haas effect of n-inversion layers in InSb grain boundaries

Hall effect and Shubnikov-de Haas effect have been investigated in a n-inversion layer adjacent to the grain boundary in p-InSb bicrystals. The observed quantum oscillations of the magnetoconductivity result from a superposition of the Shubnikov-de Haas effect in two occupied subbands. The electron densities of the subbands n_si(n_s1=3.5 × 10¹¹cm^-2;n_s0= 1.1 × 10¹²cm^-2) and the effective cyclotron mass of the lower subband m_c0=(0.023 ± 0.002)m₀ have been evaluated.     

Electronic properties of Bi2Se3 crystals

Bismuth selenide crystals were grown from melts with liquid concentrations within 0·2 per cent of stoichiometry. The resulting crystals were examined structurally showing that single crystal samples could be cut for electronic property measurements. Samples were n-type and degenerate (n ～ 2 × 10²⁵ m^?3). Hall, magnetoresistance and Shubnikov-de Haas measurements confirm that the carriers lie in a single minimum located at the centre of the Brillouin Zone. The results are discussed in terms of a non-ellipsoidal band model, and the degeneracy discussed in terms of a defect model.     

Hall effect plateaus and giant Shubnikov-de Haas oscillations in (BiSb)Telayered single crystals near the quantum limit

On bulk layered single crystals (Bi_0.25Sb_0.75)₂Te₃ with a hole concentration cm^-3 and a mobility cm²/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the damping of the amplitudes with increasing temperature the cyclotron mass m _c = 0.12m ₀ is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be . Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.     

On the Fermi surface of low carrier concentration SnTe

The multiple parallel frequency branches observed in low carrier concentration SnTe by Savage et al. in 1972 are interpreted in terms of the structural phase transition in such material in conjunction with band structure parameters derived from a study of the Shubnikov-de Haas effect in samples of Pb_1?xSn_xTe in the rhombohedral phase with normal and inverted band ordering.     

Surface quantum oscillations in (110) and (111) n-type silicon inversion layers

Shubnikov-de Haas oscillations have been studied for (110) and (111) n-type silicon inversion layers. The measured cyclotron masses m_c = (0.38 ± 0.03)m₀ and m_c = (0.40 ± 0.03)m₀ for (110) and (111) planes, respectively, are larger than theoretically predicted values. The experimental valley degeneracy factor g_v = 2 ± 0.2 for both orientations is also at variance with self consistent calculations. The electronic g-factor depends on the surface carrier concentration and is enhanced over its bulk value. There was no evidence for the occupation of other subbands.     

Fermi surface in the new organic quasi-two-dimensional metal α-(BETS)2TlHg(SeCN)4

Quantum oscillations of de Haas-van Alphen and Shubnikov-de Haas and semiclassical angular oscillations of the magnetoresistance have been observed in the quasi-two-dimensional organic metal α-(BETS)₂TlHg(SeCN)₄. The quantum oscillations are connected with the cylindrical part of the Fermi surface. The angular oscillations are associated with the carrier motion on both the cylindrical part and quasi-planar sheets of the Fermi surface. The values of the Dingle temperature, T _D ≈ 2–3 K, and the effective mass, m* ≈ 1.03m ₀, have been defined. The possibility of the weakening of multibody interactions has been shown in this compound.     

Spatial fluctuations of carrier density in n type GaxIn1−xSb determined by SH-DH effect

Variation of carrier concentration through n-type Ga_xIn_1?xSb single crystals, interpreted as due to vacancies behaving as acceptors, is deduced from Shubnikov-de Haas measurements. A quantitative agreement between calculated and experimental values of the mobility at 4.2°K is obtained with this model as well as some information about the influence of growing conditions on the quality of the crystal.     

Quantum and semiclassical oscillations in the organic metal (BEDO-TTF)2Clx(H2O)y

We study quantum (Shubnikov-de Haas and de Haas-van Alphen) oscillations and angular oscillations of the reluctance in the organic quasi-two-dimensional metal (BO)₂Cl_x(H₂O)_y. We show that the Fermi surface in this compound consists of a slightly corrugated cylinder with its axis perpendicular to the conducting plane. The cross section of the cylinder in this plane is a perfect circle of radius k _F≃3×10⁷ cm⁻¹. The effective carrier mass associated with this cylinder is m*=(1.65–2.0) m ₀ in the conducting plane, while the Dingle temperature is T _D=3–4 K. Zh. éksp. Teor. Fiz. 114, 1137–1146 (September 1998)     

Quantum oscillatory phenomena in graphite intercalated with AsF5

Both Shubnikov-de Haas and de Haas-van Alphen oscillations are reported for C_8nAsF₅ (n=1,2, is the stage number). The observed oscillations are interpreted in terms of a tight-binding model for the band structure, and good agreement with both band parameters and effective carrier masses is found. In addition, the effective charge transfer per AsF₅ molecule (f=.37 for stage 1, =.41 for stage 2) is in basic agreement with previous determinations.     

Effective electron mass in high-mobility SiGe/Si/SiGe quantum wells

The effective mass m* of the electrons confined in high-mobility SiGe/Si/SiGe quantum wells has been measured by the analysis of the temperature dependence of the Shubnikov-de Haas oscillations. In the accessible range of electron densities, n _s , the effective mass has been found to grow with decreasing n _s , obeying the relation m*/m _b = n _s /(n _s ? n _c ), where m _b is the electron band mass and n _c ≈ 0.54 × 10¹¹ cm^?2. In samples with maximum mobilities ranging between 90 and 220 m²/(V s), the dependence of the effective mass on the electron density has been found to be identical suggesting that the effective mass is disorder-independent, at least in the most perfect samples.     

Galvanomagnetic effects in graphite—III: The effect of neutron irradiation on the quantum limit Shubnikov-de Haas oscillations

Galvanomagnetic effects have been studied for a range of highly oriented, neutron-irradiated samples of graphite at 1.2–7K, in fields up to 9 Tesla. Irradiation doses were in the range $\text{0}\text{?}\text{?3× 10}{}^{17}\text{nvt}\text{(E> 1}\text{MeV}$). Asymptotic values of σ_xyB were used to obtain independent values of the carrier density difference (P-N). Shubnikov-de Haas frequencies, effective masses, Dingle temperatures and coincidence fields in the quantum limit were measured. Theoretical values for the variation of these quantities with the Fermi energy, (P-N) and with band overlap parameters were also obtained. The results could not be fitted to a simple model in which reasonable changes were allowed in ?_F and the band parameters.     

Revision of the Kosicki-Paul model for resonant and bound states in n-GaSb(Se) from hydrostatic pressure measurements

Hall effect, resistivity, and Shubnikov-de Haas results are discussed with respect to the existence of possible resonant states above the Γ₁ band edge in n-GaSb(Se). It is suggested that at helium temperatures, the states determining the Fermi energy lie much closer to the L₁ band edge than the states which account for the pressure dependent behavior in the range 77–300 K.     

Spin splitting in HgTe/CdHgTe (013) quantum well heterostructures

The electron transport and cyclotron resonance in a one-sided selectively doped HgTe/CdHgTe (013) heterostructure with a 15-nm quantum well with an inverted band structure have been investigated. The modulation of the Shubnikov-de Haas oscillations has been observed, and the spin splitting in zero magnetic field has been found to be about 30 meV. A large Δm _c/m _c ≃ 0.12 splitting of the cyclotron resonance line has been discovered and shown to be due to both the spin splitting and the strong nonparabolicity of the dispersion relation in the conduction band.     

Electronic anomalous mass near the resonant acceptor level E2 from Shubnikov-de Haas measurement in Hg0.82Cd0.18Te

Shubnikov-de Haas measurements on Hg_0.82Cd_0.18Te samples at 1.8 and 4.2 K temperature are reported. The obtained effective mass is compared with the one calculated from the non-parabolic model. The discrepancy between the two values is attributed to the presence of the E₂ resonant acceptor level. The density of states induced by this virtual level in the conduction band, is strongly dependent on stoichiometry and can be adjusted by thermal annealing.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

Trigonal warping of the Fermi surface in n-Bi2Se3

Shubnikov-de Haas investigations on n-type Bi₂Se₃ single crystals were performed in magnetic fields up to 10.5 Tesla (105 kG). The shape of the single-valley Fermi surfaces is almost an ellipsoid of revolution around the trigonal k_c-axis, the longest main axis of the Fermi surface. There is a small amount of flattening in the direction of the k_c-axis and of trigonal warping around the k_c-axis, caused by higher order terms than [k²] in the ?(k) relation.     

Quantum oscillations in heavily doped bismuth chalcogenides

The observation of Shubnikov-de Haas and Hall oscillations in high-quality Bi_{2 ? x} Cu _x Se₃ single crystals is reported. Measurements carried out upon rotating the samples with respect to the magnetic field demonstrate that the oscillations originate from two-dimensional surface states in three-dimensional single crystals and are determined only by the perpendicular component of the magnetic field.     

Quantum oscillation of carrier concentration due to fermi level pinning by doped indium impurities in Pb1−XSnXTe

The Shubnikov-de Haas like oscillation and rapid increase of the carrier concentration above the quantum limit magnetic field (H₀) are observed in Pb_1?xSn_xTe doped with indium (x=0.33 and 0.35). Experimental results can be reproduced satisfactorily by the calculation based on the Fermi level pinning model due to In-impurities, where we take into account the level broadening (Г) effect of the band structure. It is confirmed that the increasing rate of carrier concentration with respect to magnetic field above H₀ decreases with larger Г.     

Comparison of Shubnikov-de Haas effect and cyclotron resonance on Si(100) MOS transistors under uniaxial stress

The stress induced population of the non-equivalent subbands E₀ to E′₀ is investigated by measurements of the magnetoconductivity — the Shubnikov-de Haas oscillations — and the cyclotron resonance taken on the same MOS transistor under identical conditions. In cyclotron resonance with increasing stress, a gradual transfer of carriers from E₀ to E′₀ is observed, whereas the Shubnikov-de Haas periodicity is unaffected and always yields a valley degeneracy of two. A domain model is required to resolve this apparent discrepancy.