Dingle Temperature Research Articles

SINGLE PARTICLE GREEN'S FUNCTION AND QUANTUM MAGNETIC OSCILLATION IN VORTEX STATE OF UNCONVENTIONAL SUPERCONDUCTORS

Within weak-coupling model we construct the superconducting order parameter in the vortex states of the axial and hybrid wave function. In terms of these order parameters the quasi-particle Green's function in the vortex state in the vicinity of upper critical field is constructed. In general the most important modification on the quantum oscillation in the vortex state is increase of the damping constant (or the Dingle temperature). However, since this extra term is proportional to the average of | f |2 over the electron orbit at the belly or neck of the Fermi surface, we find that this exrtra term vanishes for the hybrid state for both [Formula: see text] and [Formula: see text], while it vanishes in the axial state only for [Formula: see text]. This should provide a unique probe to the nature of the superconducting wave functions.

Shubnikov–de Haas oscillations on as-grown and annealed molecular-beam-epitaxy-grown Hg1−xCdxTe alloys doped with indium

Transverse resistivity ρxx, longitudinal resistivity ρzz, and Hall resistivity ρxy on heavily indium-doped as-grown and annealed Hg1−xCdxTe (0.24<x<34) alloys in a magnetic field up to 12 T and temperature range 1.2–25 K have been measured. The as-grown and annealed samples show good quality Shubnikov–de Haas oscillations in which the effective masses m*, free-electron densities nSdH, and Dingle temperatures TD are extracted. The deduced m* and nSdH from the as-grown and annealed samples are in good agreement within 12%. However, there are considerable improvements in the low field Hall mobility μH (a maximum 54% increase) and a reduction in TD (a maximum 65% decline) in the annealed samples. Analysis at low field seems to indicate that broadening due to an inhomogeneous impurity distribution contributes to TD in addition to the partial cancellation produced by different frequencies of oscillations. An estimate of the average values of an electron density fluctuation Δn/n and its spatial extent ΔL based only on TD and Hall mobility temperature Tμ is presented. The deduced ΔL is in the order of mean free path l. This, therefore, can limit μH and the values of l and ΔL and this indicates that if there is an inhomogeneous distribution of indium donor, high-temperature annealing tends to homogenize the distribution of indium donors by diffusion.

DHvA measurements of high-T c oxides with steady high-magnetic fields

The de Haas-van Alphen (dHvA) effect has been measured in YBa 2Cu 3O 7 (Y123) and Tl 2Ba 2CuO 6+δ (T12201) with oriented-powder samples in H//c-axis direction at the temperature range between 1.6 and 4.2 K with steady high magnetic fields up to 27 T. The oscillatory magnetization was detected by a modulation technique. We performed spectral analysis by employing the maximum entropy method (MEM). In Y123, the spectral density shows apeak at 456 T which corresponds to an extremal cross-section of 0.044 A −2. The dingle temperature was evaluated to be 7 K using the effective-mass-value of 2.1 m c. In T12201, the maximum of spectral density appeared at 400 T not only for superconducting sample (δ ≅ .08) but also for metallic non-superconducting sample (δ = .1).

Subband effective mass and mobility of two-dimensional electrons in uniformly Si-doped Ga0.47In0.53As/Al0.48In0.52As multiple quantum wells

Subband effective mass and mobility of a two-dimensional electron gas in uniformly Si-doped Ga0.47In0.53As/Al0.48In0.52As multiple quantum wells are estimated. In three samples with well widths of 130, 200, and 300 Å and a fixed barrier width of 68 Å, up to three two-dimensional subbands are found. Maximum enhancement of electron effective mass is 25% over the bulk value at a Fermi energy of 108 meV. These estimated effective masses are slightly smaller than previously reported values, and this is explained by recent theories which assume only nonparabolic correction. When the temperature ratio, (Dingle temperature)/(mobility temperature), is assumed to be identical in different subbands in each sample, the electron mobility of the first excited subband is at most twice that of the ground subband in the sample with the widest well. The effects of intersubband scattering and of screening on the subband mobilities are also discussed.

Dingle tehpeiutube under strong uniaxial cohpbession up to 0.3% and intervalley scattering in Bi-Sb at 4.2K

Abstract A sharp decrease in the Dingle temperature has been observed during uniaxial compression in the alloy Bi0.gSb0. 1 along the bisector axis. The decrease occurs because the interval ley scattering mechanism turns off upon the transition from a three-valev electron spectrum to a single-valley electron spectrum in the course of the deformation.

Shubnikov–de Haas oscillations on molecular-beam-epitaxy-grown Hg1−xCdxTe alloy doped with indium

Shubnikov–de Haas oscillations on the transverse resistivity ρxx and longitudinal resistivity ρzz of as-grown indium-doped alloys of Hg1−xCdxTe (0.24<x<0.34) grown by molecular-beam epitaxy on (111)B and (100) growth directions are observed in the temperature range from 1.2 to 25 K and in fields up to 12 T. The n-type density from the periodicity, the effective mass m* from the temperature dependence of the amplitude, and the Dingle temperature TD are determined from ρxx and ρzz oscillations. The oscillations establish the high Hall density which is found at low fields. The TD in ρxx is found to be higher in comparison to TD in ρzz. However, this difference decreases as the Hall density increases. The TD discrepancy is probably due to greater inhomogeneity in the plane of the layer. The TD is higher than the temperature calculated from the weak-field Hall mobility. The density and effective mass are used to calculate the energy band gap, Fermi energy, and the band-edge effective mass. The calculated energy band gaps are in good agreement with the reported results.

Quantum oscillation in vortex states of type-II superconductors.

We examine theoretically magnetic quantum oscillations like the de Haas--van Alphen and Subnikov--de Haas effects in vortex states in type-II superconductors. For a magnetic field B not very small compared with ${\mathit{H}}_{\mathit{c}3}$(T), the main effect of superconductivity is introduction of the extra quasiparticle scattering rate proportional to \ensuremath{\Vert}\ensuremath{\Delta}${\mathrm{\ensuremath{\Vert}}}^{2}$, the square of the superconducting order parameter. Therefore the detectability of the magnetic quantum oscillation is determined from the condition that the extra Dingle temperature due to \ensuremath{\Vert}\ensuremath{\Delta}${\mathrm{\ensuremath{\Vert}}}^{2}$ is not too large. For example in a magnetic field \ensuremath{\sim}10 T, the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ has to be less than 30 K in order to have a reasonable signal.

First-principles calculations of the electronic properties of 3d transition-metal impurities in Al

A comprehensive study of 3d transition-metal impurities in Al is carried out using the self-consistent Green function, linear-muffin-tin-orbital method. Using the self-consistent potential at the impurity site the author investigates the changes in the local density of states and the charge transfer between the impurity and the neighbouring host atoms. The movement of the virtual bound states and the phase shifts at the Fermi energy are used to explain the transport properties of these alloys. For several alloys the results for the impurity resistivities, the thermoelectric powers, the Dingle temperatures and the electronic specific heats are in good agreement with experimental data and the results of other calculations.

Magnetoresistance studies of βμ-ET2AuBr2

Low-temperature transverse magnetoresistance (MR) measurements have been made on the organic metal βμ-ET2AuBr2. The MR was found to be highly anisotropic. A 2-band model was used to evaluate the carrier mobilities in the different sections of the Fermi surface. Shubnikov-de Haas (SdH) oscillations of two distinct frequencies were observed for current along the higher resistance direction. Analysis of the field and temperature dependence of these oscillations yields an effective mass of 4–5 me and a Dingle temperature of 0.3–0.5 K. An interpretation of the different oscillation frequencies gives an inter-planar bandwidth of 4tc∼2.2±0.3 meV.

Shubnikov-de Haas effect study of InAs after transmutation doping at low temperatures

Degenerate InAs single crystals have been irradiated by thermal neutrons below 6 K. The Shubnikov-de Haas effect and the electrical resistivity have been measured as a function of the neutron dose and the annealing temperature. The effects of transmutation doping and simultaneous introduction of lattice defects have been analysed in terms of the conduction electron density and the scattering rates tau p-1=pne2/m* and tau x-1=2 pi kBX/h(cross) (where X is the Dingle temperature). The measured conduction electron density after irradiation and the thermal annealing agreed well with the values calculated from the experimental and materials parameters. The effects of radiation damage may qualitatively be explained assuming neutral In vacancies to be the most common type of defect in the thermal-neutron-irradiated InAs. A comparison with similar experiments on InSb is given.

Transport properties of organic conductor (BEDT-TTF) 2KHg(SCN) 4: II. Shubnikov-de Haas oscillations and spin-splitting effect

The magnetoresistance, the Shubnikov-de Haas (SdH) effect and their orientation dependence of an organic conductor (BEDT-TTF) 2KHg(SCN) 4 have been measured at temperatures down to 0.5 K and under magnetic fields up to 13 T. The SdH frequency F=670T, the cyclotron mass m c =1.4 m 0 and the Dingle temperature T D =1.6 K are obtained when the fields are applied perpendicular to the conducting a-c plane. The dependence of F on the angle θ between the field and the b ∗-axis (⊥ a-c plane), which deviates slightly from cosθ, indicates the presence of the weakly warped cylindrical Fermi surface with an interlayer transfer integral estimated to be about 1 meV. Below 1 K and above 10 T, the spin-splitting effect is clearly observed and the direct analysis of the splitting oscillations results in the series of the g-factor; g=1.4 n±0.6 ( n is an odd number). The rigorous g-factor of 2.0 ( n=1, + sign), being consistent with ESR measurements, is obtained.

Shubnikov-de haas effect under hydrostatic pressure in HgSe: Fe

We present a study of the influence of hydrostatic pressure (up to 0.8 GPa) on Shubnikov-De Haas oscillations in unoriented HgSe: Fe samples in magnetic fields ranging from 0 to 7 T at liquid helium temperatures. A decrease in the Dingle temperature reflecting the onset of spatial correlation of charged donors is observed. The pressure experiments enable the ratio of the exchange integrals α and β between the mobile conduction electron and the localized magnetic moments of the Fe 3+ ions to be determined.

Correlation of donor electrons in diluted magnetic semiconductors with iron

Substitutional iron in HgSe forms a resonant donor state whose energy is superimposed on the conduction band continuum. Above a certain doping level the system of Fe donors is only partially occupied by electrons, i.e. two charge states, Fe3+ and Fe2+, coexist, corresponding to the inhomogeneous mixed valence regime. Under these conditions the Coulomb repulsion between the donor electrons tends to keep them apart, leading to a correlation of their positions. The existence of the correlation results in a dramatic reduction of the rate of scattering by ionised impurity potentials. The same Coulomb interactions are responsible for the formation of the Coulomb gap in the one-particle density of impurity states, which in turn suppresses (otherwise very efficient) resonant scattering. As a result, the mobility and the Dingle temperature in HgSe:Fe can exceed those in HgSe doped with Ga to similar doping levels. A review is given of relevant experimental results obtained in HgSe:Fe, Hg1-xMnxSe:Fe and HgSe1-xTex:Fe by means of the Shubnikov-de Haas effect, resistivity and Hall voltage studies. Experimental findings are compared with results of numerical simulations and with a simple model calculation which accounts for short-range correlations.

De Haas-van Alphen effect in stage 2 CuCl 2-graphite intercalation compound

DHvA torque oscillations have been observed in stage 2 CuCl 2-GIC in magnetic fields up to 21 kOe for the angular range of | θ| < 20°, θ being the angle between the field and the c-axis. At least fifteen dHvA frequency branches have been found. Angular dependence of those except for several frequency branches has revealed 1/cosθ which is a characteristic of the 2D FS. Effective mass m c/m o and Dingle temperature T d are deduced by means of a power spectrum analysis by using an expression of dHvA oscillations for the 2D electron-hole gas system. At θ=−4.5°, the values of m c/m o and T d for the 0.848 MOe branch are determined as 0.05±0.01 and 12±3 K, respectively and those for the 0.462 MOe branch as 0.09 ± 0.03 and 3±1K, respectively. No evidence of magnetic breakdown or magnetic interaction effects is found in the field dependence of the dHvA amplitudes.

Evidence of many-body renormalizations in some organic conductors

Magnetic quantum oscillations in (BEDT-TTF)-based salts have shown a correlation between the cyclotron mass m c and Dingle temperature T D of electrons in the basal planes. “Heavy-electron” systems like k-(BEDT-TTF) 2Cu(NCS) 2 with m c = (2–5) m 0 have a low T D less than 1 K, while “light-electron” systems like κ L-(BEDT-TTF) 2I 3 with m c = (0.3–0.5) m 0 have a much higher T D of several to 10 K. Both systems however have the same magnitude of the mean free path (∼ 1000 Å) and of the band width (∼0.5 eV). This is an evidence of many-body renormalizations of m c and τ. An importance of the on-site and/or nearest neighbor Coulomb correlations in heavy-electron organic conductors is discussed.

Electron impurity scattering in indium: A pseudopotential study

Lifetimes, transport relaxation times, residual resistivities and Dingle temperatures are calculated for the vacancy and a number of impurities in indium, using the 6-ψPW (pseudopotential-plane-wave) method with Heine-Abarenkov-Animalu model potentials. The results are compared with results according to more approximate models, like the phase shift model and the free electron model, and with experiment. The influence of lattice distortion is studied carefully. The impurities studied are Ag, Mg, Zn, Cd, Hg, Ga, Tl, Sn, Pb, Sb and Bi.Long range lattice distortion effects are not negligible, but if the distortion is weak to moderate they do not change the anisotropy very much. It is therefore concluded that the KKR-Green's function method will lead to reliable Dingle temperatures if it is applied in this range, but it may fail for larger distortions. Further, the Ziman approximation for the relaxation time compares very well with the exact iterative solution of the Boltzmann equation. A satisfactory agreement is found with preliminary experimental results for second zone and third zone β-arm Dingle temperatures available for the impurities Sn and Pb.

Nonthermal Spread of Quantum Levels in Solids Due to Defects

AbstractThe quantum level spread is treated in terms of the Dingle temperature, TD. The universal nature of the nonthermal spreading of the Landau levels in solids is established and explained. The importance of the low‐angle scattering of current carriers for the quantum oscillation effects is shown. The effect of the random electrostatic potential fluctuations on the magnitude of the quantum level spread is studied in detail. Experimental data are compared with theory for a wide range of compositions, x, and carrier concentrations, N, in Pb1−xSnxTe alloys.

Observation of De Haas-Shubnikov and De Haas-Van Alphen oscillations in ß-(BEDT-TTF) 2AuI 2

We present measurements of magnetoresistance and magnetic susceptibility for ß-(BEDT-TTF) 2AuI 2 in fields up to 13 T and at temperatures down to 25 mK. With the B field perpendicular to the ab plane we find oscillations periodic in 1/B for both measurements. We have identified SdH and dHvA frequencies of about 0.2 MG with a mass of 2.0±0.5m e and 2.9 MG with a mass of 0.3±0.1 m e. The Dingle temperature for the 2.9MG frequency is 6–7K. Angular dependence data suggests spherical pockets for the 2.9MG frequency. We discuss how these facts may be related to the closed surfaces determined from band structure calculations and the applicability of single-particle models for the conduction electrons in this material.

Evidence of a mobility edge in the second subband of an Al0.33Ga0.67As-GaAs heterojunction.

We report on simultaneous measurements of mobility and Dingle temperature of a two-dimensional electron gas in an AlGaAs/GaAs heterojunction, the density of which is varied by means of infrared illumination. Detailed measurements reveal that the Dingle temperature of the first subband decreases abruptly as a function of density when the second subband becomes occupied but the accompanying drop in mobility occurs smoothly over a broader density interval. We interpret these results as indicating the existence of a mobility edge at the bottom of the second subband.

De Haas-Van Alphen effect in quenched platinum

Abstract The Dingle (scattering) temperature in Pt containing vacancies is reported for cyclotron orbits on the electron and open hole sheets of the Fermi surface (FS). The anisotropy of conduction electron scattering due to vacancies is discussed.