Thickness dependence of temperature coefficient of resistivity of polycrystalline bismuth films

Results for the temperature coefficient of resistivity (TCR) of polycrystalline bismuth films deposited on to glass substrate are reported for the thickness range 30–300 nm. The film TCR is found to be negative for all thicknesses studied and its absolute value exhibits a maximum of 3.70×10^–3 K^–1 near 72.5 nm. The variation of charge carrier density with film thickness has been estimated from the presence of surface states. To include the thickness dependence of charge carrier density, a modified theory has been used to explain the observed behaviour of the TCR. The experimental results for the TCR of Bi films are found to be consistent with the theoretical values. The existence of the extremum is theoretically verified. From the analysis, the specularity parameter p is about 0.44 and the reflection coefficient R is 0.1.     

The Hall coefficient of the small polaron

The Hall coefficient of the small polaron in theHolstein model suitably generalized to three dimensions and to the presence of a magnetic field is calculated by means of the Kubo formula. A perturbation expansion of the correlation function appearing in the Kubo formula is used to introduce higher order jumps of the polaron which are the first to be affected by the magnetic field. A general expression for the Hall coefficient is obtained which essentially coincides with the result ofFriedman andHolstein obtained for special cases. Moreover, it is shown that interference processes of thermal activation and free motion of the small polaron change the Hall effect, and their contribution to the value of the Hall coefficient is calculated.     

Phonon drag thermopower in doped bismuth

The low-temperature (2<T<80 K) thermopower in bismuth doped by tellurium, a donor impurity (0<c≤0.07 at. % Te), is dominated by the phonon component, which shifts to higher temperatures with increasing dopant concentration. The temperature and concentration dependences of the phonon thermopower of doped bismuth are satisfactorily described by the theory of phonon drag of electrons. The theory is developed for a strongly anisotropic electron spectrum and includes both direct and two-step phonon drag.     

Hall coefficient of alloys of the Nd-Y system at temperature range 100–800°K

Studies were conducted on the concentration and temperature dependence of the Hall coefficient of alloys of the Nd-Y system within the entire region of concentrations and in the temperature range from 100 to 800°K. The results obtained are discussed from the point of view of electron theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 32–36, January, 1973.The authors wish to express their thanks to G. F. Kobzenko for supplying the alloys, and to A. E. Bryukhanov and V. F. Nemchenko for their assistance in the work.     

Low-temperature anomalies of the Hall coefficient in FeSi

The temperature dependence of the Hall coefficient in the interval 1.8–300 K is investigated in detail in high-quality single-crystal samples of a Kondo insulator — iron monosilicide. It is established that the parameter R _H (T,H=12.5 kOe) changes sign twice in the temperature interval employed, and at temperatures below T _m ≈7 K an anomalous (magnetic) component appears in the angular and field dependences of the Hall voltage. The results of the experimental investigations of R _H (T,H ₀ ) in FeSi are discussed on the basis of the phase diagram in the model of an excitonic insulator. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 774–778 (25 November 1998)     

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.     

Hall coefficient in heavy fermion metals

Experimental studies of the antiferromagnetic (AF) heavy fermion metal YbRh₂Si₂ in a magnetic field B indicate the presence of a jump in the Hall coefficient at a magnetic-field tuned quantum state in the zero temperature limit. This quantum state occurs at B ≥ B_c0 and induces the jump even though the change of the magnetic field at B = B_c0 is infinitesimal. We investigated this by using the model of heavy electron liquid with the fermion condensate. Within this model, the jump takes place when the magnetic field reaches the critical value B_c0 at which the ordering temperature T_N(B = B_c0) of the AF transition vanishes. We show that at B → B_c0, this second order AF phase transition becomes the first order one, making the corresponding quantum and thermal critical fluctuations vanish at the jump. At T → 0 and B = B_c0 the Grüneisen ratio as a function of the temperature T diverges. We demonstrate that both the divergence and the jump are determined by the specific low temperature behavior of the entropy \(S(T) \propto S_0 + a\sqrt T + bT\) with S₀; a and b are temperature independent constants.     

Hall coefficient factor in polar semiconductors

The Hall coefficient factor in polar semiconductors is calculated avoiding any serious approximation in the calculation. Lattice scattering (polar optical, acoustic deformation potential and piezoelectric scattering), combined lattice and ionized impurity scattering, and the effect of a nonparabolic conduction band are considered. Results are given both in the limit of vanishing magnetic field and for arbitrary values of the magnetic field. Furthermore our results are compared with experimental values reported previously.     

Effect of a positive temperature coefficient of resistance in thin films of doped strontium-barium titanate

Thin films of doped semiconducting barium-strontium titanate (Ba,Sr)TiO₃ are prepared by pulsed laser ablation. It is shown that the crystal structure, morphology, and electrical properties of (Ba,Sr)TiO₃ thin films are determined primarily by the actual ablation conditions. The ablation regimes of deposition permitting preparation of uniform polycrystalline thin films with a composition close to that of the target and with grain sizes larger than 0.1 μm are established. These samples have a positive temperature coefficient of resistance in the phase transition region. The change in the resistivity can be as much as 100%.     

Decay of photoinduced oscillations of the optical reflection coefficient of bismuth

A model describing the decay of photoinduced oscillations of the optical reflection coefficient R of bismuth is constructed, taking the crystal lattice anharmonicity into account. The decay time of oscillations of R is calculated as a function of the energy density of a laser pulse. The results of calculations explain the experimental data on the anomalously strong decay of oscillations of the optical reflection coefficient of bismuth (the decay time decreases by more than an order of magnitude with an increase in the laser pulse energy density from 0 to 4 mJ/cm²).     

Spin Hall effect in doped semiconductor structures

In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as sigma(xy)SJ/sigma(xy)SS approximately (h/tau)/epsilonF, with tau being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining sigma(s)/sigma(c) approximately 10(-3)-10(-4), where sigma(s(c)) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.     

On the Hall effect in a two-dimensional doped antiferromagnet

The conductivity and the Hall coefficient of a doped 2D antiferromagnet in the normal state are considered using the Kondo lattice model in the multimoment approximation. The anomalous temperature dependence of the kinetic coefficients is explained by the strong anisotropic charge-carrier scattering from the spin subsystem and found to be in qualitative agreement with the experimental data for the normal state of high-T _c superconductors.     

Hall effect measurements on transmutation doped semiconductors

Transmutation doping of semiconductors by neutron irradiation is a well known technique, mainly applied to achieve an extremely uniform low level n-doping of large Si crystals via the ³⁰Si(n,γ)³¹Si→³¹P nuclear reaction. Similar experiments in other semiconductors never gained a comparable importance. In the last years, however, it has been shown that the doping of semiconductors by implanting radioactive isotopes can yield valuable information about the processes occurring during the incorporation of dopant atoms into the lattice as well as the defect–dopant interactions occurring after the decay of the unstable isotope to a daughter isotope with usually different elemental properties. In this contribution, Hall effect measurements carried out so far on implanted radioactive dopants will be reviewed. The specific problems and the potential of the method will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.