Effect of impurities on thermoelectric power due to phonon drag in metals

The effect of inelastic impurity scattering of electrons on the thermoelectric power due to phonon drag in metals has been studied. It is shown that this is the main cause of the thermoelectric power suppression due to doping at low temperatures. The thermoelectric power in a metal with a quadratic electron spectrum has been calculated as a function of temperature and impurity concentration. In addition to the impurity concentration, the correction to the thermoelectric power due to inelastic scattering contains the large factor Θ_D/T. Zh. éksp. Teor. Fiz. 111, 2237–2242 (June 1997)     

Thermoelectric power of p-doped single-wall carbon nanotubes and the role of phonon drag

We measured thermoelectric power S of bulk single-wall carbon nanotube materials p doped with acids. In contrast to oxygen-exposed or degassed samples, S is very small at the lowest temperatures, increases superlinearly above a characteristic and sample-dependent T, and then levels off. We attribute this unusual behavior to 1D phonon drag, in which the depression of the Fermi energy cuts off electron-phonon scattering at temperatures below a characteristic T0. This idea is supported by a model calculation in which the low temperature behavior of phonon drag is specifically related to the one-dimensional character of the electronic spectrum.     

Effect of Coulomb correlations in a variable-valence impurity system and phonon drag on the thermoelectric constants in two-dimensional systems

The temperature behavior of the longitudinal Nernst-Ettingshausen coefficient in 2D systems is studied theoretically taking account of phonon drag and Coulomb correlations in a system of mixed-valence impurities at low temperatures. It is shown that the effect changes sign at the transition from entrainment to scattering by a correlated system of impurity centers. A sign change does not occur in the case of scattering by randomly distributed impurity centers. This temperature behavior of the Nernst-Ettingshausen coefficient is due to the radical rearrangement of the impurity system as a result of strong Coulomb correlations present in a system of impurities with mixed valence. As a result, the character of the scattering of charge carriers by the correlated system of charge centers changes substantially. Fiz. Tverd. Tela (St. Petersburg) 40, 553–556 (March 1998)     

Photo-induced magnetophonon resonance in n-InSb at 4.2°K

Spin-flip and two-phonon as well as normal magnetophonon resonance are observed in CO₂-laser-irradiated photoconductivity in n-InSb at 4.2°K. The effects are attributed to the resonant cooling of photo-excited electrons due to optical phonon emission.     

Effect of the electron and phonon mutual drag on the thermomagnetic and thermoelectric phenomena in conductors with degenerate carrier statistics

The transport coefficients of conductors with degenerate carrier statistics in a magnetic field have been calculated with the inclusion of the mutual electron and phonon drag. The calculation is carried out in the linear approximation in the degeneracy parameter. A study has been made of the mutual drag on the thermomagnetic and thermoelectric phenomena in conductors, in both isothermal and adiabatic conditions.     

Observation of magnetophonon resonance of Dirac fermions in graphite

Coherent coupling of Dirac fermion magnetoexcitons with an optical phonon is observed in graphite as marked magnetic-field dependent splittings and anticrossing behavior of the two coupled modes. The sharp magnetophonon resonance occurs in regions of the graphite sample with properties of superior single-layer graphene having enhanced lifetimes of Dirac fermions. The greatly reduced carrier broadening to values below the graphene electron-phonon coupling constant explains the appearance of sharp resonances that reveal a fundamental interaction of Dirac fermions.     

A criticism of the standard treatment of phonon drag

By the study of a simple example, namely the evolution in timet of an electron-phonon system with fixed, total momentum, it is shown that the “standard” treatment of “phonon drag”, which involves solving the (linearized and spatially homogeneous) coupled electron and phonon Boltzmann equations by an iteration procedure, is not always correct. In the asymptotic limit (t→∞), the iteration or “standard” procedure does not give the “correct” (i.e. the equilibrium statistical mechanical) result for the distribution of momentum between electrons and phonons. However, a proper treatment of the Boltzmann equations does lead to the “correct” sharing of momentum between electrons and phonons fort→∞. All the calculations in this paper are performed for metals at high temperatures (i.e.,T>Θ_D, the Debye temperature).     

Study and characterization by magnetophonon resonance of the energy structuring in GaAs/AlAs quantum-wire superlattices

We present the characterization of the band structure of GaAs/AlAs quantum-wire 1D superlattices performed by magnetophonon resonance with pulsed magnetic fields up to 35 T. The samples, generated by the ‘atomic saw method’ from original quantum-well 2D superlattices, underwent substantial modifications of their energy bands built up on the X-states of the bulk. We have calculated the band structure by a finite element method and we have studied the various miniband structures built up of the massesm_tandm_lof GaAs and AlAs at the point X. From an experimental point of view, the main result is that in the 2D case we observe only resonances when the magnetic fieldBis applied along the growth axis whereas in the 1D case we obtain resonances in all magnetic field configurations. The analysis of the maxima (or minima forB//E) in the resistivity ρ_xyas a function ofBallows us to account, qualitatively and semi-quantitatively, for the band structure theoretically expected.     

Structure of magnetophonon resonance under hot electron conditons in n-InSb

It is shown that a series of hot electron induced magnetophonon resonances recently reported can be interpreted as a hot electron induced shift of the fundamental resonance.     

Theory of hot electron magnetophonon resonance in longitudinal magnetic fields

Longitudinal magnetoresistance of hot electrons in n—InSb at low temperatures is calculated taking into account the quantization of the conduction band into Landau subbands. Negative magnetoresistance and magnetophonon resonance minima are obtained as combined effects of inter-subband transition and optical phonon emission.     

The resonance peak in the high-Tc cuprates

I present a theory in which the resonance peak observed in inelastic neutron scattering experiments on YBa₂Cu₃O_6+x and Bi₂Sr₂CaCu₂O_8+x arises from a dispersing spin mode. I argue that it is heavily damped in the normal state and becomes visible in the superconducting state due to a drastic decrease in the spin damping. I show that a spin-fermion model correctly describes the doping dependence of the peak position and of its integrated intensity. Finally, I derive a criterion for the existence of the resonance peak in other cuprate superconductors.     

Atomistic simulation of the motion of dislocations in metals under phonon drag conditions

The mobility of dislocations in the over-barrier motion in different metals (Al, Cu, Fe, Mo) has been investigated using the molecular dynamics method. The phonon drag coefficients have been calculated as a function of the pressure and temperature. The results obtained are in good agreement with the experimental data and theoretical estimates. For face-centered cubic metals, the main mechanism of dislocation drag is the phonon scattering. For body-centered cubic metals, the contribution of the radiation friction becomes significant at room temperature. It has been found that there is a correlation between the temperature dependences of the phonon drag coefficient and the lattice constant. The dependences of the phonon drag coefficient on the pressure have been calculated. In contrast to the other metals, iron is characterized by a sharp increase in the phonon drag coefficient with an increase in the pressure at low temperatures due to the α-∈ phase transition.     

A study of intervalley scattering in n-Si by stress-dependent longitudinal magnetophonon resonance

The stress dependence of the amplitude and position of the magnetophonon extrema of n-Si are employed to distinguish the f- and g-type intervalley scattering series. The sign of the extrema of the g-T.A. series changes at a critical stress. The measurements locate the conduction band minima at (0.85 ± 0.01, 0, 0) in the reduced Brillouin zone.     

The thermoelectric power of TaS3

The thermoelectric power of TaS₃ filaments was measured as a function of temperature between 90–400K. Its positive sign in the whole temperature range and its linear dependence on reciprocal temperature between 120–200K are discussed in connection with the temperature dependence of the resistance.