Thermomagnetic Coefficients Research Articles

Entropy-based theory of thermomagnetic phenomena

We show that in the linear response approximation only entropy provides coupling between thermal and electric phenomena. The dissipationless quantum currents — magnetization, superconducting, persistent and topological edge currents — do not produce and transfer entropy and may be excluded from final formulas for thermomagnetic coefficients. The magnetization energy flux, [Formula: see text], in crossed electric and magnetic fields strongly modifies the Poynting vector in magnetic materials and metamaterials, but do not contribute to the heat current. Calculating entropy fluxes of fluctuating Cooper pairs in pure and disordered superconductors, we obtained the fluctuation Nernst coefficient proportional to [Formula: see text] ([Formula: see text] is the Fermi energy). We also introduce the thermomagnetic entropy per unit charge and derive the Nernst coefficient proportional to the difference of the thermoelectric and thermomagnetic entropies. This explains the Sondheimer cancellation and high sensitivity of thermomagnetic phenomena to correlations. In 2D superconductors, the transport entropy transferred by a vortex moving through the background formed by vortex–antivortex pairs is the configuration entropy of [Formula: see text], which strongly exceeds the intrinsic entropy of vortex core. Beyond the linear response, the nonentropic forces can lead to phenomena unexpected from thermodynamics, such as vortex attraction to the moving hot spot. Quantum currents do not transfer entropy and may be used as ideal connectors to quantum nanodetectors.

Some thermophysical properties of (In2Te3)1 − x(Cd0.9Zn0.1Te)x solid solutions

Temperature dependences of total thermal conductivity and certain thermomagnetic coefficients of (In2Te3)1 − x(Cd0.9Zn0.1Te)x solid solution alloys (x = 0.01 and 0.03) were investigated and phonon scattering mechanisms were established. It was shown that ionized impurity centers and point structural defects are active in heat transfer at low temperatures, and scattering by acoustic and optical phonons dominates at high temperatures. At high temperatures, an additional thermal resistance of the crystal lattice appears in the studied solid solution, leading to a three-phonon scattering mechanism. A change in the thermomagnetic coefficients with temperature indicates a variable mechanism of phonon scattering and the elastic character of electron scattering in (In2Te3)1 − x(Cd0.9Zn0.1Te)x alloys.

The effect of magnetic field direction on thermoelectric and thermomagnetic coefficients of undoped single crystalline InSb at room temperature

Thermoelectric and thermomagnetic coefficients were calculated for n-type undoped InSb single crystals through a temperature range from 10°C up to 80°C and magnetic fields from -0.6T to 0.6T. The thermoelectric Seebeck coefficient varied only with the temperature gradient, while the thermomagnetic Nernst coefficient varied with both the temperature gradient and the magnetic field. This paper also investigated the effects of the incident angle of magnetic field on the InSb sample surface with regard to the values of thermoelectric and thermomagnetic coefficients; the results showed that thermoelectric and thermomagnetic coefficients were independent of magnetic field direction.

Gibbs Grand Thermodynamic Potential in the Theory of Kinetic Crystal Properties

In this paper, using Gibbs grand thermodynamic potential, kinetic tensors of electrical and thermal conductivity generalized equations known in non-equilibrium thermodynamics have been proven. These tensors determine calculation algorithms of the material tensors of conductor crystals and various galvanomagnetic and thermomagnetic effects coefficients. These algorithms are pragmatic formulas in calculation problems of crystals kinetic properties and in the problems for prediction of semiconductor crystals with preset properties. Their pragmatism is proven by the huge number of scientific papers dedicated to kinetic properties of semiconductor crystals study.

Nonequilibrium thermodynamics of the spin Seebeck and spin Peltier effects

We study the problem of magnetization and heat currents and their associated thermodynamic forces in a magnetic system by focusing on the magnetization transport in ferromagnetic insulators like YIG. The resulting theory is applied to the longitudinal spin Seebeck and the spin Peltier effects. By focusing on the specific geometry with one YIG layer and one Pt layer, we obtain the optimal conditions for generating large magnetization currents into Pt or large temperature effects in YIG. The theoretical predictions are compared with experiments from the literature permitting to derive the values of the thermomagnetic coefficients of YIG: the magnetization diffusion length $l_M \sim 0.4 \, \mu$m and the absolute thermomagnetic power coefficient $\epsilon_M \sim 10^{-2}$ TK$^{-1}$.

Calculation of the transport and relaxation properties of methane. II. Thermal conductivity, thermomagnetic effects, volume viscosity, and nuclear-spin relaxation

Transport properties of pure methane have been calculated in the rigid-rotor approximation using the recently proposed intermolecular potential energy hypersurface [R. Hellmann et al., J. Chem. Phys. 128, 214303 (2008)] and the classical-trajectory method. Results are reported in the dilute-gas limit for the temperature range of 80-1500 K. The calculated thermal conductivity values are in very good agreement with the measured data and correlations. In the temperature range of 310-480 K the calculated values underestimate the best experimental data by 0.5%-1.0%. We suggest that the calculated values are more accurate, especially at low and high temperatures, than the currently available correlations based on the experimental data. Our results also agree well with measurements of thermal transpiration and of the thermomagnetic coefficients. We have shown that although the dominant contribution to the thermomagnetic coefficients comes from the Wjj polarization in the spherical approximation, the contribution of a second polarization, Wj, cannot be neglected nor can a full description of the Wjj polarization. The majority of the volume viscosity measurements around room temperature are consistent with the calculated values but this is not the case at high and low temperatures. However, for nuclear-spin relaxation the calculated values consistently exceed the measurements, which are mutually consistent within a few percent.

Quantum oscillations of the thermomagnetic coefficients of layered conductors in a strong magnetic field

The linear response of the electronic system of a conductor to a perturbation in the form of an electric field and a temperature gradient in a quantizing magnetic field B is investigated theoretically. The thermoelectric effect in a layered conductor is analyzed and it is shown that the quasi-two-dimensional character of the dispersion law of the charge carriers results in gigantic oscillations of the thermo-emf.

Heat current in the magnetic field: Nernst-Ettingshausen effect above the superconducting transition

A problem of the definition of the heat transported in thermomagnetic phenomena has been realized well in the late 1960s, but not solved up to date. By ignoring this problem, numerous recent theories grossly overestimate the thermomagnetic coefficients in strongly interacting systems. Here, we develop a gauge-invariant microscopic approach, which shows that the heat transfer should include the energy of the interaction between electrons and a magnetic field. We also demonstrate that the surface currents induced by the magnetic field transfer the charge in the Nernst effect but do not transfer the heat in the Ettingshausen effect. Only with these two modifications of the theory does the physically measurable thermomagnetic coefficients satisfy the Onsager relation. We critically revised the Gaussian-fluctuation theory above the superconducting transition and show that the gauge invariance uniquely relates thermomagnetic phenomena in the Fermi liquid with the particle-hole asymmetry.

Thermopower enhancement in PbTe with Pb precipitates

The thermoelectric power of polycrystalline PbTe samples containing nanometer-sized precipitates of Pb metal is enhanced over that of bulk PbTe. Samples of PbTe containing excess Pb and Ag were prepared using conventional metallurgical heat treatments. These samples are shown, by x-ray diffraction, by microscopy, and by the presence of a superconductive transition, to contain Pb precipitates with sizes on the order of 30–40nm. The thermopower enhancement is related to an increase in the energy dependence of the relaxation time, as evidenced by a complete set of measurements of thermoelectric and thermomagnetic transport coefficients.

Calculation of the transport properties of carbon dioxide. II. Thermal conductivity and thermomagnetic effects.

The transport properties of pure carbon dioxide have been calculated from the intermolecular potential using the classical trajectory method. Results are reported in the dilute-gas limit for thermal conductivity and thermomagnetic coefficients for temperatures ranging from 200 K to 1000 K. Three recent carbon dioxide potential energy hypersurfaces have been investigated. Since thermal conductivity is influenced by vibrational degrees of freedom, not included in the rigid-rotor classical trajectory calculation, a correction for vibration has also been employed. The calculations indicate that the second-order thermal conductivity corrections due to the angular momentum polarization (< 2%) and velocity polarization (< 1%) are both small. Thermal conductivity values calculated using the potential energy hypersurface by Bukowski et al. (1999) are in good agreement with the available experimental data. They underestimate the best experimental data at room temperature by 1% and in the range up to 470 K by 1%-3%, depending on the data source. Outside this range the calculated values, we believe, may be more reliable than the currently available experimental data. Our results are consistent with measurements of the thermomagnetic effect at 300 K only when the vibrational degrees of freedom are considered fully. This excellent agreement for these properties indicates that particularly the potential surface of Bukowski et al. provides a realistic description of the anisotropy of the surface.

Thermal conductivity and thermal Hall effect from vortex motion

In the mixed state of type-II superconductors the motion of vortices in response to an applied temperature gradient $\ensuremath{\nabla}T$ leads to a longitudinal and a transverse heat current along $\ensuremath{\nabla}T$ and $\ensuremath{\nabla}T\ifmmode\times\else\texttimes\fi{}\mathbf{B},$ respectively, where $\mathbf{B}$ is the magnetic field. We calculate the corresponding contributions to the thermal conductivity and the thermal Hall effect in terms of other thermomagnetic transport coefficients and the electrical resistivity. The vortex contribution to the thermal Hall effect may be observable in superconductors with weak pinning and small quasiparticle thermal conductivity.

Reciprocal drag of electrons and phonons in strongly doped HgFeSe semiconductors

The previously observed unusual dependences of the thermoelectric and thermomagnetic coefficients of strongly doped HgFeSe crystals on temperature and magnetic field intensity are studied theoretically. It is shown that the observed dependences are due to the combined effect of electron scattering by spatially correlated charged donors Fe(3+) at low temperatures and the reciprocal drag of electrons and phonons, which plays a large role in semiconductors with a high density of itinerant charge carriers.

On the hydrodynamic theory of a magnetic liquid II. Hydrodynamic modes in the Heisenberg fluid

On the basis of our previous results (Physica A 220 (1995) 325) the collective mode spectrum of the Heisenberg ferrofluid model is studied in the hydrodynamic region. We start from the rigorous microscopic approach taking into account all conserved quantities and calculate the explicit expressions for the dispersion and damping coefficient of sound modes. It is shown that the sound velocity of Heisenberg ferrofluid at constant external magnetic field is isotropic and can be expressed by the adiabatic compressibility at constant magnetization m. We also calculate the heat and spin modes which are purely diffusive. Explicit expressions for the viscosity, thermal conductivity, spin diffusion and thermomagnetic diffusion coefficients containing time correlation functions are derived. Our results are compared with previous ones obtained mainly within phenomenological theories.

Thermoelectric and thermomagnetic effects in the mixed state analysis of the thermal angle

In this paper thermoelectric and thermomagnetic coefficients in the mixed state are discussed. Besides the contribution of the Abrikosov vortices, also the role of the vortex-antivortex pairs and of the quasi-particles unbounded and localized in the vortex core is considered. The vortex-antivortex contribution to the Seedbeck and Nernst effects is calculated in detail. To study the role of normal excitation we propose to measure the thermal angle, α th that represents the direction of the vortex velocity. In fact, taking the unbounded quasiparticles into account, or not, as the temperature varies, α th shows an important difference in behavior, easy to detect experimentally. Measurements of the Seebeck effect and Nernst effect on a Bi(2223) tape are presented and the thermal-angle behavior is discussed. The experimental data are in agreement with the models that consider the unbounded quasiparticles contribution, but some caution must be taken as to the role of the Josephson vortices.

Thermomagnetic phenomena in the mixed state of HTSC: Anisotropy and effect of pinning

We extend our model of the flux-flow thermomagnetic transport coefficients of superconductors [A. V. Samoilov, A. A. Yurgens, and N. V. Zavaritsky,Phys. Rev. B46, 6643 (1992)] to the pinning region. Using a method due to Vinokur, Geshkenbein, Feigel'man, and Blatter, we show that if the vortex dynamics in disorder-dominated,N/grxx andS/ρxx (whereN is the Nernst coefficient,S is the thermopower, and ρxx is the longitudinal resistivity) do not depend on the pinning strength. The theoretical consideration is illustrated by our experimental results on the high-temperature superconductors.

Thermoelectric power and transport entropy of dirty type-II superconductors.

The relation ${\mathcal{F}}_{0\mathit{c}2}^{\mathit{T}}$S(B,T)dT\ensuremath{\approxeq}B\ensuremath{\Elzxh}/(2mc) presented recently for the thermoelectric power S of a dirty high-${\mathit{T}}_{\mathit{c}}$ superconductor [V. V. Gridin et al., Phys. Rev. B 40, 8814 (1989)] is considered. It is shown that measurements which have been reported for the thermomagnetic coefficients of nearly reversible conventional type-II superconductors provide additional support for this relation. The result obtained from time-dependent microscopic theory for vortex motion (time-dependent Ginzburg-Landau theory and linear-response theory) is also discussed.

The effect of fluctuations on thermomagnetic phenomena in high T c superconductors

The effect of superconducting fluctuations on the thermomagnetic coefficients in clean layered superconductors is studied. A more singular fluctuation contribution as compared with that predicted before is found.

Thermomagnetic transport coefficients of a periodically modulated two-dimensional electron gas.

The impurity contribution to the thermopower and thermal conductivity of a two-dimensional electron gas that is modulated weakly and periodically along the x direction is evaluated in the presence of a perpendicular magnetic field. A type of oscillations, having the same origin as the magnetoresistance oscillations discovered recently, is predicted. The thermopower components ${\mathit{S}}_{\mathit{x}\mathit{x}}$, ${\mathit{S}}_{\mathit{y}\mathit{y}}$, and ${\mathit{S}}_{\mathit{x}\mathit{y}}$ all oscillate in phase in small magnetic fields. The oscillations in the thermal conductivity ${\mathit{K}}_{\mathit{x}\mathit{x}}$ are shifted by \ensuremath{\pi}/2 with respect to those oscillations in ${\mathit{S}}_{\mathit{x}\mathit{x}}$. $K sub xx--- oscillates out of phase with ${\mathit{K}}_{\mathit{y}\mathit{y}}$ and ${\mathit{K}}_{\mathit{x}\mathit{y}}$.

Investigation of the Weak‐Field Charge Transport in Semiconducting V2—VI3 Compounds with Trigonal Symmetry I. Expanded Model for the Transport Coefficients

AbstractIn the series of trigonal V2—VI3 semiconductorsBi2Te3, Bi2Se3, and Sb2Te3 up to now it has not been succeeded to interpret the temperature dependence of the weak—field charge transport for Sb2Te3 single crystals in terms of a physical relevant model with reasonable semiconductor data. Therefore, an expanded transport model is presented takinginto account nonparabolic manyvalley band structure as well as the simultaneous action of anisotropic mixed charge carrier scattering by acoustical phonons and ionized impurities in the relaxation time approximation. Under these conditions the expressions for the thermoelectric, galvano‐ and thermomagnetic coefficients and the Lorenz numbers are given. These formulas are also valid for Bi2Te3 at pure acoustical mode scattering and for Bi2Se3 at single‐valley band structure.

Diffusion thermoelectric power of bismuth in a magnetic field

The diffusion thermoelectric power of bismuth in a magnetic field is calculated assuming a two-band model with parabolic dispersion for the holes and either parabolic or non-parabolic dispersion for the electrons. The scattering is described by a relaxation time which is assumed to be either dependent on energy as for intravalley acoustic scattering or independent of energy. Below 80K the density of charge carriers is only weakly temperature dependent and the Bethe-Sommerfeld expansion is used to derive expressions for the weak-field thermomagnetic coefficients. Above 80K a re-evaluation of earlier mobility data is performed to take into account the thermal smearing of the Fermi surfaces, and numerical integrations of the transport integrals are used. The results give a good agreement with experimental data, but this agreement is not compatible with the existence of an energy gap in the electron spectrum, such as is found in magneto-reflection experiments.