Thermoelectric power of high-T c superconductors: superconducting fluctuations and the marginal Fermi-liquid hypothesis (original) (raw)
Thermoelectric power of high-Tc superconductors calculated from the electronic structure
2009
We have calculated the thermopower of the Bi2Sr2CuO6 and Bi2Sr2CaCu2O8 superconductors using an ARPES-derived dispersion, with a model pseudogap, and a marginal-Fermi liquid scattering rate that has a minimum with respect to energy at the van Hove singularity (vHs). Good fits with data are achieved across the entire phase diagram, thus confirming the dispersions, the locations of the vHs and the dominance of the diffusion thermopower over the phonon drag contribution.
Large thermoelectric effects in unconventional superconductors
Physical Review B, 2004
We present analytic and numerical results for the thermoelectric effect in unconventional superconductors with a dilute random distribution of impurities, each scattering isotropically but with a phase shift intermediate between the Born and unitary limits. The thermoelectric response function has a linear temperature dependence at low temperatures, with a slope that depends on the impurity concentration and phase shift. Although the thermoelectric effect vanishes identically in the strict Born and unitary limits, even a small deviation of the phase shift from these limits leads to a large response, especially in clean systems. We also discuss possibilities of measuring counter-flowing supercurrents in a SQUID-setup. The non-quantized thermoelectrically induced flux can easily be of the order of a percent of the flux quantum in clean systems at 4 He temperatures.
Theory of thermoelectric phenomena in superconductors
Physical Review B, 2002
The theory of thermoelectric effects in superconductors is discussed in connection to the recent publication by Marinescu and Overhauser [Phys. Rev. B 55, 11637 (1997)]. We argue that the charge non-conservation arguments by Marinescu and Overhauser do not require any revision of the Boltzmann transport equation in superconductors. We show that the charge current proportional to the gradient of the gap, |∆| found by Marinescu and Overhauser, is incompatible with the time-reversal symmetry, and conclude that their "electronconserving transport theory" is invalid. Possible mechanisms responsible for the discrepancy between some experimental data and the theory by Galperin, Gurevich, and Kozub Pis'ma Zh. Eksp. Teor. Fiz. 17, 689 (73) [JETP Lett. 17, 476 (1973)] are discussed.
Thermal conductivity and thermo-power of ( and ) bulk superconductors
Solid State Communications, 2010
In this paper, we present temperature dependent electrical conductivity ρ(T), thermal conductivity κ(T) and thermoelectric power S(T) for co-doped superconducting compounds Y 0.95Pr 0.5Ba 2(Cu 1- xM x) 3O 7-δ(M=Fe,Mn,Zn and Ni). The XRD patterns confirm that all the samples are single phased. Pristine Y Ba 2Cu 3O 7-δ depicts a pronounced hump-like structure in κ(T) below its transition temperature. With Pr-doping, a reduction in the peak height of the hump is observed. It is found that the hump structure is further suppressed with transition metal co-doping, and is viewed in terms of the phonon scattering with defect structure, electrons and phonons. S(T) data depicting a sign reversal with co-doping, has been analyzed in the framework of a narrow band model.
Thermoelectric Effects in Superconductors
Springer eBooks, 1981
A summary of recent theoretical and experimental work on thermoelectric and related effects in superconductorsis given. Whereas this field for a long time was characterized by large discrepancies between theory and experiment, more recent experiments confirm the theoretical concepts. Experimentswhich investigate the difference between the electrochemical potential of excitations and Cooper pairs (charge imbalance) play a prominent role. They allow one to determine the thermoelectric transport coefficient. Also a new type of thermoelectric effect is discussed: a chargeimbalance is created ifa supercurrentis flowing in the presence of a temperature gradient•
2003
By using a single-coil technique, we study the low-temperature dependence of the in-plane magnetic penetration depth ab in several Bi 2 Sr 2 CaCu 2 O 8ϩ␦ ͑BSCCO͒ single crystals prepared with various doping levels ␦ ranging from the under-to the overdoped regime. Four samples exhibit a linear dependence of thermally activated low-energy excitations ⌬ ab ϵ ab (T)Ϫ ab (0)ϳT. The thermal activation rate ϰץ ab /ץT is minimum, 8 Å/K, at optimum doping, in good quantitative agreement with the d-wave model of superconducting order parameter. The much larger rates, տ40 Å/K, observed in all under-and overdoped samples indicate that, in these samples, another type of low-energy excitations is relevant. These large rates are quantitatively consistent with a model of thermal phase fluctuations suitable for granular superconductors with short coherence length like cuprates. One underdoped sample exhibits a quadratic dependence suggesting an incipient crossover from thermal to quantum fluctuations.
Physical Review E, 2016
We report on a study of the superconducting order parameter thermodynamic fluctuations in YBa 2 Cu 3 O 7−δ , Bi 2 Sr 2 CaCu 2 O 8+δ and KOs 2 O 6 compounds. A non-perturbative technique within the framework of the renormalized Gaussian approach is proposed. The essential features are reported (analytically and numerically) through Ginzburg-Landau (GL) model-based calculations which take into account both the dimension and the microscopic parameters of the system. By presenting a self-consistent approach (SCA) improvement on the GL theory, a technique for obtaining corrections to the asymptotic critical behavior in terms of non universal parameters is developed. Therefore, corrections to the specific heat and the critical transition temperature for one-, two-and three-dimensional samples are found taking into account the fact that fluctuations occur at all length scales as the critical point of a system is approached. The GL model in the free-field approximation and the 3D-XY model are suitable for describing the weak and strong fluctuation regimes respectively. However, with a modified quadratic coefficient, the renormalized GL model is able to explain certain experimental observations including the specific heat of complicated systems, such as the cuprate superconductors and the β-pyrochlore oxides. It is clearly shown that the enhancement, suppression or rounding of the specific heat jump of high-T c cuprate superconductors at the transition are indicative of the order parameter thermodynamic fluctuations according to the dimension and the nature of interactions.
Electron-phonon contribution to thermopower in Si-doped superconducting Bi compounds
Physical Review B, 1997
Resistivity and thermoelectric power S as a function of temperature on samples of nominal composition ͑Bi 0.8 Pb 0.2) 2 Sr 2 Ca 3 ͑Cu 1Ϫx Si x) 4 O 12Ϫ␦ , for different x values at small concentrations, have been carried out. We find a correlation between and an enhancement in S observed above T c. We analyze the results in terms of conventional theoretical models that include vertex and other electron-phonon (e-p) corrections to the scattering due to impurities. It is argued that in the copper oxides the e-p effects, usually negligible in normal metals at temperatures small compared to the Debye temperature, might be significant near and above T c. A small contribution due to the phonon drag effect is also discussed. It is suggested that the trends of our results adjust to the predictions of those conventional models. ͓S0163-1829͑97͒06830-6͔ PHYSICAL REVIEW B