Recombination-Limited Energy Relaxation in a Bardeen-Cooper-Schrieffer Superconductor (original) (raw)
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2012
To gain insight into the high-T c mechanism, we need experiments which identify the parameters that determine T c and link them to the interaction(s) that establish the superconducting state. Here we show that for pnictides, cuprates, and bismuthates T c depends systematically on the primary electron energy relaxation rate 1/τ 1 . We find that 1/τ 1 is a direct experimental measure of the strength of the electron-phonon interaction (EPI) and correlates with structural parameters, in particular the length of the crystallographic a-axis. T c (1/τ 1 ) is a non-monotonic function with the maximum at intermediate relaxation rates (~16 ps -1 ), suggesting that EPI provides the attractive interaction for the high-T c pairing mechanism, where the highest T c occurs in the crossover region between weak and strong EPI.
Electrons and Phonons in High Temperature Superconductors
Journal of Materials, 2013
The defect-induced anharmonic phonon-electron problem in high-temperature superconductors has been investigated with the help of double time thermodynamic electron and phonon Green’s function theory using a comprehensive Hamiltonian which includes the contribution due to unperturbed electrons and phonons, anharmonic phonons, impurities, and interactions of electrons and phonons. This formulation enables one to resolve the problem of electronic heat transport and equilibrium phenomenon in high-temperature superconductors in an amicable way. The problem of electronic heat capacity and electron-phonon problem has been taken up with special reference to the anharmonicity, defect concentration electron-phonon coupling, and temperature dependence.
The theory of thermal conductivity of high temperature superconductors (HTS) based on electron and phonon line width (life times) formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high T c superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La 1.8 Sr 0.2 Cu O 4 in the temperature range 0 − 200K . The theory is equally and successfully applicable to all other high T c superconductors.
Physical Review Letters, 2010
The electronic relaxation times are determined via pump-probe optical spectroscopy using sub-15 fs pulses over a wide range of probe energies for the normal state of two different cuprate superconductors. We show that the primary relaxation process is electron-phonon scattering, in contrast to the basic assumptions of the two-temperature model, which is conventionally used to describe electron relaxation in metals and related materials. Based on the exact analytic solution for the electron relaxation, we extract values for the second moments of the Eliashberg functions λ ω 2 = 800±200 meV 2 for La1.85Sr0.15CuO4 and λ ω 2 = 400±100 meV 2 for YBa2Cu3O6.9. These values are consistent with a phonon-mediated polaronic pairing mechanism.
Electron-phonon interaction in high-temperature superconductors
Physics-Uspekhi, 1993
The results of experimental studies of the interaction between electrons and crystal lattice vibrations in high-temperature superconducting metal oxides are presented. Attention is directed mainly toward a critical analysis of the data obtained by means of tunneling spectroscopy.
High frequency relaxation kinetics in metal and high-Tc superconductor nanocontacts
2008
The presented work deals with an interesting and relatively simple experimental method, called Point Contact Spectroscopy that permits to study the behaviour of quasiparticles (phonons) in conductive solids: their generation, interactions with electrons, disappearance. We could investigate by this technique also more exotic processes for other quasiparticles (conduction electrons), such as their trapping in a semi metal crystal lattice (Sb), the pairing in superconducting solids, and the absorption of phonons by electrons. Point Contact Spectroscopy consists in the creation of a nanocontact (10-100 nm in diameter) between two conductors and in monitoring its response to electromagnetic fields. When kept in liquid helium, an enormous current density in the range of 109 A/cm2 can be created in such a constriction and in these conditions, the contact becomes an instrument for revealing the quantum properties of electrons and phonons.
Theory of thermal relaxation of electrons in metals
Physical Review Letters, 1987
If electrons in a metal are heated to a temperature T, greater than the lattice temperature TI, the electron-phonon interaction causes temperature relaxation dT, /dt = yr(Tt-T,) which is rapid for TL) Oo. A formula yr =3hZ(co')/nkaT, is derived, where k(ro') =q/M is an important parameter in the theory of superconductivity. Quantitative agreement with recent experiments is good.
Low-Temperature Thermal Conductivity of Superconductors with Gap Nodes
Physical Review Letters, 2005
We report a detailed analytic and numerical study of electronic thermal conductivity in d-wave superconductors. We compare theory of the cross over at low temperatures from T -dependence to T 3 -dependence for increasing temperature with recent experiments on YBa2Cu3O7 in zero magnetic field for T ∈ [0.04K, 0.4K] by Hill et al., Phys. Rev. Lett. 92, 027001 (2004). Transport theory, including impurity scattering and inelastic scattering within strong coupling superconductivity, can consistently fit the temperature dependence of the data in the lower half of the temperature regime. We discuss the conditions under which we expect power-law dependences over wide temperature intervals.
Unconventional electron-phonon interactions in high-temperature superconductors
Physical Review B, 1991
The infrared absorption of the 155-cm c-axis mode of YBa2Cu307 is calculated on the basis of an anharmonic-electron-phonon-interaction model and a large enhancement of its intensity is obtained. A double-well potential in the electron-phonon interaction gives the right order of magnitude for shifts in the bridging O(4) position in agreement with recent extended x-ray-absorption fine-structure data. Electron-density-two-phonon-interaction terms are derived which represent a violation of the Migdal theorem and a BCS-type superconducting state with nonlinearly enhanced electron-phonon coupling is expected together with an anisotropy of the superconducting energy gap.