Interaction In High-temperature Superconductors Research Articles

Bose–Einstein Condensation of Nonideal Cooper Pairs in the Hartree–Fock–Popov Theory

The Hartree–Fock–Popov theory of interacting Bose particles is generalized to the Cooper-pair system with a screened Coulomb repulsive interaction in high-temperature superconductors. At zero temperature, it is found that the condensate density \(n_c(0)\) of Cooper pairs is of the order \(n_c(0)\simeq 10^{18}\) cm\(^{-3}\), consistently with the fact that a small fraction of the total p holes participate in pairing. We find that the phonon velocity c(0) at zero temperature is of the order \(c(0)\simeq 10\) km s\(^{-1}\). The computation shows that the transition temperature \(T_c\) is a dome-shaped function of the p hole concentration \(\delta \), which is consistent with experiments. At finite temperature, we find that the condensate fraction \(n_c(T)/n\) decreases continuously from \(n_c(0)/n\) to zero as the temperature increases from zero to the transition temperature \(T_c\). For higher temperatures, we find that the repulsive interaction between Cooper pairs drives more Cooper pairs into the condensate. The computation reveals that the phonon velocity c(T) decreases continuously from c(0) to zero as the temperature increases from zero to the transition temperature \(T_c\). The Cooper-pair system undergoes a first-order phase transition from the normal state to the BEC state.

Bose–Einstein condensation of interacting Cooper pairs in cuprate superconductors

Abstract The Hartree–Fock–Popov theory of interacting Bose particles is generalized to the Cooper-pair system with a screened Coulomb repulsive interaction in high-temperature superconductors. At zero temperature, we find that the condensate density n c ( 0 ) of Cooper pairs and the phonon velocity c ( 0 ) are dome-shaped functions of the p hole concentration δ. At finite temperature T, we find that the condensate fraction n c ( T ) / n and the phonon velocity c ( T ) decrease continuously from n c ( 0 ) / n or c ( 0 ) to zero as T increases from zero to the transition temperature T c . The Cooper-pair system undergoes a first-order phase transition from the normal state to the Bose condensed state.

Signature of electron-phonon interaction in high temperature superconductors

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 Tc 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 La1.8Sr0.2CuO4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high Tc superconductors.

Calculated magnetic exchange interactions in high-temperature superconductors

Using a first principles linear response approach, we study the magnetic exchange interactions J for a series of superconducting cuprates. We reproduce the observed spin-wave dispersions together with other experimental trends, and show that different cuprates have similar J's regardless their T$_{c}$. The nearest neighbor J is not sensitive to the hole-doping, which agrees with recent experiments. For the undoped cuprates, the second nearest neighbor J is ferromagnetic, but changes its sign with hole-doping. We also find that, in contrast to the hopping integral, the exchange interaction is not sensitive to the position of apical oxygen. To see the effect of the long--range nature of the exchange on the superconducting T$_{c}$, we study the dynamical spin susceptibility $\chi (q,\omega)$ within the t--J model using a dynamical cluster approximation.

Topological theory of electron-phonon interactions in high-temperature superconductors

There are large isotope effects in the phonon kinks observed in angle-resolved photoemission spectroscopy of optimally doped cuprate high-temperature superconductors (HTSC), but they are quite different from those expected for a nearly free-electron metal (Fermi liquid) with strong electron-phonon interactions (Eliashberg model). These differences, together with many other anomalies in infrared spectra, seem to suggest that other particles (such as magnons) must be contributing to HTSC. Here we use topological methods to discuss the data, emphasizing nanoscale phase separation and the importance of a narrow band of quantum percolative states near the Fermi energy that is spatially pinned to a self-organized filamentary dopant array, resulting in a filamentary glass. Topological discrete, noncontinuum, nonperturbative methods have previously explained the form of HTSC phase diagrams without involving detailed microscopic assumptions, and they are especially useful in the presence of strong nanoscale glassy disorder. These methods also explain the ``miracle'' of an ideal nearly free-electron (gas or liquid) phonon kink in sharply defined nodal quasiparticle states in LSCO at the metal-insulator transition. Careful study of the data reveals anharmonic phonon interactions. Finally, the universality of the kink energy and Fermi velocities below the Debye cutoff in different cuprates is the result of the marginally elastic nature of these configurationally glassy materials, and specifically the isostatic character of the ${\mathrm{CuO}}_{2}$ planes.

High resolution angle-resolved photoemission study of high temperature superconductors: charge-ordering, bilayer splitting and electron–phonon coupling

The latest development of angle-resolved photoemission spectroscopy (ARPES) technique has seen extremely high energy resolution and momentum resolution, as well as multiple angle detection. These advancements have led to new findings through efficient Fermi surface mapping, fine electronic structure resolving, and direct determination of electron self-energy. In this paper, we will highlight some recent high resolution ARPES work on high temperature superconductors. These include: (1) charge-ordering and evolution of electronic structure with doping; (2) bilayer splitting and Fermi surface topology of Bi2212; and (3) strong electron–phonon coupling and electron–electron interaction in high temperature superconductors.

Electronic inhomogeneities, electron-lattice and pairing interactions in high-T c superconductors

The presence of electronic inhomogeneities strongly reduces the screening of the electron-ion interaction in high-temperature superconductors. This implies the existence of an non-totally screened long-range contribution to the electron-lattice coupling and opens an additional channel for the formation of copper pairs. We calculate the superconducting order parameter taking into account a) the longrange and the short-range parts of the electron-lattice interaction and b) the Coulomb repulsion between charge-carriers. We show that whereas the long-range electron-lattice coupling determines the anisotropy of the order parameter, the Coulomb repulsion and the short-range interactions determine its symmetry. Thus, different high-Tc superconductors may have s- or d-wave symmetry, depending on the relative strength of the interactions involved in the pairing.

Rare-earth-Cu interaction in high-temperature superconductors

In high-temperature superconductors two-dimensional CuO 2-planes are separated by metal-oxide layers. These supply charge and separate the layers. How they influence the electronic structure and whether they couple the CuO 2 layers is unclear. Using resonant photoemission we demonstrate a new technique to study such coupling. This is done by measuring the resonance of Cu-states across the rare-earth 4d level. Using Bi 2Sr 2(Ca, Nd)Cu 2O 8 as an example we show that there is a significant coupling between electronic states on Nd and Cu.

How phonon damping in high - temperature superconductors manifests itself in Raman scattering?

Detection of phonon damping due to electron - phonon interaction in high-temperature superconductors by Raman spectroscopy is more favorable in dirty metal than in pure because phonon decay into electronic continuum has no threshold there.

Elektron-fononnoe vzaimodeistvie v vysokotemperaturnykh sverkhprovodnikakh

Elektron-fononnoe vzaimodeistvie v vysokotemperaturnykh sverkhprovodnikakh

Unconventional electron-phonon interactions in high-temperature superconductors.

The infrared absorption of the 155-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ c-axis mode of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ 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 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.