Electronic structure, doping, order and disorder in cuprate superconductors

TL;DR

This paper investigates how electron-phonon and spin-phonon interactions, disorder, and dopant ordering influence superconductivity in cuprates, highlighting mechanisms affecting T_C and the potential for enhancing superconducting properties.

Contribution

It provides a detailed analysis of the effects of lattice disorder and dopant ordering on superconductivity in cuprates, combining theoretical models with implications for improving T_C.

Findings

Few spin-phonon modes are activated, supporting high T_C despite low density of states.

Thermal disorder limits long-range superconductivity by disrupting coupled modes.

Dopant stripe ordering can increase DOS and improve T_C resilience to disorder.

Abstract

The electron-phonon and spin-phonon coupling in typical high-T_C cuprates, like LSCO and HBCO are peaked for just a few q-vectors because of the 2-dimensional Fermi surface shape. The activation of few spin-phonon modes compensates for the low electronic density-of-states, and the superconducting T_C can be high. Thermal disorder of the lattice perturbs the strongly coupled modes already at moderately high temperature. This happens because of incoherent potential fluctuations of the Madelung term and reduced spin-phonon coupling. This effect puts a limit on long-range superconductivity, while fluctuations can persist on a shorter length scale at higher temperatures. BCS-type model calculations are used to show how disorder can reduce the superconducting gap and T_C. Ordering of dopants into stripes has been suggested to improve superconducting properties, mainly through an increased DOS. Such a mechanism seems to be a good way to make T_C more resistant to thermal disorder at low doping.