Low Temperature Superfluid Response of High-Tc Superconductors

TL;DR

This paper reviews theoretical and experimental findings on the low-temperature superfluid response of high-Tc superconductors, highlighting how superfluid density varies with temperature and doping, and how these behaviors relate to the superconducting gap and disorder effects.

Contribution

It provides a comprehensive analysis of superfluid density behavior in high-Tc superconductors, including new predictions and experimental confirmations of temperature dependencies in different compounds.

Findings

In-plane superfluid density varies linearly with temperature in clean high-Tc materials.

Out-of-plane superfluid density shows T^5 behavior in certain tetragonal compounds.

Disorder effects cause rho_s^c to vary as T^2 in some high anisotropy superconductors.

Abstract

We have reviewed our theoretical and experimental results of the low temperature superfluid response function of high temperature superconductors (HTSC). In clean high-Tc materials the in-plane superfluid density rho_s^{ab} varies linearly with temperature. The slope of this linear T term is found to scale approximately with 1/Tc which, according to the weak coupling BCS theory for a d-wave superconductor, implies that the gap amplitude scales approximately with Tc. A T^5 behavior of the out-of-plane superfluid density rho_s^c for clean tetragonal HTSC was predicted and observed experimentally in the single layer Hg-compound HgBa_2CuO_{4+delta}. In other tetragonal high-Tc compounds with relatively high anisotropy, such as Hg_2Ba_2Ca_2Cu_3O_{8+delta}, rho_s^c varies as T^2 due to disorder effects. In optimally doped YBa_2Cu_3O_{7-delta}, rho_s^c varies linearly with temperature at low temperatures, but in underdoped YBa_2Cu_3O_{7-delta}, rho_s^c varies as T^2 at low temperatures; these results are consistent with our theoretical calculations.