Electronic compressibility and charge imbalance relaxation in cuprate superconductors

TL;DR

This paper theoretically and experimentally investigates plasma resonance, electronic compressibility, and charge imbalance relaxation in cuprate superconductors, revealing key properties like free electron behavior and relaxation times.

Contribution

It provides a theoretical explanation for plasma peak amplitudes considering spatial dispersion and measures charge imbalance relaxation time in cuprates.

Findings

Electronic compressibility aligns with free electron model.

London penetration depth near T_c is about 1100 Å.

Charge imbalance relaxation time is approximately 100 ps.

Abstract

In the material SmLa$_{1-x}$Sr$_x$CuO$_{4-\delta}$ with alternating intrinsic Josephson junctions we explain theoretically the relative amplitude of the two plasma peaks in transmission by taking into account the spatial dispersion of the Josephson Plasma Resonance in $c$ direction due to charge coupling. From this and the magnetic field dependence of the plasma peaks in the vortex solid and liquid states it is shown that the electronic compressibility of the CuO$_2$ layers is consistent with a free electron value. Also the London penetration depth $\lambda_{ab} \approx 1100 {\rm \AA}$ near $T_c$ can be determined. The voltage response in the $IV$-curve of a Bi$_2$Sr$_2$CaCu$_2$O$_8$ mesa due to microwave irradiation or current injection in a second mesa is related to the nonequilibrium charge imbalance of quasiparticles and Cooper pairs and from our experimental data the relaxation time $\sim 100 {\rm ps}$ is obtained.