Probing mixed s+id pairing state via thermoelectric response of SND junction

TL;DR

This paper investigates how the thermoelectric response of an SND junction reveals the mixed s+id pairing state in superconductors, highlighting mechanisms influenced by phase differences and material properties.

Contribution

It introduces a theoretical framework for detecting s+id pairing states via thermopower measurements in SND junctions, considering charge imbalance and material-specific effects.

Findings

Thermopower peaks near phase difference π/2 indicate s+id pairing.

Charge imbalance enhances thermopower in specific superconductor configurations.

Different superconductor types in the junction affect thermoelectric response.

Abstract

The thermoelectric response of SND configuration is considered within the generalized Ginzburg-Landau theory for a homogeneous admixture of s-wave and d-wave superconductors. The resulting thermopower (TP) is found to strongly depend on the relative phase \theta =\phi_s-\phi_d between the two superconductors. Two independent mechanisms are shown to contribute to the TP. One, based on the charge imbalance between the quasiparticles and Cooper pairs (described by the corresponding chemical potentials) due to the normal metal insert, results in a pronounced maximum of the peak near \theta =\pi/2 (the so-called s+id mixed pairing state) for two identical superconductors with T_{cd}=T_{cs}. This mechanism can be realized in a d-wave orthorhombic sample (like YBCO) with twin boundaries represented by tetragonal regions of variable width, with a reduced chemical potential. Another mechanism (not related to the charge imbalance effects) occurs when two different superconductors with T_{cd}>T_{cs} are used for SND junction. It can be realized via the junction comprising an s-wave low-T_c superconductor (like Pb) and a d-wave high-T_c superconductor (like orthorhombic YBCO). The experimental conditions under which the predicted behavior of the induced differential thermopower can be measured are discussed.