Multicritical Phenomena of Superconductivity and Antiferromagnetism in Organic Conductor $\kappa$-(BEDT-TTF)$_2$X

TL;DR

This paper theoretically investigates the multicritical behavior of superconductivity and antiferromagnetism in organic conductors, revealing the role of symmetry and critical exponents through renormalization group analysis.

Contribution

It introduces a theoretical analysis of the phase diagram and critical phenomena, highlighting the SO(5) symmetry and the common origin of SC and AF in organic conductors.

Findings

The phase diagram aligns with experimental NMR relaxation data.

The critical exponent x is explained by the dynamical exponent z and anomalous dimension η.

The symmetry of superconductivity is identified as d-wave, sharing a common origin with antiferromagnetism.

Abstract

We study theoretically the multicritical phenomena of the superconductivity (SC) and antiferromagnetism (AF) in organic conductors $\kappa$-BEDT salts. The phase diagram and the experimental data on the NMR relaxation rate $1/T_1$ is analysed in terms of the renormalization group method. The bicritical phenomenon observed experimentally indicates the rotational symmetry, i.e., SO(5) symmetry, of the SC and the AF. The critical exponent $x$ for the divergence of $1/T_1$ is well explained by $ x = \nu (z - 1 - \eta)$ with the dynamical exponent $z = 3/2$ for the AF region while $z = \phi/\nu \sim 1.84 $ at the bicritical point. These results strongly suggest that the origin of the SC is in common with that of the AF and that its symmetry is d-wave.