Layered organic conductors κ-(BEDT-TTF)2X: magnetic and superconducting properties

Near-degeneracy of extendeds+dx2−y2anddxy

“…Those studies that do show superconductivity nevertheless agree, with the exception of Ref. 29, that it is of d x 2 −y 2 -type as in high-temperature cuprate superconductors 40 .…”

“…In theoretical approaches, the κ-(ET) 2 X family of materials is often described by a half-filled Hubbard model of (ET) 2 dimers on the anisotropic triangular lattice [21][22][23][24][25] , which is equivalent to a square lattice model with an additional coupling along one of the diagonals. Many theoretical methods have been applied to the dimer based Hubbard model, for instance, the fluctuationexchange approximation (FLEX) [26][27][28][29] , the path-integral renormalization group 30 , cluster dynamical mean field theory [31][32][33] , variational Monte Carlo [34][35][36][37] and exact diagonalization 38,39 . These studies do not agree entirely on all details of the phase diagram, especially whether superconductivity is realized in the model or not.…”

Symmetry change of $d$-wave superconductivity in $κ$-type organic superconductors

“…However, three contradictory conclusions have been suggested: s-wave [2][3][4], d x 2 −y 2 -wave (=d x 2 −y 2 +s ±wave [5]) [6][7][8][9], and d xy -wave [10,11] symmetry. Theoretical studies have also proposed d x 2 −y 2 +s ± - [12] and d xywave [13][14][15] symmetry depending on their models. Some recent theories based on a more realistic model [16][17][18][19] suggest that the two symmetries compete and the emergent symmetry is determined according to the ratio of transfer integrals.…”