Crystal structure and electronic band structure of the organic superconductor α−(BEDT−TTF)2NH4Hg(SCN)4 under uniaxial strain

Abstract

In order to investigate the relationship between the crystal structure and electronic properties, crystal structure analysis of the organic superconductor $\alpha -(\mathrm{BEDT}-\mathrm{TTF}{)}_2{\mathrm{NH}}_4\mathrm{Hg}(\mathrm{SCN}{)}_4,$ where BEDT-TTF is the abbreviation of bis(ethylenedithio)tetrathiafulvalene, was performed under uniaxial compressive strain along each crystal axis. It was found that (i) almost ideal uniaxial strain was realized, that is, the unit cell was compressed only along the direction parallel to the external force; (ii) the calculated Fermi surface in the two-dimensional conducting layer was reduced along the $k_c$ axis and expanded along the $k_a$ axis under $b^{\prime }$- and c-axial strains, but vice versa under a-axial strain; and (iii) changes in the density of states at the Fermi level $\left[\mathrm{DOS}{(E}_F\right)]$ calculated from the obtained structures were qualitatively consistent with the observed change of the superconducting transition temperature.