Magnetic field induced lattice effects in a quasi-two-dimensional organic conductor close to the Mott metal-insulator transition

Abstract

We present ultra-high-resolution dilatometric studies in magnetic fields on a quasi-two-dimensional organic conductor $\ensuremath{\kappa}$-(D8-BEDT-TTF)${}_{2}$Cu[N(CN)${}_{2}$]Br, which is located close to the Mott metal-insulator (MI) transition. The obtained thermal expansion coefficient, $\ensuremath{\alpha}(T)$, reveals two remarkable features: (i) the Mott MI transition temperature ${T}_{\mathrm{MI}}=(13.6\ifmmode\pm\else\textpm\fi{}0.6)$ K is insensitive to fields up to 10 T, the highest applied field; (ii) for fields along the interlayer $b$ axis, a magnetic field induced (FI) phase transition at ${T}_{\mathrm{FI}}=(9.5\ifmmode\pm\else\textpm\fi{}0.5)$ K is observed above a threshold field ${H}_{c}\ensuremath{\sim}1$ T, indicative of a spin reorientation with strong magnetoelastic coupling.