Suppression of a charge-density-wave ground state in high magnetic fields: Spin and orbital mechanisms

The charge density wave (CDW) transition temperature in the quasi-one-dimensional (Q1D) organic material $(\mathrm{Per}{)}_{2}\mathrm{Au}(\mathrm{mnt}{)}_{2}$ is relatively low ${(T}_{\mathrm{CDW}}\ensuremath{\sim}12\mathrm{K}).$ Hence in a mean field BCS model, the CDW state should be completely suppressed in magnetic fields of order 30\char21{}40 T. To explore this possibility, the magnetoresistance of $(\mathrm{Per}{)}_{2}\mathrm{Au}(\mathrm{mnt}{)}_{2}$ was investigated in magnetic fields to 45 T for $0.5\mathrm{K}lTl12\mathrm{K}.$ For fields directed along the Q1D molecular stacking direction, ${T}_{\mathrm{CDW}}$ decreases with field, terminating at about $\ensuremath{\sim}37\mathrm{T}$ for temperatures approaching zero. Results for this field orientation are in general agreement with theoretical predictions, including the field dependence of the magnetoresistance and the energy gap, ${\ensuremath{\Delta}}_{\mathrm{CDW}}.$ However, for fields tilted away from the stacking direction, orbital effects arise above 15 T that may be related to the return of un-nested Fermi surface sections that develop as the CDW state is suppressed. These findings are consistent with expectations that Q1D metallic behavior will return outside the CDW phase boundary.