Competing Instabilities and the High Field Phases of(TMTSF)2ClO4

Abstract
In this Letter we establish the phase diagram of (TMTSF)2 ClO4 to 30 T and above 0.5 K by transport and magnetization measurements. The high field region is bounded above by a second order transition from metallic to field induced spin density wave state at 5.5 K. Completely contained inside this boundary is a first order line terminating in a critical point. Neither phase boundary shows the large oscillations predicted in recent models. Our results suggest that there are separate transitions on each of the two Fermi surfaces, with only weak coupling between the order parameters.