Phase Transition of the Normal Metallic State to the Antiferromagnetic Spin Density Wave State in (TMTSF)2PF6

Abstract

A helium gas-pressure system has been tested and then used to investigate the nature of a phase transition from the normal metallic state to an antiferromagnetic spin density wave state in the quasi-one dimensional molecular organic conductor (TMTSF)2PF6. This metallic state superconducts at low temperature and high pressure, in such a way that the insulating antiferromagnetic state competes with the superconducting state. The physics motivation was to examine the possibility of a ¿quantum critical point¿ near the critical pressure of the sample where these latter two states may coexist. The technical motivation was to make the first tests of the pressure system at cryogenic temperatures to ensure that it is the appropriate tool for the planned investigations. Using temperature sweeps at various fixed pressures on a single crystal sample, we were able to obtain several points on the pressure versus temperature phase boundary separating the metallic and SDW states. We have thus verified that the helium gas-pressure system is indeed capable of facilitating these types of experiments, and future measurements will be done at lower temperatures accessing the superconducting state.