Coexistence of spin density waves and superconductivity in (TMTSF)2PF6

We present simultaneous measurements of angular-dependent magnetoresistance and thermopower along all three crystal axes in (TMTSF)2PF6 for pressures to 7.4 kbar and magnetic fields to 35 T. (TMTSF)2PF6 under pressure shows the coexistence of spin density wave and metal-superconducting orders. We suggest that this coexistence results neither in microscopic coexistence nor in a new soliton wall phase, contrary to previous suggestions, but in phase separation into domains of the high-pressure metal and the low-pressure spin density wave phases. Simultaneous measurement of transport along all crystal axes allows us to unambiguously describe the domain structure, whereas the superconducting transition temperature and four independent Fermi surface-sensitive magnetoresistance signatures allow us to unambiguously characterize the coexisting metallic domains.