H enhancement and giant Nernst effect in (TMTSF) ₂(PF) ₆

Abstract
We discuss two recent discoveries in the title compound: 1) A strong enhancement in the critical field as the critical pressure for the SDW-superconductor phase boundary is approached and 2) the existence of giant resonances in the thermoelectric voltage as an applied magnetic field is rotated through the "Lebed Magic Angles". 1) H is highly anisotropic in this salt, but the enhancement is present for all field orientations. We suggest a model in which the near degeneracy of the superconducting and SDW states leads to a coexistence. The critical field is enhanced by the formation of thin slabs of superconductor (less than the penetration depth) parallel to the applied field and sandwiched by insulating SDW layers. As the temperature is lowered the slabs become thinner allowing a higher H . 2) The thermoelectric voltage resonance indicates that the currents generated are "locked-in" to the interchain direction ("magic angle") nearest parallel with the applied field. With the field to one side of the magic angle there is a Lorentz force up, on the other side of the magic angle the Lorentz force is down. The size of the thermoelectric voltage is 10 ⁴ larger than might be expected from conventional transport theory.