MICROWAVE DIELECTRIC STUDIES OF THE SPIN-DENSITY-WAVE STATE IN (TMTSF)(2)PF6

We have investigated the 16.5 GHz microwave response of single-crystal samples of (TMTSF)2PF6 at temperatures from 1.7 to 15 K as a function of external magnetic field. For the magnetic field applied along the chain direction, the microwave response does not change with field. However, with the field along the hard (c*) axis direction, striking changes are observed below Tc in the microwave dielectric constant and conductivity. The 4 K feature, present with good amplitude in σ1 at zero field, moves toward higher temperature and dampens with increasing magnetic field; at H=10 T, it has disappeared. The local maximum near 4 K in σ1 is accompanied by a sharp decrease in ε1. The orbital effects are discussed within the framework of quasiparticle effects on Fermi-surface nesting properties as well as within a model for magnetic-field effects on the spin-density-wave condensate. Emphasis is placed upon the analysis of the 4 K feature, the implications for the second spin-density-wave phase, and the possible relationship to a glassy transition. © 1995 The American Physical Society.