SPIN-DENSITY-WAVE AND CHARGE-DENSITY-WAVE PHASON COHERENCE LENGTHS IN MAGNETIC-FIELDS

Within a quasi-one-dimensional model we study the phason propagator of spin- (or charge-) density wave in a magnetic field lying in a plane perpendicular to the most conducting direction (say, the a axis). When the magnetic field is tilted from the c axis, the quasiparticle motion along the b axis and the c axis becomes commensurable at tilt angles-theta, such that (c/b)tan-theta=n, with n integer. We find that T(c) (the spin-density-wave transition temperature) and xi(a) and xi(b) (the coherence lengths along the a and b axes) are insensitive to the above resonance at particular tilt angles, while xi(c) develops a series of dips at the resonance. This gives rise to a series of peaks in the torque above T = T(c), associated with the resonance, that appears to account for torque observed by Naughton et al. in tetramethyltetraselenafulvalene perchlorate [(TMTSF)2ClO4]. Further, the electric conductivity will exhibit a series of dips at the resonance. A similar resonance effect has been already observed in (TMTSF)2ClO4 by Osada et al. and by Naughton et al., but of the opposite sign.