Thermodynamics and optical conductivity of unconventional spin density waves

We consider the possibility of formation of an unconventional spin density wave (USDW) in quasi-one-dimensional electronic systems. In analogy with unconventional superconductivity, we develop a mean field theory of SDW allowing for the momentum dependent gap Delta (k) on the Fermi surface. Conditions for the appearance of such a low temperature phase are investigated. The excitation spectrum and basic thermodynamic properties of the model axe found to be very similar to those of d-wave superconductors in spite of the different topology of their Fermi surfaces. Several correlation functions are calculated, and the frequency dependent conductivity is evaluated for various gap functions. The latter is found to reflect the maximum gap value, however with no sharp onset for absorbtion.