Impurity scattering in unconventional density waves: non-crossing approximation for arbitrary scattering rate

We present a detailed theoretical study on the thermodynamic properties of impure quasi-one dimensional unconventional charge-, and spin-density waves in the framework of mean-field theory. The impurities are of the ordinary non-magnetic type. Making use of the full self-energy that takes into account all ladder-, and rainbow-type diagrams, we are able to calculate the relevant low temperature quantities for arbitrary impurity concentration and scattering rates. These are the density of states, specific heat and the shift in the chemical potential. Our results therefore cover the whole parameter space: they include both the self-consistent Born and the resonant unitary limits, and most importantly give exact results in between.Comment: 11 pages, 8 figure

Gapped optical excitations from gapless phases: imperfect nesting in unconventional density waves

We consider the effect of imperfect nesting in quasi-one-dimensional unconventional density waves in the case, when the imperfect nesting and the gap depends on the same wavevector component. The phase diagram is very similar to that in a conventional density wave. The density of states is highly asymmetric with respect to the Fermi energy. The optical conductivity at T=0 remains unchanged for small deviations from perfect nesting. For higher imperfect nesting parameter, an optical gap opens, and considerable amount of spectral weight is transferred to higher frequencies. This makes the optical response of our system very similar to that of a conventional density wave. Qualitatively similar results are expected in d-density waves.Comment: 8 pages, 7 figure

Imperfect nesting and transport properties in unconventional density waves

We consider the effect of imperfect nesting in quasi-one dimensional unconventional density waves. The phase diagram is very close to those in a conventional DW. The linear and non-linear aspects of the electric conductivity are discussed. At T=0 the frequency dependent electric conductivity develops a small dip at low frequencies. The threshold electric field depends strongly on the imperfect nesting parameter, allowing us to describe the measured threshold electric field in the low temperature phase of the quasi-two dimensional organic conductor, alpha-(BEDT-TTF)_2KHg(SCN)_4 very well.Comment: 9 pages, 9 figure

Unconventional density wave in CeCoIn_5?

Very recently large Nernst effect and Seebeck effect were observed above the superconducting transition temperature 2.3K in a heavy fermion superconductor CeCoIn_5. We shall interpret this large Nernst effect in terms of unconventional density wave (UDW), which appears around T=18K. Also the temperature dependence of the Seebeck coefficient below T=18K is described in terms of UDW. Another hallmark for UDW is the angular dependent magnetoresistance, which should be readily accessible experimentally.Comment: 4 pages, 7 figure

Impurity effects in unconventional density waves in the unitary limit

We investigate the effect of strong, nonmagnetic impurities on quasi-one-dimensional conventional and unconventional density waves (DW and UDW). The conventional case remains unaffected similarly to s-wave superconductors in the presence of weak, nonmagnetic impurities. The thermodynamic properties of UDW were found to be identical to those of a d-wave superconductor in the unitary limit. The real and imaginary part of the optical conductivity is determined for electric fields applied in the perpendicular directions. A new structure can be present corresponding to excitations from the bound state at the Fermi energy to the gap maximum in addition to the usual peak at 2\Delta. In the dc limit, universal electric conductivity is found.Comment: 9 pages, 5 figure

Unconventional charge density wave in the organic conductor alpha-(BEDT-TTF)_2KHg(SCN)_4

The low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 salt is known for its surprising angular dependent magnetoresistance (ADMR), which has been studied intensively in the last decade. However, the nature of the LTP has not been understood until now. Here we analyse theoretically ADMR in unconventional (or nodal) charge density wave (UCDW). In magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to spectacular ADMR. The present model accounts for many striking features of ADMR data in alpha-(BEDT-TTF)_2KHg(SCN)_4.Comment: 5 pages, 6 figure

Impurity scattering in unconventional density waves

We have investigated the effect of nonmagnetic impurities on the quasi-one-dimensional unconventional density wave (UDW) ground state. The thermodynamics were found to be close to those of a d-wave superconductor in the Born limit. Four different optical conductivity curves were found depending on the direction of the applied electric field and on the wavevector dependence of the gap.Comment: 14 pages, 9 figure

Magnetothermopower and Nernst effect in unconventional charge density waves

Recently we have shown that the striking angular dependent magnetoresistance in the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 is consistently described in terms of unconventional charge density wave (UCDW). Here we investigate theoretically the thermoelectric power and the Nernst effect in UDW. The present results account consistently for the recent data of magnetothermopower in alpha-(BEDT-TTF)_2KHg(SCN)_4 obtained by Choi et al. (Phys. Rev. B, 65, 205119 (2002)). This confirms further our identification of LTP in this salt as UCDW. We propose also that the Nernst effect provides a clear signature of UDW.Comment: 4 pages, 4 figure

Out of plane optical conductivity in d-wave superconductors

We study theoretically the out of plane optical conductivity of d-wave superconductors in the presence of impurities at T=0K. Unlike the usual approach, we assume that the interlayer quasi-particle transport is due to coherent tunneling. The present model describes the T^2 dependence of the out of plane superfluid density observed in YBCO and Tl2201 for example. In the optical conductivity there is no Drude peak in agreement with experiment, and the interlayer Josephson tunneling is also assured in this model. In the unitary limit we predict a step like behaviour around omega=Delta in both the real and imaginary part of the optical conductivity.Comment: 7 pages, 7 figure