Angleresolved microwave spectroscopy of the normal and superconducting states of lowdimensional molecular superconductors
Abstract
Recent studies of the microwave conductivity of lowdimensional (LD) conductors, in the presence of a magnetic field, have demonstrated several new effects. The key ingredient is the dominance of openorbit quasiparticle trajectories in kspace. In general, the Fermi surfaces (FS) of LD conductors are extended in all three dimensions: warped sheets in the quasi1D (Q1D) case, and warped cylinders in the quasi2D (Q2D) case. Quasiparticles on openorbit trajectories therefore acquire an oscillatory velocity component along the low conductivity direction. This results in a conductivity resonance, or periodic orbit resonance (POR), when the frequency of appropriately polarized microwave radiation matches any harmonic of the velocity oscillations. For Q1D systems, the POR provides a direct method for measuring the Fermi velocity (v_F), without making any assumptions about the underlying bandstructure. A new effect appears if one aligns the magnetic field within the layers of a Q2D conductor. In this situation, almost all of the quasiparticles move along open orbits parallel to the axis of the warped cylindrical FS. The period of the motion depends on the extremal velocity component perpendicular to the field (v_⊥ ext). This again leads to a POR and, from its angle dependence, one can map out v_{F} and the quasiparticle scattering rate (τ^{1}) for a Q2D conductor. We demonstrate the applicability of these methods for several organic superconductors and the lowdimensional pwave superconductor Sr_2RuO_4. Time permitting, I will also discuss the use of an interlayer Josephson plasma mode to study the superconductivity in Q2D organic conductors. The plasma frequency (ω_p) is extremely sensitive to the interlayer phase coherence associated with the condense and can, therefore, be used to study vortex physics. One can additionally tune the interlayer phase coherence with an inplane magnetic field, thereby potentially enabling angledependent phasesensitive spectroscopy of the superconducting order.
 Publication:

APS Southeastern Section Meeting Abstracts
 Pub Date:
 November 2003
 Bibcode:
 2003APS..SES.GA002H