SUBMILLIMETER SURFACE IMPEDANCE AND RELAXATION - A CASE-STUDY OF QUASI-2-DIMENSIONAL YBA2CU3OX

Surface impedance measurements in the normal and superconducting state are an excellent method to study the conduction electron dynamics in metals. This holds especially in the relaxation range, i.e., for distances traveled in one r.f. period s = upsilon(F)omega (upsilon(F) is the Fermi velocity) being smaller or of the order of the penetration depth lambda and mean free path l. For materials with upsilon(F) less-than-or-equal-to 10(7) cm/sec the relaxation range is easily accessible for f > 0.1 THz. Then, in the normal state, relaxation defines the surface impedance with a penetration depth approaching the London penetration depth lambda(L), and R almost-equal-to mu0lambda(L)/2tau as surface resistance allowing a measure of lambda(L) and relaxation time tau(T, omega). In the superconducting state the photon interaction scales with xi(F)/lambda(L) = 1/gamma (xi(F) is the dimension of Cooper pairs for l --> infinity) and causes at low frequencies an absorption rate growing with gamma, which is decreasing with xi(F)/l. The rate increase proportional to gamma turns to a decrease above 0. 1 THz, being accompanied by a decrease of lambda with frequency which is stronger for large gamma and small xi(F)/l. These characteristic dependences allow a measurement of material parameters, anisotropy, and dynamics of electrons. To evaluate the consequences of the a, b, and c-direction anisotropy, the integral kernels for normal and superconducting surface impedances in its nonintegrated, angle-dependent form are presented, analyzed, and compared with impedance measurements above 0.1 THz of YBa2Cu3Ox.