Microwave spectroscopy of quasiparticle transport in the b̂ direction of YBa₂Cu₃O_6.993

Measurements of the microwave b̂ axis surface impedance of a high quality single crystal of YBa₂Cu₃O_6.993 at five discrete frequencies between 1 and 75 GHz are presented. Despite the complication of the b̂ axis oriented chain layer, the underlying behavior of the CuO₂ planes remains evident. It is demonstrated that the b̂ axis microwave conductivity can be adequately described by the sum of a Drude term and a frequency independent background; the former being attributed to thermally excited quasiparticle transport from quasi-two-dimensional bands and the latter to a broad spectral feature associated with a quasi-one-dimensional band.