Abstract

We present measurements of the complex conductivity σ in Y₁__xPr_xBa₂Cu₃O₇_₅ thin films using impulsive THz spectroscopy, where x = 0,0, 0.2, 0.3, 0.4. Experiments performed in this system are of great interest to contemporary theories of high-T_c superconductivity for several reasons. First, the "marginal Fermi liquid" (MFL) theory of high-T_c superconductivity posits an unusual temperature and frequency dependence of the quasiparticle scattering rate τ. Ours are the first measurements of T in the THz regime for any Mgh-T_c superconductor; the effects predicted by MFL theory should be significant in this spectral range. Second, measurements of σ₂ as a function of temperature yield the London penetration depth λ(T), which is related to the superconducting carrier density n,. Different dependences of n_s upon T are expected for d- and s-wave pairing; we have measured λ(T) and compared it to theoretical predictions. Finally, the introduction of alloy scattering is expected to give rise to effects in σ₁(T). We experimentally observe the so-called "anomalous coherence peak" in σ₁(T) in all four samples.

© 1994 Optical Society of America