53 research outputs found
Models for Enhanced Absorption in Inhomogeneous Superconductors
We discuss the low-frequency absorption arising from quenched inhomogeneity
in the superfluid density rho_s of a model superconductor. Such inhomogeneities
may arise in a high-T_c superconductor from a wide variety of sources,
including quenched random disorder and static charge density waves such as
stripes. Using standard classical methods for treating randomly inhomogeneous
media, we show that both mechanisms produce additional absorption at finite
frequencies. For a two-fluid model with weak mean-square fluctuations <(d
rho_s)^2 > in rho_s and a frequency-independent quasiparticle conductivity, the
extra absorption has oscillator strength proportional to the quantity <(d
rho_s)^2>/rho_s, as observed in some experiments. Similar behavior is found in
a two-fluid model with anticorrelated fluctuations in the superfluid and normal
fluid densities. The extra absorption typically occurs as a Lorentzian centered
at zero frequency. We present simple model calculations for this extra
absorption under conditions of both weak and strong fluctuations. The relation
between our results and other model calculations is briefly discussed
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