Phase-sensitive Harmonic Measurements of Microwave Nonlinearities in Cuprate Thin Films - Condensed Matter > SuperconductivityReportar como inadecuado




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Abstract: Investigations of the intrinsic electromagnetic nonlinearity ofsuperconductors give insight into the fundamental physics of these materials.Phase-sensitive third-order harmonic voltage data$\tilde{u} {3f}=|u {3f}|expi\phi {3f}$ are acquired with a near-fieldmicrowave microscope on homogeneous YBa$ 2$Cu$ 3$O$ {7-\delta}$ YBCO thinfilms in a temperature range close to the critical temperature T$ c$. Astemperature is increased from below T$ c$, the harmonic magnitude exhibits amaximum, while the phase, $\pi-2$ in the superconducting state, goes through aminimum. It is found that samples with doping ranges from near optimal$\delta=0.16$ to underdoped $\delta=0.47$ exhibit different behavior interms of both the harmonic magnitude and phase. In optimally-doped samples, theharmonic magnitude reaches its maximum at a temperature $T M$ slightly lowerthan that associated with the minimum of phase $T m$ and drops into thenoisefloor as soon as $T m$ is exceeded. In underdoped samples $T M$ is shiftedtoward lower temperatures with respect to $T m$ and the harmonic voltagemagnitude decreases slower with temperature than in the case of optimally-dopedsamples. A field-based analytical model of $\tilde{u} {3f}$ is presented, wherethe nonlinear behavior is introduced as corrections to the low-field,linear-response complex conductivity. The model reproduces the low-temperatureregime where the $\sigma 2$ nonlinearity dominates, in agreement with publishedtheoretical and experimental results. Additionally the model identifies $T m$as the temperature where the order parameter relaxation time becomes comparableto the microwave probing period and reproduces semi-quantitatively theexperimental data.



Autor: Dragos I. Mircea, Hua Xu, Steven M. Anlage

Fuente: https://arxiv.org/







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