Analysis of nonlinearity of magnetization of YBa2Cu3O7 − x by the magnetic field modulation method

Golovashkin, A. I.; Kuz’michev, N. D.; Slavkin, V. V.

doi:10.1134/s106377610810004x

Cited by 3 publications

(1 citation statement)

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“…This doping-dependent nonlinear response could be due to enhanced Cooper pair lifetime 14,15 , to superconducting fluctuations in the pseudogap phase of underdoped cuprates 13,16,17,18 or perhaps to a transition from a pure d-wave order parameter to a d + s order parameter 19 . Another source of nonlinear response above T c could be vortex-like excitations in the pseudogap phase 27 .…”

Section: Discussionmentioning

confidence: 99%

Phase-sensitive harmonic measurements of microwave nonlinearities in cuprate thin films

Mircea

Anlage

2009

Phys. Rev. B

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Investigations of the intrinsic electromagnetic nonlinearity of superconductors give insight into the fundamental physics of these materials. Phase-sensitive third-order harmonic voltage dataũ 3f = |u 3f |exp(iφ 3f ) are acquired with a near-field microwave microscope on homogeneous YBa2Cu3O 7−δ (YBCO) thin films in a temperature range close to the critical temperature Tc. As temperature is increased from below Tc, the harmonic magnitude exhibits a maximum, while the phase, π/2 in the superconducting state, goes through a minimum. It is found that samples with doping ranges from near optimal (δ = 0.16) to underdoped (δ = 0.47) exhibit different behavior in terms of both the harmonic magnitude and phase. In optimally-doped samples, the harmonic magnitude reaches its maximum at a temperature TM slightly lower than that associated with the minimum of phase Tm and drops into the noisefloor as soon as Tm is exceeded. In underdoped samples TM is shifted toward lower temperatures with respect to Tm and the harmonic voltage magnitude decreases slower with temperature than in the case of optimally-doped samples. A field-based analytical model ofũ 3f is presented, where the nonlinear behavior is introduced as corrections to the low-field, linear-response complex conductivity. The model reproduces the low-temperature regime where the σ2 nonlinearity dominates, in agreement with published theoretical and experimental results. Additionally the model identifies Tm as the temperature where the order parameter relaxation time becomes comparable to the microwave probing period and reproduces semi-quantitatively the experimental data.

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