Linear and nonlinear microwave dynamics of vortices in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films

Journal Article · Sat Nov 01 04:00:00 EST 1997 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.56.11966· OSTI ID:544953

Belk, N ^[1]; Oates, D E ^[2]; Feld, D A ^[2]; Dresselhaus, G ^[3]; Dresselhaus, M S ^[4]

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1. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States)
2. Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02173-9108 (United States)
3. Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States)
4. Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States)

We report the results of a study of the nonlinear microwave surface impedance Z{sub s}, i.e., its dependence on microwave current Z{sub s}(I{sub rf}), resulting from vortex motion in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films in a dc magnetic field applied parallel to the film{close_quote}s c axis. Using the technique of stripline resonators we have measured the nonlinear Z{sub s} at frequencies of 1.23{endash}8.45 GHz, at temperatures from 5 to 30 K, and in magnetic fields from 0 to 4 T. In the mixed state, there is a significant increase in R{sub s} from the zero-field value, particularly at lower frequencies, causing an R{sub s}{proportional_to}f{sup 1.2} dependence at all measured temperatures and microwave powers. We also review our previously reported measurements and modeling of the linear Z{sub s} because the nonlinear results can be explained by an extension of the model that we have previously used to describe the dependence of Z{sub s} on frequency, temperature, and magnetic field in the linear I{sub rf} regime. This model explains the linear Z{sub s} data through the thermal activation of vortex segments between metastable vortex states separated by distances of order of the coherence length {approximately}{xi} and by a distribution of energy barriers U{sub b} whose magnitudes extend from U{sub b}{approximately}0 K to at least several hundred K. We further show that the behavior of Z{sub s} at high microwave powers is fully consistent with the same thermal activation of vortex segments, but the effective magnitudes of the energy barriers {tilde U}{sub b} have been reduced in proportion to the microwave current density J{sub rf}(r,t) such that {tilde U}{sub b}=U{sub b}{minus}J{sub rf(}r,t){phi}{sub 0}{xi}l. {copyright} {ital 1997} {ital The American Physical Society}

• OSTI ID: 544953
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 18 Vol. 56; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BARIUM OXIDES
COPPER OXIDES
ELECTRIC IMPEDANCE
HIGH-TC SUPERCONDUCTORS
REVIEWS
SUPERCONDUCTING FILMS
THIN FILMS
YTTRIUM OXIDES