Low-field vortex dynamics over seven time decades in a Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal for temperatures 13{le}{ital T}{le}83 K
- Laboratorium fuer Festkoerperphysik, Eidgenoessische Technische Hochschule Zuerich, 8093 Zuerich (Switzerland)
- Theoretische Physik, Eidgenoessische Technische Hochschule Zuerich, 8093 Zuerich (Switzerland)
Using a custom-made dc superconducting quantum interference device (dc-SQUID) magnetometer, we have measured the time relaxation of the remanent magnetization {ital M}{sub rem} of a Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal from the fully critical state for temperatures 13 K{le}{ital T}{le}83 K. The measurements cover a time window of seven decades 10{sup {minus}2} s{approx_lt}{ital t}{approx_lt}10{sup 5} s, so that the current density {ital j} can be studied from values very close to {ital j}{sub {ital c}} down to values considerably smaller than {ital j}{sub {ital c}}. From the data we have obtained (i) the flux-creep activation barriers {ital U} as a function of current density {ital j}, (ii) the current-voltage characteristics {ital E}({ital j}) in a typical range of 10{sup {minus}7}{endash}10{sup {minus}15} V/cm, and (iii) the critical current density {ital j}{sub {ital c}}(0) at {ital T}=0. Three different regimes of vortex dynamics are observed: For temperatures {ital T}{approx_lt}20 K the activation barrier {ital U}({ital j}) is logarithmic, no unique functional dependence {ital U}({ital j}) could be found for the intermediate-temperature interval 20 K{approx_lt}{ital T}{approx_lt}40 K, and finally for {ital T}{approx_gt}40 K the activation barrier {ital U}({ital j}) follows a power-law behavior with an exponent {mu}{approx_equal}0.6. From the analysis of the data within the weak collective pinning theory for strongly layered superconductors, it is argued that for temperatures {ital T}{approx_lt}20 K pancake vortices are pinned individually, while for temperatures {ital T}{approx_gt}40 K pinning involves large collectively pinned vortex bundles. A description of the vortex dynamics in the intermediate-temperature interval 20 K{approx_lt}{ital T}{approx_lt}40 K is given on the basis of a qualitative low-field phase diagram of the vortex state in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. (Abstract Truncated)
- OSTI ID:
- 280191
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 53, Issue 14; Other Information: PBD: Apr 1996
- Country of Publication:
- United States
- Language:
- English
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