Abstract
We present an extensive study of vortex dynamics in a high-quality single crystal of HgBa2CuO4+δ, a highly anisotropic superconductor that is a model system for studying the effects of anisotropy. From magnetization M measurements over a wide range of temperatures T and fields H, we construct a detailed vortex phase diagram. We find that the temperature-dependent vortex penetration field Hp(T), second magnetization peak Hsmp(T), and irreversibility field Hirr(T) all decay exponentially at low temperatures and exhibit an abrupt change in behavior at high temperatures T/Tc >~ 0.5. By measuring the rates of thermally activated vortex motion (creep) S(T, H) = |dlnM(T, H)/dlnt|, we reveal glassy behavior involving collective creep of bundles of 2D pancake vortices as well as temperature- and time-tuned crossovers from elastic (collective) dynamics to plastic flow. Based on the creep results, we show that the second magnetization peak coincides with the elastic-to-plastic crossover at low T, yet the mechanism changes at higher temperatures.
Highlights
We present an extensive study of vortex dynamics in a high-quality single crystal of HgBa2CuO4+δ, a highly anisotropic superconductor that is a model system for studying the effects of anisotropy
We find that the temperature-dependent vortex penetration field Hp(T), second magnetization peak Hsmp(T), and irreversibility field Hirr(T) all decay exponentially at low temperatures and exhibit an abrupt change in behavior at high temperatures
We show that the second magnetization peak does not originate from elastic-to-plastic crossovers over most of the phase diagram; these crossovers only coincide with the second magnetization peak at low temperatures T/Tc < 0.2
Summary
We present an extensive study of vortex dynamics in a high-quality single crystal of HgBa2CuO4+δ, a highly anisotropic superconductor that is a model system for studying the effects of anisotropy. When evaluating the potential of superconductors for technological applications, high anisotropy compels considerations beyond the typical metrics of high critical temperature Tc, critical current density Jc, and upper critical field Hc2 This is because thermal fluctuations profoundly impact anisotropic materials’ electronic and magnetic properties, which are significantly influenced by the dynamics of vortices. Hg1201 crystals do not contain common defects, such as twin-boundaries and rare-earth-oxide precipitates[3,4,5] It has a simple tetragonal structure and optimally doped Hg1201 has the highest Tc among single Cu-O layer materials, permitting thorough studies of the effects of thermal fluctuations on the superconducting state. We show that the second magnetization peak does not originate from elastic-to-plastic crossovers over most of the phase diagram; these crossovers only coincide with the second magnetization peak at low temperatures T/Tc < 0.2
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