Sequential vortex states upon lattice melting in untwinned single-crystalYBa2Cu3O

Abstract

Simultaneous measurements of the ac susceptibility and the dc magnetization of an untwinned single-crystal YBa 2 Cu 3 O 7 have been carried out to clarify the nature of vortex lattice melting. The first-order melting transition appears as a jump in the dc magnetization. Evidence for effectual pinning at temperatures above the melting transition is obtained as a sharp transition in Ј and a sharp peak in Љ of width 0.2 K in 10 kG. In addition, a precursor lattice softening phenomenon can be seen in Ј and Љ at temperatures below the melting temperature. This sequential change is more visible when the ac susceptibility is given in the Ј-Љ representation. It has been confirmed that there exists a melting transition of YBa 2 Cu 3 O 7 even below 10 kG.

Disordered type-II superconductors: a universal phase diagram for low-Tc systems

“…Thermodynamic signatures of the underlying (discontinuous) melting transition in the pure system should thus be strongest across this boundary; this is consistent with magnetization experiments on untwinned and twinned single crystals of YBCO [6,38,[48][49][50]. However, the two stage nature of the transition implies that some part of the difference in density between ordered and liquid phases can be accomodated across the width of the sliver regime [52].…”

Effects of weak point disorder on the vortex matter phase diagram in untwinnedYBa2Cu3ONishizaki1, Naito2, Okayasu3 et al. 2000Phys. Rev. B9111660View full textAdd to dashboardCite

“…Since H*(T) above T cp decreases along H m (T) and disappears, the second peak effect just below H m (T) is closely related to the enhanced vortex pinning due to the vortex lattice softening prior to the vortex lattice melting as reported previously. [39][40][41] These results indicate that H*(H) merges with both H m (T) and the premelting peak effect at the critical point for irradiated YBa 2 Cu 3 O y . The region between H*(T) and H m (T) above T cp is very narrow in the present study, so the result above mentioned is completely different from the recently reported second peak 29,42 which intersects H m (T) well below H cp for optimally doped and slightly underdoped YBa 2 Cu 3 O y .…”

Origin of the magnetization peak effect in theNb3Snsuperconductor

“…19,28,29 We would like to mention that a similar "premelting peak" very close to or even coincidental with thermally induced vortex melting has also been reported in YBa 2 Cu 3 O x at fields below the fishtail effect. 30,31 The relaxation behavior of induced critical currents in the region of this premelting peak shows many features, which are known from highly "fragile" 32 structural glass transitions in undercooled liquids. 31 This all suggests that the presently observed magnetization peak effect in Nb 3 Sn ͑and probably also in many other type-II superconductors͒ follows the same phenomenology, as found in supercooled structural liquids despite the fact that the vortex system is not supercooled in the traditional sense.…”