Amorphization of vortex matter and indication of a reentrant peak effect in YBa2Cu3O7-δ

Abstract

The peak effect (PE) has been observed in a twinned crystal of YBa 2 Cu 3 O 7−δ for H c in the low field range, close to the zero field superconducting transition temperature (T c (0)) . A sharp depinning transition succeeds the peak temperature T p of the PE. The PE phenomenon broadens and its internal structure smoothens out as the field is increased or decreased beyond the interval between 250 Oe and 1000 Oe. Moreover, the PE could not be observed above 10 kOe and below 20 Oe. The locus of the T p (H) values shows a reentrant characteristic with a nose like feature located at T p (H)/T c (0)≈0.99 and H≈100 Oe (where the FLL constant a 0 ≈penetration depth λ). The upper part of the PE curve (0.5 kOe<H<10 kOe) can be fitted to a melting scenario with the Lindemann number c L ≈0.25. The vortex phase diagram near T c (0) determined from the characteristic features of the PE in YBa 2 Cu 3 O 7−δ (H c) bears close resemblance to that in the 2H-NbSe 2 system, in which a reentrant PE had been observed earlier.

Phase behavior of type-II superconductors with quenched point pinning disorder: A phenomenological proposal

“…Evidence for this phase is strongest in the low-T c materials, in particular 2H-NbSe 2 , [57] although there have been recent reports of similiar low-field glassiness in the high-T c material YBCO [58,59]. The possibility of a lowfield glassy phase has been raised theoretically [60]; simulations provide some support to this hypothesis [61].…”

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

“…These proposals have their precise counterpart in Fig. 1; as argued here and elsewhere [25,28,35,58], the peak effect in 2H-NbSe 2 and related materials actually comprises two separate transitions -the BG-VG and the VG-DL transitions. The phase diagram of We emphasize that the putative multicritical point and the single sharp thermal melting transition featured in theoretical models of the phase behaviour of high-T c materials [4,14] are not mandated by theory.…”

Possible reordering of vortex matter near the end point of the second peak line in theYBa2Cu3OΣταμόπουλος1, Pissas2, Bondarenko3 2002Phys. Rev. B273220View full textAdd to dashboardCite

“…Finally, we observed pronounced hysteretic behavior below the SP in our local ac permeability curves for increasing and decreasing the temperature, in agreeement to recent experimental works. 27,28 …”