Unified order-disorder vortex phase transition in high-Tcsuperconductors

Abstract

The diversity of vortex melting and solid-solid transition lines measured in different high-T c superconductors is explained, postulating a unified orderdisorder phase transition driven by both thermally-and disorder-induced fluctuations. The temperature dependence of the transition line and the nature of the disordered phase (solid, liquid, or pinned liquid) are determined by the relative contributions of these fluctuations and by the pinning mechanism. By varying the pinning mechanism and the pinning strength one obtains a spectrum of monotonic and non-monotonic transition lines similar to those measured in Bi 2 Sr 2 CaCu 2 O 8 , YBa 2 Cu 3 O 7−δ , Nd 1.85 Ce 0.15 CuO 4−δ , Bi 1.6 Pb 0.4 Sr 2 CaCu 2 O 8+δ and (La 0.937 Sr 0.063 ) 2 CuO 4 .Typeset using REVT E X

Ginzburg-Landau theory of type II superconductors in magnetic field

“…The elastic medium and the vortex dynamics within the London approximation were discussed beyond linear response in numerous analytic and numerical works. Although qualitatively the glass lines obtained here resemble the ones in phenomenological approaches based on comparison of disorder strength with thermal fluctuations and interaction (Ertas and Nelson, 1996;Kierfeld and Vinokur, 2000;Brandt, 2001, 2003;Radzyner et al, 2002), detailed form is different.…”

“…(Blatter et al, 1994). We speculate that the low temperature part of the "unified" line corresponds to the solid -vortex glass transition H * (T ) observed in numerous experiments (Bouquet et al, 2001;Kokkaliaris et al, 2000;Pal et al, 2001Pal et al, , 2002Radzyner et al, 2002;Schilling et al, 1996Schilling et al, , 1997Shibata et al, 2002), see data (squares in Fig.12) taken from ( Shibata et al, 2002). A complicated shape of the "wiggling" line has been recently observed (Pal et al, 2001(Pal et al, , 2002).…”

“…The resulting maximum at which the magnetization and the entropy jump vanish is a Kauzmann point . This universal "order -disorder" transition line (ODT), which appeared first in the strongly layered superconductors (BSCCO (Fuchs et al, 1998)) was extended to the moderately anisotropic superconductors (LaSCCO (Radzyner et al, 2002)) and to the more isotropic ones like Y BCO Pal et al, 2001Pal et al, , 2002. The symmetry characterization of the transition is clear: spontaneous breaking of both the continuous translation and the rotation symmetries down to a discrete symmetry group of the lattice.…”

“…The Kauzmann point observed at a lower temperature in YBCO in ref. (Radzyner et al, 2002) is different from E ent since it is a minimum rather than a maximum of magnetic field. It is also located slightly outside the region of applicability of our solution.…”

“…To summarize we have several transition lines 1) The first order (Bouquet et al, 2001;Schilling et al, 1996Schilling et al, , 1997Zeldov et al, 1995) melting line due to thermal fluctuations was shown to merge with the "second magnetization peak" line due to pinning forming the universal order -disorder phase transition line (Fuchs et al, 1998;Radzyner et al, 2002). At the low temperatures the location of this line strongly depends on disorder and generally exhibits a positive slope (termed also the "inverse" melting (Paltiel et al, 2000a,b)), while in the "melting" section it is dominated by thermal fluctuations and has a large negative slope.…”