Anisotropic Latent Heat of Vortex-Lattice Melting in UntwinnedYBa2Cu3O7−

Andreas Schilling

¹

,

Robert A. Fisher

²

,

N. E. Phillips

³

et al.

Abstract

We report a distinct thermal signature of the first-order vortex-lattice melting for the external magnetic field H both parallel and perpendicular to the c axis of an untwinned YBa 2 Cu 3 O 72d single crystal. Latent heats and discontinuities in specific heat were observed for each configuration. The entropies of melting and the melting lines H m ͑T ͒ both scale with an anisotropy parameter g ഠ 8. The specific heat of the vortex fluid is considerably larger than that of the vortex solid (by up to 2 mJ͞mole K 2 ), which is not explained by simple arguments based on counting the numbers of thermodynamic degrees of freedom. [S0031-9007(97)

Ginzburg-Landau theory of type II superconductors in magnetic field

“…Melting lines of optimally doped untwined (Bouquet et al, 2001;Schilling et al, 1996Schilling et al, , 1997Welp et al, 1991Welp et al, , 1996Willemin et al, 1998 (Revaz et al, 1998;Roulin et al, 1996a,b) are also fitted extremely well . More recently both N bSe 2 and thick films of N b 3 Ge were fitted in ref.…”

“…Several remarkable experiments determined that the vortex lattice melting in high T c superconductors is first order with magnetization jumps (Beidenkopf et al, 2005(Beidenkopf et al, , 2007Nishizaki et al, 2000;Willemin et al, 1998;Zeldov et al, 1995), and spikes in specific heat (it was found that in addition to the spike there is also a jump in specific heat which was measured as well) (Bouquet et al, 2001;Lortz et al, 2006Lortz et al, , 2007Nishizaki et al, 2000;Schilling et al, 1996Schilling et al, , 1997. These and other measurements like the resistivity and shear modulus point towards a need to develop a quantitative theoretical description of thermal fluctuations in vortex matter (Liang et al, 1996;Matl et al, 2002;Pastoriza et al, 1994) To tackle the difficult problem of melting, the description of both the solid and the liquid phase should reach the precision level below 1% since the internal energy difference between the phases near the transition temperature is quite small.…”

“…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.…”

Anomalous paramagnetic effects in the mixed state ofLuNi2B2C

“…The in-phase and out-of-phase components of the ac susceptibility χ ac show a dip and the specific heat data show a feature at the corresponding temperature, reminiscent of vortex melting in high-T c cuprates. 18 Electrical transport measurements, however, do not exhibit any feature corresponding to the paramagnetic effect; e.g., a sharp drop in the electrical resistivity. The zero-resistance transition, rather, occurs at a much higher temperature, suggesting that the paramag- …”

“…18 For a structural change in the vortex lattice, the transition is probably of 2nd order because an infinitesimally small change of the angle β between adjacent vortex lines changes the symmetry. Based on the paramagnetic jump ( Fig.…”