Comparison of critical and lowest-Landau-level scaling of the specific heat of severalYBa2Cu3

Abstract

The specific heat of two twinned and one detwinned single-crystal samples of YBa 2 Cu 3 O 7Ϫ␦ have been measured with magnetic fields up to 8 T applied parallel to the c axes of the crystals. The crystals have zero-field transition widths of 0.3, 1.0, and 1.5 K. The zero-field data are analyzed in terms of the critical and Gaussian fluctuation models and the in-field data are analyzed in terms of critical and lowest-Landau-level ͑LLL͒ scaling. The data scale using the three-dimensional X-Y model in magnetic fields up to 8 T ͑the highest field we used͒. We also find LLL scaling to work, but only above 6 T. The implication is that there may be a crossover from three-dimensional XY to LLL scaling at some sample-dependent field of the order of 10 T. The results agree with recent measurements of the penetration depth and provide strong evidence for the existence of a critical regime within which there is scaling behavior characteristic of the three-dimensional X-Y model with critical exponents consistent with those observed in superfluid 4 He. We then perform the same analysis on previously published specific-heat data on YBa 2 Cu 3 O 7Ϫ␦ and LuBa 2 Cu 3 O 7Ϫ␦ in order to demonstrate the universality of the scaling functions.

Upper critical field and fluctuation conductivity in the critical regime of doped SmFeAsO

“…Polycrystalline samples 27,24 display similar behavior as single crystals. A 3D behavior has been observed in the case of YBa 2 Cu 3 O x 25,26,24 and a 2D one in the case of Tl 2 2…”

“…Ba CaCu O 27 and Bi 2 Sr 2 CaCu 2 O 8 28 . μ 0 H LLL values are found to range from 1T 25, , , 27 29 24 to ~10T 30,26 for high-T c cuprates.…”

Asymmetry of Critical Exponents inYBa2Cu3O7−<

“…First, specific heat data in YBCO single crystals were interpreted in terms of Gaussian fluctuations [11]. More recently, C p data were interpreted within the 3D XY framework [12][13][14][15], accommodating also data in large magnetic fields [16]. However, those exponents are not obtained over more than one decade in reduced temperature and a clear discussion of the error bars for the exponent at zero field is nonexistent.…”

Peltier microcalorimeter

“…Thus, it seems that ac calorimetry 5,6 is more suitable for this purpose. Indeed, various ac calorimetric techniques with noncontact energy sources such as chopped light 6 and light-emitting diodes 7 were developed as microcalorimetry. However, it is pointed out that these power sources cannot act as a heat sink and, therefore, the average temperature of a sample is always above that of the heat bath in these traditional ac calorimetric methods.…”