Critical dynamics, duality, and the exact dynamic exponent in extreme type II superconductors

The critical dynamics of superconductors is studied using renormalization group and duality arguments. We show that in extreme type II superconductors the dynamic critical exponent is given exactly by $z=3/2$. This result does not rely on the widely used models of critical dynamics. Instead, it is shown that $z=3/2$ follows from the duality between the extreme type II superconductor and a model with a critically fluctuating gauge field. Our result is in agreement with Monte Carlo simulations.Comment: 7 pages, no figures; version accepted for publication in PR

Observation of Magnetic Flux Generated Spontaneously During a Rapid Quench of Superconducting Films

We report observations of spontaneous formation of magnetic flux lines during a rapid quench of YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films through T$_{c}$. This effect is predicted according to the Kibble-Zurek mechanism of creation of topological defects of the order parameter during a symmetry-breaking phase transition. Our previous experiment, at a quench rate of 20K/sec, gave null results. In the present experiment, the quench rate was increased to \TEXTsymbol{>} 10$^{8}$ K/sec. Within experimental resolution, the dependence of the measured flux on the cooling rate is consistent with the prediction

Specific heat of heavy fermion CePd2Si2 in high magnetic fields

We report specific heat measurements on the heavy fermion compound CePd2Si2 in magnetic fields up to 16 T and in the temperature range 1.4-16 K. A sharp peak in the specific heat signals the antiferromagnetic transition at T_N ~ 9.3 K in zero field. The transition is found to shift to lower temperatures when a magnetic field is applied along the crystallographic a-axis, while a field applied parallel to the tetragonal c-axis does not affect the transition. The magnetic contribution to the specific heat below T_N is well described by a sum of a linear electronic term and an antiferromagnetic spin wave contribution. Just below T_N, an additional positive curvature, especially at high fields, arises most probably due to thermal fluctuations. The field dependence of the coefficient of the low temperature linear term, gamma_0, extracted from the fits shows a maximum at about 6 T, at the point where an anomaly was detected in susceptibility measurements. The relative field dependence of both T_N and the magnetic entropy at T_N scales as [1-(B/B_0)^2] for B // a, suggesting the disappearance of antiferromagnetism at B_0 ~ 42 T. The expected suppression of the antiferromagnetic transition temperature to zero makes the existence of a magnetic quantum critical point possible.Comment: to be published in Journal of Physics: Condensed Matte

Differential-thermal analysis around and below the critical temperature Tc of various low-Tc superconductors: A comparative study

We present specific-heat data on the type-II superconductors V3Si, LuNi2B2C and NbSe2 which were acquired with a low-temperature thermal analysis (DTA) technique. We compare our data with available literature data on these superconductors. In the first part we show that the DTA technique allows for fast measurements while providing a very high resolution on the temperature scale. Sharp features in the specific heat such as at the one at the transition to superconductivity are resolved virtually without instrumental broadening. In the second part we investigate the magnetic-field dependence of the specific heats of V3Si and LuNi2B2C at a fixed temperature T=7.5K to demonstrate that DTA techniques also allow for sufficiently precise measurements of absolute values of cp even in the absence of a sharp phase transition. The corresponding data for V3Si and LuNi2B2C are briefly discussed

Specific heat and magnetization of a ZrB12 single crystal: characterization of a type II/1 superconductor

We measured the specific heat, the magnetization, and the magnetoresistance of a single crystal of ZrB12, which is superconducting below Tc ~ 6 K. The specific heat in zero field shows a BCS-type superconducting transition. The normal- to superconducting-state transition changes from first order (with a latent heat) to second order (without latent heat) with increasing magnetic field, indicating that the pure compound is a low-kappa, type-II/1 superconductor in the classification of Auer and Ullmaier [J. Auer and H. Ullmaier, Phys. Rev.B 7, 136 (1973)]. This behavior is confirmed by magnetization measurements. The H-T phase diagram based on specific-heat and magnetization data yields Hc2(0) =550 G for the bulk upper critical field, whereas the critical field defined by vanishing resistance is a surface critical field Hc3(0) ~ 1000 G.Comment: 17 pages, 8 figures, submitted to PR

SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties

In this paper we present calculations of the SO(5) quantum rotor theory of high-T$_{c}$ superconductivity in Zeeman magnetic field. We use the spherical approach for five-component quantum rotors in three-dimensional lattice to obtain formulas for critical lines, free energy, entropy and specific heat and present temperature dependences of these quantities for different values of magnetic field. Our results are in qualitative agreement with relevant experiments on high-T$_{c}$ cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or

Magnetic resonance at 41 meV and charge dynamics in YBa_2Cu_3O_6.95

We report an Eliashberg analysis of the electron dynamics in YBa_2Cu_3O_6.95. The magnetic resonance at 41 meV couples to charge carriers and defines the characteristic shape in energy of the scattering rate \tau^{-1}(T,\omega) which allows us to construct the charge-spin spectral density I^2\chi(\omega,T) at temperature T. The T dependence of the weight under the resonance peak in I^2\chi(\omega,T) agrees with experiment as does that of the London penetration depth and of the microwave conductivity. Als, at T=0 condensation energy, the fractional oscillator strength in the condensate, and the ratio of gap to critical temperature agree well with the data.Comment: 7 Pages, 3 Figures, accepted for publication in Europhysics Letter

Electron Spin-Lattice Relaxation of doped Yb3+ ions in YBa2Cu3Ox

The electron spin-lattice relaxation (SLR) times T1 of Yb3+‡ ions were measured from the temperature dependence of electron spin resonance linewidth in Y0.99Yb0.01Ba2Cu3Ox with different oxygen contents. Raman relaxation processes dominate the electron SLR. Derived from the temperature dependence of the SLR rate, the Debye temperature (Td) increases with the critical temperature Tc and oxygen content x. Keywords: EPR; ESR; Electron spin-lattice relaxation; Debye temperature; Critical temperatureComment: 5 Pages 4 Figure

In-plane optical spectral weight transfer in optimally doped Bi2_{2}Sr2_{2}Ca2_{2}Cu3_{3}O10_{10}

We examine the redistribution of the in-plane optical spectral weight in the normal and superconducting state in tri-layer \bbb (Bi2223) near optimal doping ($T_c$ = 110 K) on a single crystal via infrared reflectivity and spectroscopic ellipsometry. We report the temperature dependence of the low-frequency integrated spectral weight $W(\Omega_c)$ for different values of the cutoff energy $\Omega_c$. Two different model-independent analyses consistently show that for $\Omega_c$ = 1 eV, which is below the charge transfer gap, $W(\Omega_c)$ increases below $T_c$, implying the lowering of the kinetic energy of the holes. This is opposite to the BCS scenario, but it follows the same trend observed in the bi-layer compound \bb (Bi2212). The size of this effect is larger in Bi2223 than in Bi2212, approximately scaling with the critical temperature. In the normal state, the temperature dependence of $W(\Omega_c)$ is close to $T^2$ up to 300 K

Thermal fluctuations and vortex melting in the classical superconductor Nb3Sn from high-resolution specific-heat measurements

The range of critical thermal fluctuations in classical bulk superconductors is extremely small and especially in low fields hardly experimentally inaccessible. With a new type of calorimeter we have been able to resolve a small lambda anomaly within a narrow temperature range around the Hc2 line. We show that the evolution of the anomaly as a function of magnetic field follows scaling laws expected in the presence of critical fluctuations. The lower onset of the fluctuation regime shows many characteristics of a continuous solid-to-liquid transition in the vortex matter. It can be driven into a first-order vortex melting transition by a small AC field which helps the vortex matter to reach equilibrium.Comment: 12 pages, 5 figures new extended version, more figures added, more detailed discussion about the vortex melting transitio