Amplitude Of Order Parameter Research Articles

A phenomenological model for the rounding of the electrical conductivity above T g co in polycrystalline copper oxide superconductors

Abstract The amplitude and temperature behavior of the electrical resistivity of ceramic superconductors above the mean-field critical temperature of the individual grains is explained by combining the current phenomenological ideas on the electrical conductivity in granular superconductors with the effects of the fluctuations of the superconducting order parameter amplitude. As an example of application, we analyze the phase-breaking time in ceramic YBCO samples.

Universal functions in finite-size scaling: a numerical study in the Ising and Potts q=3 universality class

The universality of the correlation length, order parameter and susceptibility amplitudes is studied in the vicinity of the critical point of two-dimensional models on strips with periodic boundary conditions for the Ising and Potts q=3 universality class. The results confirm Privman-Fisher conjecture (1984).

Excitation Spectrum and Effects of Normal Impurities on Heavy Electron Superconductors

Excited states in superconductors formed at normal impurities are investigated in the circumstance that the effective fermi energy is at most an order or magnitude larger than the superconducting gap and consequently the coherence length is roughly an order of magnitude larger than the lattice constant. It is discussed that the substantial spatial variation of the order parameter amplitude around an impurity easily occurs. The excitation energy of the bound state around the impurity extends down to a tenth of the gap in typical examples, which results in a new type of gapless-like behavior except at extremely low temperatures. The specific heat shows qualitatively different behavior from the BCS result and does not follow simple temperature dependence.

Landau-Khalatnikov Damping of Ultrasound in Heavy-Fermion Superconductors

The Landau-Khalatnikov mechanism associated with the relaxation of the order-parameter amplitude gives a peak in the longitudinal ultrasonic attenuation $\ensuremath{\alpha}$ near ${T}_{c}$, which quantitatively accounts for the observed peak in U${\mathrm{Be}}_{13}$ and U${\mathrm{Pt}}_{3}$. At lower temperatures this mechanism gives a power-law attenuation.

Two-dimensional-to-one-dimensional crossover in the Ising model

It is shown that for the Ising model when the two-dimensional (2d) model approaches the one-dimensional (1d) model, the 2d heat capacity amplitude goes to zero whereas the 2d scale factor of inverse correlation length and the 2d order parameter amplitude diverge.

Tricritical point in the incommensurate systems

The character of the incommensurate-commensurate phase transitions is discussed with the framework of the Landau-type theory. It is shown that the variation of the order parameter amplitude could induce an attractive interaction between phase solitons, and consequently lead to a discontinuous phase transition. In models relevant to corresponding transitions in ferroelectrics and liquid crystals, the tricritical point can thus be reached by varying the temperature and the anisotropy parameter.

Lattice dynamics of commensurate and incommensurateK2SeO4

K/sub 2/SeO/sub 4/ undergoes an incommensurate structural transformation at T/sub 0/=128 K followed by a commensurate ''lock-in'' transformation at T/sub c/=93 K. Below T/sub 0/, the soft-phonon mode associated with the transformation is ''split'' into modes representing fluctuations in amplitude and phase of the complex order parameter. We have studied the dispersion and temperature dependence of these modes at T < or = 118 K. We have also seen intensity anomalies which can be explained by interactions between a transverse-acoustic-phonon branch and the low-lying ''phason'' branch.