Influence of s±s_{\pm} symmetry on unconventional superconductivity in pnictides above the Pauli limit -- two-band model study

The theoretical analysis of the Cooper pair susceptibility shows the two-band Fe-based superconductors (FeSC) to support the existence of the phase with nonzero Cooper pair momentum (called the Fulde--Ferrel--Larkin--Ovchinnikov phase or shortly FFLO), regardless of the order parameter symmetry. Moreover this phase for the FeSC model with $s_{\pm}$ symmetry is the ground state of the system near the Pauli limit. This article discusses the phase diagram $h-T$ for FeSC in the two-band model and its physical consequences. We compare the results for the superconducting order parameter with s-wave and $s_{\pm}$-wave symmetry -- in first case the FFLO phase can occur in both bands, while in second case only in one band. We analyze the resulting order parameter in real space -- showing that the FeSC with $s_{\pm}$-wave symmetry in the Pauli limit have typical properties of one-band systems, such as oscillations of the order parameter in real space with constant amplitude, whereas with s-wave symmetry the oscillations have an amplitude modulation. Discussing the free energy in the superconducting state we show that in absence of orbital effects, the phase transition from the BCS to the FFLO state is always first order, whereas from the FFLO phase to normal state is second order.Comment: European Physical Journal B (2013

Closing and opening phase variability in dysphonia

Four examples of the use of vocal fold contact phase measurement are discussed for unilateral paresis. In each case this aspect of voice quality is of greater importance than the physical measurement of loudness and pitch related parameters. For three of the cases electro-stimulation has been used as a main part of the treatment. Phonation in both connected speech and, for comparison, in sustained sound production has been used with electro-laryngograph / egg signals providing the basis for measurement. The main new descriptors that have been found to be useful relate to: vocal fold closure and closure duration regularities and distributions; but reference is also made to related measures of peak acoustic amplitude. The new measures described give, in some cases, quite striking results that are of auditory significance and potentially of clinical value

Unconventional superconductivity in iron-base superconductors in a three-band model

Iron-base superconductors exhibits features of systems where the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase, a superconducting state with non-zero total momentum of Cooper pairs, is actively sought. Experimental and theoretical evidence points strongly to the FFLO phase in these materials above the Pauli limit. In this article we discuss the ground state of iron-base superconductors near the critical magnetic field and the full $h-T$ phase diagram for pnictides in case of intra-band pairing, in a three-band model with $s_{\pm}$ symmetry.Comment: RevTeX, 5 pages, 3 figures. Presented on "XVI National Conference of Superconductivity", October 7-12, 2013, Zakopane, Polan

The Fulde-Ferrell-Larkin-Ovchinnikov Superconductivity in Disordered Systems

The Fulde–Ferrell–Larkin–Ovchinnikov phase, with a spatially oscillating order parameter, may be induced by strongly magnetic field at low temperature. It is believed that the Fulde–Ferrell–Larkin–Ovchinnikov phase can exist only in homogeneous superconductors, and even weak impurity potential can lead to its destruction. The analysis of the Fulde–Ferrell–Larkin–Ovchinnikov phase in the Bogoliubov–de Gennes equation shows however, that this phase can exist in the presence of weak disorder. Using Bogoliubov–de Gennes equations, we discussed the influence of diagonal and off-diagonal disorder on the Fulde–Ferrell–Larkin–Ovchinnikov phase