Magnetic field induced enlargement of the regime of critical fluctuations in the classical superconductor V3Si from high-resolution specific heat experiments

We report high-resolution specific heat data on a high-quality single crystal of the classical superconductor V3Si, which reveal tiny lambda-shape anomalies appearing superimposed onto the BCS specific heat jump at the superconducting transition in magnetic fields of 2 T and higher. The appearance of these anomalies is accompanied by a magnetic-field-induced broadening of the superconducting transition. We demonstrate, using scaling relations predicted by the fluctuation models of the 3d-XY and the 3d-Lowest-Landau-Level (3d-LLL) universality class, that the effect of critical fluctuations becomes experimentally observable due to of a magnetic field-induced enlargement of the regime of critical fluctuations. The scaling indicates that a reduction of the effective dimensionality due to the confinement of quasiparticles into low Landau levels is responsible for this effect.

$gamma$-ray linear polarization measurements and $(g_{9/2})^{-3}$ neutron alignment in $^{91}$Ru

Linear polarization measurements have been performed for $gamma$-rays in $^{91}$Ru produced with the $^{58}$Ni($^{36}$Ar, $2p1n$$gamma$)$^{91}$Ru reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the $gamma$-$gamma$ coincidences, $gamma$-ray linear polarization and $gamma$-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3$-$1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in $^{91}$Ru. More specifically, calculations using a semi-empirical shell model were performed to understand the structures of the first and second (21/2$^{+}$) and (17/2$^{+}$) levels. The results are in good agreement with the experimental data, supporting the interpretation of the non yrast (21/2$^{+}$) and (17/2$^{+}$) states in terms of the $J_{rm max}$ and $J_{rm max}-2$ members of the seniority-three $ u(g_{9/2})^{-3}$ multiplet.

Coherent control of single photons in the cross resonator arrays via the dark state mechanism

We study the single photon transfer in a hybrid system where the normal modes of two coupled resonator arrays interact with two transition arms of a ?-type atom localized in the intersectional resonator. It is found that, due to the Fano-Feshbach effect based on the dark state of the ?-type atom, the photon transfer in one array can be well controlled by the bound state of the photon in the other array. This conceptual setup could be implemented in some practical cavity QED system to realize a quantum switch for single photon.