We present a variational approach to treat the metastable superconducting state in an array of small Josephson junctions driven by an applied current. Using this approach, we calculate an approximate phase diagram of such an array with a current bias. Our approach is a generalization of one previously used for such an array at zero applied current. We find that, for a given array, a superconduc...

We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which “Anderson’s theorem” does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superc...

Considering the low-temperature (T ) and high-baryon-number-density (nB) region of the QCD phase diagram, we present a model for the first-order phase transition between the quark-gluon plasma (QGP) and the recently proposed colour superconducting phase. We study nucleation of a droplet of the superconducting phase within the metastable QGP gas. Numerical results for the activation energy, radi...

We report how the superconducting phase forms in pseudo-single-crystal KxFe2−ySe2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase, whereas a small quantity of the high-temperature phase retains its structure an...

CaFe2As2 has been found to be exceptionally sensitive to the application of hydrostatic pressure and can be tuned to reveal all the salient features associated with FeAs superconductivity without introducing any disorder. The ambient pressure, 170 K, structural/magnetic, first-order phase transition is suppressed to 128 K by 3.5 kbar. At 5.5 kbar a new transition is detected at 104 K, increasin...

We report on a fully self-consistent determination of a phase transition to a superconducting state in a conserving approximation. The transition temperature calculated for a two-dimensional Hubbard model with an attractive interaction in the fluctuation exchange approximation agrees with quantum Monte Carlo calculations. The temperature dependences of the superfluid density and of the specific...

The electronic band structure, density of states, structural phase transition and super conducting transition temperature of group –IV B element Zirconium (Zr) under normal and high pressure are reported. The normal pressure band structure, density of states and superconducting transition temperature of hcp Zr agree well with the previous calculations. The high pressure band structure exhibits ...

The crystal structure, electrical resistivity, magnetic susceptibility, and heat capacity of single crystals of BaFe2As2, BaNi2As2, and BaFeNiAs2 are reported. BaFe2As2 data indicate the equivalence of C T , d T /dT, and d /dT results in determining the antiferromagnetic transition at TN=132 1 K. BaNi2As2 shows a structural phase transition from a high-temperature tetragonal phase to a low-temp...

The crystal structure, anisotropic electrical resistivity and magnetic susceptibility, as well as specific heat results from single crystals of BaFe2As2, BaNi2As2, and BaFeNiAs2 are surveyed. BaFe2As2 properties demonstrate the equivalence of C(T), Fisher’s d(T)/dT, and d/dT results in determining the antiferromagnetic transition at TN = 132(1) K. BaNi2As2 shows a structural phase transition ...

FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, F...