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Register a new userA microscopic model for Josephson currents
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A microscopic model of a Josephson junction between two superconducting plates is proposed and analysed. For this model, the nonequilibrium steady state of the total system is explicitly constructed and its properties are analysed. In particular, the Josephson current is rigorously computed as a function of the phase difference of the two plates and the typical properties of the Josephson current are recovered.
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We first show some properties such as smoothness and monotone decreasingness of the solution to the BCS-Bogoliubov gap equation for superconductivity. Moreover we give the behavior of the solution with respect to the temperature near the transition temperature. On the basis of these results, dealing with the thermodynamic potential, we then show that the transition from a normal conducting state to a superconducting state is a second-order phase transition in the BCS-Bogoliubov model of superconductivity from the viewpoint of operator theory. Here we have no magnetic field and we need to introduce a cutoff $varepsilon>0$, which is sufficiently small and fixed (see Remark ref{rmk:varepsilon}). Moreover we obtain the exact and explicit expression for the gap in the specific heat at constant volume at the transition temperature.
We show that the transition from a normal conducting state to a superconducting state is a second-order phase transition in the BCS-Bogoliubov model of superconductivity from the viewpoint of operator theory. Here we have no magnetic field. Moreover we obtain the exact and explicit expression for the gap in the specific heat at constant volume at the transition temperature. To this end, we have to differentiate the thermodynamic potential with respect to the temperature two times. Since there is the solution to the BCS-Bogoliubov gap equation in the form of the thermodynamic potential, we have to differentiate the solution with respect to the temperature two times. Therefore, we need to show that the solution to the BCS-Bogoliubov gap equation is differentiable with respect to the temperature two times as well as its existence and uniqueness. We carry out its proof on the basis of fixed point theorems.
We prove the hydrodynamic limit for the symmetric exclusion process with long jumps given by a mean zero probability transition rate with infinite variance and in contact with infinitely many reservoirs with density $alpha$ at the left of the system and $beta$ at the right of the system. The strength of the reservoirs is ruled by $kappa$N --$theta$ > 0. Here N is the size of the system, $kappa$ > 0 and $theta$ $in$. Our results are valid for $theta$ $le$ 0. For $theta$ = 0, we obtain a collection of fractional reaction-diffusion equations indexed by the parameter $kappa$ and with Dirichlet boundary conditions. Their solutions also depend on $kappa$. For $theta$ < 0, the hydrodynamic equation corresponds to a reaction equation with Dirichlet boundary conditions. The case $theta$ > 0 is still open. For that reason we also analyze the convergence of the unique weak solution of the equation in the case $theta$ = 0 when we send the parameter $kappa$ to zero. Indeed, we conjecture that the limiting profile when $kappa$ $rightarrow$ 0 is the one that we should obtain when taking small values of $theta$ > 0.
In the preceding paper, introducing a cutoff, the present author gave a proof of the statement that the transition to a superconducting state is a second-order phase transition in the BCS-Bogoliubov model of superconductivity on the basis of fixed-point theorems, and solved the long-standing problem of the second-order phase transition from the viewpoint of operator theory. In this paper we study the temperature dependence of the specific heat and the critical magnetic field in the model from the viewpoint of operator theory. We first show some properties of the solution to the BCS-Bogoliubov gap equation with respect to the temperature, and give the exact and explicit expression for the gap in the specific heat divided by the specific heat. We then show that it does not depend on superconductors and is a universal constant. Moreover, we show that the critical magnetic field is smooth with respect to the temperature, and point out the behavior of both the critical magnetic field and its derivative.
We create and study persistent currents in a toroidal two-component Bose gas, consisting of $^{87}$Rb atoms in two different spin states. For a large spin-population imbalance we observe supercurrents persisting for over two minutes. However we find that the supercurrent is unstable for spin polarisation below a well defined critical value. We also investigate the role of phase coherence between the two spin components and show that only the magnitude of the spin-polarisation vector, rather than its orientation in spin space, is relevant for supercurrent stability.
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