Nonmagnetic scattering induced suppression of superfluid density in Bi-2212

Nonlinear current-voltage (IV) characteristics of Bi-2212 observed in the presence of the nonmagnetic impurity have been explained incorporating the idea of Berezinskii-Kosterlitz - Thouless (BKT). An exponent (η) is extracted as a function of temperature (T) for several Bi2-xSr2 CaCu2-x ZnxO8+δ (Bi-2212) superconducting samples. Within the framework of the Ambegaokar-Halperin-Nelson-Siggia (AHNS) theory we have extracted the superfluid phase stiffness (SPS) as a function of T. A scaling between the SPS and critical temperature is observed. Strong suppression by the nonmagnetic impurity has been explained using the idea of localized phase fluctuations in the superconducting planes.

Superfluid Phonons in Neutron Star Core

In neutron stars the nuclear asymmetric matter is expected to undergo phase transitions to a superfluid state. According to simple estimates, neutron matter in the inner crust and just below should be in the s-wave superfluid phase, corresponding to the neutron-neutron 1S0 channel. At higher density in the core also the proton component should be superfluid, while in the inner core the neutron matter can be in the 3P2 superfluid phase. Superluidity is believed to be at the basis of the glitches phenomenon and to play a decisive influence on many processes like transport, neutrino emission and cooling, and so on. One of the peculiarity of the superfluid phase is the presence of characteristic collective excitation, the so called ’phonons’, that correspond to smooth modulations of the order parameter and display a linear spectrum at low enough momentum. This paper is a brief review of the different phonons that can appear in Neutron Star superfuid matter and their role in several dynamical processes. Particular emphasis is put on the spectral functions of the different components, that is neutron, protons and electrons, which reveal their mutual influence. The open problems are discussed and indications on the work that remain to be done are given.

Transition of large R-charge operators on a conformal manifold

We study the transition between phases at large R-charge on a conformal manifold. These phases are characterized by the behaviour of the lowest operator dimension ∆(QR) for fixed and large R-charge QR. We focus, as an example, on the D = 3, $$ \mathcal{N} $$ N = 2 Wess-Zumino model with cubic superpotential $$ W= XYZ+\frac{\tau }{6}\left({X}^3+{Y}^3+{Z}^3\right) $$ W = XYZ + τ 6 X 3 + Y 3 + Z 3 , and compute ∆(QR, τ) using the ϵ-expansion in three interesting limits. In two of these limits the (leading order) result turns out to be$$ \Delta \left({Q}_{R,\tau}\right)=\left\{\begin{array}{ll}\left(\mathrm{BPS}\;\mathrm{bound}\right)\left[1+O\left(\epsilon {\left|\tau \right|}^2{Q}_R\right)\right],& {Q}_R\ll \left\{\frac{1}{\epsilon },\kern0.5em \frac{1}{\epsilon {\left|\tau \right|}^2}\right\}\\ {}\frac{9}{8}{\left(\frac{\epsilon {\left|\tau \right|}^2}{2+{\left|\tau \right|}^2}\right)}^{\frac{1}{D-1}}{Q}_R^{\frac{D}{D-1}}\left[1+O\left({\left(\epsilon {\left|\tau \right|}^2{Q}_R\right)}^{-\frac{2}{D-1}}\right)\right],& {Q}_R\gg \left\{\begin{array}{ll}\frac{1}{\epsilon },& \frac{1}{\epsilon {\left|\tau \right|}^2}\end{array}\right\}\end{array}\right. $$ Δ Q R , τ = BPS bound 1 + O ϵ τ 2 Q R , Q R ≪ 1 ϵ 1 ϵ τ 2 9 8 ϵ τ 2 2 + τ 2 1 D − 1 Q R D D − 1 1 + O ϵ τ 2 Q R − 2 D − 1 , Q R ≫ 1 ϵ , 1 ϵ τ 2 which leads us to the double-scaling parameter, ϵ|τ|2QR, which interpolates between the “near-BPS phase” (∆(Q) ∼ Q) and the “superfluid phase” (∆(Q) ∼ QD/(D−1)) at large R-charge. This smooth transition, happening near τ = 0, is a large-R-charge manifestation of the existence of a moduli space and an infinite chiral ring at τ = 0. We also argue that this behavior can be extended to three dimensions with minimal modifications, and so we conclude that ∆(QR, τ) experiences a smooth transition around QR ∼ 1/|τ|2. Additionally, we find a first-order phase transition for ∆(QR, τ) as a function of τ, as a consequence of the duality of the model. We also comment on the applicability of our result down to small R-charge.