17–21 Aug 2017
AlbaNova
Europe/Stockholm timezone

Mats Granath - Exploring an effective model for finite momentum paring states

21 Aug 2017, 11:50
35m
FB52 (AlbaNova)

FB52

AlbaNova

Description

We discuss an extension of the standard effective model of d- wave superconductivity of a single band tight-binding Hamiltonian with nearest neighbor attraction to include finite range periodically modulated pair-hopping. The pair-hopping is characterized by a fixed wave number $\vec{Q}$ breaking lattice rotational but not translational symmetry, assuming an underlying nematic order. Within self-consistent BCS theory we study the general variational state consisting of two incommensurate singlet pair amplitude order parameters $\Delta_{\vec{Q}_1}$ and $\Delta_{\vec{Q}_2}$. We find two types of near degenerate ground states; of the Larkin- Ovchnnikov (LO) type with $\Delta_{\vec{Q}_1}=\Delta_{\vec{Q}_2}$ and $\vec{Q}_1=-\vec{Q}_2\approx \vec{Q}$ or of the Fulde- Ferrell (FF) type with $\Delta_{\vec{Q}_2}=0$ and $\vec{Q}_1\approx \pm\vec{Q}$. An anomalous term in the current operator arising from the pair-hopping ensures that Blochs's theorem on zero current in the ground state is enforced also for the FF ground state, despite the spontaneously broken time-reversal symmetry. We also discuss states with a uniform current by exploring the space of pair-momenta $\vec{Q}_1$ and $\vec{Q}_2$. We find a rich phenomenology including the possibility of inhomogeneous current densities due to phase separation and unconventional directional dependence of the depairing current.

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