Inherent spin density wave instability by vortices in superconductors with strong Pauli effects

TL;DR

This paper proposes a novel mechanism for spin density wave instability in superconductors with strong Pauli effects, explaining high field low temperature phases in CeCoIn$_5$ through vortex-induced spectral enhancements and nesting conditions.

Contribution

It introduces a new SDW instability mechanism driven by vortices and Pauli effects, elucidating experimental observations in CeCoIn$_5$ under high magnetic fields.

Findings

SDW is enhanced along the nodal direction under high fields.

The SDW wavevector ${f Q}$ is aligned with the nodal direction regardless of field orientation.

The SDW transition line in the phase diagram has a positive slope.

Abstract

A novel spin density wave (SDW) instability mechanism enhanced by vortices under fields is proposed to explain the high field and low temperature (HL) phase in CeCoIn$_5$. In the vortex state the strong Pauli effect and the nodal gap conspire to enhance the momentum resolved spectral weight exclusively along the nodal direction over the normal value, providing a favorable nesting condition for SDW with ${\bf Q}=(2k_F, 2k_F, 0.5)$ only under high field ($H$). Observed mysteries of the field-induced SDW confined within $H_{c2}$ are understood consistently, such facts that ${\bf Q}$ is directed to the nodal direction independent of $H$, SDW diminishes under tilting field from the $ab$ plane, and the SDW transition line in $(H,T)$ has a positive slope.