# Switching dynamics of the spin density wave in superconducting CeCoIn5

## TL;DR

This paper investigates the switching dynamics of the spin density wave in superconducting CeCoIn5, revealing how magnetic field direction influences SDW order through a gap closing and reopening process, supported by theoretical and experimental agreement.

## Contribution

The study introduces a free energy model describing SDW switching dynamics and demonstrates the linear dependence of hysteresis width on magnetic field deviation, linking theory with thermal conductivity experiments.

## Key findings

- SDW Q vector switches via gap closing and reopening.
- Hysteresis width depends linearly on magnetic field deviation.
- Magnetic field direction critically influences SDW order.

## Abstract

The ordering wave vector $\mathbf{Q}$ of a spin density wave (SDW), stabilized within the superconducting state of $\mathrm{CeCoIn_5}$ in a high magnetic field, has been shown to be hypersensitive to the direction of the field. $\mathbf{Q}$ can be switched from a nodal direction of the $d$-wave superconducting order parameter to a perpendicular node by rotating the in-plane magnetic field through the antinodal direction within a fraction of a degree. Here, we address the dynamics of the switching of $\mathbf{Q}$. We use a free energy functional based on the magnetization density, which describes the condensation of magnetic fluctuations of nodal quasiparticles, and show that the switching process includes closing of the SDW gap at one $\mathbf{Q}$ and then reopening the SDW gap at another $\mathbf{Q}$ perpendicular to the first one. The magnetic field couples to $\mathbf{Q}$ through the spin-orbit interaction. Our calculations show that the width of the hysteretic region of switching depends linearly on the deviation of magnetic field from the critical field associated with the SDW transition, consistent with our thermal conductivity measurements. The agreement between theory and experiment supports our scenario of the hypersensitivity of the $Q$ phase on the direction of magnetic field, as well as the magnon condensation as the origin of the SDW phase in $\mathrm{CeCoIn_5}$.