Non-equilibrium control of the effective free energy landscape in a frustrated magnet*

Geometrically frustrated magnets often possess accidentally degenerate ground states at zero temperature. At low temperature, thermal fluctuations lift the accidental degeneracy and tend to stabilize ground states with maximal entropy. This phenomenon, known as “order by disorder”, underlines the fluctuation contribution to the free energy landscape in frustrated magnets.

In this talk, I show that one can control such free energy landscape in a non-equilibrium setting [1]. In a frustrated magnet with precessional dynamics, the system’s slow drift motion within the degenerate ground state manifold is governed by the fast modes out of the manifold [2]. Exciting these fast modes can generate a tuneable effective free energy landscape with minima located at thermodynamically unstable portions of the ground state manifold. I demonstrate this phenomenon in pyrochlore XY antiferromagnet, whose effective free energy landscape can be controlled straightforwardly with a magnetic field pulse.

[1] Yuan Wan and Roderich Moessner, Phys. Rev. Lett. 119, 167203 (2017).
[2] Benoit Douçot and Pascal Simon, J. Phys. A: Math. Gen. 31 5855 (1998).