*

The superconducting vortex lattice (VL) of MgB₂ hosts three structural phases associated with
distinct rotations of the VL with respect to the crystal lattice. One of these phases, the L phase, contains two
degenerate orientations with respect to the a axis, causing the VL to fracture into domains. Domain boundaries
inhibit structural transitions to and from the L phase, giving rise to robust metastability and an activation barrier
which grows rapidly as the VL approaches equilibrium [1]. These domain-dominated kinetics are ubiquitous in
material science, from martensitic phase transitions to ferroelectric domain switching, however, unique to the
VL of MgB₂ is the ability to externally tune this behavior. By rotating the crystal with respect to the applied field,
we can suppress the geometric degeneracy between the two domain orientations and inhibit domain wall
formation. In this talk, we will discuss the effect of this broken symmetry on both the VL phase diagram and the
kinetic behavior of the structural phase transitions.

[1] E. R. Louden et al., Phys. Rev. B 99, 060502(R) (2019); ibid. 99, 144515 (2019).