Unconventional phase transitions in the classical J1-J2 XY antiferromagnet on the kagome lattice

Frustrated XY antiferromagnets have been investigated extensively in the past decades due to exotic phenomena arising from geometrical frustration. The classical nearest-neighbor XY antiferromagnet on the kagome lattice is a typical 2D frustrated magnet with macroscopic ground-state degeneracy. The macroscopic degeneracy can be lifted by small perturbations, such as thermal fluctuations. This gives rise to various exotic phenomena, including emergent fractional vortex pairs. A fundamental but unresolved issue is how next-nearest-neighbor interaction affects the competition of degenerated states at finite temperature. In this talk, we investigate the finite-temperature phase diagram of classical J1-J2 XY antiferromagnets on the kagome lattice through extensive Monte Carlo simulations. We show that a weak antiferromagnetic J2 induces an unconventional first-order transition at low temperatures. Furthermore, in the vicinity of the first-order transition, we find two competing quasi-long-range orders with different wavevectors. We will discuss the relation between the phase competition and the unconventional first-order transition.