The Magnetic Unbinding

In a two-dimensional superfluid, vortex-antivortex pairs are bound at low temperature — confined by a logarithmic potential. The Berezinskii-Kosterlitz-Thouless (BKT) transition unbinds them at a critical temperature, destroying superfluidity. The mechanism is thermal: enough energy to overcome the confining potential.

Yi-Thomas, Long, and Sau show a different pathway to unbinding. In a spin-orbit coupled Bose gas, the bosons condense at one of two nonzero momenta, breaking an Ising symmetry. Domain walls form between the two condensate phases. Vortex-antivortex pairs can separate along these domain walls — the wall provides a channel for vortices to escape confinement.

The through-claim: the Ising transition drives the BKT transition. Critical fluctuations near the magnetic ordering point generate enough domain wall structure to deconfine vortex pairs, destroying superfluid stiffness. Two phase transitions that seem unrelated — one magnetic, one topological — become causally coupled.

The coupling goes further: the Ising transition itself becomes first-order, pushed there by the interaction with vortex physics. The magnetic ordering affects the topological transition, and the topological transition feeds back to change the character of the magnetic one.

Two seemingly independent orderings — magnetic symmetry breaking and vortex confinement — locked into a single mechanism by spin-orbit coupling.