All-temperature superfluidity in two dimensions
Abstract
In local theories with short-range interactions, continuous symmetries cannot be spontaneously broken in two spatial dimensions at nonzero temperature. U(1)-symmetric models instead admit a Berezinskii--Kosterlitz--Thouless (BKT) phase with quasi-long-range order and nonzero phase stiffness, which is normally destroyed at high temperatures by vortex proliferation. Here, we show that a BKT phase, and with it superfluidity, can persist to arbitrarily high temperatures. Using the large-N expansion, we study a (2+1)-dimensional quantum field theory in which a complex scalar is coupled to the critical O(N) model. At the biconical fixed point, where the inter-sector coupling is negative, the thermal effective potential has a circle of minima with nonzero U(1) amplitude. Integrating out the gapped fluctuations yields an effective theory for the compact phase mode at distances large compared to 1/T. Since temperature is the only scale at the fixed point, the phase stiffness grows linearly with temperature, with a proportionality factor that scales linearly with N and is fixed entirely by the fixed point. This renders vortex operators irrelevant for sufficiently large N. We further show that the vortex fugacity is exponentially small in N.
Related
- Reentrant d=2+1 Superfluidity at High Temperature
- Achieving ultrahigh-temperature superfluidity in atomic Fermi gases by suppressing pairing fluctuations
- Long-Range Toric Code: Finite-Temperature Topological Order in Two Dimensions
- Conformal defects of general dimensions at finite temperature
- Non-Hermitian engineering of superfluidity in a Rashba spin-orbit-coupled Fermi gas
BibTeX
@misc{hawashin2026alltemperature,
title = {{All-temperature superfluidity in two dimensions}},
author = {Bilal Hawashin and Soumyadeep Chaudhuri and Igor F. Herbut and Michael M. Scherer},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.20717},
eprint = {2610.20717},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.20717},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - All-temperature superfluidity in two dimensions
AU - Bilal Hawashin
AU - Soumyadeep Chaudhuri
AU - Igor F. Herbut
AU - Michael M. Scherer
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.20717
UR - https://arxiv.org/abs/2610.20717
AB - In local theories with short-range interactions, continuous symmetries cannot be spontaneously broken in two spatial dimensions at nonzero temperature. U(1)-symmetric models instead admit a Berezinskii--Kosterlitz--Thouless (BKT) phase with quasi-long-range order and nonzero phase stiffness, which is normally destroyed at high temperatures by vortex proliferation. Here, we show that a BKT phase, and with it superfluidity, can persist to arbitrarily high temperatures. Using the large-N expansion, we study a (2+1)-dimensional quantum field theory in which a complex scalar is coupled to the critical O(N) model. At the biconical fixed point, where the inter-sector coupling is negative, the thermal effective potential has a circle of minima with nonzero U(1) amplitude. Integrating out the gapped fluctuations yields an effective theory for the compact phase mode at distances large compared to 1/T. Since temperature is the only scale at the fixed point, the phase stiffness grows linearly with temperature, with a proportionality factor that scales linearly with N and is fixed entirely by the fixed point. This renders vortex operators irrelevant for sufficiently large N. We further show that the vortex fugacity is exponentially small in N.
ER -