Characteristic BEC scaling close to Quantum Critical Point in BaCuSi2O6

TL;DR

This paper experimentally investigates the phase transition in BaCuSi2O6, confirming it follows the 3D XY universality class with a critical exponent close to theoretical predictions for Bose-Einstein condensation.

Contribution

It provides the first experimental measurement of the critical exponent near the quantum critical point in BaCuSi2O6, supporting the Bose-Einstein condensation description of the phase transition.

Findings

Critical exponent nu = 0.63 +/- 0.03 measured

Phase boundary follows power law near quantum critical point

Results agree with mean field 3D XY model predictions

Abstract

We report an experimental determination of the phase boundary between a quantum paramagnetic state and the proposed spin Bose-Einstein condensate of triplons in the spin gap compound BaCuSi2O6. The ordering temperature is related to the proximity to a quantum critical point at the lower critical magnetic field H_c1 = 23.52 +/- 0.03T by a power law parameterized by critical exponent nu. We obtain an experimental estimate of nu = 0.63 +/- 0.03 which is in good agreement with the mean field prediction of nu = 2/3 for the 3D XY model, used to describe the Bose condensation of a 3D dilute interacting Bose gas.