Magnetic Field-Induced Condensation of Triplons in Han Purple Pigment BaCuSi$_2$O$_6$

TL;DR

This paper investigates how strong magnetic fields induce Bose-Einstein condensation of triplons in the quasi-2D insulator BaCuSi$_2$O$_6$, revealing phase transition signatures consistent with quantum simulations.

Contribution

It provides experimental evidence of magnetic field-induced triplon condensation in BaCuSi$_2$O$_6$, confirming theoretical predictions and quantum Monte Carlo simulation results.

Findings

Observation of lambda-anomaly in specific heat

Maximum in magnetic susceptibility at low temperatures

Agreement with quantum Monte Carlo simulations

Abstract

Besides being an ancient pigment, BaCuSi$_2$O$_6$ is a quasi-2D magnetic insulator with a gapped spin dimer ground state. The application of strong magnetic fields closes this gap creating a gas of bosonic spin triplet excitations called triplons. The topology of the spin lattice makes BaCuSi$_2$O$_6$ an ideal candidate for studying the Bose-Einstein condensation of triplons as a function of the external magnetic field, which acts as a chemical potential. In agreement with quantum Monte Carlo numerical simulations, we observe a distinct lambda-anomaly in the specific heat together with a maximum in the magnetic susceptibility upon cooling down to liquid Helium temperatures.