Fraction of Bose-Einstein condensed triplons in TlCuCl3 from magnetization data

Abstract

TlCuCl3 is a quantum-spin-(1/2) system which shows a gap between the singlet ground state of the Cu2+ dimers and the first excited triplet Sz=+1 state for magnetic fields µ0H<~µ0Hc[approximate]5.5 T. At larger magnetic fields the gap is suppressed, and a Bose-Einstein condensation of triplets is supposed to occur, leading to a magnetic phase with antiferromagnetic long-range order of the transverse spin components. In this study we calculate the fraction of condensed magnetic quasiparticles of TlCuCl3 from magnetization M(T,H) data. At T=0 K and right above the critical field Hc, this fraction is [approximate]98% of the total number of triplons, and is independent of the direction of the magnetic field if we assume the presence of a small intrinsic magnetic background with S=1 magnetic moments.