We report the magnetic-field-induced Bose glass-Bose-Einstein condensate (BEC) transition of triplons in Tl1-xKxCuCl3 and its critical behavior, which were investigated through specific heat and electron spin resonance (ESR) measurements. The field dependence of the BEC transition temperature TN can be described by the power law [H-H c]TNφ near the quantum critical point Hc∼3 T. The critical exponent . tends to reach a value smaller than 1/2 with decreasing fitting window in contrast to φ→3/2 for the standard BEC in a pure system. At sufficiently low temperatures, the ESR line shape for H≃Hc is intermediate between Gaussian and Lorentzian functions. This implies the localization of triplons for H<Hc at T=0.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2011 Jan 21