Field induced magnetic phase transition as a magnon Bose Einstein condensation

We report specific heat, magnetocaloric effect and magnetization measurements on single crystals of the frustrated quasi-2D spin -12 antiferromagnet Cs2CuCl4 in the external magnetic field 0⩽B⩽12T along a-axis and in the temperature range 0.03K⩽T⩽6K. Decreasing the applied magnetic field B from high fields leads to the closure of the field induced gap in the magnon spectrum at a critical field Bc≃8.44T and a long-range incommensurate state below Bc. In the vicinity of Bc, the phase transition boundary is well described by the power law TN∼(Bc-B)1/φ with the measured critical exponent φ≃1.5. These findings provide experimental evidence that the scaling law of the transition temperature TN can be described by the universality class of 3D Bose-Einstein condensation (BEC) of magnons.