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 –½ antiferromagnet Cs2CuCl4 in the external magnetic field 0≤B≤12 T along a-axis and in the temperature range 0:03 K≤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 ≃ 8:44 T 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/ø with the measured critical exponent ø ≃ 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.