Ultrasonic Investigations Near The B-Induced Quantum Critical Point Of The Triangular-Lattice Antiferromagnet Cs2cucl4

Measurements of the longitudinal elastic constants c(11), c(22) and c(33) and the ultrasonic attenuation alpha of the quasi-two-dimensional triangular-lattice spin-1/2 Heisenberg antiferromagnet Cs2CuCl4 reveal distinct anomalies near the B-induced quantum-critical point (QCP). These anomalies are particularly strongly pronounced in the ultrasonic attenuation. In isothermal field sweeps performed at low temperatures 0.027 K <= T <= 0.3 K around the saturation field B-s, the ultrasonic attenuation of all three modes shows a pronounced double-peak structure, indicating two anomalies of different origin. Upon cooling, however, both features merge suggesting a coincidence at the QCP. While one peak, which can be attributed to the ordering temperature T-N(B), becomes critically enhanced upon approaching the QCP, the other one reduces in size and narrows upon cooling. The latter effect has been tentatively assigned to the material's spin-liquid features which precede the long-range antiferromagnetic ordering.