Ultrasonic investigations near the B-induced quantum critical point of the triangular-lattice antiferromagnet Cs2CuCl4

Abstract

Measurements of the longitudinal elastic constants c11, c22 and c33 and the ultrasonic attenuation α 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 Bs, 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 TN(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.