Dresden 2011 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 22: CE: Low-dimensional Systems - Materials 2
TT 22.5: Talk
Tuesday, March 15, 2011, 11:30–11:45, HSZ 304
Ultrasonic investigation in the vicinity of the quantum-critical point in Cs2CuCl4 — •P. T. Cong, B. Wolf, S. Belz, N. Krüger, F. Ritter, W. Assmuss, and M. Lang — Physikalisches Institut, Goethe Universität-Frankfurt, SFB/TR 49, D-60438 Frankfurt(M)
The insulator Cs2CuCl4 is a quasi-two-dimensional triangular lattice (bc plane) spin-1/2 antiferromagnet (AFM) with a weak interlayer coupling. This material has been considered as one of the prime example for studying the phenomenon of Bose-Einstein condensation (BEC) of magnetic excitations [1]. The long-range antiferromagnetic order (TN = 0.6 K at B = 0) can be suppressed to TN = 0 in a magnetic field Bc ∼ 8.5 T (B∥a), which constitutes a quantum-critical point (QCP). Anomalous physical properties at finite temperature are expected to be observed at Bc due to quantum-critical fluctuations. Here we present a detailed investigation of the elastic constants c11, c22 and c33 together with the ultrasonic attenuation near the B-induced QCP. Distinct anomalies were found at Bc ∼ 8.5 T, which are particularly strongly pronounced in the ultrasonic attenuation. At low temperature and around Bc, the ultrasonic attenuation of the all three modes exhibits a pronounced double peak structures, indicating two anomalies of different origin. While one of them is very sharp, strongly temperature dependent and coinciding with TN(B), the other one is distinctly broader and located at slightly higher fields. Upon cooling both features merge and extrapolate to Bc ∼ 8.5 T for T → 0.
T. Radu et al., Phys. Rev. Lett. 95, 127202 (2005).