Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 15: MLT: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ... 1

TT 15.3: Talk

Tuesday, March 23, 2010, 14:30–14:45, H18

Elastic anomalies at the field-induced quantum-critical point in the quasi 2D-antiferromagnet Cs₂CuCl₄ — •P. T. Cong, B. Wolf, S. Belz, N. Krüger, F. Ritter, W. Aßmus, and M. Lang — Physikalisches Institut, Goethe- Universität, SFB/TR 49, D-60438 Frankfurt(M).

The quasi-2D antiferromagnet Cs₂CuCl₄ is one of the prime examples where the phenomenon of Bose-Einstein condensation (BEC) of magnetic excitations has been discussed [1]. The long-range antiferromagnetic order can be suppressed to T_N = 0 in a magnetic field B_c ∼ 8.5 T (B//a), which constitutes a quantum critical point (QCP). At B_c, quantum-critical fluctuations are expected to give rise to anomalous physical properties at finite temperatures. Here we present a detailed investigation of the elastic constants and ultrasonic attenuation near the B-induced QCP. Distinct anomalies were found at B_c ∼ 8.5 T, which are particularly strongly pronounced in the ultrasonic attenuation. Around B_c below 0.2 K the ultrasonic attenuation of the c₁1 mode exhibits a pronounced double structure, reminiscent of two anomalies of different origin. One is very sharp, strongly temperature dependent and is located at T_N(B) and the other one is distinctly broader at slightly higher fields. [1] T. Radu et al.,PRL 95, 127202, (2005)