Dresden 2017 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 41: Correlated Electrons: Quantum-Critical Phenomena

TT 41.13: Vortrag

Mittwoch, 22. März 2017, 12:45–13:00, HSZ 204

Magneto-acoustic investigations of field-induced quantum criticality in Cs₂CuCl₄ — •Bernd Wolf¹, Lars Postulka¹, Yeekin Tsui¹, Pham Thang Cong^1,2, Natalia van Well^1,3, Franz Ritter¹, Cornelius Krellner¹, and Michael Lang¹ — ¹Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt(M) — ²Dresden-HFFL, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden — ³Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen

Magnetoelastic investigations of the frustrated triangular-lattice antiferromagnet Cs₂CuCl₄ were performed for the longitudinal modes c₁₁, c₂₂ and c₃₃ in magnetic fields up to 10 T and down to 0.032 K. Acoustic anomalies have been found both in the temperature and in the field dependence of these modes. For temperatures 0.8 K > T > 2.0 K in the 1D-regime of Cs₂CuCl₄, the magnetoelastic behaviour can be well described with a microscopic theory. The field-dependent measurements for T > T_N around the quantum-critical point (QCP) at B_s ∼ 8.5 T display two distinct anomalies which are attributed to the transition into long-range afm order and signatures of the preceding spin-liquid state. At the lowest temperatures of our experiment c₃₃(B) can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/k_B = 2.8 K. The observation of rather classical behaviour at lowest temperatures and the deviations from the classical behaviour at somewhat higher temperatures are assigned to the opening of a small gap in the magnetic excitations spectrum for B < B_s which drives the system away from quantum criticality.