Regensburg 2019 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 23: Frustrated Magnets - General 1 (joint session TT/MA)

TT 23.4: Vortrag

Dienstag, 2. April 2019, 10:15–10:30, Theater

Magnetic excitations in the correlated paramagnetic state of the frustrated quantum antiferromagnet Cs₂CuCl₄ — •Bernd Wolf, Paul Eibisch, Lars Postulka, Franz Ritter, Cornelius Krellner, and Michael Lang — Physikalisches Institut, Goethe Universität, SFB/TR49, D-60438 Frankfurt (M)

We present a magnetoelastic investigation of the frustrated triangular-lattice S = 1/2 antiferromagnet Cs₂CuCl₄ by studying the longitudinal modes c₁₁, c₂₂ and c₃₃. The measurements were performed in magnetic fields up to 10 T and down to 0.032 K to cover the the long range order and the spin-liquid regime. At the lowest temperatures of our experiment the field dependence of the c₃₃ mode can be well described using a Landau free energy model which combines the elastic constant with the magnetic susceptibility data, measured independently. From fits to the experimental c₃₃ data we obtain a very small magnetoelastic coupling constant G/k_B = 2.8 K for Cs₂CuCl₄ consistent with the results of susceptibility measurements under hydrostatic pressure. Remarkably, we find that the classical approach provides an excellent description of the data at lowest temperatures, i.e., close to the putative quantum critical point at B = 8.5 T of this material. However, at somewhat higher temperatures, there are deviations between the experimental data and the theoretical curves. At these temperatures we also observe anomalies in the ultrasonic attenuation α and χ″, the imaginary part of the magnetic susceptibility. We discuss these losses with respect to the peculiarities of the magnetic excitation spectrum for this low dimensional spin system.