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TT: Fachverband Tiefe Temperaturen

TT 35: CE: Low-dimensional Systems - Materials 3

TT 35.4: Vortrag

Mittwoch, 16. März 2011, 14:45–15:00, HSZ 301

Evidence for strong orbital fluctuations below the Jahn-Teller transition in Sr₃Cr₂O₈ — •Zhe Wang¹, Michael Schmidt¹, Axel Günther¹, Sebastian Schaile¹, Nikola Pascher¹, Franz Mayr¹, Yurri Goncharov¹, Diana Quintero-Castro^{2, 3}, A. T. M. Nazmul Islam², Bella Lake^{2, 3}, Hans-Albrecht Krug von Nidda¹, Alois Loidl¹, and Joachim Deisenhofer¹ — ¹Experimental Physics V, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, D-86135 Augsburg, Germany — ²Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany — ³Institut für Festkörperphysik, Technische Universität Berlin, D-10623 Berlin, Germany

We report on the magnetic and phononic excitation spectrum of Sr₃Cr₂O₈ determined by THz and infrared (IR) spectroscopy, specific heat, and electron spin resonance measurements. We identify the singlet-triplet excitations in the dimerized ground state and observe an extended temperature range 125 K < T < 285 K below the Jahn-Teller transition, where the IR active phonons change only gradually with decreasing temperature. A clear anomaly in the specific heat marks the onset of orbital ordering at 285 K, but a detailed analysis of the orbital contribution to the specific heat shows the persistence of strong fluctuations down to 125 K in agreement with the IR data. Due to these fluctuations we can observe electron spin resonance absorptions only below 125 K with a linewidth proportional to exp(-Δ/kT) indicating an Orbach-type spin relaxation via the excited orbital state of the Cr e-doublet split by Δ/k=388 K.