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Zhe Wang, M. Schmidt, A. Günther, S. Schaile, N. Pascher, F. Mayr, Y. Goncharov, D. L. Quintero-Castro, A. T. M. N. Islam, B. Lake, H.-A. Krug von Nidda, A. Loidl, and J. Deisenhofer
The magnetic-field induced Bose-Einstein condensation (BEC) of magnons can occur in dimerized quantum antiferromagnets where the excited triplet states obtain a finite bandwidth due to interdimer couplings in the system [1-5]. Recently, a BEC of magnons was reported to occur in Sr3Cr2O8 [6]. In this talk, we will 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 Jahn-Teller transition, 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. References [1] T. Giamarchi et al., Nature Physics 4, 198 (2008). [2] T. Nikuni et al., Phys. Rev. Lett. 84, 5868 (2000). [3] C. Rüegg et al., Nature (London) 423, 62 (2003). [4] M. Jaime et al., Phys. Rev. Lett. 93, 087203 (2004). [5] M. Kofu et al., Phys. Rev. Lett. 102, 037206 (2009). [6] A. A. Aczel et al., Phys. Rev. Lett. 103, 207203 (2009). |
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