Phase transition and lattice distortion in the proposed spin-liquid system

✍ Scribed by M. Lang; R.S. Manna; M. de Souza; A. Brühl; J.A. Schlueter

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 327 KB
• Volume: 405
• Category: Article
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2009.11.096

✦ Synopsis

We report measurements of the uniaxial coefficients of thermal expansion a i and the specific heat C on the spin-liquid candidate kÀðBEDT À TTFÞ 2 Cu 2 ðCNÞ 3 . We observe anomalous and strongly anisotropic in-plane expansivities, implying (i) distinct T-induced b-c lattice distortions and (ii) an increase in the ratio of the hopping amplitudes t 0 =t upon cooling into the low-temperature regime. Most importantly, the a i data reveal clear evidence for a second-order phase transition around 6 K, accompanied by distinct lattice effects. By using a Gr üneisen-scaling Ansatz, we are able to extract the corresponding anomaly to the specific heat. Estimates of the entropy indicate that spin degrees of freedom alone cannot account for the phase transition anomaly, suggesting that charge degrees of freedom are involved.