Inhomogeneous 1H NMR spin-lattice relaxation in the organic superconductor κ-(BEDT-TTF)2-Cu[N(CN)2]Br

magnetic resonance;organic superconductor;Nernst effect;stretched exponential;spin-lattice relaxation

Gezo, Joseph

关键词: magnetic resonance;    organic superconductor;    Nernst effect;    stretched exponential;    spin-lattice relaxation;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42132/Joseph_Gezo.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The two-dimensional superconductors based on the organic molecule “ET” have been an active area of research since their discovery over two decades ago. The member of this family with the highest critical temperature, κ-(ET)2Cu[N(CN)2]Br (Tc=11.7 K), has seen renewed interest since the observation of an anomalous Nernst signal by Nam et al in 2007 [51]. A similar effect was seen earlier by Ong’s group in some of the high-temperature cuprate superconductors by [78,84]. This is interpreted to be evidence of a picture of superconductivity in which the resistive transition is driven by thermal fluctuations in the phase of the superconducting order parameter. Below Tc, these fluctuations take the form of bound vortex-antivortex pairs that have no long-range effect on the phase. At Tc, they undergo a Kosterlitz-Thouless unbinding transition; the unbound vortices destroy long-range phase coherence.Previously reported proton NMR measurements on this material have shown a high sensitivity to vortex motion, but reported no interesting behavior above the phase transition [15,25,42]. In this thesis, we revisit the 1H NMR properties of κ-(ET)2Cu[N(CN)2]Br, paying specific attention to the spin-lattice relaxation, to look for some fingerprint of the phenomenon observed by Nam et al.