J. Phys. I France 6 (1996) 1865-1873
Hall Effect Anomalies and Phase Transitions in the Organic Superconductors, (BEDT-TTF) Cu(NCS) and -(BEDT-TTF) IKeizo Murata
Electrotechnical Laboratory, 1-1-4, Umezono, Tsukuba Ibaraki, 305 Japan
(Received 13 May 1996, revised 22 August 1996, accepted 5 September 1996)
The Hall coefficient, for organic conductors is strongly temperature dependent even if they are metallic. The temperature dependence of is found to exhibit one-to-one correspondence with the structure of the Fermi surface, hence can be called "standard" for each surface. It turned out that the simple temperature-independent is only realized in a material where the Fermi surface is round and simple for these low dimensional systems. The "standard" for each Fermi surface is obtained empirically by comparing 's of relatively high pressure, where low temperature novel states or excitations are suppressed. In some cases, deviates abruptly from the standard -behavior, which suggests a phase transition or its precursor. We show the examples of -(BEDT-TTF) 2Cu(NCS) 2 and of -(BEDT-TTF) 2I 3 in which the anomaly in corresponds to a peak ( K) of antiferromagnetic fluctuation, and to 20 K-phase transition which is associated with low- superconductivity, respectively. As seen in these two examples, the Hall effect is strongly influenced by the electronic state, and therefore, can be a useful tool for locating phase transitions.
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