J. Phys. Soc. Jpn. 75 (2006) 051010 (10 pages)  |Previous Article| |Next Article|  |Table of Contents|
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SPECIAL TOPICS

Organic Conductors

Electronic Phases in an Organic Conductor α-(BEDT-TTF)2I3: Ultra Narrow Gap Semiconductor, Superconductor, Metal, and Charge-Ordered Insulator

Naoya Tajima, Shigeharu Sugawara1, Masafumi Tamura, Yutaka Nishio1 and Koji Kajita1

RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198
1Department of Physics, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510

(Received November 11, 2005; Accepted December 12, 2005; Published May 10, 2006)

We review the transport phenomena in an organic conductor α-(BEDT-TTF)2I3. It exhibits various types of transport depending on the circumstance in which it is placed. Under the ambient pressure, it is a charge-ordered insulator below 135 K. When high hydrostatic pressures are applied, it changes to a new type of narrow gap (or zero gap) semiconductor. The conductivity of this system is nearly constant between 300 and 1.5 K. In the same region, however, both the carrier (hole) density and the mobility change by about six orders of magnitude, in a manner so that the effects just cancel out giving rise to the temperature independent conductivity. The temperature (T) dependence of the carrier density n obey nT2 below 50 K. When it is compressed along the crystallographic a-axis, it changes from the charge ordered insulator to a narrow gap semiconductor. At the boundary between these phases, there appears a superconducting phase. On the other hand, when compressed in the b-axis, the system changes to a metal with a large Fermi surface. The effect of magnetic fields on samples in the narrow gap semiconductor phase was examined. Photo-induced transition from the charge ordered insulating state to a metallic state is also discussed. ©2006 The Physical Society of Japan

URL: http://jpsj.ipap.jp/link?JPSJ/75/051010/
DOI: 10.1143/JPSJ.75.051010


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