| Co-Investigator(Kenkyū-buntansha) |
NAGAOSA Naoto Department of Physics, Graduate School of Science, Hokkaido University, associate professor, 大学院・工学系研究科, 教授 (60164406)
KAWAMOTO Atsushi Department of Applied Physics, Faculty of Engineering University of Tokyo, professor, 大学院・物理学研究科, 助教授 (60251691)
NAKAZAWA Yasuhiro Department of Chemistry, Graduate School of Science, Osaka University, research associate, 大学院・理学研究科, 助手 (60222163)
|
|---|
| Research Abstract |
In the present study, we aim at doping carriers into the correlation-induced molecular insulators based on a) BEDT-TTF and b) DCNQI molecules, and explore possible novel phases.
a) (BEDT-TTF)_4X [X=Hg_<2.89>Br_8Hg_<2.78>Cl_8]
A family of two-dimensional organic systems, κ-(BEDT-TTF)_2X, with half-filled bands span the phase diagram of the 1 st-order Mott transition between the superconducting and antiferromagnetic phases as a function of band-width. In the present sudy, we first measured the ^<13>C-NMR spectra and relaxation rate, 1/T, for a doped organic Mott insulator, κ-(BEDT-TTF)_4Hg_<2.78>Cl_8, down to 30 mK.The l/(T_1T) continues to increase in proportion to 1/T down to 100 mK and then forms a broad peak. The spectra show low-temperature broadening indicative of the short-range AF ordering, but not the three-dimensional one. This is the first observation of the quantum critical spin fluctuations in organics and indicates a surprising contrast to the widely studied case of κ-(BEDT-TTF)_2X with fixed band-filling.
b) (DI-DCNOl)_2M
(DI-DCNQI)_2Ag, which has a quasi-one-dimensional quarter-filled π band, is a paramagnetic insulator. By ^<13>C-NMR study, this insulating phase is found to be in a charge-rodered state, into which the carrier doping was attempted by Cu doping into the Ag sites. As the Cu content is increased, the charge-gapped insulator changes to the nongapped insulator with the variable range hopping behaviour, eventually followed by the metallic phase. This result shows a manner of the collapse of the charge ordering and a route to the metallic phase with introduction of carriers and disorder.
|
