Pseudogap, Mott scaling and spin liquid states in k-(ET)2X
* SPEAKERS
Name
Affiliation
E-mail
Kazushi Kanoda
Univ. of Tokyo
* HOST(Applicant)
Name
Affiliation
E-mail
-
* DATE / TIME
2004-05-11, 3:00 pm
* PLACE
Bldg 3, Room#201, POSTECH
* ABSTRACT
The layered organics, 꺵-(ET)2X, are model systems for study of the Mott transition on triangular lattice. I present our recent NMR and transport studies on this topic. The 13C NMR study revealed that the pseudo-gapped superconducting phase abuts on the commensurate antiferromagnetic phase in case of anisotropic triangular lattice. The resistance measurements of the Mott insulator, 꺵-(ET)2Cu[N(CN)2]Cl, under continuously controllable He gas pressure demonstrated that the first-order Mott transition evidenced by clear resistive jump ends around 39 K. The endpoint is featured by vanishing of the resistive jump and critical divergence in pressure derivative of resistance, which are qualitatively consistent with the prediction of the dynamical mean field theory. The critical exponents of the Mott transition in two dimensions were determined and found to make qualitative difference with the reported values for a three dimensional system, Cr-doped V2O3.
While the transfer integrals between the dimers are anisotropic in most systems, 꺵-(ET)2Cu2(CN)3 is an exceptional case with nearly isotropic ones and therefore is a model system of frustrated quantum spins. The susceptibility is finite down to 2 K without any sign of magnetic ordering. The 1H NMR experiments showed no indication of magnetic ordering in either spectra or relaxation rate, 1/T1, down to 30 mK. The spin is likely in the quantum liquid state. The temperature dependence of T1 suggests gapless nature in spin excitation. Under pressure, the spin liquid undergoes Mott transition into the Fermi liquid which shows superconductivity at low temperatures.
