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Quasi-two dimensional (q2D) organic Mott insulators as seen by inelastic light scattering: from spin liquid to dipole liquid
日程 : 2017年10月2日(月) 11:00 - 12:00 場所 : 物性研究所本館6階 第5セミナー室 (A615) 講師 : Prof. Natalia Drichko 所属 : Department of Physics and Astronomy, Johns Hopkins University 世話人 : 森 初果(63444) ,中辻 知(63240)

Mott insulators are commonly pictured with electrons completely localized on lattice sites. Their low-energy physics involves spins only. In addition, it was shown theoretically that new charge degrees of freedom can emerge in molecule-based Mott insulators as electrons occupy extended molecular orbitals, and can result in a quantum dipole liquid state.
We probe few BEDT-TTF-based 2D Mott insulators using Raman scattering technique. We identify magnetic excitation in an antiferromagnetic compound κ-(BEDT-TTF)2Cu[N(CN)2]Cl and a spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3. We show that their spectrum of excitations is very different from that of a new triangular lattice  Mott insulator k-(BEDT-TTF)2Hg(SCN)2Br. Our data  demonstrate an existence of quantum dipole liquid in this compound. Here, when in the Mott insulating state electrons localize on dimer (BEDT-TTF)2 lattice sites, they form electric dipoles which do not order at low temperatures. We experimentally detect charge fluctuation with frequency of about 50 cm-1using Raman spectra of vibrations of BEDT-TTF molecule. In addition, in the low frequency Raman scattering response we detect a collective mode at about 50 cm-1 due to respective dipole fluctuations.  Heat capacity of κ-(BEDT-TTF)2Hg(SCN)2Br demonstrates a linear term at low temperatures, supporting a scenario where the composite spin and electric dipole degrees of freedom remain fluctuating down to the lowest temperatures.


(公開日: 2017年09月25日)