Mott-Insulator

Mott insulators are a class of materials that should conduct electricity imder conventional band theories, but are insulators when measmed (particularly at low temperatures). This effect is due to electron-electron interactions which are not considered in conventional band theory. Mott insulators are of growing interest in advanced physics research, and are not yet fully imderstood. They have applications in thin-film magnetic hetero structures and high-temperature superconductivity, for example. 

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Terakura K, Williams A R, Qguchi T and Kubler J 1984 Transition-metal monoxides Band or Mott insulators Phys. Rev. Lett. 52 1830... 

O. K. (1991) Band theory and Mott insulators Hubbard Uinstead of Stoner I. Physical Review B - Condensed Matter, 44, 943-954. 

Since the discovery of the first organic conductors based on TTF, [TTF]C1 in 1972 [38] and TTF - TCNQ in 1973 [39], TTF has been the elementary building block of hundreds of conducting salts [40] (1) charge-transfer salts if an electron acceptor such as TCNQ is used, and (2) cation radical salts when an innocent anion is introduced by electrocrystallization [41]. In both cases, a mixed-valence state of the TTF is required to allow for a metallic conductivity (Scheme 5), as the fully oxidized salts of TTF+ cation radicals most often either behave as Mott insulators (weakly interacting spins) or associate into... 

Mott insulator (21,22), anti nomagnet, spin-Peieiis,... 

The fully ionic solids (region I) afforded band insulators, 1 1 Mott insulators with ground states of antiferromagnets (E b(21) and F b(22) in Fig. 1) or spin-Peierls systems, ferroelectrics, ferromagnets, spin-ladders, and nonlinear transport materials (switching and memory). 

The switching or memory phenomena induced by electric field application or photo irradiation have been studied on Mott insulators, charge ordered insulators, and N-I transition systems and were found to be fast phase transitions in general. For the former two systems, the phase transitions caused a pronounced change in reflectance and conductivity from insulating to metallic features. The third system also exhibited a change in conductivity and dielectric response connected with the transports of solitons and/or domain walls, dynamic dimerization, and... 

Table 6 Four typical K-type superconductors with Tc above 10 K (29 - 32) and a Mott insulator (34)...

The anion structure of the Mott insulator k-(ET)2Cu2(CN)3 34 in Fig. 21 revealed the disorder in the position of C and N atoms of the C=N groups (L2 part Table 6, Fig. 21a) [205-207, 370], due to the existence of an inversion center. However, NMR experiments observed very sharp resonance lines due to the homogeneous local field in the metallic state [371], which suggests that the C/N disorder, if any, does not work as the disorder potential in the conduction layer. 

These experimental facts indicate that this system can be an excellent model of band-filling control, and will be a good candidate for making a superlattice composed of Mott insulator/superconductor hetero-junctions. It should be emphasized that their lattice parameters are nearly kept constant through such an anion modification, which is the most essential feature for achieving the successful tuning of Tc in an organic superconductor. 

Auban-Senzier P, Pasquier C, Jerome D, Carcel C, Fabre JM (2003) From Mott insulator to superconductivity in (TMTTF)2BF4 high pressure transport measurements. Synth Met 133-134 11-14... 

Shimizu Y, Maesato M, Saito G, Drozdova O, Ouahab L (2003) Transport properties of a Mott insulator k-(ET)2Cu2(CN)3 under the uniaxial strain. Synth Met 133-134 225-226... 

Shimizu Y, Miyagawa K, Kanoda K, Maesato M, Saito G (2005) Spin liquid in a spin-frustrated organic Mott insulator. Prog Theor Phys Suppl 159 52-60... 

Kezsmarki I, Shimizu Y, Mihaly G, Tokura Y, Kanoda K, Saito G (2006) Depressed charge gap in the triangular-lattice Mott insulator k-(ET)2Cu2(CN)3. Phys Rev B74 201101/1-4... 

Komatsu T, Saito G (1996) Carrier-doping in a Mott-insulator k-(BEDT-TTF)2Cu2(CN)3. Mol Cryst Liq Cryst 285 51-56... 

Komatsu T, Kojima N, Saito G (1997) Ambient-pressure superconductivity of k -(BEDT-TTF)2Cu2(CN)3 realized by a carrier-doping into a Mott-insulating state. Synth Met 85 1519-1520... 

The above simple picture of solids is not universally true because we have a class of crystalline solids, known as Mott insulators, whose electronic properties radically contradict the elementary band theory. Typical examples of Mott insulators are MnO, CoO and NiO, possessing the rocksalt structure. Here the only states in the vicinity of the Fermi level would be the 3d states. The cation d orbitals in the rocksalt structure would be split into t g and eg sets by the octahedral crystal field of the anions. In the transition-metal monoxides, TiO-NiO (3d -3d% the d levels would be partly filled and hence the simple band theory predicts them to be metallic. The prediction is true in TiO... 

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