The persistent proximity of insulating and metallic phases, a puzzling characterestic of manganites, is argued to arise from the self organization of the twofold degenerate eg orbitals of M n into localized Jahn-Teller(JT) polaronic levels and broad band states due to the large electron -JT phonon coupling present in them. We describe a new two band model with strong correlations and a dynamical mean-field theory calculation of equilibrium and transport properties. These explain the insulator metal transition and colossal magnetoresistance quantitatively, as well as other consequences of two state coexistence. ∼ 0.5) into a metal in a relatively small(5-7 T esla) magnetic field all suggest that metallic and insulating phases are always very close in free energy. This is also reflected in the ubiquitous coexistence (static or dynamic) of two 'phases', one insulating with local lattice distortion and the other metallic without lattice distortion, with length scales varying from 10A• to 10These phenomena are due to the dynamics of the e g electrons of M n constrained by three strong on-site interactions, namely electron lattice or Jahn-Teller (JT) coupling which splits the twofold e g orbital degeneracy, ferromagnetic e g spin-t 2g spin exchange or Hund's coupling J H and e g electron repulsion U . The respective energies are E JT ≃ 0.5 eV , J H ≃ 2 eV and U ≃ 5 eV , compared to the e g electron intersite hopping t ≃ 0.2 eV which sets the kinetic energy scale [4]. Understanding their observed consequences is one of the major challenges in the physics of strongly interacting electrons. Earlier theoretical attempts neglect one or more of these strong interactions and make further approximations; the predictions do not agree with many characteristics of manganites. For example the ferromagnetic Curie transition in a number of manganites is from an insulator to a metal, for 0.2 < ∼ x < ∼ 0.5. However, a theory with just Hund's coupling, due to Furukawa [5], finds only a metallic phase, while Millis, Muller and Shraiman [6], who additionally include the electron-JT phonon coupling g but treat the JT distortions as static displacements, obtain a metalmetal transition crossing over to an insulator-insulator transition as g increases.We propose and implement here a new approach which incorporates the crucial effects of all the three interactions and is based on a new idea, namely that of coexisting JT polaronic and broad band e g states, which we believe is the key to manganite physics. The idea and some of its consequences are described and calculations based on a new two band model are then outlined.We first discuss the effect of large JT coupling g on the initially twofold degenerate e g orbitals at each lattice site. There is one superposition (labelled ℓ) which, when singly occupied,leads to a polaronic state with local octahedral symmetry breaking M n − O bond distortion and energy −E JT . Its intersite hopping is reduced (for (E JT /hω 0 ) ≫ 1 where ω 0 is the JT phonon mode frequency) by the exponential Huang-Rhys ...

Motivated by the recent experiment on the Bose-Einstein condensation of 52 Cr atoms with long-range dipolar interactions (Werner J. et al., Phys. Rev. Lett., 94 (2005) 183201), we consider a system of bosons with repulsive nearest and next-nearest neighbor interactions in an optical lattice. The ground state phase diagram, calculated using the Gutzwiller ansatz, shows, apart from the superfluid (SF) and the Mott insulator (MI), two modulated phases, i.e., the charge density wave (CDW) and the supersolid (SS). Excitation spectra are also calculated which show a gap in the insulators, gapless, phonon mode in the superfluid and the supersolid, and a mode softening of superfluid excitations in the vicinity of the modulated phases. We discuss the possibility of observing these phases in cold dipolar atoms and propose experiments to detect them.

We analyze the dissipative conductance of the zero-plateau quantum Hall state appearing in undoped graphene in strong magnetic fields. Charge transport in this state is assumed to be carried by a magnetic domain wall, which forms by hybridization of two counterpropagating edge states of opposing spin due to interactions. The resulting nonchiral edge mode is a Luttinger liquid of parameter K, which enters a gapped, perfectly conducting state below a critical value K_{c} approximately 1/2. Backscattering in this system involves spin flip, so that interaction with localized magnetic moments generates a finite resistivity Rxx via a "chiral Kondo effect." At finite temperatures T, Rxx(T) exhibits a crossover from metallic to insulating behavior as K is tuned across a threshold K_{MI}. For T --> 0, Rxx in the intermediate regime K_{MI} < K < K_{c} is finite, but diverges as K approaches K_{c}. This model provides a natural interpretation of recent experiments.