Category Archives: 2010

Emergence of superconductivity, valence bond order and Mott insulators in Pd[(dmit)2] based organic salts

The EtMe3P and EtMe3Sb nearly triangular organic salts are distinguished from most other Pd[(dmit)2] based salts, as they display valence bond and no long range order, respectively. Under pressure, a superconducting phase is revealed in EtMe3P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe3P salt, where the re-entrant transitions of the type insulator-metal-insulator can be explained by an entropy difference between metal and the U(1) spin liquid. We find that the superconducting pairing symmetry is d±id, and predict different temperature dependences of the specific heat between the spin liquid and metal.

Jeffrey G. Rau1  and Hae-Young Kee1, 2,
1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
2Canadian Institute for Advanced Research/Quantum Materials Program, Toronto, Ontario MSG 1Z8, Canada

Searching for topological density wave insulators in multi-orbital square lattice systems

We study topological properties of density wave states with broken translational symmetry in two-dimensional multi-orbital systems with a particular focus on t2g orbitals in square lattice. Due to distinct symmetry properties of d-orbitals, a nodal charge or spin density wave state with Dirac points protected by lattice symmetries can be achieved. When an additional order parameter with opposite reflection symmetry is introduced to a nodal density wave state, the system can be fully gapped leading to a band insulator. Among those, topological density wave (TDW) insulators can be realized, when an effective staggered on-site potential generates a gap to a pair of Dirac points connected by the inversion symmetry which have the same topological winding numbers. We also present a mean-field phase diagram for various density wave states, and discuss experimental implications of our results.

Bohm-Jung Yang1  and Hae-Young Kee1, 2,
1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
2Canadian Institute for Advanced Research, Quantum Materials program, Toronto, Ontario M5G 1Z8, Canada

Microscopic route to nematicity in Sr3Ru2O7

An anisotropic metallic phase dubbed electronic nematic phase bounded by two consecutive metamagnetic transitions has been reported in the bilayer ruthenate Sr3Ru2O7. It has also been shown that the nematic and the accompanying metamagnetic transitions are driven by an effective momentum-dependent quadrupole-type interaction. Here, we study the microscopic origin of such an effective interaction. To elucidate the mechanism behind the spontaneous Fermi surface distortion associated with the nematic, we identify a simple tight binding model based on t2g orbitals, spin-orbit coupling and the rotation of RuO6 octahedra as starting point, consistent with the Fermi surface obtained from recent angle-resolved photoemission data. Within an extended Hubbard model the nematic state, characterized by an anisotropy between the bands near (±, 0) and (0,±), then strongly competes with ferromagnetic order but pre-empts it via a finite nearest neighbor interaction. We discuss experimental means to confirm our proposal.

Christoph M. Puetter,1  Jeffrey G. Rau,1  and Hae-Young Kee1, 2,
1Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7
2School of Physics, Korea Institute for Advanced Study, Seoul 130-722, Republic of Korea