Tomonori Shirakawa

Ring-exchange mechanism for triplet superconductivity in a two-chain Hubbard model : Possible relevance to Bechgaard salts

The density-matrix renormalization group method is used to study the ground state of the two-chain zigzag-bond Hubbard model at quarter filling. We show that, with a proper choice of the signs of hopping integrals, the ring-exchange mechanism yields ferromagnetic spin correlations between interchain neighboring sites and produces an attractive interaction between electrons as well as long-range pair correlations in the spin-triplet channel, thereby leading the system to triplet superconductivity. We argue that this mechanism may have possible relevance to the superconductivity observed in Bechgaard salts.

Spin-orbit-induced exotic insulators in a three-orbital Hubbard model with ( t 2 g ) 5 electrons

On the basis of the multiorbital dynamical mean-field theory, a three-orbital Hubbard model with relativistic spin-orbit coupling (SOC) is studied at five electrons per site. The numerical calculations are performed by employing the continuous-time quantum Monte Carlo (CTQMC) method based on the strong-coupling expansion. We find that appropriately choosing bases, i.e., the maximally spin-orbit-entangled bases, drastically improves the sign problem in the CTQMC calculations, which enables us to treat exactly the full Hunds coupling and pair-hopping terms. This improvement is also essential to reach at low temperatures for a large SOC region where the SOC most significantly affects the electronic structure. We show that a metal-insulator transition is induced by the SOC for fixed Coulomb interactions. The insulating state for smaller Coulomb interactions is antiferromagnetically ordered with the local effective total angular momentum

Emergence of massless Dirac quasiparticles in correlated hydrogenated graphene with broken sublattice symmetry

j=1/2

Block Lanczos density-matrix renormalization group method for general Anderson impurity models: Application to magnetic impurity problems in graphene

, in which the (

Spin and density excitations in the triangular-lattice t-J model with multiple-spin exchange interactions : 3He on graphite

j=1/2

Variational Monte Carlo study for superconductivity in multi-orbital systems

)-based band is essentially half filled, while the (

Microscopic Study of Electronic and Magnetic Properties for Ir Oxide

j=3/2

Ground-state phase diagram of the triangular lattice Hubbard model by the density-matrix renormalization group method

)-based bands are completely occupied. More interestingly, for larger Coulomb interactions, we find that an excitonic insulating state emerges, where the condensation of an electron-hole pair in the (

A density matrix renormalization group study in energy space for a single impurity Anderson model and an impurity quantum phase transition

j=1/2

Ferrimagnetism and single-particle excitations in a periodic Anderson model on the honeycomb lattice

)- and (