Unjong Yu

Unconventional superconductivity on the triangular lattice Hubbard model

Using large-scale dynamical cluster quantum Monte Carlo simulations, we explore the unconventional superconductivity in the hole-doped Hubbard model on the triangular lattice. Due to the interplay of electronic correlations, geometric frustration, and Fermi surface topology, we find a doubly degenerate singlet pairing state at an interaction strength close to the bare bandwidth. Such an unconventional superconducting state is mediated by antiferromagnetic spin fluctuations along the � -K direction, where the Fermi surface is nested. An exact decomposition of the irreducible particle-particle vertex further confirms the dominant component of the effective pairing interaction comes from the spin channel. Our findings suggest the existence of chiral d + id superconductivity in a hole-doped Hubbard triangular lattice in a strongly correlated regime, and provide insight into the superconducting phases of the water-intercalated sodium cobaltates NaxCoO2 · yH2O, as well as the organic compounds κ-(ET)2X and Pd(dmit)2.

Nonlocal effects on magnetism in the diluted magnetic semiconductor Ga1-xMnxAs.

The magnetic properties of the diluted magnetic semiconductor Ga1-xMnxAs are studied within the dynamical cluster approximation. We use the k x p Hamiltonian to describe the electronic structure of GaAs with spin-orbit coupling and strain effects. We show that nonlocal effects are essential for explaining the experimentally observed transition temperature and saturation magnetization. We also demonstrate that the cluster anisotropy is very strong and induces rotational frustration and a cube-edge direction magnetic anisotropy at low temperature. With this, we explain the temperature-driven spin reorientation in this system.

Isotope effects and charge-gap formation in the charge-ordered phase of colossal magnetoresistance manganites

Giant oxygen isotope effects observed in colossal magnetoresistance manganites are investigated by employing the combined model of the double exchange and interacting lattice polaron mechanism. We have shown that the isotope effects on

Generalized multiband typical medium dynamical cluster approximation: Application to (Ga,Mn)N

T_C

Effects of band broadening and shape of the density of states on the magnetic phase diagram

in the metallic phase and

Role of magnetic polarons in transport properties of EuB6

T_{CO}

Magnetic phase diagram of doped CMR manganites

in the charge ordered phase of manganites can be explained well in terms of the double exchange and polaron narrowing factors with reasonable physical parameters.

Anomalous specific heat and its field dependence in the magnetic polaron system: EuB6

We generalize the multiband typical medium dynamical cluster approximation and the formalism introduced by Blackman, Esterling, and Berk so that it can deal with localization in multiband disordered systems with both diagonal and off-diagonal disorder with complicated potentials. We also introduce an ansatz for the momentum-resolved typical density of states that greatly improves the numerical stability of the method while preserving the independence of scattering events at different frequencies. Starting from the first-principles effective Hamiltonian, we apply this method to the diluted magnetic semiconductor

Thermoelectric power in the double exchange model

{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{N}

Polaron transport and isotope effects in colossal magnetoresistive manganites

, and find the impurity band is completely localized for Mn concentrations