TY  - JOUR
A1  - Hansmann, P.
A1  - Parragh, N.
A1  - Toschi, A.
A1  - Sangiovanni, G.
A1  - Held, K.
T1  - Importance of d-p Coulomb interaction for high T-C cuprates and other oxides
JF  - New Journal of Physics
N2  - Current theoretical studies of electronic correlations in transition metal oxides typically only account for the local repulsion between d-electrons even if oxygen ligand p-states are an explicit part of the effective Hamiltonian. Interatomic interactions such as U-pd between d- and (ligand) p-electrons, as well as the local interaction between p-electrons, are neglected. Often, the relative d-p orbital splitting has to be adjusted 'ad hoc' on the basis of the experimental evidence. By applying the merger of local density approximation and dynamical mean field theory to the prototypical case of the three-band Emery dp model for the cuprates, we demonstrate that, without any 'ad hoc' adjustment of the orbital splitting, the charge transfer insulating state is stabilized by the interatomic interaction U-pd. Our study hence shows how to improve realistic material calculations that explicitly include the p-orbitals.
KW  - correlated electrons
KW  - dynamical mean field theory
KW  - transition metal oxides
KW  - fermions
KW  - superconductivity
KW  - energy bands
KW  - transition metals
KW  - correlated systems
KW  - mean-field theory
KW  - electronic-structure calculations
KW  - inplane spectral weight
KW  - Hubbard model
KW  - infinite dimensions
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117165
SN  - 1367-2630
VL  - 16
IS  - 33009
ER  - 
TY  - JOUR
A1  - Kim, N. Y.
A1  - Kusudo, K.
A1  - Löffler, A.
A1  - Höfling, S.
A1  - Forchel, A.
A1  - Yamamoto, Y.
T1  - Exciton-polariton condensates near the Dirac point in a triangular lattice
JF  - New Journal of Physics
N2  - Dirac particles, massless relativistic entities, obey linear energy dispersions and hold important implications in particle physics. The recent discovery of Dirac fermions in condensed matter systems including graphene and topological insulators has generated a great deal of interest in exploring the relativistic properties associated with Dirac physics in solid-state materials. In addition, there are stimulating research activities to engineer Dirac particles, elucidating their exotic physical properties in a controllable setting. One of the successful platforms is the ultracold atom-optical lattice system, whose dynamics can be manipulated and probed in a clean environment. A microcavity exciton-polariton-lattice system offers the advantage of forming high-orbital condensation in non-equilibrium conditions, which enables one to explore novel quantum orbital order in two dimensions. In this paper, we experimentally construct the band structures near Dirac points, the vertices of the first hexagonal Brillouin zone with exciton-polariton condensates trapped in a triangular lattice. Due to the finite spectral linewidth, the direct map of band structures at Dirac points is elusive; however, we identify the linear part above Dirac points and its associated velocity value is similar to ~0.9-2 x \(10^8 cm s^{-1}\), consistent with the theoretical estimate \(1 x 10^8 cm s^{-1}\) with a \(2 \mu m\) lattice constant. We envision that the exciton-polariton condensates in lattices would be a promising solid-state platform, where the system order parameter can be accessed in both real and momentum spaces.
KW  - Bose-Einstein condensation
KW  - carbon nanotubes
KW  - graphene
KW  - electron
KW  - dynamics
KW  - fermions
KW  - trap
KW  - gas
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-123103
SN  - 1367-2630
VL  - 15
IS  - 035032
ER  -