arXiv subjects

Karim Steiner

Publications and source records attributed to Karim Steiner.

2 recordsLinked to original sources

arXiv2016

Long-range orders, spin- and orbital-freezing in the two-band Hubbard model

We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J, an intra-orbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital freezing phenomenon. This is the negative-J analogue of the recently discovered fluctuating-moment induced s-wave spin-triplet superconductivity in the spin-freezing regime of multi-orbital models with J>0.

cond-mat.str-el↗

arXiv2015

Double-expansion impurity solver for multiorbital models with dynamically screened U and J

We present a continuous-time Monte Carlo impurity solver for multiorbital impurity models which combines a strong-coupling hybridization expansion and a weak-coupling expansion in the Hund's coupling parameter J. This double-expansion approach allows to treat the dominant density-density interactions U within the efficient segment representation. We test the approach for a two-orbital model with static interactions, and then explain how the double-expansion allows to simulate models with frequency dependent U(ω) and J(ω). The method is used to investigate spin state transitions in a toy model for fullerides, with repulsive bare J but attractive screened J.

cond-mat.str-el↗