Quantum orbital selective Mott (OSM) transitions are investigated within dynamical mean-field theory based on a two-orbital Hubbard model with different bandwidth at half filling. We find two distinct OSM phases both showing coexistence of itinerant electrons and localized spins, dependent on whether the Hund's coupling is full or of Ising type. The critical values and the nature of the OSM transitions are efficiently determined by entanglement entropy. We reveal that vanishing of the Kondo energy scale evidenced by absence of local spin fluctuations at low frequency in local dynamical spin susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase in Ising Hund's coupling case. We argue that this scenario can also be applied to account for emergent quantum non-Fermi liquid in one-band Hubbard model when short-range antiferromagnetic order is considered.PACS numbers:
I.arXiv:1808.05786v1 [cond-mat.str-el]
Groundstate magnetism of the one-band Hubbard model on the frustrated square lattice where both nearest-neighbour t
1 and next-nearest-neighbour t
2 hoppings are considered at half-filling are revisited within mean field approximation. Two new magnetic phases are detected at intermediate strength of Hubbard U and relative strong frustration of t
2/t
1, named double-stripe and plaquette antiferromagnetic states, both of which are metallic and stable even at finite temperature and electron doping. The nature of the phase transitions between different phases and the properties of the two new states are analyzed in detail. Our results of various magnetic states emerging from geometric frustration in the minimal model suggests that distinct antiferromagnetism observed experimentally in the parent states of two high-T
c superconducting families, i.e. cuprates and iron-based superconductors, may be understood from a unified microscopic origin, irrespective of orbital degrees of freedom, or hoppings further than next-nearest neighbor, etc.
The ground-state properties of CuFeAs were investigated by applying density functional theory calculations within generalized gradient approximation (GGA) and GGA+U. We find that the bicollinear antiferromagnetic state with antiparallel orbital magnetic moments on each iron which violates the Hund's rule is favored by the on-site Coulomb interaction, which is further stabilized by Cu vacancy. The magnetic ground state can be used to understand weak antiferromagnetism in CuFeAs observed experimentally. We argue that breakdown of the Hund's rule may be the possible origin for reduced magnetism in iron pnictides, rather than magnetic fluctuations induced by electronic correlations.
We show that spin-orbit coupling (SOC) plays Janus-faced roles on the orbitally-selective Mott transitions in a three-orbital Hubbard model with crystal field splitting at a specific filling of 2/3, which is a minimal Hamiltonian for ruthenates. While the SOC favors metallic state due to enhancement of orbital hybridization at smaller on-site Coulomb repulsions, it stabilizes the Mott insulating state ascribed to lifting of orbital degeneracies and enhancement of band polarizations at larger electronic interaction. Moreover, an orbitally-selective non-Fermi liquid (OSnFL), where breakdown and retention of the Fermi liquid coexist in different orbitals, emerges between the orbitally-selective Mott phase and the Fermi-liquid state. This novel state can be used to account for the exotic metallic behavior observed in 4d materials, such as Ca1.8Sr0.2RuO4, Ba2RuO4 under strain and Sr2RuO4 under uniaxial pressure. We propose that orbitally-selective Kondo breakdown may account for the OSnFL.
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