17,136 research outputs found
Mott Transition in Multi-Orbital Models for Iron Pnictides
The bad-metal behavior of the iron pnictides has motivated a theoretical
description in terms of a proximity to Mott localization. Since the parent
compounds of the iron pnictides contain an even number of 3d-electrons per Fe,
it is important to determine whether a Mott transition robustly exists and the
nature of the possible Mott insulating phases. We address these issues in a
minimal two-orbital model and a more realistic four-orbital model for the
parent iron pnictides using a slave-spin approach. In the two-orbital model
with two electrons per Fe, we identify a transition from metal to Mott
insulator. The critical coupling, , is greatly reduced by the Hund's
coupling. Depending on the ratio between the inter- and intra-orbital Coulomb
repulsions, the insulating state can be either a spin-Mott insulator or an
orbital-Mott insulator. In the four-orbital model with four electrons per Fe,
we find an orbitally selective metal-to-insulator transition in the case of
zero Hund's coupling; the transition to a Mott insulator in the and
orbitals takes place at the same critical coupling as the transition to a band
insulator in the and orbitals. In the presence of a finite
Hund's coupling, however, the localization transition is into a spin-Mott
state.Comment: 12 pages, 11 figures, to appear in Phys. Rev.
Orbital-selective Mott Phase in Multiorbital Models for Alkaline Iron Selenides K(1-x)Fe(2-y)Se2
We study a multiorbital model for the alkaline iron selenides
K(1-x)Fe(2-y)Se2 using a slave-spin method. With or without ordered vacancies,
we identify a metal-to-Mott-insulator transition at the commensurate filling of
six 3d electrons per iron ion. For Hund's couplings beyond a threshold value,
this occurs via an intermediate orbital-selective Mott phase, in which the 3d
xy orbital is Mott localized while the other 3d orbitals remain itinerant. This
phase is still stabilized over a range of carrier dopings. Our results lead to
an overall phase diagram for the alkaline iron selenides, which provides a
unified framework to understand the interplay between the strength of vacancy
order and carrier doping. In this phase diagram, the orbital-selective Mott
phase provides a natural link between the superconducting K(1-x)Fe(2-y)Se2 and
its Mott-insulating parent compound.Comment: 6 pages, 5 figures, including supplementary informatio
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