16 research outputs found
Switching between Mott-Hubbard and Hund physics in moir\'e quantum simulators
Mott-Hubbard and Hund electron correlations have been realized thus far in
separate classes of materials. Here, we show that a single moir\'e homobilayer
encompasses both kinds of physics in a controllable manner. We develop a
microscopic multiband model that we solve by dynamical mean-field theory to
nonperturbatively address the local many-body correlations. We demonstrate how
tuning with twist angle, dielectric screening, and hole density allows us to
switch between Mott-Hubbard and Hund correlated states in a twisted WSe
bilayer. The underlying mechanism is based on controlling
Coulomb-interaction-driven orbital polarization and the energetics of
concomitant local singlet and triplet spin configurations. From a comparison to
recent experimental transport data, we find signatures of a filling-controlled
transition from a triplet charge-transfer insulator to a Hund-Mott metal. Our
finding establishes twisted transition metal dichalcogenides as a tunable
platform for exotic phases of quantum matter emerging from large local spin
moments
Critical role of interlayer dimer correlations in the superconductivity of LaNiO
The recent discovery of superconductivity in LaNiO with
under high pressure opens up a new route to
high- superconductivity. This material realizes a bilayer square
lattice model featuring a strong interlayer hybridization unlike many
unconventional superconductors. A key question in this regard concerns how
electronic correlations driven by the interlayer hybridization affect the
low-energy electronic structure and the concomitant superconductivity. Here, we
demonstrate using a cluster dynamical mean-field theory that the interlayer
electronic correlations (IECs) induce a Lifshitz transition resulting in a
change of Fermi surface topology. By solving an appropriate gap equation, we
further show that the dominant pairing instability (intraorbital
-wave/interorbital -wave) is enhanced by the IECs. The
underlying mechanism is the quenching of a strong ferromagnetic channel,
resulting from the Lifshitz transition driven by the IECs. Our finding
establishes the role of IECs in LaNiO and potentially paves the way
to designing higher-\Tc nickelates
Frozen spin ratio and the detection of Hund correlations
We propose a way to detect strongly Hund-correlated materials by unveiling
key signatures of Hund correlations at the two-particle level. The defining
feature is the {\it sign} of the response of the {\it frozen spin ratio} (the
long-time local spin-spin correlation function divided by the instantaneous
value) under variation of electron density. The underlying physical reason is
that the sign is closely related to the strength of charge fluctuations between
the dominant atomic multiplets and higher-spin ones in a neighboring charge
subspace. It is the predominance of these fluctuations that promotes Hund
metallicity. Furthermore, the temperature dependence of the frozen spin ratio
can reveal a non-Fermi-liquid behavior. We analyze both degenerate and
non-degenerate multiorbital Hubbard models and corroborate our argument by
taking doped cuprates and Fe-pnictides as representative material examples,
respectively, of Mott and Hund metals
Charge density functional plus calculation of lacunar spinel GaMSe (M = Nb, Mo, Ta, and W)
Charge density functional plus calculations are carried out to examine
the validity of molecular =1/2 and 3/2 state in lacunar spinel
GaMX (M = Nb, Mo, Ta, and W). With LDA (spin-unpolarized local density
approximation), which has recently been suggested as the more desirable
choice than LSDA (local spin density approximation), we examine the band
structure in comparison with the previous prediction based on the
spin-polarized version of functional and with the prototypical
=1/2 material SrIrO. It is found that the previously
suggested =1/2 and 3/2 band characters remain valid still in
LDA calculations while the use of charge-only density causes some minor
differences. Our result provides the further support for the novel molecular
state in this series of materials, which can hopefully motivate
the future exploration toward its verification and the further search for new
functionalities