3,091 research outputs found
Ground-state phase diagram of the square lattice Hubbard model from density matrix embedding theory
We compute the ground-state phase diagram of the Hubbard and frustrated
Hubbard models on the square lattice with density matrix embedding theory using
clusters of up to 16 sites. We provide an error model to estimate the
reliability of the computations and complexity of the physics at different
points in the diagram. We find superconductivity in the ground-state as well as
competition between inhomogeneous charge, spin, and pairing states at low
doping. The estimated errors in the study are below T in the cuprates and
on the scale of contributions in real materials that are neglected in the
Hubbard model
Dynamically encircling exceptional points: in situ control of encircling loops and the role of the starting point
The most intriguing properties of non-Hermitian systems are found near the
exceptional points (EPs) at which the Hamiltonian matrix becomes defective. Due
to the complex topological structure of the energy Riemann surfaces close to an
EP and the breakdown of the adiabatic theorem due to non-Hermiticity, the state
evolution in non-Hermitian systems is much more complex than that in Hermitian
systems. For example, recent experimental work [Doppler et al. Nature 537, 76
(2016)] demonstrated that dynamically encircling an EP can lead to chiral
behaviors, i.e., encircling an EP in different directions results in different
output states. Here, we propose a coupled ferromagnetic waveguide system that
carries two EPs and design an experimental setup in which the trajectory of
state evolution can be controlled in situ using a tunable external field,
allowing us to dynamically encircle zero, one or even two EPs experimentally.
The tunability allows us to control the trajectory of encircling in the
parameter space, including the size of the encircling loop and the starting/end
point. We discovered that whether or not the dynamics is chiral actually
depends on the starting point of the loop. In particular, dynamically
encircling an EP with a starting point in the parity-time-broken phase results
in non-chiral behaviors such that the output state is the same no matter which
direction the encircling takes. The proposed system is a useful platform to
explore the topology of energy surfaces and the dynamics of state evolution in
non-Hermitian systems and will likely find applications in mode switching
controlled with external parameters.Comment: 15 pages, 11 figure
Ground-state phase diagram of the three-band Hubbard model from density matrix embedding theory
We determine the ground-state phase diagram of the three-band Hubbard model across a range of model parameters using density matrix embedding theory. We study the atomic-scale nature of the antiferromagnetic (AFM) and superconducting (SC) orders, explicitly including the oxygen degrees of freedom. All parametrizations of the model display AFM and SC phases, but the decay of AFM order with doping is too slow compared to the experimental phase diagram, and further, coexistence of AFM and SC orders occurs in all parameter sets. The local magnetic moment localizes entirely at the copper sites. The magnetic phase diagram is particularly sensitive to Δ_(pd) and t_(pp), and existing estimates of the charge transfer gap Δ_(pd) appear too large in so-called minimal model parametrizations. The electron-doped side of the phase diagram is qualitatively distinct from the hole-doped side and we find an unusual two-peak structure in the SC in the full model parametrization. Examining the SC order at the atomic scale, within the larger scale d_(x²−y²)-wave SC pairing order between Cu-Cu and O-O, we also observe a local p_(x(y)) [or d_(xz(yz))] symmetry modulation of the pair density on the Cu-O bonds. Our work highlights some of the features that arise in a three-band versus one-band picture, the role of the oxygen degrees of freedom in new kinds of atomic-scale SC orders, and the necessity of re-evaluating current parametrizations of the three-band Hubbard model
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