67 research outputs found
Insulator to superfluid transition in coupled photonic cavities in two dimensions
A system of coupled photonic cavities on a two-dimensional square lattice is systematically investigated using the stochastic series expansion quantum Monte Carlo method. The ground state phase diagram contains insulating phases with integer polariton densities surrounded by a superfluid phase. The finite-size scaling of the superfluid density is used to determine the phase boundaries accurately. We find that the critical behavior is that of the generic, density-driven Mott-superfluid transition with dynamic exponent z=2, with no special multicritical points with z=1 at the tips of the insulating-phase lobes (as exist in the case of the Bose-Hubbard model). This demonstrates a limitation of the description of polaritons as structureless bosons.First author draf
Ground-state phase diagram of an anisotropic spin- model on the triangular lattice
Motivated by the recent experiment on a rare-earth material YbMgGaO [Y.
Li \textit{et al.}, Phys. Rev. Lett. \textbf{115}, 167203 (2015)], which found
that the ground state of YbMgGaO is a quantum spin liquid, we study the
ground-state phase diagram of an anisotropic spin- model that was proposed
to describe YbMgGaO. Using the density-matrix renormalization group method
in combination with the exact diagonalization, we calculate a variety of
physical quantities, including the ground-state energy, the fidelity, the
entanglement entropy and spin-spin correlation functions. Our studies show that
in the quantum phase diagram there is a phase and two distinct
stripe phases. The transitions from the two stripe phases to the
phase are of the first order. However, the transition between the two stripe
phases is not the first order, which is different from its classical
counterpart. Additionally, we find no evidence for a quantum spin liquid in
this model. Our results suggest that additional terms may be also important to
model the material YbMgGaO. These findings will stimulate further
experimental and theoretical works in understanding the quantum spin liquid
ground state in YbMgGaO.Comment: minor change
The evolution of magnetic structure driven by a synthetic spin-orbit coupling in two-component Bose-Hubbard model
We study the evolution of magnetic structure driven by a synthetic spin-orbit
coupling in a one-dimensional two-component Bose-Hubbard model. In addition to
the Mott insulator-superfluid transition, we found in Mott insulator phases a
transition from a gapped ferromagnetic phase to a gapless chiral phase by
increasing the strength of spin-orbit coupling. Further increasing the
spin-orbit coupling drives a transition from the gapless chiral phase to a
gapped antiferromagnetic phase. These magnetic structures persist in superfluid
phases. In particular, in the chiral Mott insulator and chiral superfluid
phases, incommensurability is observed in characteristic correlation functions.
These unconventional Mott insulator phase and superfluid phase demonstrate the
novel effects arising from the competition between the kinetic energy and the
spin-orbit coupling.Comment: 9 fig; English polished, note adde
Ground-state phase diagram of the frustrated spin-1/2 two-leg honeycomb ladder
We investigate a spin- two-leg honeycomb ladder with frustrating
next-nearest-neighbor (NNN) coupling along the legs, which is equivalent to two
- spin chains coupled with at odd rungs. The full parameter
region of the model is systematically studied using conventional and infinite
density-matrix renormalization group as well as bosonization. The rich phase
diagram consists of five distinct phases: A Haldane phase, a NNN-Haldane phase
and a staggered dimer phase when ; a rung singlet phase and a
columnar dimer phase when . An interesting reentrant behavior
from the dimerized phase into the Haldane phase is found as the frustration
increases. The universalities of the critical phase transitions are fully
analyzed. Phase transitions between dimerized and disordered phases belong to
the two-dimensional Ising class with central charge . The transition
from the Haldane phase to NNN-Haldane phase is of a weak topological first
order, while the continuous transition between the Haldane phase and rung
singlet phase has central charge .Comment: 14 pages, 17 figures, for latest version and additional information
see https://www.physik.uni-kl.de/eggert/papers/index.htm
Hund-Heisenberg model in superconducting infinite-layer nickelates
We theoretically investigate the unconventional superconductivity in the
newly discovered infinite-layer nickelates NdSrNiO based on
a two-band model. By analyzing the transport experiments, we propose that the
doped holes dominantly enter the Ni or/and orbitals
as charged carriers, and form a conducting band. Via the onsite Hund coupling,
the doped holes are coupled to the Ni localized holes in the
orbital band. We demonstrate that this two-band model could be further reduced
to a Hund-Heisenberg model. Using the reduced model, we show the non-Fermi
liquid state above the critical could stem from the carriers coupled to
the spin fluctuations of the localized holes. In the superconducting phase, the
short-range spin fluctuations mediate the carriers into Cooper pairs and
establish -wave superconductivity. We further predict that the
doped holes ferromagnetically coupled with the local magnetic moments remain
itinerant even at very low temperature, and thus the pseudogap hardly emerges
in nickelates. Our work provides a new superconductivity mechanism for strongly
correlated multi-orbital systems and paves a distinct way to exploring new
superconductors in transition or rare-earth metal oxides.Comment: the paper was expanded, 7 pages, 1 figur
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