40 research outputs found
The competition between antiferromagnetism and superconductivity in a doped Hubbard model with anisotropic interaction
The competition between antiferromagnetism and superconductivity is one of
the central questions in the research of strong correlated systems. In this
work, we utilize a double layer model containing Hubbard interaction and
interlayer Heisenberg interaction to reveal their competitions. This model is
free of sign problem at certain conditions, and we perform projector quantum
Monte Carlo simulations to extract the ground state correlations of magnetism
and superconductivity. Our results shows that the superconductivity emerges
when the antiferromagnetism is suppressed by tuning the filling or the
anisotropy of the interlayer Heisenberg interaction. This model can be seen as
an analogue of unconventional superconductors and may help us to understand the
transition from an antiferromagnetic insulator to a superconductor.Comment: 5 pages and 8 figure
Strong ferromagnetic fluctuations in a doped checkerboard lattice
Using the determinant quantum Monte Carlo method, we study the magnetic
susceptibility in the parameter space of the on-site interaction ,
temperature , electron filling \avg{n}, and the frustration control
parameter within the Hubbard model on a two-dimensional
checkerboard lattice. It is shown that the system exhibits stable and strong
ferromagnetic fluctuations about the electron filling \avg{n}\ge1.2 for
different , and the ferromagnetic susceptibility is strongly
enhanced by the increasing interaction and decreasing tempeture. We also
discuss the sign problem to clarify which parameter region is accessible and
reliable. Our findings not only demonstrate important implications for
modulating magnetism in the checkerboard lattice, but will also provide a
theoretical platform for a flat-band model that demonstrates a variety of
physical properties.Comment: 6 pages, 6 figure
Transport anisotropy and metal-insulator transition in striped Dirac fermion systems
Using the determinant quantum Monte Carlo method, we investigate the
metal-insulator transitions induced by the stripe of charge density in an
interacting two-dimensional Dirac fermion system. The stripe will introduce the
transport anisotropy and insulating intermediate phase into the system,
accompanied by the change of band structure and a peak of density of states
around Fermi energy. In the case of strong correlation, stripe exhibits
competition with Coulomb repulsion through closing the energy gap and
disrupting the magnetic order, and finally drives the system in Mott insulating
phase back to the metallic state. Our results may provide a feasible way to
modify transport properties by setting charge stripes in experiments.Comment: 8 pages, 9 figure
Evolution of magnetic correlation in an inhomogeneous square lattice
We explore the magnetic properties of a two-dimensional Hubbard model on an
inhomogeneous square lattice, which provides a platform for tuning the
bandwidth of the flat band. In its limit, this inhomogeneous square lattice
turns into a Lieb lattice, and it exhibits abundant properties due to the flat
band structure at the Fermi level. By using the determinant quantum Monte Carlo
simulation, we calculate the spin susceptibility, double occupancy,
magnetization, spin structure factor, and effective pairing interaction of the
system. It is found that the antiferromagnetic correlation is suppressed by the
inhomogeneous strength and that the ferromagnetic correlation is enhanced. Both
the antiferromagnetic correlation and ferromagnetic correlation are enhanced as
the interaction increases. It is also found that the effective -wave pairing
interaction is suppressed by the increasing inhomogeneity. In addition, we also
study the thermodynamic properties of the inhomogeneous square lattice, and the
calculation of specific heat provide good support for our point. Our intensive
numerical results provide a rich magnetic phase diagram over both the
inhomogeneity and interaction
Antiferromagnetic fluctuations and a dominant -wave pairing symmetry in nickelate-based superconductors
Motivated by recent experimental studies on superconductivity found in
nickelate-based materials, we study the temperature dependence of the spin
correlation and the superconducting pairing interaction within an effective
two-band Hubbard model by the quantum Monte Carlo method. Based on parameters
extracted from first-principles calculations, our intensive numerical results
reveal that the pairing with a -wave symmetry firmly dominates over
other pairings at low temperature, which is mainly determined by the Ni 3
orbital. It is also found that the effective pairing interaction is enhanced as
the on-site interaction increases, demonstrating that the superconductivity is
driven by strong electron-electron correlation. Even though the
antiferromagnetic correlation could be enhanced by electronic interaction,
there is no evidence for long-range antiferromagnetic order exhibited in
nickelate-based superconductors. Moreover, our results offer possible evidence
that the pure electron correlation may not account for the charge density wave
state observed in nickelates.Comment: Published versio
Spin triplet superconducting pairing in doped MoS
Searching for triplet superconductivity has been pursued intensively in a
broad field of material science and quantum information for decades.
Nevertheless, these novel states remain rare. Within a simplified effective
three-orbital model, we reveal a spin triplet pairing in doped MoS by
employing both the finite temperature determinant quantum Monte Carlo approach
and the ground state constrained-phase quantum Monte Carlo method. In a wide
filling region of \avg{n}=0.60-0.80 around charge neutrality \avg{n}=2/3,
the -wave pairing dominates over other symmetries. The pairing
susceptibility strongly increases as the on-site Coulomb interaction increases,
and it is insensitive to spin-orbit coupling.Comment: Accepted for publication as a Regular Article in Physical Review
Numerical study on the nucleation law of water vapor condensation in laval nozzle.
In order to explore the formation of condensed droplets and the process of agglomeration into droplets during the gas-liquid separation in the Laval nozzle, the wet gas is taken as the research object, and the numerical simulation model and control equations for the condensation of wet gas are established, which are simulated by Fluent software the effects of three parameters, the inlet relative humidity, the inlet and outlet pressure ratio and the inlet temperature, on the law of water vapor condensation and nucleation in the supersonic nozzle were analyzed. The results show that the higher the relative humidity is, the greater the peak value of the nucleation rate is, and the location of water vapor nucleation is getting closer to the throat of the nozzle; as the pressure ratio increases, the peak value of the nucleation rate becomes larger, and the pressure ratio is. It has an impact on the peak value of the nucleation rate; the lower the inlet temperature, the greater the peak value of the nucleation rate, and the inlet temperature has the greatest influence on the nucleation rate. When the inlet temperature is 285K, the nucleation rate reaches the maximum value and the nucleation position is closest to Throat, that is, the time of nucleation is the shortest, and the position of nucleation is the most forward. Therefore, in the actual application process, the length of the expansion section can be adjusted by the relative humidity of the wet gas, and the equipment can be simplified; at the same time, the dehydration efficiency of the Laval nozzle can be improved by increasing the inlet and outlet pressure ratio or reducing the inlet temperature of the nozzle