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 $U$, temperature $T$, electron filling \avg{n}, and the frustration control parameter $t^{\prime}$ 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 $t^{\prime}$, 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 $d$-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 dxyd_{xy}-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 $d_{xy}$-wave symmetry firmly dominates over other pairings at low temperature, which is mainly determined by the Ni 3$d$ 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 $(\pi,\pi)$ 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 MoS2_2

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$_2$ 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 $f$-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