Analysis of the coupling degree between regional logistics efficiency and economic development coordination.

This paper aims to study the relationship between regional logistics efficiency and economic development in 31 provinces of China and analyze their coupling coordination. To comprehensively evaluate the coordination between logistics and the economy, we introduced external indicators, such as carbon emissions, based on traditional evaluation indicators. We constructed an evaluation index system to coordinate regional logistics efficiency and economic development. The research approach used in this paper is the cross-DEA method, and data from 2010 to 2019 were selected for empirical calculation. The research findings indicate that Eastern and Northern regions of China show higher logistics efficiency, while Northwestern and Southwestern regions exhibit lower logistics efficiency. Coastal areas have relatively higher economic development levels compared to inland areas. Regarding the coupling coordination between logistics efficiency and economic development, different regions show temporal fluctuations and spatial disparities. Some regions demonstrate higher coordination between logistics efficiency and economic development, while others show lower coordination. Additionally, as the economy experiences rapid growth, logistics efficiency also improves, but the level of coordination varies among different provinces.

Antiferromagnetically ordered Mott insulator and d+id superconductivity in twisted bilayer graphene: a quantum Monte Carlo study.

Using exact quantum Monte Carlo method, we examine the recent novel electronic states seen in magic-angle graphene superlattices. From the Hubbard model on a double-layer honeycomb lattice with a rotation angle θ=1.08°, we reveal that an antiferromagnetically ordered Mott insulator emerges beyond a critical Uc at half filling, and with a small doping, the pairing with d+id symmetry dominates over other pairings at low temperature. The effective d+id pairing interaction strongly increases as the on-site Coulomb interaction increases, indicating that the superconductivity is driven by electron-electron correlation. Our non-biased numerical results demonstrate that the twisted bilayer graphene shares the similar superconducting mechanism of high temperature superconductors, which is a new and ideal platform for further investigating the strongly correlated phenomena.

Numerical study of magnetic and pairing correlation in a bilayer triangular lattice.

By using the determinant Quantum Monte Carlo method, the magnetic and pairing correlation of the NaxCoO2⋅yH2O system are studied within the Hubbard model on a bilayer triangular lattice. The temperature dependence of the spin correlation function and pairing susceptibility with several kinds of symmetries at different electron fillings and interlayer coupling terms are investigated. It is found that the system shows antiferromagnetic correlation around half filling, and the fn-wave pairing correlation dominates over other kinds of pairing symmetry in the low doping region. As the electron filling decreases from half filling, both ferromagnetic correlation and the f-wave pairing susceptibility are enhanced and tend to dominate. It is also shown that both the magnetic susceptibility and pairing susceptibility decrease as the interlayer coupling increases.

Quantum Monte Carlo study of a dominant s-wave pairing symmetry in iron-based superconductors.

We perform a systematic quantum Monte Carlo study of the pairing correlation in the S(4) symmetric microscopic model for iron-based superconductors. It is found that the pairing with an extensive s-wave symmetry robustly dominates over other pairings at low temperature in a reasonable parameter region regardless of the change of Fermi surface topologies. The pairing susceptibility, the effective pairing interaction, and the (π, 0) antiferromagnetic correlation strongly increase as the on-site Coulomb interaction increases, indicating the importance of the effect of electron-electron correlation. Our nonbiased numerical results provide a unified understanding of the superconducting mechanism in iron pnictides and iron chalcogenides and demonstrate that the superconductivity is driven by strong electron-electron correlation effects.