非均匀二维蜂巢晶格中手征性d + id超导态的量子蒙特卡罗探究

Quantum Monte Carlo Study of the Chiral d + id Superconducting State on the Inhomogeneous Two-Dimensional Honeycomb Lattice

摘要: 本文基于哈伯德模型采用约束路径量子蒙特卡罗方法研究了非均匀二维蜂巢晶格中手征性d + id超导态随非均匀度(由蜂巢内和蜂巢间的跃迁积分之间的比值来表征)的演化特性。研究结果表明当在位库仑相互作用U较小时，手征性d + id电子配对关联函数随着非均匀度的增大先明显增加后逐渐减小，而在较大U的情况下手征性d + id电子配对关联函数随非均匀度的增大趋势被强烈抑制。我们的研究结果说明在较小U的情况下存在一个最佳的非均匀度，使得体系具有最强的手征性d + id超导态。进一步的理论分析显示磁性并不是导致超导态变化的原因。根据体系中费米能附近的电子状态数与有效在位库仑相互作用随非均匀度的变化特征，我们对手征性d + id超导态随非均匀度的演化给出了合理的解释。我们的研究对量子调控二维蜂巢晶格中的超导态提供了重要的理论思路。

Abstract: On the basis of the Hubbard model, the evolution of the chiral d + id superconducting state with the inhomogeneity on the two-dimensional honeycomb lattice is studied by using the constrained-path Monte Carlo method. We find that when the on-site U is small, the d + id pairing correlation function firstly increases with increasing the inhomogeneity, and then decreases beyond a certain inhomo-geneity. For relatively larger U, the enhancement tendency of d + id pairing correlation function is strongly suppressed. Our results indicate that there exists an optimal inhomogeneity at small U values, which optimizes the d + id superconducting state on the honeycomb lattice. Further analysis shows that magnetism is not responsible for the inhomogeneity-dependent superconductivity. In terms of the changes of the density of states at the Fermi level and the effective on-site interaction as a function of inhomogeneity, we offer a reasonable explanation for the inhomogeneity-dependent superconductivity. Our study provides an important route for controlling the superconducting state on the honeycomb lattice.