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arXiv 2310.08474cond-mat.mes-hallcond-mat.stat-mechquant-ph
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二维费米子导线中的拓扑保护亚扩散输运

Topologically protected subdiffusive transport in two-dimensional fermionic wires

Junaid Majeed Bhat

AI总结:

本文通过非平衡格林函数方法研究二维费米子导线的输运性质,证明电导渐近行为由矩阵 $A(ω)$ 的谱决定,并发现当 $A(ω)$ 具有非平凡拓扑时,系统可呈现拓扑保护的亚扩散输运行为。

摘要:

已有研究表明,具有 $N$ 个格点的一维费米子导线在带边处的电导呈现亚扩散 $(1/N^2)$ 行为。本文在二维费米子导线中研究这一问题,该系统由 $N_x\ imes N_y$ 矩形晶格上的跳跃模型描述,晶格由垂直链组成,链内和链间的厄米跳跃矩阵分别由 $H_0$ 和 $H_1$ 给出。我们采用非平衡格林函数方法研究粒子输运,并证明在费米能级 $ω$ 处电导 $T(ω)$ 的渐近行为由无量纲矩阵 $A(ω)=(-ω+H_0)H_1^{-1}$ 的谱所控制。这给出了关于 $A(ω)$ 谱的三个简单条件,分别对应观测到相对于 $N_x$ 的弹道、亚扩散和指数衰减的 $T(ω)$ 行为。我们证明 $A(ω)$ 的某些本征值会产生电导中的亚扩散贡献,并且这些本征值对应于孤立导线的带边。我们证明,如果 $A(ω)$ 具有非平凡拓扑,则可以满足观测亚扩散行为的条件。在这种情况下,当跳跃参数在拓扑区域内调节时,可以观察到电导从弹道行为到亚扩散行为的转变。我们认为在转变点处,由于 $A(ω)$ 的平凡体带也会产生亚扩散贡献,电导可能出现不同的行为。我们通过数值计算电导随 $N_x$ 的变化,在一个简单模型中说明了上述发现。数值结果表明在转变点处电导呈现不同的亚扩散行为($1/N_x^3$)。我们发现数值结果与理论预测吻合良好。

英文摘要:

The conductance at the band edges of one-dimensional fermionic wires, with $N$ sites, has been shown to have subdiffusive $(1/N^2)$ behavior. We investigate this issue in two-dimensional fermionic wires described by a hopping model on an $N_x\times N_y$ rectangular lattice comprised of vertical chains with a Hermitian intra-chain and inter-chain hopping matrices given by $H_0$ and $H_1$, respectively. We study particle transport using the non-equilibrium Green's function formalism, and show that the asymptotic behavior of the conductance, $T(ω)$, at the Fermi level $ω$, is controlled by the spectrum of a dimensionless matrix $A(ω)=(-ω+H_0)H_1^{-1}$. This gives three simple conditions on the spectrum of $A(ω)$ for observing ballistic, subdiffusive, and exponentially decaying $T(ω)$ with respect to $N_x$. We show that certain eigenvalues of $A(ω)$ give rise to subdiffusive contributions in the conductance, and correspond to the band edges of the isolated wire. We demonstrate that the condition for observing the subdiffusive behavior can be satisfied if $A(ω)$ has nontrivial topology. In that case, a transition from ballistic behavior to subdiffusive behavior of the conductance is observed as the hopping parameters are tuned within the topological regime. We argue that at the transition point, different behaviors of the conductance can arise as the trivial bulk bands of $A(ω)$ also contribute subdiffusively. We illustrate our findings in a simple model by numerically computing the variation of the conductance with $N_x$. Our numerical results indicate a different subdiffusive behavior ($1/N_x^3$) of the conductance at the transition point. We find the numerical results in good agreement with the theoretical predictions.

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