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arXiv 1607.08201cond-mat.supr-con
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阻挫约瑟夫森结梯中的边缘电流

Edge currents in frustrated Josephson junction ladders

A. M. Marques, F. D. R. Santos, R. G. Dias

摘要:

在大电容极限下,对具有对角耦合和开边界条件的准一维阻挫约瑟夫森结梯进行了数值研究。我们导出了这个约瑟夫森结阶梯的能量与类似的紧束缚模型的哈密顿量的期望值之间的对应关系,并说明了在具有均匀密度的单粒子态的子空间中,整个超导链的态是如何等价于紧束缚模型的最小能态的.为了满足均匀密度的约束,梯形的超导态被写为紧束缚模型的允许k-态的线性组合与开放边界。在参数t(梯级内和梯级间约瑟夫森耦合之间的比率)的临界值以上,阶梯在边缘处自发地产生电流,随着t的增加,电流扩散到本体,直到达到完全覆盖。超过一定的t值,随着阶梯的大小而变化(对于无限大小的阶梯,t = 1),边缘电流被破坏。在紧束缚模型中,值t = 1对应于两个带之间的间隙的打开。我们认为,边缘电流的消失与此间隙开放是不是巧合,这表明这些边缘电流状态的拓扑起源。

英文摘要:

We present a numerical study of quasi-1D frustrated Josephson junction ladders with diagonal couplings and open boundary conditions, in the large capacitance limit. We derive a correspondence between the energy of this Josephson junction ladder and the expectation value of the Hamiltonian of an analogous tight-binding model, and show how the overall superconducting state of the chain is equivalent to the minimum energy state of the tight-binding model in the subspace of one-particle states with uniform density. To satisfy the constraint of uniform density, the superconducting state of the ladder is written as a linear combination of the allowed k-states of the tight-binding model with open boundaries. Above a critical value of the parameter t (ratio between the intra-rung and inter-rung Josephson couplings), the ladder spontaneously develop currents at the edges which spread to the bulk as t is increased until complete coverage is reached. Above a certain value of t, which varies with ladder size (t = 1 for an infinite-sized ladder), the edge currents are destroyed. The value t = 1 corresponds, in the tight-binding model, to the opening of a gap between two bands. We argue that the disappearance of the edge currents with this gap opening is not coincidental, and that this points to a topological origin for these edge current states.

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