Odd-frequency Cooper pair around a magnetic impurity
Odd-frequency Cooper pair around a magnetic impurity
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磁性杂质周围的奇频库珀对
DOI：
10.1103/physrevb.106.104518
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发表时间：
2022
影响因子：
3.7
通讯作者：
Asano Yasuhiro
中科院分区：
文献类型：
--
作者：
Suzuki Shu-Ichiro;Sato Takumi;Asano Yasuhiro
Yu-Shiba-Rusinov（YSR）态是准粒子在嵌入超导体的磁性原子上的束缚态。我们讨论了为什么YSR态的能量低于超导能隙，为什么对势改变了磁性原子的符号。虽然自20世纪60年代以来，超导体中的磁性原子一直被认为是对断路器，但我们提出了另一种物理图像来解释这些原因。绿色函数的解析表达式表明，磁性原子将自旋单重波库珀对转换为奇频库珀对，而不是打破它，并且奇频配对关联与差距以下的YSR态共存。利用Eilenberger方程的自洽解，讨论了自由能密度、对关联函数的幅值和磁性杂质对势的符号变化之间的关系.我们的结论是，对势的符号变化只发生在奇频配对关联的振幅占主导地位的磁性杂质。在对电势存在局部相移的情况下，奇频对可以降低那里的自由能密度，因为它们对磁场的响应是顺磁性的。
The Yu-Shiba-Rusinov (YSR) state appears as a bound state of a quasiparticle at a magnetic atom embedded in a superconductor. We discuss why the YSR state has energy below the superconducting gap and why the pair potential changes the sign at the magnetic atom. Although a magnetic atom in a superconductor has been considered as a pair breaker since the 1960s, we propose an alternative physical picture to explain these reasons. The analytical expression of the Green's function indicates that a magnetic atom converts a spin-singlet-wave Cooper pair into odd-frequency Cooper pairs rather than breaking it and that the odd-frequency pairing correlations coexist with the YSR states below the gap. The relationships among the free-energy density, the amplitudes of pairing correlation functions, and the sign change of the pair potential at a magnetic impurity are discussed utilizing the self-consistent solution of the Eilenberger equation. We conclude that the sign change of the pair potential happens only when the amplitudes of odd-frequency pairing correlations are dominant at the magnetic impurity. In the presence of the local-phase shift in the pair potential, odd-frequency pairs can decrease the free-energy density there because their response to a magnetic field is paramagnetic.