Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal/triplet superconductor junctions
Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal/triplet superconductor junctions
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DOI：
10.1103/physrevb.71.094513
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发表时间：
2004-11
影响因子：
3.7
通讯作者：
Yukio Tanaka;S. Kashiwaya;T. Yokoyama
中科院分区：
文献类型：
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作者：
Yukio Tanaka;S. Kashiwaya;T. Yokoyama
基于Keldysh-Nambu准经典格林函数理论，研究了扩散正常金属/绝缘体/三重态超导体(DN/TS)结中禁带安德烈夫共振态(MARS)增强的邻近效应。以p波超导体为例，计算了结的电导和dN中准粒子局域态密度(LDOS)的空间变化，得到了dN中电阻、无功能量和绝缘势垒透明度的函数.得到的电导谱具有零偏置电导峰(ZBCP)，LDOS具有零能峰(ZEP)，但确保数学{α}=确保数学{pi}/2$$(0\ensuremath{\leqslant}\ensuremath{\alpha}\ensuremath{\leqslant}\ensuremath{\pi}∕2)$，除外，其中，确保数学{α}表示$p$波对电势的波瓣方向与界面法线之间的角度。ZBCP和ZEP的宽度随着{R}{d}$的增加而减小，而高度则显著增加。这些峰值被发现通过施加磁场而被抑制。当值${R}_{d}/{R}_{0}$足够大时，结的总零电压电阻几乎与$\ensuremath{\alpha}\ensuremath{\ne}\ensuremath{\pi}∕2$.的${R}_{d}$无关最极端的情况是$\EnsureMath{\Alpha}=0$，其中总零电压电阻始终为${R}_{0}/2$。我们还研究了{p}_{x}+i{p}_{y}波结中的电荷输运，其中只有垂直注入的准粒子才能感觉到火星。即使在这种情况下，在DN中产生的LDOS也具有ZEP。因此，在DN区的LDOS中ZEP的存在对于DN/TS结来说是一个显着的特征，这对于MARS和邻近效应相互竞争的DN/单重态超导体结来说是从来没有预料到的。在此基础上，提出了一种基于隧穿实验的识别三重态配对超导体的测试方法。
Enhanced proximity effect by the midgap Andreev resonant state (MARS) in a diffusive normal-metal/insulator/triplet superconductor (DN/TS) junction is studied based on the Keldysh-Nambu quasiclassical Green's-function formalism. By choosing a $p$-wave superconductor as a typical example of the TS, conductance of the junction and the spatial variation of the quasiparticle local density of states (LDOS) in the DN are calculated as the function of the magnitudes of the resistance ${R}_{d}$, Thouless energy in the DN, and the transparency of the insulating barrier. The resulting conductance spectrum has a zero-bias conductance peak (ZBCP) and the LDOS has a zero energy peak (ZEP) except for $\ensuremath{\alpha}=\ensuremath{\pi}∕2$ $(0\ensuremath{\leqslant}\ensuremath{\alpha}\ensuremath{\leqslant}\ensuremath{\pi}∕2)$, where $\ensuremath{\alpha}$ denotes the angle between the lobe direction of the $p$-wave pair potential and the normal to the interface. The widths of the ZBCP and the ZEP are reduced with the increase of ${R}_{d}$ while their heights are drastically enhanced. These peaks are revealed to be suppressed by applying a magnetic field. When the magnitude of ${R}_{d}∕{R}_{0}$ is sufficiently large, the total zero voltage resistance of the junction is almost independent of the ${R}_{d}$ for $\ensuremath{\alpha}\ensuremath{\ne}\ensuremath{\pi}∕2$. The extreme case is $\ensuremath{\alpha}=0$, where total zero voltage resistance is always ${R}_{0}∕2$. We also studied the charge transport in ${p}_{x}+i{p}_{y}$-wave junctions, where only the quasiparticles with perpendicular injection feel the MARS. Even in this case, the resulting LDOS in the DN has a ZEP. Thus the existence of the ZEP in the LDOS of the DN region is a remarkable feature for DN/TS junctions which have never been expected for the DN/singlet superconductor junctions where the MARS and proximity effect compete with each other. Based on these results, a crucial test to identify triplet pairing superconductors based on tunneling experiments is proposed.