Theory of enhanced proximity effect by mid gap Andreev resonant state in diffusive normal metal / triplet superconductor junctions

摘要

Enhanced proximity effect by mid gap Andreev resonant state (MARS) in adiffusive normal metal / insulator / triplet superconductor (DN/TS) junction isstudied based on the Keldysh-Nambu quasiclassical Green's function formalism.By choosing a p-wave superconductor as a typical example of TS, conductance ofthe junction and the spatial variation of quasiparticle local density of states(LDOS) in DN are calculated as the function of the magnitudes of the resistance$R_{d}$, Thouless energy in DN and the transparency of the insulating barrier.The resulting conductance spectrum has a zero bias conductance peak (ZBCP) andLDOS has a zero energy peak (ZEP) except for $\alpha = \pi/2$ $(0 \leq \alpha\leq \pi/2)$, where $\alpha$ denotes the angle between the lobe direction ofthe p-wave pair potential to the normal to the interface. These peaks arerevealed 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 thejunction is almost independent of the $R_{d}$ for $\alpha \neq \pi/2$. Theextreme case is $\alpha=0$, where total zero voltage resistance is always$R_{0}/2$. Based on these results, a crucial test to identify triplet pairingsuperconductors based on tunneling experiments is proposed.