Light-induced Andreev phase coherence and tunneling Hall effect in semi-Dirac systems

Abstract

We theoretically investigate the charge transport in a normal metal/normal metal/superconductor junction based on semi-Dirac materials. It is shown that off-resonant circularly polarized light applied to the central normal region induces an additional phase for the backreflected states. This light-induced phase depends on the electron's transverse momenta and becomes coherent via multiple reflections, leading to a transversely asymmetric Andreev reflection, which in turn produces a tunneling Hall effect. Both the longitudinal and transverse conductances are obtained within the nonequilibrium Green's function formalism. While the longitudinal conductance is insensitive to the light handedness and only acquires a finite phase shift with varying intensity, the transverse conductance reverses sign upon switching the handedness, indicating the reversal of the tunneling Hall current. Our results establish a phase-coherence mechanism for generating tunneling Hall currents in superconducting tunnel junctions, suggesting potential applications in superconducting electronics.

Figures (6)

• Figure 1: (a) Schematic illustrations of the honeycomb lattice and the first Brillouin zone. (b) Schematic of a light-irradiated tunnel junction. The central normal region ($0<x<L$) is irradiated by the off-resonant circularly polarized light (CPL). The superconducting region (S) occupies $x>L$, while the left normal lead (N) occupies $x<0$. The width of the junction is $W$.
• Figure 2: $|a_A|^2$ vs $k_y$ for the central normal region irradiated by the right-handed circularly polarized light (blue), left-handed circularly polarized light (red), in the absence of the irradiated light (black), and at zero bias (green). The arrow marks the curves for the illumination parameter $\lambda$ varying from $30$ to $60$ in increments of $10$ (in units of $\Delta\cdot a$). The incident energy is set as $eV=0.8\Delta$ (black) and $eV=0.95\Delta$ (blue and red). The other parameters are $\mu_L=10\Delta$, $\mu_C=4\Delta$, $\mu_S=100\Delta$, $L=20a$, and $W=10000a$.
• Figure 3: Multiple-reflection processes in the central region of the junction: no normal reflections at the left boundary (left) versus two normal reflections at the left boundary (right). The solid and dashed lines denote electron and hole states, respectively.
• Figure 4: $G$ as a function $eV$ (a) and as a function of $\mu_C$ (b). Parameters are $\mu_C=40\Delta$ in (a) and $eV=0.5\Delta$ in (b). Other parameters are the same as in Fig. \ref{['fig:ar']}.
• Figure 5: $G_T$ as a function $eV$ (a) and as a function of $\mu_C$ (b). Parameters are $\mu_C=45\Delta$ in (a) and $eV=0.8\Delta$ in (b). Other parameters are the same as in Fig. \ref{['fig:ar']}.