Directional Photocurrent Generated by Quantum Interference Control

Abstract

Although the absorption of light in a bulk homogeneous semiconductor produces photocarriers with non-zero momentum, it generally does not produce a current in the absence of an applied electric field because equal amounts of carriers with opposite momentum are injected. The interference of absorption processes, for example, between one-photon and two-photon absorption, can produce a current because constructive interference for carriers with one momentum can correspond to destructive interference for carriers with the opposite momentum. We show that for the interference between two-photon and three-photon absorption, the current has a narrower angular spread, i.e., a ``beam'' of electrons in a specified direction is produced in the semiconductor.

Figures (4)

• Figure 1: Conceptual diagrams of QuIC processes in semiconductors. In QuIC, the carriers injected into the conduction band are imbalanced in k-space. For the correct phase, the process is constructive for one direction in k-space, but destructive in the opposite direction. The (a) 1+2 QuIC and (b) 2+3 QuIC processes have the same transition energy. The calculated carrier distributions are projected to the virtual plane, shown as rings. The carrier distributions are maximum along the polarization direction ($\bm{k}_p$).
• Figure 2: Conceptual experimental apparatus. (a) The experimental setup for 1+2 QuIC. (b) The experimental setup for 2+3 QuIC. (c) image of the sample showing the two sets of orthogonal electrodes. The $\bm{x}$ and $\bm{y}$ directions as well as the polarization direction, $\bm{p}$, are labeled.
• Figure 3: Co-linearly polarized results. Polar plots of the photocurrent produced by (a) 1+2 QuIC and (b) by 2+3 QuIC as a function of the angle between the polarization direction and the x-direction, The dashed line is the experimental result for the electrodes in the x-direction while the dotted line is the result for the electrodes in the y-direction, the shaded region indicates the experimentally estimated uncertainty, and the solid line is theory for the y-oriented electrodes. Red indicates a positive signal and purple indicates a negative signal. (c) calculated QuIC current injection rate ($\eta$) as function of angle in the k-space for both 1+2 and 2+3 QuIC. $\theta_k$ is the angle between a direction in the k-space and the polarization of co-linearly-polarized two-color field. The relative phase between the two colors ($\Delta\phi$) is adjusted to be $\pi/2$ for both 1+2 QuIC and 2+3 QuIC.
• Figure 4: Non-colinear polarization dependencies. (a) & (b) The non-colinear polarization dependencies of the 1+2 QuIC current and (c) & (d) the 2+3 QuIC current. The red dashed lines and black dashed lines are the average QuIC currents collected by the x-direction and y-direction electrodes, respectively. The shaded areas represent the measurement uncertainty. The solid lines are the theory results In all plots the non-rotating polarization is in the x-direction. In (a), the polarization of 520 nm light is rotated. 1+2 QuIC has a one-fold symmetry with respect to the angle of the 520 nm polarization. In (b), the polarization of 1040 nm light is rotated. 1+2 QUIC has a two-fold symmetry with respect to the angle of the 1040 nm polarization. In (c), the polarization of 1040 nm light is rotated. 2+3 QUIC has a two-fold symmetry with respect to the angle of the 1040 nm polarization. In (d), the polarization of 1560 nm light is rotated. 2+3 QUIC has a one-fold symmetry with respect to the angle of the 1560 nm polarization.