Fig. 11

Shift current. a, b Electron density in the [110] plane of GaAs at \(\Gamma\) point for a the highest valence band, and b the lowest conduction band. c–f Experimental observation of the shift current in the Weyl semimetal TaAs. c Setup scheme. The polarization is controlled via rotation of the quarter-wave plate (QWP). d False colored scanning electron microscopy (SEM) image of a microscopic TaAs (purple) device with gold (yellow) contacts. e Polarization dependence of the thermal (\(J^{a}_{\text {thermal}}\)) and shift (\(J^{a}_{\text {shift}}\)) photocurrent contributions. The radius and angle of the polar plot correspond to the magnitude of the photocurrents and the angle (\(\phi\)) the fast axis of QWP makes with the crystal a axis, respectively. These responses exhibit out-of-phase minima and maxima due to the different electric field combinations. f Measured power dependence of QWP angle-independent (D), fourfold shift (\(L_s\)), and photothermal (\(L_c\)) terms. The dependence is linear as expected from the generation mechanisms of the shift and photothermal current. Figures are reproduced with permission from a, b Ref. [202], Copyright 2006 American Physical Society; c–f Ref. [197], Copyright 2019 Springer Nature