Fig. 10
Injection current. a Scheme of injection current via interband absorption involving different polarization component \(\varvec{E}_h\) (horizontal) and \(\varvec{E}_v\) (vertical). b The injection current from a single Weyl cone depends on its chirality and tilt. c, d Injection currents in Weyl semimetals. Each Weyl node produces an injection current with chirality-independent (\(\varvec{J}_0\)) and chirality-dependent (\(\varvec{J}_\chi\)) components. c Inversion symmetry relates two Weyl nodes with opposite tilt and opposite chirality, leading to the cancellation of photocurrents. IC: the inversion center. d Time-reversal symmetry relates two Weyl nodes with opposite tilt but the same chirality. Two pairs of Weyl nodes give rise to an overall injection current \(2(\varvec{J}_\chi - \varvec{J}'_\chi )\). TRIM: the time-reversal invariant momentum. e–g Experimental observation of the injection current in the Weyl semimetal TaAs. e Setup scheme. f A photograph of the sample. \(\varvec{a}, \varvec{b}, \varvec{c}\) denote the crystal axes. Scale bar: \({300}{\mu \hbox {m}}\). g Polarization-dependent photocurrents at \(T={10}{\hbox {K}}\) measured along the \(\varvec{b}\) direction with the laser focused on the pink, black and blue dots in f. Figures are reproduced with permission from c, d Ref. [188], Copyright 2017 American Physical Society; e–g Ref. [186], Copyright 2017 Springer Nature