All-optical coherent control of electrical currents in centrosymmetric semiconductors

Abstract

The absorption of phase-related near-infrared fundamental ͑ , 0.7 eVഛប ഛ 0.9 eV͒ and second harmonic ͑2͒ pulses of 150 fs duration results in ballistic electrical currents in clean bulk germanium and silicon at room temperature. The ultrafast charge motion is directly monitored via a time-resolved analysis of the emitted bursts of terahertz radiation. The current generation process relies on a third-order optical nonlinearity with a current injection efficiency only slightly reduced compared to the established current injection in direct-gap semiconductors such as GaAs. In the present case, current injection takes place across the direct band gap of germanium, whereas it involves indirect optical transitions in silicon. The vector direction of the current is defined by the polarization of the two-color pump field and the relative phase ⌬⌽ =2⌽ − ⌽ 2. Microscopically, current injection can be understood as arising from the quantum interference of one-and two-photon absorption processes. In the case of silicon, these indirect optical transitions may involve different types of phonons and can occur via numerous pathways. We therefore propose a model based on third-order perturbation theory which qualitatively explains why a current injection can occur across an indirect band gap.

Strong-Field Resonant Dynamics in Semiconductors

“…This regime is not specific to GaAs, and similar dynamics can be driven and controlled using broadband optical waveforms (light transients). The predicted effects are experimentally observable: the asymmetric momentum distribution can be directly observed using angular resolved photoemission spectroscopy (ARPES) [29][30][31][32] , and the residual current can be detected through accompanying terahertz radiation 33,34 . Our findings add resonant processes to the toolkit of petahertz solid-state technology where potential applications may range from CEP detection 35 to sub-laser-cycle spectroscopy 36 and ultrafast signal processing 6 .…”

Optical injection and control in germanium: Thirty-bandk⋅ptheory

“…18-20͒ and Ge. 21 By taking advantage of spin-orbit splitting in the valence bands, spinpolarized and pure spin currents have been injected in GaAs. [22][23][24][25] While a recent experiment reports the detection of optically injected pure spin current in Ge, 3 that semiconductor has been the subject of many fewer studies than GaAs.…”

Microscopic analysis of charge and spin photocurrents injected by circularly polarized one-color laser pulses in GaAs quantum wells

“…The two-color current generation process uses the interference of one-and two-photon excitations, and is a third-order nonlinear optical process that does not rely on the material symmetry or details of the band structure. [2][3][4]7,[12][13][14][15][16][17]20,25,26,[28][29][30] One-color injection currents however arise from a spin splitting of the energy bands in systems of reduced symmetry and are of second order in the light field, i.e., the currents are proportional to the light intensity. Since this current is maximal for circularly polarized excitation, it is referred to as circular photogalvanic effect.…”