Abstract
The direct measurement of Berry phases is still a great challenge in condensed matter systems. The bottleneck has been the ability to adiabatically drive an electron coherently across a large portion of the Brillouin zone in a solid where the scattering is strong and complicated. We break through this bottleneck and show that high-order sideband generation (HSG) in semiconductors is intimately affected by Berry phases. Electron-hole recollisions and HSG occur when a near-band gap laser beam excites a semiconductor that is driven by sufficiently strong terahertz (THz)-frequency electric fields. We carried out experimental and theoretical studies of HSG from three GaAs/AlGaAs quantum wells. The observed HSG spectra contain sidebands up to the 90th order, to our knowledge the highest-order optical nonlinearity observed in solids. The highest-order sidebands are associated with electron-hole pairs driven coherently across roughly 10% of the Brillouin zone around the \Gamma point. The principal experimental claim is a dynamical birefringence: the sidebands, when the order is high enough (> 20), are usually stronger when the exciting near-infrared (NIR) and the THz electric fields are polarized perpendicular than parallel; the sideband intensities depend on the angles between the THz field and the crystal axes in samples with sufficiently weak quenched disorder; and the sidebands exhibit significant ellipticity that increases with increasing sideband order, despite nearly linear excitation and driving fields. We explain dynamical birefringence by generalizing the three-step model for high order harmonic generation. The hole accumulates Berry phases due to variation of its internal state as the quasi-momentum changes under the THz field. Dynamical birefringence arises from quantum interference between time-reversed pairs of electron-hole recollision pathways.
Highlights
When parameters in a quantum system change adiabatically, the quantum states of the system accumulate both dynamic and Berry phases [1]
High-order sideband generation experiments are performed on three samples with different degrees of quantum confinement and disorder
The large number of sidebands observed in the HSG spectra we report here enable systematic testing of a threestep model of high-order sideband generation
Summary
When parameters in a quantum system change adiabatically, the quantum states of the system accumulate both dynamic and Berry phases [1]. Berry phases are of fundamental importance in many branches of physics, such as quantum field theories [2], optics [3], ultracold atoms [4], quantum computing [5], and condensed-matter physics [6,7]. There has been recent progress in ultracold atoms [11,12,13] and optical systems [14], Berry curvature has largely resisted direct experimental measurement in solids [15,16] because it is difficult to coherently and adiabatically drive an electron across a large portion of the Brillouin zone without the quantum pathway being destroyed by scattering
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
