Monitoring in real time the photon-dressing and undressing of quasiparticles from first principles time-resolved photoelectron spectroscopy

摘要

Optical pumping of solids creates a non-equilibrium electronic structurewhere electrons and photons combine to form quasiparticles of dressedelectronic states. The resulting shift of electronic levels is known as theoptical Stark effect, visible as a red shift in the optical spectrum. Here weshow that in a pump-probe setup we can uniquely define a non-equilibriumquasiparticle bandstructure that can be directly measurable with photo-electronspectroscopy. The dynamical photon-dressing (and undressing) of the many-bodyelectronic states can be monitored by pump-probe time and angular resolvedphotoelectron spectroscopy (tr-ARPES) as the photon-dressed bandstructureevolves in time depending on the pump-probe pulse overlap. The computedtr-ARPES spectrum agrees perfectly with the quasi-energy spectrum of Floquettheory at maximum overlap and goes to the the equilibrium bandstructure as thepump-probe overlap goes to zero. Additionally, we show how this time-dependentnon-equilibrium quasiparticle structure can be understood to be thebandstructure underlying the optical Stark effect. The extension tospin-resolved PES can be used to predict asymmetric dichroic response linked tothe valley selective optical excitations in monolayer transition metaldichalcogenides (TMDs).