Hour: From 15:00h to 16:00h
Place: SMR
SEMINAR: Ultrafast Spectroscopy of 3D-Topological Insulators by High-Order Harmonics
Junior Research Group Leader, Max Plank Research-Initiative Korea, MPK
We observe an anomalous strong-field optical response of the prototypical 3D topological insulator Bi2Se3, revealed through the process of high-harmonic generation driven by ultrashort mid-infrared fields. We find that the harmonic yield increases as the polarization of laser field is changed from linear to elliptical and it becomes maximum for a fully circular polarization.
With the aid of a microscopic quantum-mechanical theory, we reveal that the observed anomalous enhancement arises from the unique band structure of the gapless topological surface
states (TSSs). Our results bear implications for the ultrafast probing of topological phase transitions.
In the last decades, high-order harmonic generation (HHG) in gases established itself as a powerful tool for investigating electron structure and dynamics. Ghimire et al expanded the HHG process from gases to condensed matter systems. Surprisingly, one of the main features of HHG, the high-energy cut-off exhibits a linear scaling with respect to the laser-field strength in solids, while in gases, this scaling is quadratic. Microscopically, HHG in solids entails a plethora of interesting dynamical phenomena occurring at the attosecond time scale, such as inter-band electron tunneling, Bloch oscillations, and electron-hole (e-h) quasiparticle dynamics.
In this work, we extend the scope of HHG to a distinctly different class of matter, namely, topological materials. Our measurements on the prototypical topological insulator Bi2Se3 reveal an anomalous laser-ellipticity dependence of the high-harmonic generation process, manifested in a substantial enhancement of selected high-harmonic (H) orders for circularly polarized laser fields. We attribute the latter results to the nontrivial topology of the surface Bloch bands and states, in particular the dipole couplings and Berry connections close to the -point of the Brillouin zone and the influence of the high-order “warping” terms at higher momenta [4]. Our interpretation is supported by a fully quantum-mechanical treatment of the HHG process in the framework of the semiconductor Bloch equations formalism.
Hour: From 15:00h to 16:00h
Place: SMR
SEMINAR: Ultrafast Spectroscopy of 3D-Topological Insulators by High-Order Harmonics
Junior Research Group Leader, Max Plank Research-Initiative Korea, MPK
We observe an anomalous strong-field optical response of the prototypical 3D topological insulator Bi2Se3, revealed through the process of high-harmonic generation driven by ultrashort mid-infrared fields. We find that the harmonic yield increases as the polarization of laser field is changed from linear to elliptical and it becomes maximum for a fully circular polarization.
With the aid of a microscopic quantum-mechanical theory, we reveal that the observed anomalous enhancement arises from the unique band structure of the gapless topological surface
states (TSSs). Our results bear implications for the ultrafast probing of topological phase transitions.
In the last decades, high-order harmonic generation (HHG) in gases established itself as a powerful tool for investigating electron structure and dynamics. Ghimire et al expanded the HHG process from gases to condensed matter systems. Surprisingly, one of the main features of HHG, the high-energy cut-off exhibits a linear scaling with respect to the laser-field strength in solids, while in gases, this scaling is quadratic. Microscopically, HHG in solids entails a plethora of interesting dynamical phenomena occurring at the attosecond time scale, such as inter-band electron tunneling, Bloch oscillations, and electron-hole (e-h) quasiparticle dynamics.
In this work, we extend the scope of HHG to a distinctly different class of matter, namely, topological materials. Our measurements on the prototypical topological insulator Bi2Se3 reveal an anomalous laser-ellipticity dependence of the high-harmonic generation process, manifested in a substantial enhancement of selected high-harmonic (H) orders for circularly polarized laser fields. We attribute the latter results to the nontrivial topology of the surface Bloch bands and states, in particular the dipole couplings and Berry connections close to the -point of the Brillouin zone and the influence of the high-order “warping” terms at higher momenta [4]. Our interpretation is supported by a fully quantum-mechanical treatment of the HHG process in the framework of the semiconductor Bloch equations formalism.