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Selective scattering between Floquet-Bloch and Volkov states in a topological insulator (1512.05714v1)

Published 17 Dec 2015 in cond-mat.mes-hall

Abstract: The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter. The strong time periodic potential of intense laser light can be used to generate hybrid photon-electron states. Interaction of light with Bloch states leads to Floquet-Bloch states which are essential in realizing new photo-induced quantum phases. Similarly, dressing of free electron states near the surface of a solid generates Volkov states which are used to study non-linear optics in atoms and semiconductors. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use Time and Angle Resolved Photoemission Spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states in order to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.

Citations (282)

Summary

  • The paper presents a theoretical framework that models laser-driven Floquet-Bloch and Volkov states using an effective Hamiltonian and Peierls substitution.
  • The calculated Tr-ARPES signals showcase discrete Floquet sidebands with Bessel-function weights and reveal the influence of laser-assisted photoemission.
  • The study’s findings provide actionable insights for manipulating surface states in topological insulators via tailored light-matter interactions.

Selective Scattering between Floquet-Bloch and Volkov States in a Topological Insulator

The paper "Selective scattering between Floquet-Bloch and Volkov states in a topological insulator" presents a detailed theoretical investigation into the phenomena observed in time-resolved angle-resolved photoemission spectroscopy (Tr-ARPES) experiments on topological insulators. This paper explores the dynamics of surface states under the presence of a driving laser field, focusing on the formation and experimental implications of Floquet-Bloch and Volkov states and the effects of laser-assisted photoemission (LAPE).

Key Concepts and Methodologies

A central aspect of this paper is the description of the driven system using an effective Hamiltonian for the surface states of a three-dimensional topological insulator. By employing a Floquet formalism, the authors account for external driving effects using the Peierls substitution to incorporate a time-dependent gauge potential. The authors analyze the contributions of both Floquet-Bloch and Volkov states to the Tr-ARPES intensity and investigate the effects of spin-probe interactions and LAPE.

The methodology revolves around solving the equations of motion for two-time correlation functions under various experimental constraints. These calculations involve intricate matrix elements describing the system-probe coupling, which incorporate both spin-momentum locking and mirror symmetry considerations. The theoretical framework allows for the computation of Tr-ARPES signals under the influence of different polarization orientations for both the pump and probe beams.

Notable Numerical Findings and Claims

The paper reports that intrinsic Floquet sidebands appear at discrete frequencies characterized by their Bessel-function-weighted intensities. These results indicate the presence of Floquet-Bloch states robust under the conditions modeled. The influence of LAPE is quantitatively captured by the parameter α, which shifts these bands and interacts with the intrinsic Floquet peaks. The presence of spin-probe effects further modify these interactions by inducing asymmetries in the Tr-ARPES spectra.

The agreement between the theoretical predictions and the experimentally observed angular dependence of the sideband intensities implies a precise understanding of the laser-induced states. The derived intensity expressions match the experimental Tr-ARPES signals when considering both intrinsic effects and interaction parameters, such as α and β, indicating a comprehensive modeling approach.

Implications and Future Work

The results presented in this paper have significant implications for the understanding and manipulation of driven quantum states in topological insulators. The interaction between light and matter elucidated here offers pathways to customize material properties using external fields, potentially enabling novel electronic applications.

Future research may expand upon this foundation to explore more complex geometric configurations or stronger coupling regimes, which could provide further insights into the non-equilibrium properties of quantum systems. Additionally, experimental studies could extend these findings by varying pulse characteristics or introducing other topological materials into similar experimental frameworks.

Conclusion

This paper offers a rigorous and insightful analysis of the interactions between Floquet-Bloch and Volkov states in topological insulators, delivering a framework that successfully predicts and explains Tr-ARPES observations. Through sophisticated modeling and comprehensive analysis, this research enhances the theoretical understanding of dynamic quantum states in these materials and sets a precedent for further explorations in the field.