A long standing question in topologic matter remains: how to protect Dirac fermions from “topological breakdown” due to surface-bulk coupling that results in their strong scattering from bulk phonons, carriers and impurities not protected by “spontaneous” symmetry. Here we demonstrate a terahertz (THz) phonon driven coherence mechanism which suppresses the dissipative surface-bulk coupling channel.
This provides compelling evidence that coherently driven states can protect and enhance the stability of quantum systems. An analogy of such dynamic stabilization is the periodically driven Kapitza pendulum where an inverted, yet stable, orientation can be achieved by imposing a sufficiently high frequency vibration of its pivot point. In a similar manner, additional dynamic stabilization can be achieved by driving a THz field that exceeds a threshold lattice vibration. This complements and enhances the spontaneous symmetry protection mechanism at the surface.
Applying this approach to topological insulator Bi2Se3, coherent lattice vibrations are shown to have direct and profound effects on surface transport, via periodic modulation of electronic states. Imposing vibrational coherence into topological states of matter may become a universal light control principle for reinforcing the protected quantum transport. Addressing this cross-cutting issue has far reaching consequences to many scientific and technological disciplines, such as disorder-tolerant quantum information and communications applications and spin-based, lightwave quantum electronics.
X. Yang, L. Luo, C. Vaswani, X. Zhao, Y. Yao, D. Cheng, Z. Liu, R. H. J. Kim, X. Liu, M. Dobrowolska, J. K. Furdyna, I. E. Perakis, C.-Z. Wang, K.-M. Ho and J. Wang, “Light Control of Surface–Bulk Coupling by Terahertz Vibrational Coherence in a Topological Insulator”, npj Quantum Materials, 5:13, (2020). https://doi.org/10.1038/s41535-020-0215-7