Abstract
A grand challenge underlies the entire field of topology-enabled quantum logic and information science: how to establish topological control principles driven by quantum coherence and understand the time-dependence of such periodic driving? Here we demonstrate a THz pulse-induced phase transition in Dirac materials that is periodically driven by vibrational coherence due to excitation of the lowest Raman-active mode. Above a critical field threshold, there emerges a long-lived metastable phase with unique Raman coherent phonon-assisted switching dynamics, absent for optical pumping. The switching also manifest itself by non-thermal spectral shape, relaxation slowing down near the Lifshitz transition where the critical Dirac point (DP) occurs, and diminishing signals at the same temperature that the Berry curvature induced Anomalous Hall Effect varnishes. These results, together with first-principles modeling, identify a mode-selective Raman coupling that drives the system from strong to weak topological insulators, STI to WTI, with a Dirac semimetal phase established at a critical atomic displacement controlled by the phonon pumping. Harnessing of vibrational coherence can be extended to steer symmetry-breaking transitions, i.e., Dirac to Weyl ones, with implications on THz topological quantum gate and error correction applications.
Highlights
Dynamic driving by periodic lattice vibrations represents a powerful approach to manipulate topological band structures, in stark contrast to equilibrium tuning methods, e.g., temperature, chemical substitution, and static strain, electric, or magnetic fields [1,2]
We provide evidence for a distinct topology switching driven by THz Raman phonon coherence in a Dirac semimetal
Note that our observed slow decay is consistent with similar “tens of” for clarity of ps lifetimes reported in carrier-density-tuned topological insulators [30] and should be distinguished from the dynamic slowing mechanism in symmetry-breaking phase transitions [31]
Summary
Dynamic driving by periodic lattice vibrations represents a powerful approach to manipulate topological band structures, in stark contrast to equilibrium tuning methods, e.g., temperature, chemical substitution, and static strain, electric, or magnetic fields [1,2]. Coherent excitation of the A1g phonon is expected to create a periodically driven state via lattice vibrations that modulate the topological bands and switch from STI [top, Fig. 1(a)] to Dirac semimetal (middle) to WTI (bottom) phases. Dephasing of this topological coherent state via Dirac fermion-phonon interaction leads to the conversion of Raman phonon coherence into population, i.e., into finite atomic displacement associated with the establishment of a final state with highly nonthermal characteristics. Harnessing the driven coherence of tailored phonon modes with an intense near-single-cycle THz pulse may become a universal principle for steering topological phase transitions
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
