Lecture: Micro/Nano Electro Mechanical Systems (MEMS): EE | November 2 | 2-3 p.m. | 390 Hearst Memorial Mining Building
Prof. Aaron Lindenberg, Stanford Univ., Materials Science & Engineering
Manipulation of topological invariants in quantum materials plays a key role in topological switching applications and can stabilize emergent topological phases in otherwise trivial materials. Lattice strain has been proposed as one means of tuning these topological invariants. However, conventional means of applying strain are not extendable to controllable time-varying protocols. In particular, integration into a functional device requires the ability to go beyond these robust, topologically protected properties and discover ways to engineer and manipulate the topology of materials at high speeds.
In this talk I will describe femtosecond-resolution crystallographic measurements probing dynamical switching responses of the Weyl semimetal WTe2. We demonstrate that terahertz light pulses can be used to induce large amplitude interlayer shear oscillations with ~1% strain amplitudes, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements show that this transition is associated with a symmetry change from a non-centrosymmetric to centrosymmetric structure and therefore corresponds to a transition to a topologically trivial phase. We further show that such shear strain serves as an ultrafast, energy-efficient means to induce more robust, well-separated Weyl points or to annihilate all Weyl points of opposite chirality.
This work defines new possibilities for ultrafast manipulation of the topological properties in solids and for a topological switch operating at THz frequencies.