Tuesday, January 29th: Ultrafast Optical Control of Quantum Materials

Event Date: 

Tuesday, January 29, 2019 - 3:45pm

Event Date Details: 

Refreshments served at 3:30pm.

Event Location: 

  • Broida 1640
  • Physics Department Colloquium

A primary goal of modern condensed matter physics is to discover novel phases of quantum matter and control their properties. Although many approaches using material synthesis or static electromagnetic fields have been used at thermal equilibrium, there exists a vast unexplored phase space and associated symmetries at non-equilibrium. In this talk, I will discuss how we use light pulses to manipulate the space-time symmetries in materials out of equilibrium and discover new quantum phenomena that were previously inaccessible. First, I will show how breaking time-reversal symmetry with light enables us to lift the pseudospin degeneracy in monolayer WS2 and selectively tune their energy levels. Here we can completely disentangle the fundamental light-matter interaction into two previously inseparable quantum processes known as the optical Stark effect and the Bloch-Siegert shift. Second, I will show how manipulating inversion symmetry with light allows us to induce topological phase transitions in the Weyl semimetal WTe2 through strain-tuning of the lattice. The induced atomic displacements were crystallographically measured using relativistic electron diffraction at sub-picometer length scale and sub-picosecond time scale. These results offer nonequilibrium pathways for designing exotic quantum systems with tunable properties towards terahertz electronics, quantum information, and energy conversion technologies.

Edbert Sie, Stanford University