My group utilizes a suite of spectroscopic tools such as angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), synchrotron light sources around the world, controlled nanoscale growth techniques and ab-initio simulations to create, manipulate and study the electronic and magnetic structure, topological order, and phase transitions in quantum materials systems, such as high-temperature superconductors, topological insulators, topological magnets, topological superconductors, and quantum spin-liquids. We are developing unique instrumentation in our laboratory, including laser-ARPES, and ultrafast pump-probe THz and sub-atomic resolution vector-field STM-MBE-ARPES.
In 2008, my group discovered topological order in a three-dimensional bulk solid, BiSb, a semiconducting alloy. The unusual, topologically protected surface states were mapped using spin ARPES spectroscopic measurements. Our experimental demonstration of this first three-dimensional topological insulator has opened many new research opportunities in fundamental condensed matter physics and application-oriented sciences. In 2015, we discovered a new class of topological materials — Weyl semimetals. These materials have topologically protected low-energy excitations in the bulk, and these excitations behave like massless Weyl-fermions, which have a well-defined chirality and propagate with minimal energy dissipation. We have also made seminal contributions in the study of topological magnets, topological phase transitions and topological superconductors.
My group is currently working on applying our successful scientific approach, based on combining ab-initio theoretical calculations with spin-resolved and phase-sensitive spectroscopic and microscopic measurements, to identify novel magnetic and superconducting materials with quantum states whose underlying wavefunction is topologically non-trivial. This goal is a challenging and stimulating endeavor since ab-initio theory is currently known to be less predictive in magnetic and superconducting materials. Furthermore, my team is developing a time-resolved angle-resolved photoelectron spectroscopy technique operating in the terahertz range and at low temperatures. The goal is to couple this instrumentation to other techniques to have a very robust and comprehensive suite of experimental tools to create, probe, and control quantum properties in systems like topological magnets, Chern insulators, exotic superconductors, doped Mott insulators and quantum spin liquids.
Emergent Phenomena in Quantum Systems
Princeton University, Department of Physics