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Emergent phenomena in light-driven quantum materials
Emergent phenomena in light-driven quantum materials
Our lab applies non-linear optical and time-resolved photoemission spectroscopies to solve problems at the intersection of strongly correlated quantum materials and non-equilibrium phenomena. The principle goal is to use laser light to engineer electronic interactions in materials, probe their spatial and temporal correlations, and realize model Hamiltonians and novel phases of matter.
Typical experiments use a short (~ 100 fs) laser pulse to perturb a material, e.g., by coupling to charge or spin degrees of freedom, exciting specific collective modes, or modifying the local energy landscape over short (femtosecond) timescales. We then use custom-built spectroscopic tools (see Techniques) to examine the resulting evolution of electronic states, measure changes in low-energy electrodynamics, and disentangle coupled excitations.
See below for short descriptions of the main research directions.
Topologically nontrivial materials
Topologically nontrivial materials
Topological materials, from Weyl semimetals to magnetic topological insulators, have been a burgeoning area of quantum material research. Via techniques such as Floquet engineering, which involves driving a system with a strong periodic electric field, we can induce topological phase transitions. Recently, we demonstrated the role of magnetic disorder in an antiferromagnetic topological insulator MnBi₂Te₄ by using Floquet engineering to manipulate the Dirac mass gap.
Our research also delves into the nonlinear electrodynamics of these materials. We employ THz emission spectroscopy to examine the low-frequency photocurrents produced by ultrafast photoexcitation within these materials. These nonlinear photocurrents are sensitive probes of spin and charge order, Bloch wave functions' geometry, and broken symmetries of collective excitations.
Strongly correlated materials
Strongly correlated materials
Novel phases of matter that exhibit strongly correlated electron behaviors are among the most vigorously debated topics in physics. We investigate systems including Mott insulators, heavy fermion materials, and unconventional superconductors. We are particularly interested in cuprate superconductors, in which various coexisting and competing phases of matter demonstrate rich correlation physics. Our lab elucidates the nature of these electron-electron interactions using time- and angle-resolved photoemission spectroscopy (tr-ARPES) and two-electron photoemission spectroscopy (2e-ARPES).
Frustrated magnets and quantum spin liquids
Frustrated magnets and quantum spin liquids
We explore disordered magnetic states using THz spectroscopy. Frustrated magnets are materials in which localized magnetic moments interact through competing exchange interactions that cannot be simultaneously satisfied, causing a large degeneracy of the ground state. Quantum spin liquids are a disordered state where spins are strongly correlated but fluctuate at temperatures down to absolute zero.
Experimental detection of quantum spin liquids remains challenging because quantum spin liquids do not spontaneously break any lattice symmetries and no local order parameter exists to describe such a state. THz spectroscopy can be used to probe the excitations in the first Brillouin zone with zero momentum transfer, since the wavelength of THz radiation is much longer than the lattice constants.
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