Our primary interest is in the physics of strongly-correlated electron systems, a broad-brush term to describe materials from iron-and copper based superconductors, to so-called "heavy" fermion systems to 4d and 5d transition metal oxides. These materials are characterized by electron-electron interactions so strong as to invalidate a picture wherein constituent quasiparticles can be considered non-interacting entities within a mean field of their cohorts. They are the primary hosts of emergent phenomena - the collective behavior of the many constituent charges and spins conspire to create a macroscopic quantum ground state. Our goal is to understand, at a microscopic level, how emergent behavior arises using the cutting-edge tools of modern nonlinear and ultrafast optical spectroscopy.
Quantum Criticality and Proximate Phases
One of the hallmarks of strongly correlated physics is the presence of unconventional superconductivity. The most famous example is high temperature superconductivity in the copper and iron-based materials. In our current understanding, unconventional superconductivity is the result of quantum critical fluctuations emanating from a quantum critical point (QCP), a locus on the material's phase diagram where a phase transition, e.g., antiferromagnetism or charge density wave ordering, has been tuned to 0 K by an external parameter such as chemical doping or pressure. At the QCP, the fluctuations of the interrupted order modify electron-electron interactions and induce the emergent superconducting phase.
However, detection of quantum critical points and their fluctuations as well as classification of quantum critical universality classes are longstanding issues, leaving the matter of how proximate phases interact a critical, yet unanswered, question. One of our primary goals is to leverage the techniques of nonlinear and ultrafast spectroscopies to disentangle the relationships between these proximate phases and examine the role that fluctuating order plays in driving emergent phenomena.
Ultrafast Spectroscopic Development and Photonics
Nonlinear optical and ultrafast methods have long been a cornerstone in studying complex chemical events, but their application to strongly correlated matter is in a comparatively nascent stage. We are adapting existing metrologies from the world of chemistry to the examination of strongly correlated electron systems along with developing entirely novel spectroscopic tools suited for strongly correlated materials. We are also interested in the manipulation of light to create fields with exotic properties, such as twisted photons and accelerating electromagnetic waves, with the goal of studying their interaction with condensed phase systems.