Laser-induced phase transitions in correlated insulators

     Phase diagrams of materials are usually constructed by ramping a set of time-independent control parameters, such as electric/magnetic fields, doping, temperature, pressure, etc. The long-range orders appearing in such phase diagrams place the system at the free energy minima in thermal equilibrium. Over the past decades, scientists become increasingly curious about quantum orders that would emerge along a dynamical (time-varying) tuning knob. Light radiation is a natural candidate due to the oscillative nature of their fields in time. It has been predicted that illuminating materials by light can induce a diverse range of exotic behaviors, manifesting as unusual phases that would otherwise be inaccessible in the equilibrium.
  The advent of intense ultrafast lasers is providing experimentalists with an ideal tool to investigate the feasibility of these proposals. With these instruments, high intensity light energy is concentrated in an ultrashort time duration and, upon being delivered to materials, selectively drives a particular degree of freedom of the material far away from equilibrium. Snapshots of subsequent time evolution can be filmed by stroboscopic systems arranged in the so-called pump-probe configuration.
  Our team focuses on two specific strategies within this grand picture of experimental pursuit. The first is how the excitation laser pulse could be properly tailored to impart the most desirable and most efficient modification to the material. The emphasis would be on the study of how microscopic Hamiltonians would be modified as light field renormalizes a targeted set of interaction parameters, which in turn leads the material to spontaneously reorganize to a new ground state. The second is transitioning into metastable phases of matter by impulsive stimulation. When laser drive occurs in a time duration shorter than the response time of microscopic degrees of freedom, the system would steered into motion in its free energy landscape, which could be trapped and settled in states that correspond to local, rather than global free energy minimum in the landscape.

 

Selected publications of our work in this area:

• Phys. Rev. Lett. 125, 167401 (2020).

• Phys. Rev. B. 106, 205118 (2022).

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