The Physics & Astronomy Colloquium Series presents Matteo Mitrano of Harvard, discussing "Driven Quantum Materials under the X-ray Spotlight" on April 21.

Abstract: Ultrafast optical excitation, especially when resonant to specific lattice modes, has recently emerged as a powerful means to control and induce new functionalities in quantum materials. One of the most ambitious goals is to selectively drive structural or electronic degrees of freedom to bring about nonequilibrium superconductivity at temperatures far above the equilibrium critical temperature T _c . While this phenomenon has been observed in a variety of systems ranging from copper oxides to organic molecular metals, the microscopic physics of these dynamics is still largely unexplored. Novel ultrafast x-ray spectroscopic methods, such as time-resolved x-ray absorption (trXAS) and time-resolved resonant inelastic x-ray scattering (trRIXS), enable tackling this problem with unprecedented detail.

By focusing on the paradigmatic example of light-driven La _2-x Ba _x CuO ₄ , I will show how trRIXS provides access to the finite-momentum charge fluctuation spectrum of these transient phases [1,2,3]. I will then discuss how changes of the electronic structure translate into a modification of the finite-momentum spin fluctuation spectrum [4] and, finally, how the dynamics of the effective electronic interactions in the CuO ₂ plane can be accurately quantified via trXAS [5].

[1]        M. Mitrano, et al. , Sci. Adv. 5 , eaax3346 (2019).

[2]        M. Mitrano, et al. , Phys. Rev. B 100 , 205125 (2019).

[3]        M Mitrano & Y. Wang, Commun. Phys. 3 , 184 (2020).

[4]        Y. Wang, et al. , Commun. Phys. 4 , 212 (2021).

[5]        D. R. Baykusheva, et al., Phys. Rev. X 12 , 011013 (2022).