CPM Seminar

Probing and Controlling Quantum Materials with Light

Albert Liu

Brookhaven National Laboratory

Quantum materials, systems in which quantum effects lead to unique macroscopic phenomena with tremendous technological potential, comprise the forefront of condensed matter physics research. In recent years, developments in intense light sources at low (terahertz) frequencies now allow us to both probe and control quantum materials at their fundamental energy scales with light.

In the first part of my talk, we translate a technique known as 2-D spectroscopy, an optical analogue of multi-dimensional NMR spectroscopy, into the terahertz frequency range [1]. We apply this technique to the Josephson plasma resonance in La2-xSrxCuO4, a layered high-temperature superconductor, to distill the underlying plasmon correlations and reveal a disordered superconducting state [2]. We then measure this superconducting disorder at temperatures approaching the phase transition for the first time.

In the second part of my talk, I will describe how we use intense terahertz light fields to control quantum materials. I will present our recent experiment on the fluctuating ferromagnet YTiO3 [3], in which optical excitation of the crystal lattice allows us to selectively enhance or suppress ferromagnetic order. Most notably, a light-induced ferromagnetic state is observed at temperatures in excess of triple the equilibrium Curie temperature.

[1] Albert Liu, arXiV:2409.03719
[2] Albert Liu et al., Nat. Phys. (2024)
[3] Ankit Disa et al., Nature (2023)