Research Seminars @ Illinois

Quantum materials exhibit emergent phenomena driven by interactions, topology, and dimensionality. My group develops techniques for integrating microstructured quantum materials and heterostructures into on-chip optoelectronic devices, enabling both the manipulation and direct probing of their low-energy electrodynamics on femtosecond timescales and terahertz (THz) frequencies.

In the first part of my talk, I will show how femtosecond laser pulses can drive materials into topological states absent in equilibrium [1]. Probing time-resolved transport in graphene and T_d-MoTe₂, we observed light-induced Hall responses and rectified photocurrents that defy the standard laws of nonlinear optics, revealing photon-dressed, or “Floquet,” anomalous Hall and Weyl states [2,3]. These results demonstrate how strong-field light–matter coupling can transiently reshape a material’s band topology, generating effective magnetic fields of tens of tesla through the Berry curvature of driven (“Floquet-Bloch”) electronic bands.

 In the second part, I will explore whether comparable coupling effects can be achieved without strong laser fields by embedding materials in resonant cavities. This approach opens a pathway toward modifying ground states through their interaction with the vacuum field [4]. As a first step in this direction, we find that the graphite gates routinely used in van der Waals heterostructures naturally act as THz plasmonic self-cavities. Using on-chip THz spectroscopy, we observe ultrastrong coupling between these cavity modes and plasmons in graphene, establishing a key prerequisite for cavity-based control [5]. These techniques also provide a powerful means to sense the low-energy electrodynamics of correlated and topological phases that emerge on the THz (meV) energy scale in two-dimensional materials, offering new insight into their underlying microscopic interactions [6].

Together, these studies establish an integrated platform for exploring quantum matter through THz light–matter interaction.

 References: 
[1] Colloquium: Nonthermal pathways to ultrafast control in quantum materials
 A. de la Torre, D.M. Kennes, M. Claassen, S. Gerber, J.W. McIver & M.A. Sentef
Reviews of Modern Physics 93, 041002 (2021)

 [2] Light-induced anomalous Hall effect in graphene
 J.W. McIver, B. Schulte, F.-U. Stein, T. Matsuyama, G. Jotzu, G. Meier & A. Cavalleri
Nature Physics 16, 38-41 (2020) 

 [3] Nonperturbative Nonlinear Transport in a Floquet-Weyl Semimetal
 M.W. Day et al.  
arXiv:2409.04531 

[4] Cavity quantum materials
F. Schlawin, D.M. Kennes & M.A. Sentef
Appl. Phys. Rev. 9, 011312 (2022)

[5] Cavity electrodynamics of van der Waals heterostructures
G. Kipp*, H.M. Bretscher* et al.  
Nature Physics (2025)

 [6] Resolving self-cavity effects in two-dimensional quantum material
M.H. Michael et al. 
arXiv:2505.12799