Speaker
Description
The electromagnetic vacuum is usually regarded as a passive background for condensed matter. Recent experiments, however, suggest that modifying the surrounding photonic environment can alter equilibrium properties of quantum materials even in the absence of external illumination. In this talk, I will discuss experiments on the molecular superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br [1], where covering the material with hexagonal boron nitride (hBN)produces a pronounced suppression of the superconducting superfluid density. The effect is associated with resonant coupling between hyperbolic phonon-polariton modes of hBN and infrared-active molecular vibrations of the superconductor, and is absent in non-resonant control heterostructures. Remarkably, the modification of superconductivity appears to extend far beyond the immediate interface. I will then introduce a theoretical framework for understanding how hyperbolic materials can mediate such long-range control [2]. When two anisotropic materials with overlapping hyperbolic frequency windows are combined, their polaritonic modes hybridize and reshape the electromagnetic vacuum throughout the heterostructure. This allows the magnitude, polarization and spatial distribution of vacuum fluctuations experienced by embedded matter to be controlled remotely by an adjacent layer. As an illustration, I will show how these modified vacuum fields can alter the effective interactions and critical temperature of an embedded two-dimensional superconductor. These results suggest a route beyond conventional cavity quantum materials, in which the electromagnetic environment is engineered directly inside a solid using van der Waals heterostructures and hyperbolic polaritons.
[1] Keren et al., Cavity-altered superconductivity, Nature 650, 864–868 (2026) [2] Feng et al., Engineering Vacuum Fluctuations in Hyperbolic Heterostructures, arXiv:2609.37182