Aitana Tarazaga Martin-Luengo

arXiv2026

Disentangling pre-transitional fluctuations in metallic VO2

VO2 features concomitant structural and metal-insulator transitions. This poses a challenge for understanding the underlying mechanism: is the transition triggered by a structural or by an electronic instability? The two scenarios are expected to produce very different pre-transitional fluctuations above TC. By combining magnetic susceptibility, IR reflectivity and X-ray diffuse scattering measurements, we observe that metallic VO2 features strong electronic and structural fluctuations towards the insulating monoclinic phase. By measuring resonant diffuse X-ray scattering across the Vanadium K-edge, we search for a potential decoupling between electronic and structural ordering in these fluctuations, finding no evidence of it. While our results do not completely rule out pure electronic fluctuations, they constrain them, favoring the interpretation that the VO2 metal-insulator transition is triggered by a structural instability. Our work offers a novel approach to solve similar problems in other strongly correlated systems.

cond-mat.str-el↗

arXiv2024

Canalization-based super-resolution imaging using a single van der Waals layer

Canalization is an optical phenomenon that enables unidirectional propagation of light in a natural way, i.e., without the need for predefined waveguiding designs. Predicted years ago, it was recently demonstrated using highly confined phonon polaritons (PhPs) in twisted layers of the van der Waals (vdW) crystal alpha-MoO3, offering unprecedented possibilities for controlling light-matter interactions at the nanoscale. However, despite this finding, applications based on polariton canalization have remained elusive so far, which can be explained by the complex sample fabrication of twisted stacks. In this work, we introduce a novel canalization phenomenon, arising in a single vdW thin layer (alpha-MoO3) when it is interfaced with a substrate exhibiting a given negative permittivity, that allows us to demonstrate a proof-of-concept application based on polariton canalization: super-resolution (up to ~λ0/220) nanoimaging. Importantly, we find that canalization-based imaging transcends conventional projection constraints, allowing the super-resolution images to be obtained at any desired location in the image plane. This versatility stems from the synergetic manipulation of three distinct parameters: incident frequency, rotation angle of the thin vdW layer, and thickness. These results provide valuable insights into the fundamental properties of canalization and constitute a seminal step towards multifaceted photonic applications, encompassing imaging, data transmission, and ultra-compact photonic integration.

physics.optics↗