arXiv subjects

Nitzan Hirshberg

Publications and source records attributed to Nitzan Hirshberg.

3 recordsLinked to original sources

arXiv2026

Quantitative infrared nanoscopy: Probe-cavity eigenmodes and nano-gap polaritons for strongly coupled nanoscale optics

Optical nanoscopies including near-field optical microscopy and spectroscopy circumvent the diffraction limit of conventional optics thanks to the nanoscale light focus emerging at the apex of a sharp irradiated probe. However, while strong optical coupling between the apex and its dielectric environment affords both enhanced nanoscopic measurement sensitivity and potentially ultra-strong fields within a nano-gap cavity, the conditions for this coupling remain poorly quantified by prevailing analytic models. Here we present a robust formalism of probe-cavity eigenmodes that fully describes how mutual near-field interactions between probe and environment produce a composite response to external fields qualitatively distinct from that of its distinct components. This "EigenProbe" model identifies the fundamental excitations of realistic optical nanoscopies as nano-gap polaritons, which provide an elegant basis to accurately predict near-field microscopy and spectroscopy experiments especially when probe-sample interactions are non-perturbative. Through comparison to carefully controlled nanoscopies of polar phonons and molecular vibrations alike, we show how nano-gap polaritons are both realized and utilized for reliable and rapid "inversion" of local optical constants. This advance demands both a careful understanding of the probe response through quantitative calibration, and our efficient semi-analytic description of cavity eigenmode scattering at the probe apex. Our EigenProbe formalism sets the stage for maturing diverse and proliferating optical nanoscopies into precision metrologies of nano-scale optical environments, and guides future use of nano-gap cavities to manipulate local excitations of quantum materials and to achieve strong coupling over photonic emitters.

physics.optics↗

arXiv2025

Machine Learning-Assisted Nano-imaging and Spectroscopy of Phase Coexistence in a Wide-Bandgap Semiconductor

Wide bandgap semiconductors with high room temperature mobilities are promising materials for high-power electronics. Stannate films provide wide bandgaps and optical transparency, although electron-phonon scattering can limit mobilities. In SrSnO3, epitaxial strain engineering stabilizes a high-mobility tetragonal phase at room temperature, resulting in a threefold increase in electron mobility among doped films. However, strain relaxation in thicker films leads to nanotextured coexistence of tetragonal and orthorhombic phases with unclear implications for optoelectronic performance. The observed nanoscale phase coexistence demands nano-spectroscopy to supply spatial resolution beyond conventional, diffraction-limited microscopy. With nano-infrared spectroscopy, we provide a comprehensive analysis of phase coexistence in SrSnO3 over a broad energy range, distinguishing inhomogeneous phonon and plasma responses arising from structural and electronic domains. We establish Nanoscale Imaging and Spectroscopy with Machine-learning Assistance (NISMA) to map nanotextured phases and quantify their distinct optical responses through a robust quantitative analysis, which can be applied to a broad array of complex oxide materials.

cond-mat.mtrl-sci↗

arXiv2025

Interfacial strong coupling and negative dispersion of propagating polaritons in freestanding oxide membranes

Membranes of complex oxides like perovskite SrTiO3 extend the multi-functional promise of oxide electronics into the nanoscale regime of two-dimensional materials. Here we demonstrate that free-standing oxide membranes supply a reconfigurable platform for nano-photonics based on propagating surface phonon polaritons. We apply infrared near-field imaging and -spectroscopy enabled by a tunable ultrafast laser to study pristine nano-thick SrTiO3 membranes prepared by hybrid molecular beam epitaxy. As predicted by coupled mode theory, we find that strong coupling of interfacial polaritons realizes symmetric and antisymmetric hybridized modes with simultaneously tunable negative and positive group velocities. By resolving reflection of these propagating modes from membrane edges, defects, and substrate structures, we quantify their dispersion with position-resolved nano-spectroscopy. Remarkably, we find polariton negative dispersion is both robust and tunable through choice of membrane dielectric environment and thickness and propose a novel design for in-plane Veselago lensing harnessing this control. Our work lays the foundation for tunable transformation optics at the nanoscale using polaritons in a wide range of freestanding complex oxide membranes.

cond-mat.mes-hall↗