arXiv subjects

Masahiro Shibuta

Publications and source records attributed to Masahiro Shibuta.

3 recordsLinked to original sources

arXiv2026

Tuning of Photoexcited Electron Dynamics at Monolayer h-BN/Metal Interfaces by Corrugation

Atomic-scale corrugation in two-dimensional materials can modify interfacial electronic coupling, yet its influence on ultrafast carrier relaxation remains poorly established. Here, we compare image potential states (IPS) at monolayer h-BN/Ir(111) and h-BN/Pt(111) interfaces using structural characterization and time-resolved two-photon photoemission spectroscopy. Consistent with literature, h-BN is strongly corrugated on Ir(111) but comparatively flat on Pt(111). The first (n = 1) and second (n = 2) IPS appears at similar energies on both substrates, whereas their relaxation dynamics differ markedly. On h-BN/Ir(111), the IPS decay is response-limited (<20 fs), while h-BN/Pt(111) exhibits lifetimes of 56 fs (n = 1) and 75 fs (n = 2). The lifetime contrast is most consistently explained by corrugation-enhanced overlap of the IPS wavefunction with the metal substrate, which accelerates electron decay. These results indicate that atomic-scale corrugation is an effective physical parameter for tuning ultrafast electron dynamics at two-dimensional material and metal interfaces.

cond-mat.mtrl-sci↗

arXiv2026

Oscillator-driven broadband femtosecond transient microspectroscopy with supercontinuum probes generated in a photonic crystal fiber

We present an oscillator-driven femtosecond transient microspectroscopy system based on supercontinuum generation in a photonic crystal fiber (PCF). The system operates at 80 MHz without pulse amplification, enabling high-sensitivity measurements with a detection sensitivity better than $10^{-4}$ while using low pulse energies suitable for microspectroscopy. Optimization of the PCF length ($\leq 50$ mm) suppresses dispersion-induced chirp, achieving nearly uniform temporal resolution below 100 fs across 450-900 nm. The high-repetition-rate operation allows rapid spectral acquisition and efficient noise reduction. The developed system provides micrometer-scale spatial resolution and supports both reflection and transmission configurations. Ultrafast carrier dynamics in multilayer and monolayer MoS$_2$ are successfully resolved, including spatially dependent relaxation within a single monolayer flake. These results demonstrate a versatile platform for probing local ultrafast dynamics in low-dimensional materials.

physics.optics↗

arXiv2026

Ultrafast Nano-Imaging and Optical Control of Hyperbolic Phonon Polaritons at hBN/WS$_2$ Heterojunctions

Manipulating nanoscale light-matter interactions on ultrafast time scales is indispensable for future polaritonic devices. Hyperbolic phonon polaritons (HPhPs) in van der Waals materials enable deep subwavelength confinement of electromagnetic fields in the infrared region and long-distance propagation of polaritonic waves. However, achieving ultrafast imaging and optical control of HPhPs remains a major challenge. Here, we demonstrate the direct observation of transient modulation of HPhPs induced by local photocarrier generation in WS$_2$/hBN heterostructures using ultrafast infrared scanning near-field optical microscopy. We implement grating-based spectral filtering of broadband near-field scattering to simultaneously achieve nanoscale and femtosecond spatiotemporal resolution together with fine spectral selectivity. This ultrafast nano-imaging technique reveals that photocarriers in WS$_2$ modulate the polaritonic field amplitudes and wavelengths of HPhPs in hBN. Theoretical simulations corroborate that these changes arise from photoinduced changes in WS$_2$ dielectric properties. This approach offers a versatile platform for exploring ultrafast polaritonic dynamics at the nanoscale.

physics.optics↗