arXiv subjects

Toshiaki Kato

Publications and source records attributed to Toshiaki Kato.

4 recordsLinked to original sources

arXiv2026

Strong phonon-coupled trion emission in Janus homobilayer

Janus transition metal dichalcogenides with broken mirror symmetry provide a novel platform for exploring many-body effects mediated by spin-valley-phonon interactions. Strong electron-phonon coupling demands a precise match between a strong effective dipole moment and nanometer-scale charge confinement. Here, we report thermally robust and enhanced trion emission in a symmetric bilayer WSeS with an S/S stacking configuration. The inward-pointing antiparallel built-in electric fields induce a strong electron confinement effect at the interface, driving dominant trion emission at cryogenic temperatures. Furthermore, a massive electron-phonon coupling strength (3.9) resonant with the optical phonon A_1^2 energy (51 meV) contributes to the thermal stability of this trion emission at elevated temperatures. By tailoring the interfacial architecture in Janus WSeS homobilayers, this study overcomes the thermal decoherence limits inherent to traditional semiconductor systems, offering novel insights into room-temperature many-body interactions.

cond-mat.mes-hall↗

arXiv2026

Exceptional Superconducting Interfaces between Graphene and Atomic Chains in A15-MoRe

Realizing highly transparent and magnetic-field-resilient superconducting contacts is a critical bottleneck for the advancement of two-dimensional (2D) quantum devices. Molybdenum-rhenium (MoRe) alloys have been empirically favored as they uniquely yield ballistic, highly transparent contacts to graphene that survive in high-magnetic-field regimes; however, the microscopic origin of this anomalous transparency has remained a long-standing puzzle. Here, we resolve this paradox by revealing that pristine graphene/MoRe interfaces are governed by the classical A15 superconducting phase. Combining low-temperature transport, X-ray diffraction, and atomic-resolution electron microscopy, we demonstrate that as-deposited MoRe spontaneously forms the A15 phase in direct contact with graphene, whereas thermal annealing triggers a phase transition to a hexagonal close-packed (hcp) structure that severely degrades the Josephson transparency. Crucially, the one-dimensional (1D) transition-metal atomic chains unique to the A15 structure exhibit a near-perfect lattice match (mismatch < 1%) with graphene edges. First-principles calculations further prove that the d-orbitals of these historically renowned 1D chains possibly hybridize with graphene's Dirac cone near the K point. These findings not only uncover the structural and electronic origins of optimal MoRe contacts but also establish A15-phase superconductors as a geometrically ideal, universal platform for realizing robust quantum electronics based on 2D materials.

cond-mat.mtrl-sci↗

arXiv2025

Direct observation of band structure modifications from monolayer WSe2 to Janus WSSe

Janus monolayer transition metal dichalcogenides (TMDs), created by post-growth substitution of the top chalcogen layer, represent a new direction for engineering 2D crystal properties. However, their rapid ambient degradation and the difficulty of obtaining large-area monolayer samples have limited the available experimental probes, leaving their detailed electronic structure near the Fermi level largely unexplored. In this work, by performing micro-focused angle-resolved photoemission spectroscopy (μ-ARPES) on an identical sample transformed from monolayer WSe2 to Janus WSSe via a H2 plasma-assisted chalcogen-exchange method, we reveal the evolution of its electronic band structure. We observe ARPES signature consistent with the Rashba-type spin splitting due to broken horizontal mirror symmetry, and a significant upward shift of the highest valence band at the Γ-point by approximately 160 meV. These direct observations clarify the key electronic modifications that govern the material's properties and provide a pathway for band engineering in Janus TMDs.

cond-mat.mtrl-sci↗

arXiv2025

Lattice-guided growth of dense arrays of aligned transition metal dichalcogenide nanoribbons with high catalytic reactivity

Transition metal dichalcogenides (TMDs) exhibit unique properties and potential applications when reduced to one-dimensional (1D) nanoribbons (NRs), owing to quantum confinement and high edge densities. However, effective growth methods for self-aligned TMD NRs are still lacking. We demonstrate a versatile approach for lattice-guided growth of dense, aligned MoS2 NR arrays via chemical vapor deposition (CVD) on anisotropic sapphire substrates, without tailored surface steps. This method enables the synthesis of NRs with widths below 10 nm and longitudinal axis parallel to the zigzag direction, being also extensible to the growth of WS2 NRs and MoS2-WS2 hetero-nanoribbons. Growth is influenced by both substrate and CVD temperature, indicating the role of anisotropic precursor diffusion and substrate interaction. The 1D nature of the NRs was asserted by the observation of Coulomb blockade at low temperature. Pronounced catalytic activity was observed at the edges of the NRs, indicating their promise for efficient catalysis.

cond-mat.mes-hall↗