arXiv subjects

Keita Funayama

Publications and source records attributed to Keita Funayama.

5 recordsLinked to original sources

arXiv2026

N-fold topological mode replication in hierarchical honeycomb lattices

Multi-band topological states enable robust and versatile wave manipulation across a variety of physical platforms. However, the emergence of multi-band topological states has relied on higher-frequency modes with complex spatial profiles, which constrains the realization of robust topological states due to fragile symmetry and pseudospin hybridization in these modes. Here, we show a general design principle for scalable multi-band topological states by replicating a robust fundamental topological mode in the frequency domain. By introducing hierarchical resonators as an internal degree of freedom into a quantum spin Hall-based lattice, multiple topological states emerge discretely in correspondence with the hierarchical levels while preserving the spatial profile of the fundamental mode at the host lattice. Implementing this design principle in a versatile microelectromechanical platform, we experimentally demonstrate that the fundamental and replicated topological modes propagate simultaneously in a single waveguide while suppressing mutual cross-talk. Our results establish topology replication as a universal strategy for designing multi-band topological systems and open routes toward multi-channel topological wave devices.

cond-mat.mes-hall↗

arXiv2026

Realization of a universal topological waveguide by tuning adiabatic geometry

Quantum valley Hall-based topological phases have been attracting attention across diverse fields as a robust platform for wave guidance due to their high compatibility with engineering frameworks. Combining three representative boundary types enables topological waveguides with flexible designability and enhanced functionality. However, one of the three, namely the armchair boundary, has long been limited by inter-valley scattering, resulting in weak topological protection and severely restricting its use in practical devices. This long-standing constraint is a major barrier to realizing broadly applicable topological waveguide systems. Here, to address this challenge toward a broadly applicable design framework for topological waveguides, we experimentally demonstrate that topological adiabatic geometry implemented in a micro electromechanical system suppresses valley mixing. We found that the adiabaticity enhances immunity to defects and increases the transmission efficiency of the armchair boundary. As the adiabaticity increases, topological protection is recovered over an increasingly broad portion of the bulk band gap, extending from low to high frequencies. Furthermore, we show that the recovery of protection in the adiabatic armchair boundary enables waves to propagate through 90^° and 150^°-bent waveguides by coupling with other interface geometries. Suppressing valley mixing via adiabaticity paves the way for a universal design framework for topological waveguides and for restoring robust topological characteristics across a wide range of wave phenomena.

cond-mat.mes-hall↗

arXiv2025

Topological Phononic Crystal on the Scale of Quasi-Ballistic Phonon Transport

Phonon engineering technology has opened up the functional thermal management of semiconductor-based classical and quantum electronics at the micro- and nanoscales. However, challenges have remained in designing accurate thermal characteristics based on quasi-ballistic phonon transport. The quasi-ballistic thermal transport arises from the combination of wave-like and diffusive phonon behaviors unlike pure diffusion. The topological nature has been known to be compatible with both wave and diffusive phenomena. Therefore, topological phononic crystals have great potential for the development of controllable and designable thermal transport based on quasi-ballistic phonons. In this study, we experimentally investigated the thermal behavior at the scale of quasi-ballistic phonon transport using a 1D Su-Schrieffer-Heeger model-based topological phononic crystal. Quasi-ballistic phonon transport was observed through change in thermal conductivity depending on the structural parameters of topological systems using micro-thermoreflectance. Furthermore, using topological interface states, the experimentally observed thermal behaviors were found to agree well with the theoretically expected those. Accordingly, the topological nature is an effective approach for thermal management in micro- and nanoscale systems with quasi-ballistic phonon transport. Our results pave the way for a unified control scheme for wave and diffusion phenomena, such as quasi-ballistic phonons.

cond-mat.mes-hall↗

arXiv2023

Selectable diffusion direction with topologically protected edge modes

Topological insulators provide great potentials to control diffusion phenomena as well as waves. Here, we show that the direction of thermal diffusion can be selected by the contributions of the topologically protected edge modes via the quantum spin Hall effect in a honeycomb-shaped structure. We demonstrate that when we set our structure to the temperature corresponding to the type of edge mode, the direction of thermal diffusion can be tuned. Moreover, this diffusion system is found to be immune to defects owing to the robustness of topological states. Our work points to exciting new avenues for controlling diffusion phenomena.

cond-mat.mes-hall↗

arXiv2020

Nanomechanical system meets ultra-small, robust, and ultra-low-powered digital communication receiver

Nanomechanical systems offer a versatile platform for both fundamental science and industrial applications. Resonating vibration has been demonstrated to enable an ultrasensitive detection of various physical quantities, with emerging applications including signal processing, biological detection and fundamental tests of quantum mechanics. It has also been shown that the mechanical vibration of a nanoscale cantilever can be used to detect electromagnetic analogue-modulated waves. However, signals obtained with nanoscale receivers are so weak that the data transfer often fails; to the best of our knowledge, no successful practical demonstration has yet been reported. Here, we present the first experimental demonstration of the use of nanomechanical systems for digital data transfer with a digital image. Furthermore, our fabrication method achieved a tiny gap around field emitter of vibrational nano-antenna, which enables the receiver to work with quite a low power consumption, on the order of 10nW.

physics.app-ph↗