arXiv subjects

Hajime Ishihara

Publications and source records attributed to Hajime Ishihara.

At least 19 recordsLinked to original sources

arXiv2026

Local Chiral Optical Responses in Phthalocyanine Molecular Assemblies Revealed by Photoinduced Force Microscopy

Photoinduced force microscopy (PiFM) provides a force-based probe of nanoscale polarization-dependent molecular excitations. Here, we theoretically investigate PiFM images of zinc phthalocyanine assemblies using the discrete dipole approximation with nonlocal molecular susceptibilities. Under linearly polarized illumination, intermolecular dipole coupling splits the molecular resonance into bonding and antibonding modes. These modes produce distinct force distributions: bonding modes enhance signals at molecular termini, whereas antibonding modes localize responses in intermolecular regions, reflecting collective intermolecular polarization modes. Under circularly polarized illumination, intermolecular coupling and anisotropic molecular packing generate spatially varying local circular dichroism signals with enhanced asymmetric force factors. These results establish PiFM as a real-space probe of collective polarization modes and coupling-induced local chiral optical responses.

physics.optics↗

arXiv2025

Radiative coupling between plasmon and electron-hole pairs in a metallic film based on extended Bohm-Pines theory

Hot carrier generation in metals, where high-energy electron-hole pairs are produced via plasmon excitation, has emerged as a promising mechanism for photoelectric conversion and photocatalysis. However, conventional theories often describe this process through phenomenological relaxation via Landau damping, which fails to account for the microscopic origin of the frequency-dependent internal quantum efficiency (IQE) observed in experiments. To address this gap, we develop an extended Bohm-Pines theory for a metallic thin film that explicitly incorporates light-matter interactions within a non-local response framework. Our approach treats collective (plasmonic) and individual (electron-hole) excitations on equal footing and includes their coupling mediated by both longitudinal and transverse electromagnetic fields. This results in a self-consistent theory of the optical response of metallic films. The derived total Hamiltonian includes radiative corrections that recover the known dispersion of surface plasmon polaritons and, importantly, predict a frequency-dependent radiative coupling between collective and individual modes. This previously neglected transverse coupling naturally explains the IQE peak near the plasmon resonance and reveals a new mechanism of hot carrier generation distinct from conventional Landau damping. Our results provide a unified theoretical foundation for understanding plasmon-induced hot carrier dynamics and offer guidance for resonance-based photonic design strategies to enhance energy conversion efficiency in metal nanostructures.

physics.optics↗

arXiv2025

Proposed optomechanical systems based on luminescence-induced optical forces

We propose an optomechanical system utilizing luminescence-induced optical forces (LIOFs). Anisotropic dielectric structures enhance the recoil force from the luminescence. The optomechanical resonator consists of a composite film with a dielectric membrane, luminescent nanofilm, and a metallic substrate. The LIOF causes a mechanical frequency shift in the oscillator known as the optical spring effect. These results link the quantum properties of luminescent nanomaterials with those of other quantum-mechanical systems with vastly different frequency regimes via induced vibrational modes.

physics.optics↗

arXiv2023

Size dependent optical response in coupled systems of plasmons and electron-hole pairs in metallic nanostructures

In bulk materials, the collective modes and individual modes are orthogonal each other, and no connection occurs if there is no damping processes. In the presence of damping, the collective modes, i.e., plasmons decay into the hot carriers. In finite systems, the collective and individual modes are coupled by the Coulomb interaction. Such couplings by longitudinal (L) field have been intensively investigated, whereas a coupling via transverse (T) field has been poorly studied although the plasmon is excited by an irradiated light on surface and in finite nanostructures. Then, the T field would play a significant role in the coupling between the collective and individual excitations. In this study, we investigate how the T field mediates the coherent coupling. This study is based on the recently developed microscopic nonlocal theory of electronic systems in metals and the results of eigenmode analyses by this theory. To tune the coupling strength in a single nanorod, we examine three parameters: Rod length $L_z$, background refractive index $n_{\rm b}$, and Fermi energy $\varepsilon_{\rm F}$. We discuss the modulation ratio of the spectrum of optical response coefficients to evaluate the coupling by the T field. The T field shifts the collective excitation energy, which causes a finite modulation at both collective excitation and individual excitations. The three parameters can change the energy distance between the collective and individual excitations. Thus, the coherent coupling by the T field is enhanced for a proper tuning of the parameters. The results of the investigation of system parameter dependence would give insight into the guiding principle of designing the materials for highly efficient hot carrier generation.

cond-mat.mes-hall↗

arXiv2023

Nanorod Size Dependence of Coherent Coupling between Individual and Collective Excitations via Transverse Electromagnetic Field

Plasmon is a collective excitation in metals formed through the Coulomb interaction between individual excitations of electron-hole pairs. In many previous studies on the plasmonic response, the role of the longitudinal field has been focused almost exclusively on the light-induced plasmonic phenomena, e.g., hot-carrier generation. In our previous study [Phys. Rev. B 105, 165408 (2022)], we have revealed the significant contribution of the transverse electromagnetic field to connect plasmons and electron-hole pairs in nanostructures based on the self-consistent and nonlocal response theory. In this study, we examine how this contribution appears depending on the system parameters, e.g., length and refractive index. The elucidation of roles of coherent coupling between the collective and individual excitations by the transverse field will lead to the principle of controlling bidirectional energy transfer between the plasmons and electron-hole pairs, which could significantly enhance hot-carrier generation efficiency.

cond-mat.mes-hall↗

arXiv2022

Reflexive combinatory algebras

We introduce the notion of reflexivity for combinatory algebras. Reflexivity can be thought of as an equational counterpart of the Meyer-Scott axiom of combinatory models, which indeed allows us to characterise an equationally definable counterpart of combinatory models. This new structure, called strongly reflexive combinatory algebra, admits a finite axiomatisation with seven closed equations, and the structure is shown to be exactly the retract of combinatory models. Lambda algebras can be characterised as strongly reflexive combinatory algebras which are stable. Moreover, there is a canonical construction of a lambda algebra from a strongly reflexive combinatory algebra. The resulting axiomatisation of lambda algebras by the seven axioms for strong reflexivity together with those for stability is shown to correspond to the axiomatisation of lambda algebras due to Selinger [J.Funct.Programming, 12(6), 549--566, 2002].

cs.LO↗

arXiv2022

Comprehensive Microscopic Theory for Coupling of Longitudinal--Transverse Fields and Individual--Collective Excitations

A plasmon is a collective excitation of electrons due to the Coulomb interaction. Both plasmons and single-particle excitations (SPEs) are eigenstates of bulk metallic systems and they are orthogonal to each other. However, in non-translationally symmetric systems such as nanostructures, plasmons and SPEs coherently interact. It has been well discussed that the plasmons and SPEs, respectively, can couple with transverse (T) electric field in such systems, and also that they are coupled with each other via longitudinal (L) field. However, there has been a missing link in the previous studies: the coherent coupling between the plasmons and SPEs mediated by the T field. Herein, we develop a theoretical framework to describe the self-consistent relationship between plasmons and SPEs through both the L and T fields. The excitations are described in terms of the charge and current densities in a constitutive equation with a nonlocal susceptibility, where the densities include the L and T components. The electromagnetic fields originating from the densities are described in terms of the Green's function in the Maxwell equations. The T field is generated from both densities, whereas the L component is attributed to the charge density only. We introduce a four-vector representation incorporating the vector and scalar potentials in the Coulomb gauge, in which the T and L fields are separated explicitly. The eigenvalues of the matrix for the self-consistent equations appear as the poles of the system excitations. The developed formulation enables to approach unknown mechanisms for enhancement of the coherent coupling between plasmons and the hot carriers generated by radiative fields.

cond-mat.mes-hall↗

arXiv2021

Functionalized high-speed magnon-polaritons resulting from the magnetic antenna effect

Magnon-polaritons (MPs) refer to a light--magnon coupled state and can potentially act as information carriers, possibly enabling charge-free computation. However, the light--magnon coupling is inherently weak. To achieve sufficiently strong coupling, a large ferromagnet or coupling with a microwave cavity is necessary. Herein, we theoretically propose a fundamental platform for magnonic and magnon--optical information storage devices and discuss the transport properties of MP's. The proposed multi-layered structure overcomes the aforementioned issues. Owing to the waveguide modes, magnons placed in a nanometer-thin layer are strongly coupled with light, exhibiting rich functionalities of thick-layer MPs via the `magnetic antenna effect'. Thus, the thin-layer MPs are faster, and the direction is switchable. The results of this study will enable the integration of ferromagnetic micro and nanostructures for MP-based information devices without any restrictions due to cavities.

cond-mat.mes-hall↗

arXiv2021

Nonlocal inelastic scattering of light: Enhanced and noiseless signals in remote-coupled optomechanical systems

The inelastic scatterings of matter systems, such as Raman scattering, contain rich information on mechanical vibrations like as resonant frequencies, which lead to various applications, for example, a sensor for specific molecules. However, observing output signals requires a sensitive setup because an inelastic signal is inherently weak and is disturbed by strong input. In this study, we theoretically investigate a physical scheme to avoid detrimental impact of the input by distancing it from the emitter and greatly enhancing the output signals. If two bodies are coupled mechanically and direct optical communication is forbidden, the nonlocal inelastic scattering signals can be considerably boosted. We demonstrate this mechanism by considering coupled optomechanical systems as a typical example that enables control of the two-body interaction strength. The results present a general scheme to boost nonlocal inelastic scattering for noiseless and pure signals.

quant-ph↗

arXiv2021

Twisted light-induced spin-spin interaction in a chiral helimagnet

We theoretically investigate how the orbital angular momentum of light can affect a chiral magnetic order. Here, we consider a metallic chiral helimagnet, which is under stationary radiation of a resonant optical vortex beam. We propose a novel interaction between local spins considering microscopic interactions between an optical vortex and electrons. This vortex-induced interaction modulates the chiral magnetic order in an entirely different way than an external magnetic field does. Our spin modulation technique may pave a route to create a unique topological or chiral structure for future opto-spintronics devices.

cond-mat.mes-hall↗

arXiv2021

Rotation of optically bound particle assembly due to scattering induced spin-orbit coupling of light

The optical binding of many particles has great potential to achieve the wide-area formation of a "crystal" of small materials. Unlike conventional optical binding, where the whole assembly of targeted particles is irradiated with light, if one can indirectly manipulate remote particles using a single trapped particle through optical binding, the degrees of freedom to create ordered structures will be greatly enhanced. In this Letter, we theoretically investigate the dynamics of the assembly of gold nanoparticles that is manipulated using a single particle trapped by a focused laser. As a result, we demonstrate that the spin--orbit coupling and angular momentum generation of light via scattering induce the assembly and rotational motion of particles through indirect optical force. This result opens the possibility of creating ordered structures with a wide area and manipulating them, controlling local properties using scanning laser beams.

physics.optics↗

arXiv2020

Theoretical Analysis of Optically Selective Imaging in Photoinduced Force Microscopy

We present a theoretical study of the measurements of photoinduced force microscopy (PiFM) for composite molecular systems. Using the discrete dipole approximation, we calculate the self-consistent response electric field of the entire sample including the PiFM tip, substrate, and composite molecules. We demonstrate a higher sensitivity for the PiFM measurement on resonant molecules than by the previously obtained tip-sample distance dependency $z^{-4}$ owing of the multifold enhancement of the field between the localized electric field induced at the tip-substrate nanogap and the molecular polarization. The enhanced localized electric field induced at the tip-substrate nanogap in PiFM allows high-resolution observation of the forbidden optical electronic transition in dimer molecules. We investigated the wavelength dependence of PiFM for dimer molecules and obtained images at incident light wavelengths corresponding to allowed and forbidden transitions. We reveal that these PiFM images drastically change with the frequency-dependent spatial structures of the localized electric field vectors and resolve different types of nanoparticles beyond the resolution for the optically allowed transitions. This study demonstrates that PiFM provides multifaceted information based on microscopic interactions between nanomaterials and light.

physics.optics↗

arXiv2019

Equivalents of the finitary non-deterministic inductive definitions

We present statements equivalent to some fragments of the principle of non-deterministic inductive definitions (NID) by van den Berg (2013), working in a weak subsystem of constructive set theory CZF. We show that several statements in constructive topology which were initially proved using NID are equivalent to the elementary and finitary NIDs. We also show that the finitary NID is equivalent to its binary fragment and that the elementary NID is equivalent to a variant of NID based on the notion of biclosed subset. Our result suggests that proving these statements in constructive topology requires genuine extensions of CZF with the elementary or finitary NID.

math.LO↗

arXiv2017

Proposal of highly efficient photoemitter with strong photon-harvesting capability and exciton superradiance

We propose a system of highly efficient photoemitters comprising metal-dielectric (plasmonic-excitonic) multilayered structures. In the proposed structure, the absorption in the excitonic layer is greatly enhanced through quantum interference between the split modes arising from the coupling of the layered excitons and the plasmons sustained by the metallic layer. Furthermore, the large interaction volume between surface plasmons and excitons causes exciton superradiance, which results in the extremely efficient photoemission. This finding indicates the possibility of designing highly efficient photoemitters based on simple layered structures.

cond-mat.mes-hall↗

arXiv2017

Weak-Light Nonlinearity Using a Dark State in Coupled Quantum Dots

We propose a scheme to induce weak-light nonlinearity in a double quantum dot. The scheme positively utilizes locality and dissipation of an external auxiliary system. As a plausible setup, we consider a complex system in which a localized plasmon field from a metallic nanotip couples with only one of the coupled quantum dots. The perturbative calculation with respect to the light intensity shows that, even by a sufficiently weak light, a dipole-forbidden two-exciton NOON state is prepared as the steady state. This result can be explained by combining the two factors: decoherence-induced quantum state preparation and two-photon resonance. The present work implies that the positive usage of both the locality and the dissipation in the external auxiliary system is promising for inducing two-photon processes effectively, and provides one guideline to weak-light nonlinearities.

cond-mat.mes-hall↗

arXiv2017

Synchronization dynamics in a designed open system

We theoretically propose a unifying expression for synchronization dynamics between two-level constituents. Although synchronization phenomena require some substantial mediators, the distinct repercussions of their propagation delays remain obscure, especially in open systems. Our scheme directly incorporates the details of the constituents and mediators in an arbitrary environment. As one example, we demonstrate the synchronization dynamics of optical emitters on a dielectric microsphere. We reveal that the whispering gallery modes (WGMs) bridge the well-separated emitters and accelerate the synchronized fluorescence, known as superfluorescence. The emitters are found to overcome the significant and nonuniform retardation, and to build up their pronounced coherence by the WGMs, striking a balance between the roles of resonator and intermediary. Our work directly illustrates the dynamical aspects of many-body synchronizations and contributes to the exploration of research paradigms that consider designed open systems.

cond-mat.other↗

arXiv2016

Design of nonlinear optical response of multipole-type excitons by film thickness and incident pulse width

We theoretically investigate the nonlinear optical pulse responses of excitons in a thin film where the excitonic center-of-mass motion is confined. A large interaction volume between excitons and radiation yields particular coupled states with radiative decay times reaching several femto-seconds. By considering two polarization directions of light, we reveal that these fast-decay modes dominantly survive in an optical Kerr spectra even under a massive nonradiative damping $Γ=30$ meV. The results clearly show that there is an optimal combination of the incident pulse width and the film thickness for maximizing the integrated intensity of nonlinear signals.

cond-mat.mtrl-sci↗

arXiv2016

Radiative coupling of A and B excitons in ZnO

Radiation-induced coupling between A and B excitons in ZnO is theoretically studied. Considering the center-of-mass motion of excitons in bulk and thin film structures, we reveal the eigenmodes of an exciton--radiation coupled system and the ratio of each excitonic component, which is determined from diagonalization of the self-consistent equation between the polarization and the Maxwell electric field. In particular, in a nano-to-bulk crossover size regime, the large interaction volume between multipole-type excitonic waves and radiation waves causes radiative coupling between excitons from different valence bands, which leads to an enhancement of the radiative correction. The results presented in this study are in striking contrast with the conventional view of the optical response of excitons in ZnO, where A and B excitons are independently assigned to their respective spectral structures. It is also clarified that the density of each excitonic component is of a significant value for attribution of nonlinear optical signals.

cond-mat.mes-hall↗