arXiv subjects

Tomohiro Ishii

Publications and source records attributed to Tomohiro Ishii.

4 recordsLinked to original sources

arXiv2026

Switchable Magnetoelectric Transport in Graphene via a Van der Waals Multiferroic

Electric and magnetic control of transport properties at atomic interfaces is central to the development of next generation electronics and spintronics. Van der Waals multiferroics materials that simultaneously host dielectric and magnetic orders down to the monolayer limit offer a promising platform for such interfacial control, yet the realization of electronic functionalities that exploit the unique attributes of van der Waals multiferroics has largely remained elusive. Here, we realize a van der Waals heterostructure comprising graphene and the multiferroic CuCrP2S6, enabling gate-switchable magnetoelectric transport in graphene, mediated by the multiferroic layer. The charge-neutrality resistance peak of graphene exhibits pronounced hysteresis arising from polarization flip in the multiferroic state. Application of an in-plane magnetic field shifts this peak in a polarization-dependent manner, revealing magnetic-field-induced polarization modulation a direct signature of the magnetoelectric effect. Furthermore, cooling the device under an applied electric field enables domain control of the multiferroic order, allowing reversible switching of the interfacial magnetoelectric transport. These results provide the first demonstration of interfacial magnetoelectric transport in a vdW heterostructure, and establish a pathway for engineering two-dimensional van der Waals interfaces for functional device applications.

cond-mat.mes-hall↗

arXiv2026

Planar Microcavities can Suppress Exciplex Formation and Increase the Emission Efficiency of Organic Semiconductors

Optical microcavities are widely used to control the emission of organic semiconductors, but their ability to reshape the molecular pathways that precede emission remains largely unexplored. Here we show that embedding a ZnPc:TPBi blend in a planar Fabry-Pérot microcavity suppresses the formation of non-radiative exciplexes and removes bimolecular annihilation at high excitation densities, increasing the photoluminescence quantum yield by more than forty-fold under continuous-wave excitation. This enhancement is far larger than expected from the weak Purcell effect. Instead, transient spectroscopy, power-dependent photoluminescence and kinetic modelling point to a cavity-induced rebalancing of excited-state populations: long-range Förster energy transfer from ZnPc monomers to emissive aggregates is enhanced, allowing it to outcompete charge transfer to dark exciplexes. Electromagnetic calculations predict FRET enhancements of up to ~400-fold at relevant distances, consistent with the observed suppression of exciplex-mediated losses. Our results show that optical cavities can control not only how molecules emit, but also which excited states they form, opening a route to improved efficiency and reduced roll-off in organic optoelectronic and photonic devices.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic resonance and microwave resistance modulation in van der Waals colossal-magnetoresistance material

Colossal magnetoresistance (CMR) is a fascinating quantum phenomenon that continues to draw significant interest in condensed matter physics. Mn3Si2Te6 has emerged as a prototypical CMR material, notable for its puzzling magnetoresistance behavior and pronounced directional anisotropy. Despite extensive research, the mechanisms driving CMR in Mn3Si2Te6 remain elusive [1-4]. In this work, we explore the magnetic resonance of Mn3Si2Te6 and observe a reduced g-factor for magnetic fields applied along the crystalline c-axis compared to the ab-plane, indicating a substantial orbital magnetization contribution along the c-axis. Furthermore, we detect resistance modulation under resonance conditions, suggesting that CMR in Mn3Si2Te6 is sensitive to the out-of-the plane spin polarization. These findings shed new light on the role of orbital magnetic moment in Mn3Si2Te6, offering a deeper understanding of the interplay between spin, orbital and lattice degrees of freedom of electrons in this system.

cond-mat.mtrl-sci↗

arXiv2019

Modification of magnetic fluctuations by interfacial interactions in artificially engineered heavy-fermion superlattices

Recent progress in the fabrication techniques of superlattices (SLs) has made it possible to sandwich several-layer-thick block layers (BLs) of heavy-fermion superconductor CeCoIn5 between conventional-metal YbCoIn5 BLs or spin-density-wave-metal CeRhIn5 BLs of a similar thickness. However, the magnetic state in each BL, particularly at the interface, is not yet understood, as experimental techniques applicable to the SL system are limited. Here, we report measurements of 59Co nuclear magnetic resonance, which is a microscopic probe of the magnetic properties inside the target BLs. In the CeCoIn5/YbCoIn5 SL, the low-temperature magnetic fluctuations of the CeCoIn5 BL are weakened as expected from the Rashba spin-orbit effect. However, in the CeCoIn5/CeRhIn5 SL, the fluctuations show an anomalous enhancement below 6 K, highlighting the importance of the magnetic proximity effect occurring near a magnetic-ordering temperature TN ~ 3 K of the CeRhIn5 BL. We suggest that the magnetic properties of the BLs can be altered by the interfacial interaction, which is an alternative route to modify the magnetic properties.

cond-mat.str-el↗