Observation of mirror-odd and mirror-even spin texture in ultrathin epitaxially strained RuO2 films
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36 MATERIALS SCIENCE↗
Engineering topics
Kono, Junichiro
Publications and source records attributed to Kono, Junichiro.
Persistent flat band splitting and strong selective band renormalization in a kagome magnet thin film
Magnetic kagome materials provide a fascinating playground for exploring the interplay of magnetism, correlation and topology. Many magnetic kagome systems have been reported including the binary Fe m X n (X = Sn, Ge; m:n = 3:1, 3:2, 1:1) family and the rare earth RMn 6 Sn 6 (R = rare earth) family, where their kagome flat bands are calculated to be near the Fermi level in the para magnetic phase. While partially filling a kagome flat band is predicted to give rise to a Stoner-type ferromagnetism, experimental visualization of the mag netic splitting across the ordering temperature has not been reported for any of these systems due to the high ordering temperatures, hence leaving the nature of magnetism in kagome magnets an open question. Here, we probe the electronic structure with angle-resolved photoemission spectroscopy in a kagome magnet thin film FeSn synthesized using molecular beam epitaxy. We identify the exchange-split kagome flat bands, whose splitting persists above the magnetic ordering temperature, indicative of a local moment picture. Such local moments in the presence of the topological flat band are consistent with the compact molecular orbitals predicted in theory. We further observe a large spin-orbital selective band renormalization in the Fe d xy + d x 2 -y 2 spin majority channel reminiscent of the orbital selective correlation effects in the iron based superconductors. Our discovery of the coexistence of local moments with topological flat bands in a kagome system echoes similar findings in magic-angle twisted bilayer graphene, and provides a basis for theoretical effort towards modeling correlation effects in magnetic flat band systems.
36 MATERIALS SCIENCE↗
Magnetoelastic coupling driven magnon gap in a honeycomb antiferromagnet
Not provided.
Materials Science↗
Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method
Abstract In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
Engineering↗
Spectral evidence for local-moment ferromagnetism in the van der Waals metals $\mathrm{Fe_3GaTe_2}$ and $\mathrm{Fe_3GeTe_2}$
Magnetism in two-dimensional (2D) materials has attracted considerable attention recently for both fundamental understanding of magnetism and its tunability towards device applications. The isostructural Fe 3 GeTe 2 and Fe 3 GaTe 2 are two members of the Fe-based van der Waals (vdW) ferromagnet family, but exhibit very different Curie temperatures (T C ) of 210 and 360 K, respectively. In this report by using angle-resolved photoemission spectroscopy and density functional theory, we systematically compare the electronic structures of the two compounds. Qualitative similarities in the Fermi surface can be found between the two compounds, with expanded hole pockets in Fe 3 GaTe 2 suggesting additional hole carriers compared to Fe 3 GeTe 2 . Interestingly, we observe almost no band shift in Fe 3 GaTe 2 across its T C of 360 K, compared to a small shift in Fe 3 GeTe 2 across its T C of 210 K. The weak temperature-dependent evolution strongly deviates from the expectations of an itinerant Stoner mechanism. Our results suggest that itinerant electrons have minimal contributions to the enhancement of T C in Fe 3 GaTe 2 compared to Fe 3 GeTe 2 , and that the nature of ferromagnetism in these Fe-based vdW ferromagnets must be understood with considerations of the electron correlations.
36 MATERIALS SCIENCE↗
Nanoscale visualization and spectral fingerprints of the charge order in ScV 6 Sn 6 distinct from other kagome metals
Charge density waves (CDWs) in kagome metals have been tied to many exotic phenomena. Here, using spectroscopic-imaging scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we study the charge order in kagome metal ScV 6 Sn 6 . The similarity of electronic band structures of ScV 6 Sn 6 and TbV 6 Sn6 (where charge ordering is absent) suggests that charge ordering in ScV 6 Sn 6 is unlikely to be primarily driven by Fermi surface nesting of the Van Hove singularities. In contrast to the CDW state of cousin kagome metals, we find no evidence supporting rotation symmetry breaking. Differential conductance dI/dV spectra show a partial gap Δ 1 CO ≈ 20 meV at the Fermi level. Interestingly, dI/dV maps reveal that charge modulations exhibit an abrupt phase shift as a function of energy at energy much higher than Δ 1 CO , which we attribute to another spectral gap. Our experiments reveal a distinctive nature of the charge order in ScV 6 Sn 6 with fundamental differences compared to other kagome metals.
36 MATERIALS SCIENCE↗
Two-step electronic response to magnetic ordering in a van der Waals ferromagnet
The two-dimensional material Cr 2 Ge 2 Te 6 is a member of the class of insulating van der Waals (vdW) magnets. Here, using high resolution angle-resolved photoemission spectroscopy in a detailed temperature dependence study, we identify a clear response of the electronic structure to a dimensional crossover in the form of two distinct temperature scales marking onsets of modifications in the electronic structure. Specifically, we observe Te 𝑝-orbital-dominated bands to undergo changes at the Curie transition temperature 𝑇 𝐶 while the Cr 𝑑-orbital-dominated bands begin evolving at a higher temperature scale. Combined with neutron scattering, density functional theory calculations, and Monte Carlo simulations, we find that the electronic system can be consistently understood to respond sequentially to the distinct temperatures at which in-plane and out-of-plane spin correlations exceed a characteristic length scale. Finally, our findings reveal the sensitivity of the orbital-selective electronic structure for probing the dynamical evolution of local moment correlations in vdW insulating magnets.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Engineering chirality at wafer scale with ordered carbon nanotube architectures
Creating artificial matter with controllable chirality in a simple and scalable manner brings new opportunities to diverse areas. Here we show two such methods based on controlled vacuum filtration - twist stacking and mechanical rotation - for fabricating wafer-scale chiral architectures of ordered carbon nanotubes (CNTs) with tunable and large circular dichroism (CD). By controlling the stacking angle and handedness in the twist-stacking approach, we maximize the CD response and achieve a high deep-ultraviolet ellipticity of 40 ± 1 mdeg nm -1 . Our theoretical simulations using the transfer matrix method reproduce the experimentally observed CD spectra and further predict that an optimized film of twist-stacked CNTs can exhibit an ellipticity as high as 150 mdeg nm -1 , corresponding to a g factor of 0.22. Furthermore, the mechanical rotation method not only accelerates the fabrication of twisted structures but also produces both chiralities simultaneously in a single sample, in a single run, and in a controllable manner. The created wafer-scale objects represent an alternative type of synthetic chiral matter consisting of ordered quantum wires whose macroscopic properties are governed by nanoscopic electronic signatures and can be used to explore chiral phenomena and develop chiral photonic and optoelectronic devices.
36 MATERIALS SCIENCE↗
Spectral evidence for unidirectional charge density wave in detwinned BaNi 2 As 2
In the iron-based superconductors, unconventional superconductivity emerges in proximity to intertwined electronic orders consisting of an electronic nematic order and a spin density wave (SDW). Recently, BaNi 2 As 2 , like its well-known iron-based analog BaFe 2 As 2 , has been discovered to host a symmetry-breaking structural transition but coupled to a unidirectional charge density wave (CDW) instead of SDW, providing a novel platform to study intertwined orders. Here, in this work, through a systematic angle-resolved photoemission spectroscopy study combined with a detwinning B 1 g uniaxial strain, we identify distinct spectral evidence of band evolution due to the structural transition as well as CDW-induced band folding. In contrast to the nematicity and spin density wave in BaFe 2 As 2 , the structural and CDW order parameters in BaNi 2 As 2 are observed to be strongly coupled and do not separate in the presence of uniaxial strain. Furthermore, no nematic band splitting is resolved above the structural transition. Our measurements point to a likely lattice origin of the CDW order in BaNi 2 As 2 .
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Kramers nodal lines and Weyl fermions in SmAlSi
Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy connecting time-reversal invariant momenta. KNLs are robust to spin orbit coupling and are inherent to all non-centrosymmetric achiral crystal structures, leading to unusual spin, magneto-electric, and optical properties. However, their existence in in real quantum materials has not been experimentally established. Here we gather the experimental evidence pointing at the presence of KNLs in SmAlSi, a non-centrosymmetric metal that develops incommensurate spin density wave order at low temperature. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and magneto-transport methods, we provide evidence suggesting the presence of KNLs, together with observing Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. We discuss the nesting possibilities regarding the emergent magnetic orders in SmAlSi. Our results provide a solid basis of experimental observations for exploring correlated topology in SmAlSi.
36 MATERIALS SCIENCE↗
Transition from Diffusive to Superdiffusive Transport in Carbon Nanotube Networks via Nematic Order Control
Not Available
42 ENGINEERING↗
Phonon-Assisted Intertube Electronic Transport in an Armchair Carbon Nanotube Film
The electrical conductivity of a macroscopic assembly of nanomaterials is determined through a complex interplay of electronic transport within and between constituent nano-objects. Phonons play dual roles in this situation: their increased populations tend to reduce the conductivity via electron scattering, while they can boost the conductivity by assisting electrons to propagate through the potential-energy landscape. Here, we identified a phonon-assisted coherent electron transport process between neighboring nanotubes in temperature-dependent conductivity measurements on a macroscopic film of armchair single-wall carbon nanotubes. Through atomistic modeling of electronic states and calculations of both electronic and phonon-assisted junction conductances, we conclude that phonon-assisted conductance is the dominant mechanism for observed high-temperature transport in armchair carbon nanotubes. The unambiguous manifestation of coherent intertube dynamics proves a single-chirality armchair nanotube film to be a unique macroscopic solid-state ensemble of nano-objects promising for the development of room-temperature coherent electronic devices.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
The 2023 terahertz science and technology roadmap
Abstract Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Spectroscopy of Degenerate One-Dimensional Electrons in Carbon Nanotubes (Final Report)
The goal of this research program was to understand the fundamental properties of degenerate one-dimensional (1-D) electrons in single-wall carbon nanotubes (SWCNTs). SWCNTs provide an ideal 1-D environment in which to study many-body physics. Semiconducting SWCNTs exhibit rich optical spectra dominated by extremely stable 1-D excitons, whereas metallic SWCNTs contain massless 1-D carriers with ultralong mean-free paths. Despite the large number of electrical, optical, and magnetic studies of SWCNTs during the last two decades, most of the predicted exotic properties of interacting 1-D electrons have yet to be observed, and some reported experimental results remain highly controversial. Here, we report on our research projects for the last 16 years summarizing spectroscopy on SWCNTs using an arsenal of spectroscopic methods from the terahertz to the visible spectral range, including ultrafast optical spectroscopy and ultrahigh magnetic fields. These studies provided a wealth of new insights into the nature of strongly correlated carriers in the ultimate 1-D limit that will lead to novel nanodevice concepts and implementations. Particular emphasis was placed on dynamical 1-D phenomena in the terahertz, infrared, and optical frequency ranges. Because SWCNTs are direct-band-gap materials, they are one of the leading candidates to unify electronic and optical functions in nanoscale circuits and elucidate how electron correlations can affect and control finite-frequency phenomena in 1-D systems. As a result, we have published 78 research articles (Web of Science), including ten reviews and book volumes/chapters. Below, we highlight and summarize several accomplishments that provided new insights into the fundamental properties of1-D carriers, excitons, and phonons of SWCNTs.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Technology Development of Miniaturized Far-Infrared Sources for Biomolecular Spectroscopy
The objective of this project was to develop a purely solid-state based, thus miniaturized, far-infrared (FIR) (also known as terahertz (THz)) wave source using III-V semiconductor nanostructures for biomolecular detection and sensing. Many biomolecules, such as DNA and proteins, have distinct spectroscopic features in the FIR wavelength range as a result of vibration-rotation-tunneling motions and various inter- and intra-molecule collective motions. Spectroscopic characterization of such molecules requires narrow linewidth, sufficiently high power, tunable (in wavelength), and coherent FIR sources. Unfortunately, the FIR frequency is one of the least technologically developed ranges in the electromagnetic spectrum. Currently available FIR sources based on non-solid state technology are bulky, inefficient, and very often incoherent. In this project we investigated antimonide based compound semiconductor (ABCS) nanostructures as the active medium to generate FIR radiation. The final goal of this project was to demonstrate a semiconductor THz source integrated with a pumping diode laser module to achieve a compact system for biomolecular applications.
Kono, Junichiro↗