Results for "Takashi Taniguchi"

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LRG J0239-0134: A Ring Galaxy or a Pair of Superbubbles at z=1 ?Nov 03 2000The unusual morphology of LRG J0239$-$0134 at $z$ =1.062 has been interpreted as a ring galaxy. Here we propose an alternative idea that the ring-like morphology is attributed to a pair of superbubbles driven by the intense starburst in the central region ... More
Poststarburst Models of LINERsMay 16 2000Since the discovery of low-ionization nuclear emission-line regions in many galaxies (LINERs), it has been recognized that they constitute a class of active galactic nuclei (AGNs) which are thought to be powered by gas accretion onto a central, supermassive ... More
New Mid-Infrared Diagnostic of the Dusty Torus Model for Seyfert NucleiAug 24 1999We propose a new diagnostic of the ``dusty torus'' model for Seyfert nuclei. Dust grains in the torus are heated by the nuclear continuum, and reradiate mostly in the mid-infrared wavelengths. From the torus geometry, it is predicted that the emission ... More
On proportional constants of the mean value of class numbers of quadratic extensionsOct 04 2004In this article, we slightly refine the mean value theorem for the class number of quadratic extensions obtained by Goldfeld-Hoffstein and Datskovsky. We determine all the proportional constants of the mean value with respect to the local conditions including ... More
Distributions of discriminants of cubic algebrasJun 05 2006We study the space of binary cubic and quadratic forms over the ring of integers $O$ of an algebraic number field $k$. By applying the theory of prehomogeneous vector spaces founded by M. Sato and T. Shintani, we can associate the zeta functions for these ... More
Distributions of discriminants of cubic algebras IIAug 26 2006Let $k$ be a number field and $O$ the ring of integers. In the previous paper [T06] we study the Dirichlet series counting discriminants of cubic algebras of $O$ and derive some density theorems on distributions of the discriminants by using the theory ... More
A mean value theorem for orders of degree zero divisor class groups of quadratic extensions over a function fieldMar 14 2002Let $k$ be a function field of one variable over a finite field with the characteristic not equal to two. In this paper, we consider the prehomogeneous representation of the space of binary quadratic forms over $k$. We have two main results. The first ... More
On parameterizations of rational orbits of some forms of prehomogeneous vector spacesAug 26 2006In this paper, we consider the structure of rational orbit of some prehomogeneous vector spaces originally motivated by Wright and Yukie. After we give a refinement of Wright-Yukie's construction, we apply it to the inner forms of the $D_5$ and $E_7$ ... More
Iron is not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic NucleiDec 27 2002In order to examine whether or not high-ionization nuclear emission-line regions (HINERs) in narrow-line regions of active galactic nuclei are dusty, we focus on two high-ionization forbidden emission lines, [Fe VII]6087 and [Ne V]3426. We perform photoionization ... More
On the zeta functions of prehomogeneous vector spaces for pair of simple algebrasMar 16 2004In this paper, we consider the prehomogeneous vector space for pair of simple algebras which are $k$-forms of the $D_4$ type and the $E_6$ type. We mainly study the non-split cases. The main purpose of this paper is to determine the principal parts of ... More
A mean value theorem for the square of class number times regulator of quadratic extensionsOct 25 2004Jul 03 2006Let $k$ be a number field. In this paper, we give a formula for the mean value of the square of class numbers times regulators for certain families of quadratic extensions of $k$ characterized by finitely many local conditions. We approach this by using ... More
Multiscale Simulation of History Dependent Flow in Polymer MeltDec 14 2010Mar 09 2011We have developed a new multiscale simulation technique to investigate history-dependent flow behavior of entangled polymer melt, using a smoothed particle hydrodynamics simulation with microscopic simulators that account for the dynamics of entangled ... More
An error estimate for counting $S_3$-sextic number fieldsAug 10 2012Oct 01 2013In this note, we prove a power-saving remainder term for the function counting $S_3$-sextic number fields. We also give a prediction on the second main term. We also present numerical data on counting functions for $S_3$-sextic number fields. Our data ... More
Equilibrium sequences of irrotational binary polytropic stars : The case of double polytropic starsApr 03 2000Solutions to equilibrium sequences of irrotational binary polytropic stars in Newtonian gravity are expanded in a power of $\epsilon=a_0/R$, where R and $a_0$ are the orbital separation of the binary system and the radius of each star for $R=\infty$. ... More
Almost analytic solutions to equilibrium sequences of irrotational binary polytropic stars for n=1Nov 23 1999A solution to an equilibrium of irrotational binary polytropic stars in Newtonian gravity is expanded in a power of \epsilon=a_0/R, where R and a_0 are the separation of the binary system and the radius of each star for R=\infty. For the polytropic index ... More
A New Dual-Component Photoionization Model for the Narrow Emission-Line Regions in Active Galactic NucleiJun 22 1998Having found that type 1 Seyfert nuclei have excess [FeVII]6087 emission with respect to type 2s, Murayama & Taniguchi have proposed that the high-ionization nuclear emission-line region (HINER) traced by the [FeVII]6087 emission resides in the inner ... More
Thermal Conductivity and Phonon Transport in Suspended Few-Layer Hexagonal Boron NitrideFeb 07 2013The thermal conductivity of suspended few-layer hexagonal boron nitride (h-BN) was measured using a micro-bridge device with built-in resistance thermometers. Based on the measured thermal resistance values of 11-12 atomic layer h-BN samples with suspended ... More
Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation By Inelastic ScatteringJan 22 2016Jan 26 2016We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due ... More
Aharonov-Bohm oscillations and magnetic focusing in ballistic graphene ringsSep 02 2017We present low-temperature magnetotransport measurements on graphene rings encapsulated in hexagonal boron nitride. We investigate phase-coherent transport and show Aharonov-Bohm (AB) oscillations in quasi-ballistic graphene rings with hard confinement. ... More
Control of interlayer excitons in two-dimensional van der Waals heterostructuresMar 16 2018Long-lived interlayer excitons with distinct spin-valley physics in van der Waals heterostructures based on transition metal dichalcogenides make them promising for information processing in next-generation devices. While the emission characteristics ... More
Reliable post-processing improvement of van der Waals heterostructuresMar 25 2019The successful assembly of heterostructures consisting of several layers of different 2D materials in arbitrary order by exploiting van der Waals forces has truly been a game changer in the field of low dimensional physics. For instance, the encapsulation ... More
Flow-History-Dependent Behavior in Entangled Polymer Melt Flow with Multiscale SimulationOct 05 2011Polymer melts represent the flow-history-dependent behavior. To clearly show this behavior, we have investigated flow behavior of an entangled polymer melt around two cylinders placed in tandem along the flow direction in a two dimensional periodic system. ... More
Secondary terms in counting functions for cubic fieldsFeb 14 2011We prove the existence of secondary terms of order X^{5/6} in the Davenport-Heilbronn theorems on cubic fields and 3-torsion in class groups of quadratic fields. For cubic fields this confirms a conjecture of Datskovsky-Wright and Roberts. We also prove ... More
Multiscale Lagrangian Fluid Dynamics Simulation for Polymeric FluidMay 13 2009Dec 10 2009We have developed a simulation technique of multiscale Lagrangian fluid dynamics to tackle hierarchical problems relating to historical dependency of polymeric fluid. We investigate flow dynamics of dilute polymeric fluid by using the multiscale simulation ... More
Why Does NGC 1068 Have a More Powerful Active Galactic Nucleus than NGC 4258 ?May 12 1997The nuclear gas kinematics probed by water vapor maser emission has shown that two nearby active galaxies, NGC 1068 and NGC 4258, have a supermassive object in their nuclei and their masses are nearly comparable; a few 10^7 solar masses. Nevertheless, ... More
Dusty Tori of Seyfert Nuclei Probed by the Water Vapor Maser Emission: How Large are the Dusty Tori ?May 08 1998Geometrical and physical properties of dusty tori of Seyfert nuclei probed by the water vapor maser emission at 22 GHz are discussed. We assume that the dusty torus has a simple cylindrical form and the maser emission can be detected only when we observe ... More
Gate-defined electron-hole double dots in bilayer grapheneMar 28 2018Jun 25 2018We present gate-controlled single, double, and triple dot operation in electrostatically gapped bilayer graphene. Thanks to the recent advancements in sample fabrication, which include the encapsulation of bilayer graphene in hexagonal boron nitride and ... More
Light from van der Waals quantum tunneling devicesApr 17 2018Jan 19 2019The understanding of and control over light emission from quantum tunneling has challenged researchers for more than four decades due to the intricate interplay of electrical and optical properties in atomic scale volumes. Here we introduce a device architecture ... More
One-dimensional edge contacts to monolayer semiconductorsFeb 14 2019Feb 17 2019Integration of Ohmic contacts into van der Waals (vdW) heterostructures is critical for realizing electronic and optoelectronic functionalities. However, to date no scalable methodology for gaining electrical access to buried monolayer two-dimensional ... More
Relations among Dirichlet series whose coefficients are class numbers of binary cubic forms IIDec 21 2011As a continuation of the authors and Wakatsuki's previous paper [5], we study relations among Dirichlet series whose coefficients are class numbers of binary cubic forms. We show that for any integral models of the space of binary cubic forms, the associated ... More
Where is the coronal line region in active galactic nuclei?Feb 11 1998We report the new finding that type 1 Seyfert nuclei (S1s) have excess [FeVII]6087 emission with respect to type 2s (S2s). The S1s exhibit broad emission lines which are attributed to ionized gas within 1 pc of the black hole, whereas the S2s do not show ... More
Giant Frictional Drag in Double Bilayer Graphene HeterostructuresMar 02 2016We study the frictional drag between carriers in two bilayer graphene flakes separated by a 2 $-$ 5 nm thick hexagonal boron nitride dielectric. At temperatures ($T$) lower than $\sim$ 10 K, we observe a large anomalous negative drag emerging predominantly ... More
Metallic Phase and Temperature Dependence of the $ν= 0$ Quantum Hall State in Bilayer GrapheneMar 11 2019The $\nu = 0$ quantum Hall state of bilayer graphene is a fertile playground to realize many-body ground states with various broken symmetries. Here we report the experimental observations of a previously unreported metallic phase. The metallic phase ... More
Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect TransistorsMar 24 2017The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device ... More
Quantitative transport measurements of fractional quantum Hall energy gaps in edgeless graphene devicesMay 10 2018Sep 05 2018Owing to their wide tunability, spin- and valley internal degrees of freedom, and low disorder, graphene heterostructures are emerging as a promising experimental platform for fractional quantum Hall (FQH) studies. Surprisingly, however, transport measurements ... More
Orbital exponential sums for prehomogeneous vector spacesJul 26 2016Let (G, V) be a prehomogeneous vector space, let O be any G(F_q)-invariant subset of V(F_q), and let f be the characteristic function of O. In this paper we develop a method for explicitly and efficiently evaluating the Fourier transform of f, based on ... More
Innermost Stable Circular Orbit of Coalescing Neutron Star-Black Hole Binary --- Generalized Pseudo-Newtonian Potential Approach ---Sep 02 1996The innermost stable circular orbits (ISCO) of coalescing neutron star-black hole binary are studied taking into account both the tidal and relativistic effects. We adopt the generalized pseudo-Newtonian potential to mimic the general relativistic effects ... More
Orbital L-functions for the space of binary cubic formsDec 21 2011We introduce the notion of orbital L-functions for the space of binary cubic forms and investigate their analytic properties. We study their functional equations and residue formulas in some detail. Aside from the intrinsic interest, results from this ... More
Spin-valley Hall transport induced by spontaneous symmetry breaking in half-filled zero Landau level of bilayer grapheneMay 08 2019Intrinsic Hall conductivity, emerging when chiral symmetry is broken, is at the heart of future low energy consumption devices because it can generate non-dissipative charge neutral current. A symmetry breaking state is also induced by electronic correlation ... More
Tin-Vacancy Quantum Emitters in DiamondAug 11 2017Tin-vacancy (SnV) color centers were created in diamond by ion implantation and subsequent high temperature annealing up to 2100 {\deg}C at 7.7 GPa. The first-principles calculation suggests that the large atom of tin can be incorporated into the diamond ... More
Hybridized indirect excitons in MoS2/WS2 heterobilayersDec 27 2018Ensembles of indirect or interlayer excitons (IXs) are intriguing systems to explore classical and quantum phases of interacting bosonic ensembles. IXs are composite bosons that feature enlarged lifetimes due to the reduced overlap of the electron-hole ... More
Tunneling spin valves based on Fe$_3$GeTe$_2$/hBN/Fe$_3$GeTe$_2$ van der Waals heterostructuresJun 14 2018Thin van der Waals (vdW) layered magnetic materials disclose the possibility to realize vdW heterostructures with new functionalities. Here we report on the realization and investigation of tunneling spin valves based on van der Waals heterostructures ... More
Observation of fractional Chern insulators in a van der Waals heterostructureJun 19 2017Nov 27 2017Topologically ordered phases are characterized by long-range quantum entanglement and fractional statistics rather than by symmetry breaking. First observed in a fractionally filled continuum Landau level, topological order has since been proposed to ... More
Gate-tunable black phosphorus spin valve with nanosecond spin lifetimesJun 07 2017Two-dimensional materials offer new opportunities for both fundamental science and technological applications, by exploiting the electron spin. While graphene is very promising for spin communication due to its extraordinary electron mobility, the lack ... More
Landau level splittings, phase transitions, and non-uniform charge distribution in trilayer grapheneJul 04 2016We report on magneto-transport studies of dual-gated, Bernal-stacked trilayer graphene (TLG) encapsulated in boron nitride crystals. We observe a quantum Hall effect staircase which indicates a complete lifting of the twelve-fold degeneracy of the zeroth ... More
Gate tunable dark trions in monolayer WSe$_2$Jan 30 2019We report the observation and gate manipulation of intrinsic dark trions in monolayer WSe$_2$. By using ultraclean WSe$_2$ devices encapsulated by boron nitride, we directly resolve the weak photoluminescence of dark trions. The dark trions can be tuned ... More
Strong electron-hole symmetric Rashba spin-orbit coupling in graphene/monolayer transition metal dichalcogenide heterostructuresJul 11 2017Despite its extremely weak intrinsic spin-orbit coupling (SOC), graphene has been shown to acquire considerable SOC by proximity coupling with exfoliated transition metal dichalcogenides (TMDs). Here we demonstrate strong induced Rashba SOC in graphene ... More
Band gap and broken chirality in single-layer and bilayer grapheneAug 11 2015Aug 21 2015Chirality is one of the key features governing the electronic properties of single- and bilayer graphene: the basics of this concept and its consequences on transport are presented in this review. By breaking the inversion symmetry, a band gap can be ... More
Quantum confined Stark effect in a MoS$_2$ monolayer van der Waals heterostructureOct 26 2017The optics of dangling-bond-free van der Waals heterostructures containing transition metal dichalcogenides are dominated by excitons. A crucial property of a confined exciton is the quantum confined Stark effect (QCSE). Here, such a heterostructure is ... More
Co-existence of classical snake states and Aharanov-Bohm oscillations along graphene p-n junctionsApr 07 2018Snake states and Aharonov-Bohm interferences are examples of magnetoconductance oscillations that can be observed in a graphene p-n junction. Even though they have already been reported in suspended and encapsulated devices including different geometries, ... More
Giant valley-isospin conductance oscillations in ballistic grapheneAug 31 2017At high magnetic fields the conductance of graphene is governed by the half-integer quantum Hall effect. By local electrostatic gating a \textit{p-n} junction perpendicular to the graphene edges can be formed, along which quantum Hall channels co-propagate. ... More
Tunneling spectroscopy of graphene nanodevices coupled to large-gap superconductorsSep 25 2018We performed tunneling spectroscopy measurements of graphene coupled to niobium/niobium-nitride superconducting electrodes. Due to the proximity effect, the graphene density of states depends on the phase difference between the superconductors and exhibits ... More
Tunable transmission of quantum Hall edge channels with full degeneracy lifting in split-gated graphene devicesMay 27 2016Mar 05 2017Charge carriers in the quantum Hall regime propagate via one-dimensional conducting channels that form along the edges of a two-dimensional electron gas. Controlling their transmission through a gate-tunable constriction, also called quantum point contact ... More
Chemical Potential and Quantum Hall Ferromagnetism in Bilayer GrapheneJan 03 2014Jul 07 2014Bilayer graphene has a unique electronic structure influenced by a complex interplay between various degrees of freedom. We probe its chemical potential using double bilayer graphene heterostructures, separated by a hexagonal boron nitride dielectric. ... More
Imaging Dirac fermions flow though a circular Veselago lensNov 07 2018Nov 16 2018Graphene charge carriers behave as relativistic massless fermions, thereby exhibiting a variety of counter-intuitive behaviors. In particular, at p-n junctions, they behave as photons encountering a negative index media, therefore experiencing a peculiar ... More
Edge channel confinement in a bilayer graphene $n$-$p$-$n$ quantum dotSep 04 2017Jan 17 2018We combine electrostatic and magnetic confinement to define a quantum dot in bilayer graphene. The employed geometry couples $n$-doped reservoirs to a $p$-doped dot. At magnetic field values around $B = 2~$T, Coulomb blockade is observed. This demonstrates ... More
Seyfert-Type Dependences of Narrow Emission-Line Ratios and Physical Properties of High-Ionization Nuclear Emission-Line Regions in Seyfert GalaxiesJul 02 2001In order to examine how narrow emission-line flux ratios depend on the Seyfert type, we compiled various narrow emission-line flux ratios of 355 Seyfert galaxies from the literature. We present in this paper that the intensity of the high-ionization emission ... More
Dusty Tori of Seyfert NucleiJan 26 2000Dusty tori around active galactic nuclei (AGNs) play an important role in the classification of Seyfert galaxies. Therefore, physical properties of dusty tori are of great interest. We briefly introduce three statistical studies investigating properties ... More
Multiscale simulation of polymer melt spinning by using the dumbbell modelSep 03 2016We investigated the spinning process of a polymeric material by using a multiscale simulation method which connects the macroscopic and microscopic states through the stress and strain-rate tensor fields, by using Lagrangian particles (filled with polymer ... More
van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus DevicesAug 17 2017Due to the chemical inertness of 2D hexagonal-Boron Nitride (h-BN), few atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such as Black Phosphorus (BP). However, the effects of h-BN on Schottky barrier height, doping and contact ... More
Fabry-Pérot resonances and a crossover to the quantum Hall regime in ballistic graphene quantum point contactsJan 18 2019We report on the observation of quantum transport and interference in a graphene device that is attached with a pair of split gates to form an electrostatically-defined quantum point contact (QPC). In the low magnetic field regime, the resistance exhibited ... More
Photonic Crystal Cavities from Hexagonal Boron NitrideJan 13 2018Development of scalable quantum photonic technologies requires on-chip integration of components such as photonic crystal cavities and waveguides with nonclassical light sources. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform ... More
The [O III]4363 Emitting Region Obscured by Dusty ToriJun 17 2001The emission-line flux ratio of [O III]4363/[O III]5007 is a useful diagnostic for the ionization mechanism and physical properties of narrow-line regions in active galactic nuclei. However, it is known that simple photoionization models underpredict ... More
What Are Narrow-Line Seyfert 1 Galaxies ?: Toward A Viewing-Angle-Dependent Unified Model for Seyfert GalaxiesOct 03 1999Recently growing evidence has been accumulated that the NLS1s are viewed from nearly pole-on viewing angles. However, there has been no theoretical model which explains the following important correlations; 1) weaker optical Fe II emitters always have ... More
Ballistic Josephson junctions in edge-contacted grapheneJan 27 2015Jun 17 2015Hybrid graphene-superconductor devices have attracted much attention since the early days of graphene research. So far, these studies have been limited to the case of diffusive transport through graphene with poorly defined and modest quality graphene-superconductor ... More
Landau level evolution driven by band hybridization in mirror symmetry broken ABA-stacked trilayer grapheneNov 08 2016Layer stacking and crystal lattice symmetry play important roles in the band structure and the Landau levels of multilayer graphene. ABA-stacked trilayer graphene possesses mirror-symmetry-protected monolayer-like and bilayer-like band structures. Broken ... More
Supercurrent Flow in Multi-Terminal Graphene Josephson JunctionsOct 27 2018We investigate the electronic properties of ballistic planar Josephson junctions with multiple superconducting terminals. Our devices consist of monolayer graphene encapsulated in boron nitride with molybdenum-rhenium contacts. Resistance measurements ... More
Gate Tunable Magneto-resistance of Ultra-Thin WTe2 DevicesFeb 20 2017In this work, the magneto-resistance (MR) of ultra-thin WTe2/BN heterostructures far away from electron-hole equilibrium is measured. The change of MR of such devices is found to be determined largely by a single tunable parameter, i.e. the amount of ... More
Observation of the Dirac fluid and the breakdown of the Wiedemann-Franz law in grapheneSep 15 2015Interactions between particles in quantum many-body systems can lead to collective behavior described by hydrodynamics. One such system is the electron-hole plasma in graphene near the charge neutrality point which can form a strongly coupled Dirac fluid. ... More
Very Large Tunneling Magnetoresistance in Layered Magnetic Semiconductor CrI$_3$Jan 24 2018Jun 28 2018Magnetic layered van der Waals crystals are an emerging class of materials giving access to new physical phenomena, as illustrated by the recent observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest in semiconductors is the interplay ... More
Observation of Ultralong Valley Lifetime in WSe2/MoS2 HeterostructuresDec 16 2016The valley degree of freedom in two-dimensional (2D) crystals recently emerged as a novel information carrier in addition to spin and charge. The intrinsic valley lifetime in 2D transition metal dichalcoginides (TMD) is expected to be remarkably long ... More
The High-Ionization Nuclear Emission-Line Region of Seyfert GalaxiesMar 04 2000Recently Murayama & Taniguchi proposed that a significant part of the high-ionization nuclear emission-line region (HINER) in Seyfert nuclei arises from the inner wall of dusty tori because type 1 Seyfert nuclei (S1s) show the excess HINER emission with ... More
Electronic Spin Transport in Dual-Gated Bilayer GrapheneFeb 25 2016Jul 21 2016The elimination of extrinsic sources of spin relaxation is key in realizing the exceptional intrinsic spin transport performance of graphene. Towards this, we study charge and spin transport in bilayer graphene-based spin valve devices fabricated in a ... More
Emergent Dirac gullies and gully-symmetry breaking quantum Hall states in ABA trilayer grapheneMay 02 2018Jul 19 2018We report on quantum capacitance measurements of high quality, graphite- and hexagonal boron nitride encapsulated Bernal stacked trilayer graphene devices. At zero applied magnetic field, we observe a number of electron density- and electrical displacement-tuned ... More
Location of the innermost stable circular orbit of binary neutron stars in the post Newtonian approximations of general relativityJan 05 1998In this paper, we present results obtained from our recent studies on the location of the innermost stable circular orbit (ISCO) for binary neutron stars (BNSs) in several levels of post Newtonian (PN) approximations. We reach the following conclusion ... More
Where is the [O III]4363 emitting region in active galactic nuclei?Nov 04 2000The emission-line flux ratio of [O III]4363/[O III]5007 (R_OIII)is a useful diagnostic for the ionization mechanism and physical properties of emission-line regions in active galactic nuclei (AGNs). However, it is known that simple photoionization models ... More
Broken-Symmetry Quantum Hall States in Twisted Bilayer GrapheneDec 01 2016Dec 04 2016Twisted bilayer graphene offers a unique bilayer two-dimensional-electron system where the layer separation is only in sub-nanometer scale. Unlike Bernal-stacked bilayer, the layer degree of freedom is disentangled from spin and valley, providing eight-fold ... More
Heterointerface effects in the electro-intercalation of van der Waals heterostructuresNov 09 2017Mar 27 2018Molecular-scale manipulation of electronic/ionic charge accumulation in materials is a preeminent challenge, particularly in electrochemical energy storage. Layered van der Waals (vdW) crystals exemplify a diverse family of materials that permit ions ... More
Tunable Lifshitz Transitions and Multiband Transport in Tetralayer GrapheneFeb 21 2018As the Fermi level and band structure of two-dimensional materials are readily tunable, they constitute an ideal platform for exploring Lifshitz transition, a change in the topology of a material's Fermi surface. Using tetralayer graphene that host two ... More
Mach-Zehnder interferometry using spin- and valley-polarized quantum Hall edge states in grapheneMar 01 2017Confined to a two-dimensional plane, electrons in a strong magnetic field travel along the edge in one-dimensional quantum Hall channels that are protected against backscattering. These channels can be used as solid-state analogues of monochromatic beams ... More
Flat Bands in Buckled Graphene SuperlatticesApr 23 2019Interactions between stacked two-dimensional (2D) atomic crystals can radically change their properties, leading to essentially new materials in terms of the electronic structure. Here we show that monolayers placed on an atomically flat substrate can ... More
Visualizing the Effect of an Electrostatic Gate with Angle-Resolved Photoemission SpectroscopyApr 20 2019Electrostatic gating is pervasive in materials science, yet its effects on the electronic band structure of materials has never been revealed directly by angle-resolved photoemission spectroscopy (ARPES), the technique of choice to non-invasively probe ... More
Cubic BN optical gap and intragap optically active defectsJun 29 2018We report a comprehensive study on the optical properties of cubic boron nitride (c-BN) and its optically active defects. Using electron energy-loss spectroscopy (EELS) within a monochromated scanning transmission electron microscope (STEM) on the highest-quality ... More
Correlated Insulating and Superconducting States in Twisted Bilayer Graphene Below the Magic AngleFeb 13 2019The emergence of flat bands and correlated behaviors in 'magic angle' twisted bilayer graphene (tBLG) has sparked tremendous interest, though many aspects of the system are under intense debate. Here we report observation of both superconductivity and ... More
Raman Spectroscopy, Photocatalytic Degradation and Stabilization of Atomically Thin Chromium TriiodideMay 23 2018As a 2D ferromagnetic semiconductor with magnetic ordering, atomically thin chromium triiodide is the latest addition to the family of two-dimensional (2D) materials. However, realistic exploration of CrI3-based devices and heterostructures is challenging, ... More
Phase-separation transitions in asymmetric lipid bilayersApr 13 2015Morphological transitions of phase separation associated with the asymmetry of lipid composition were investigated using micrometer-sized vesicles of lipid bilayers made from a lipid mixture. The complete macro-phase-separated morphology undergoes a transition ... More
On relations among Dirichlet series whose coefficients are class numbers of binary cubic formsNov 04 2007We study the class numbers of integral binary cubic forms. For each $SL_2(Z)$ invariant lattice $L$, Shintani introduced Dirichlet series whose coefficients are the class numbers of binary cubic forms in $L$. We classify the invariant lattices, and investigate ... More
The Atomic and Electronic structure of 0° and 60° grain boundaries in MoS2Sep 03 2018Mar 28 2019We have investigated atomic and electronic structure of grain boundaries in monolayer MoS2, where relative angles between two different grains are 0 and 60 degree. The grain boundaries with specific relative angle have been formed with chemical vapor ... More
High-Yield Proximity-Induced Chemical Vapor Deposition of Graphene Over Millimeter-Sized Hexagonal Boron NitrideJan 21 2017We present a transfer-free preparation method for graphene on hexagonal boron nitride (h-BN) crystals by chemical vapor deposition of graphene via a catalytic proximity effect, i.e. activated by a Cu catalyst close-by . We demonstrate the full coverage ... More
Coupled quantum dots in bilayer grapheneMay 08 2018Aug 06 2018Electrostatic confinement of charge carriers in bilayer graphene provides a unique platform for carbon-based spin, charge or exchange qubits. By exploiting the possibility to induce a band gap with electrostatic gating, we form a versatile and widely ... More
Substrate-Induced Shifts and Screening in the Fluorescence Spectra of Supramolecular Adsorbed Organic MonolayersMay 29 2018We have investigated the influence of the substrate on the fluorescence of adsorbed organic molecules. Monolayer films of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI), a supramolecular network formed from PTCDI and melamine, and perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride ... More
Inducing Superconducting Correlation in Quantum Hall Edge StatesSep 26 2016Sep 28 2016The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a 2-dimensional electron gas (2DEG) system. A superconductor (SC) contacting these states induces correlation of the quasi-particles in the dissipationless 1D chiral ... More
Nanospot Angle-Resolved Photoemission Study of Bernal-Stacked Bilayer Graphene on Hexagonal Boron Nitride: Band Structure and Local Variation of Lattice AlignmentApr 24 2019Hexagonal boron nitride (hBN) is the supporting substrate of choice for two-dimensional material devices because it is atomically flat and chemically inert. However, due to the small size of mechanically exfoliated hBN flakes, electronic structure studies ... More
Evidence of Gate-Tunable Mott Insulator in Trilayer Graphene-Boron Nitride Moiré SuperlatticeMar 06 2018Jan 19 2019Mott insulator plays a central role in strongly correlated physics, where the repulsive Coulomb interaction dominates over the electron kinetic energy and leads to insulating states with one electron occupying each unit cell. Doped Mott insulator is often ... More
Revealing the Biexciton and Trion-exciton Complexes in BN Encapsulated WSe2Jun 11 2018Strong Coulomb interactions in single-layer transition metal dichalcogenides (TMDs) result in the emergence of strongly bound excitons, trions and biexcitons. These excitonic complexes possess the valley degree of freedom, which can be exploited for quantum ... More
Inclusive and exclusive $b\to s/dγ$Oct 03 2008Oct 09 2008In this article, I review the recent results for inclusive and exclusive measurements for $b\to s\gamma$ and $b\to d\gamma$ decays from $B$ factories Belle and Babar. I describe the measurement of branching fraction and direct CP violating asymmetry for ... More
Nonperturbative Renormalization Group Function for Quantum Hall Plateau Transitions Imposed by Global SymmetriesOct 26 1998As a unified theory of integer and fractional quantum Hall plateau transitions, a nonperturbative theory of the two-parameter scaling renormalization group function is presented. By imposing global symmetries known as ``the law of corresponding states'', ... More
On Ratliff-Rush closure of modulesApr 03 2018In this paper, we introduce the notion of Ratliff-Rush closure of modules and explore whether the condition of the Ratliff-Rush closure coincides with the integral closure. The main result characterizes the condition in terms of the normality of the projective ... More
Deformation of two body quantum Calogero-Moser-Sutherland modelsJul 25 2006The possibility of deformation of two body quantum Calogero-Moser-Sutherland models is studied. Obtained are some necessary conditions for the singular locus of the potential function. Such locus is determined if it consists of two, three or four lines. ... More
Coupled dynamics of magnetizations in spin-Hall oscillators via spin current injectionJan 23 2019An array of spin torque oscillators (STOs) for practical applications such as pattern recognition was recently proposed, where several STOs are connected by a common nonmagnet. In this structure, in addition to the electric and/or magnetic interactions ... More