Results for "Michinari Kono"

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wavEMS: Improving Signal Variation Freedom of Electrical Muscle StimulationFeb 08 2019There has been a long history in electrical muscle stimulation (EMS), which has been used for medical and interaction purposes. Human-computer interaction (HCI) researchers are now working on various applications, including virtual reality (VR), notification, ... More
Post-Data Augmentation to Improve Deep Pose Estimation of Extreme and Wild MotionsFeb 12 2019Contributions of recent deep-neural-network (DNN) based techniques have been playing a significant role in human-computer interaction (HCI) and user interface (UI) domains. One of the commonly used DNNs is human pose estimation. This kind of technique ... More
On the homotopy types of $\mathrm{Sp}(n)$ gauge groupsMar 17 2018May 17 2018Let $\mathcal{G}_{k,n}$ be the gauge group of the principal $\mathrm{Sp}(n)$-bundle over $S^4$ corresponding to $k\in\mathbb{Z}\cong\pi_3(\mathrm{Sp}(n))$. We refine the result of Sutherland on the homotopy types of $\mathcal{G}_{k,n}$ and relate it with ... More
Electroweak Strings and FermionsJul 19 1995Z-strings in the Weinberg-Salam model including fermions are unstable for all values of the parameters. The cause of this instability is the fermion vacuum energy in the Z-string background. Z-strings with non-zero fermion densities, however, may still ... More
Gyro-viscosity and linear dispersion relations in pair-ion magnetized plasmasOct 17 2015A fluid theory has been developed by taking account of gyro-viscosity to study wave propagation characteristics in a homogeneous pair-ion magnetized plasma with a cylindrical symmetry. The exact dispersion relations derived by the Hankel-Fourier transformation ... More
Bound-bound transitions in the emission spectra of Ba$^{+}$--He excimerApr 29 2016We present an experimental and theoretical study of the emission and absorption spectra of the Ba$^{+}$ ions and Ba$^{+\ast}$He excimer quasimolecules in the cryogenic Ba--He plasma. We observe several new spectral features in the emission spectrum which ... More
Photon-induced vanishing of magnetoconductance in 2D electrons on liquid HeJun 02 2010Sep 17 2010We report on a novel transport phenomenon realized by optical pumping in surface state electrons on helium subjected to perpendicular magnetic fields. The electron dynamics is governed by the photon-induced excitation and scattering-mediated transitions ... More
Diffusion-limited exciton-exciton annihilation in single-walled carbon nanotubes: A time-dependent analysisOct 31 2008To provide physical insight into the recently observed photoluminescence saturation behaviors in single-walled carbon nanotubes implying the existence of an upper limit of exciton densities, we have performed a time-dependent theoretical study of diffusion-limited ... More
Nonlinear Photoluminescence Excitation Spectroscopy of Carbon Nanotubes: Exploring the Upper Density Limit of One-Dimensional ExcitonsApr 20 2008We have studied emission properties of high-density excitons in single-walled carbon nanotubes through nonlinear photoluminescence excitation spectroscopy. As the excitation intensity was increased, all emission peaks arising from different chiralities ... More
On the Alfven wave cut-off in partly ionized collisional plasmasJan 26 2014The cut-off of the Alfven wave, caused by plasma collisions with neutrals in multi-component partially ionized plasmas, is discussed. Full multi-component theory is used, and similarities and differences regarding the classic magnetohydrodynamic theory ... More
Ion plasma wave and its instability in interpenetrating plasmasApr 04 2014Some essential features of the ion plasma wave in both kinetic and fluid descriptions are presented. The wave develops at wavelengths shorter than the electron Debye radius. Thermal motion of electrons at this scale is such that they overshoot the electrostatic ... More
Lusternik-Schnirelmann category of Spin{9}Jul 23 2005Let G be a compact connected Lie group and p : E \to {\Sigma}^2V a principal G-bundle with a characteristic map \alpha : A={\Sigma}V \to G. By combining cone decomposition arguments in Iwase-Mimura-Nishimoto [3,5] with computations of higher Hopf invariants ... More
Nonlinear Wigner solid transport over superfluid helium under AC conditionsJan 12 2009Nonlinear transport properties of the two-dimensional Wigner solid of surface electrons on superfluid helium are studied for alternating current conditions. For time-averaged quantities like Fourier coefficients, the field-velocity characteristics are ... More
Energy in density gradientJan 15 2015Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. ... More
Phase retrieval from single biomolecule diffraction patternJan 07 2011Dec 09 2011In this paper, we propose the SPR (sparse phase retrieval) method, which is a new phase retrieval method for coherent x-ray diffraction imaging (CXDI). Conventional phase retrieval methods effectively solve the problem for high signal-to-noise ratio measurements, ... More
Review: Observation of Majorana Bound States at a Free Surface of $^3$He-BMay 29 2018Aug 25 2018The $p$-wave superfluid $^3$He is a textbook example of topological superfluids. Among its multiple superfluid phases, the B phase ($^3$He-B) is known as a topological state protected by time-reversal symmetry. One of the important topological features ... More
Science and applications of wafer-scale crystalline carbon nanotube films prepared through controlled vacuum filtrationOct 06 2018Carbon nanotubes (CNTs) make an ideal one-dimensional (1D) material platform for the exploration of exotic physical phenomena under extremely strong quantum confinement. The 1D character of electrons, phonons and excitons in individual CNTs features extraordinary ... More
First Study of Intersubband Absorption in Electrons on Helium under Quantizing Magnetic FieldsMar 25 2013We present the first measurements of inter-subband absorption of microwaves in surface electrons on liquid helium subjected to perpendicular magnetic field B. In quantizing B, the power absorption shows intermittent regions of enhanced and suppressed ... More
Novel Radiation-induced Magnetoresistance Oscillations in a Nondegenerate 2DES on Liquid HeliumOct 16 2009Nov 02 2009We report the observation of novel magnetoresistance oscillations induced by the resonant inter-subband absorption in nondegenerate 2D electrons bound to the surface of liquid helium. The oscillations are periodic in 1/B and originate from the scattering-mediated ... More
Existence of an upper limit on the density of excitons in carbon nanotubes by diffusion-limited exciton-exciton annihilation: Experiment and theoryJan 02 2009Through an investigation of photoemission properties of highly-photoexcited single-walled carbon nanotubes, we demonstrate that there is an upper limit on the achievable excitonic density. As the intensity of optical excitation increases, all photoluminescence ... More
Dark Matter Detection With Electron Neutrinos in Liquid Scintillation DetectorsMar 16 2011Jul 26 2011We consider the prospects for liquid scintillation experiments (with a focus on KamLAND) to detect the flux of electron neutrinos arising from dark matter annihilation in the core of the sun. We show that, with data already taken, KamLAND can provide ... More
Influence Analysis in the BlogosphereDec 24 2012In this paper we analyze influence in the blogosphere. Recently, influence analysis has become an increasingly important research topic, as online communities, such as social networks and e-commerce sites, playing a more and more significant role in our ... More
Effects of space-time noncommutativity on the angular power spectrum of the CMBJul 02 2003Jan 20 2004We investigate an inflationary model of the universe based on the assumption that space-time is noncommutative in the very early universe. We analyze the effects of space-time noncommutativity on the quantum fluctuations of an inflaton field and investigate ... More
Selective Heating Mechanism of Magnetic Metal Oxides by Alternating Magnetic Field in Microwave Sintering ProcessJun 18 2008Feb 13 2009The mechanism of rapid and selective heating of magnetic metal oxides under the magnetic field of microwaves which continues beyond the Curie temperature $ T_{c} $ is identified by using the Heisenberg model. Monte Carlo calculations based on the energy ... More
The ATLAS trigger menu for early data-takingAug 29 2008The ATLAS trigger system is based on three levels of event selection that select the physics of interest from an initial bunch-crossing rate of 40 MHz. During nominal LHC operations at a luminosity of 10^34 cm^-2 s^-1, decisions must be taken every 25 ... More
A mechanism of the large-scale damping in the CMB anisotropyDec 28 2003Sep 22 2004We present a mechanism through which a certain class of short-distance cutoff affects the CMB anisotropies at large angular scales. Our analysis is performed in two steps. The first is given in an intuitive way, using the property of the inflationary ... More
Noncommutative inflation and the large-scale damping in the CMB anisotropyJan 22 2004Jan 23 2004We show that a certain class of short-distance cutoff can give rise to large suppression on the CMB anisotropies at large angular scales.
Theory of Coupled Multipole Moments Probed by X-ray Scattering in CeB$_6$Apr 21 2004A minimal model for multipole orders in CeB$_6$ shows that degeneracy of the quadrupole order parameters and strong spin-orbit coupling lead to peculiar temperature and magnetic-field dependences of the X-ray reflection intensity at superlattice Bragg ... More
Resonant Photovoltaic Effect in Surface-State Electrons on Liquid HeliumJan 29 2011Aug 12 2012We observed an ultra-strong photovoltaic effect induced by resonant intersubband absorption of microwaves in a two-dimensional electrons system on the surface of liquid helium. The effect emerges in the regime of microwave-induced vanishing of dissipative ... More
Terahertz Strong-Field Physics without a Strong External Terahertz FieldJan 20 2019Traditionally, strong-field physics explores phenomena in matter (atoms, molecules, and solids) driven by an extremely strong laser field nonperturbatively. However, even in the complete absence of an external electromagnetic field, strong-field phenomena ... More
Uncooled Carbon Nanotube PhotodetectorsMay 11 2015Photodetectors play key roles in many applications such as remote sensing, night vision, reconnaissance, medical imaging, thermal imaging, and chemical detection. Several properties such as performance, reliability, ease of integration, cost, weight, ... More
EEG Signal Processing and Classification for the Novel Tactile-Force Brain-Computer Interface ParadigmOct 06 2013Oct 17 2013The presented study explores the extent to which tactile-force stimulus delivered to a hand holding a joystick can serve as a platform for a brain computer interface (BCI). The four pressure directions are used to evoke tactile brain potential responses, ... More
Charge exchange in fluid description of partially ionized plasmasNov 03 2015The effects of charge exchange on waves propagating in weakly ionized plasmas are discussed. It is shown that for low-frequency processes, ions and neutrals should be treated as a single fluid with some effective charge on all of them. We have derived ... More
Anisotropic Decay Dynamics of Photoexcited Aligned Carbon Nanotube BundlesDec 31 2006We have performed polarization-dependent ultrafast pump-probe spectroscopy of a film of aligned single-walled carbon nanotube bundles. By taking into account imperfect nanotube alignment as well as anisotropic absorption cross sections, we quantitatively ... More
Photo-thermal transitions of magneto-excitons in quantum wellsJul 12 2002By monitoring changes in excitonic photoluminescence (PL) that are induced by terahertz (THz) radiation, we observe resonant THz absorption by magnetoexcitons in GaAs/AlGaAs quantum wells. Changes in the PL spectrum are explored as a function of temperature ... More
Direct Observation of Dark Excitons in Individual Carbon Nanotubes: Role of Local EnvironmentsApr 05 2008We report the direct observation of the spin-singlet dark excitonic state in individual single-walled carbon nanotubes through low-temperature micro-photoluminescence spectroscopy in magnetic fields. A magnetic field up to 5 T, applied along the nanotube ... More
Collisional energy transfer in two-component plasmasAug 18 2008The friction in plasmas consisting of two species with different temperatures is discussed together with the consequent energy transfer. It is shown that the friction between the two species has no effect on the ion acoustic mode in a quasi-neutral plasma. ... More
Resistive detection of nuclear spins in a single quantum dot under Kondo effect regimeJan 31 2013We study dynamic polarization and resistive detection of nuclear spins in a semiconductor quantum dot (QD) under the Kondo effect regime. We find that the differential conductance spectra of the QD exhibit hysteresis under the Kondo effect regime in magnetic ... More
Dynamics of the vortex-particle complexes bound to the free surface of superfluid heliumSep 04 2018We present an experimental and theoretical study of the 2D dynamics of electrically charged nanoparticles trapped under a free surface of superfluid helium in a static vertical electric field. We focus on the dynamics of particles driven by the interaction ... More
Ripplonic Lamb shift for electrons on liquid heliumJul 10 2017We study the shift of the energy levels of electrons on helium surface due to the coupling to the quantum field of surface vibrations. As in quantum electrodynamics, the coupling is known, and it is known to lead to an ultraviolet divergence of the level ... More
Anomalous magneto-optical Kerr hysteresis loops in Fe$_{0.25}$TaS$_{2}$May 12 2011Dec 13 2011We have performed magneto-optical Kerr spectroscopy measurements on intercalated transition-metal dichalcogenide Fe$_{0.25}$TaS$_{2}$ in the polar Kerr geometry as a function of temperature, magnetic field, and wavelength. The Kerr angle exhibits pronounced ... More
Terahertz Science and Technology of Carbon NanomaterialsNov 23 2013The diverse applications of terahertz radiation and its importance to fundamental science makes finding ways to generate, manipulate, and detect terahertz radiation one of the key areas of modern applied physics. One approach is to utilize carbon nanomaterials, ... More
Electronic magnetization of a quantum point contact measured by nuclear magnetic resonanceJun 17 2015We report an electronic magnetization measurement of a quantum point contact (QPC) based on nuclear magnetic resonance (NMR) spectroscopy. We find that NMR signals can be detected by measuring the QPC conductance under in-plane magnetic fields. This makes ... More
Laser-Induced Above-Bandgap Transparency in GaAsMar 20 2004We report the observation of large ($\sim 40%$) laser-induced above-bandgap transparency in GaAs at room temperature. The induced transparency is present only during the pulse width of the driving midinfrard laser pulses and its spectral shape is consistent ... More
Thermodynamic evidence for novel quantum criticality in a frustrated metalApr 18 2019Various exotic phases of matter have been discovered near a quantum critical point where magnetic order is suppressed to absolute zero temperature by strong quantum fluctuations. There have remained fundamental questions whether geometrical frustration ... More
Search for Kaluza-Klein gravitons in extra dimension models via forward detectors at the LHCMar 19 2015Jun 11 2015We investigate contributions of Kaluza-Klein (KK) graviton in extra dimension models to the process $pp \to p\gamma p \to p\gamma j X$, where a proton emits a quasireal photon and is detected by using the very forward detectors planned at the LHC. In ... More
Voltage-Selective Bi-directional Polarization and Coherent Rotation of Nuclear Spins in Quantum DotsDec 21 2010Apr 19 2011We proposed and demonstrated that the nuclear spins of the host lattice in GaAs double quantum dots can be strongly polarized in either of two opposite directions, parallel or antiparallel to an external magnetic field. The direction is selected simply ... More
Spatial gradient of dynamic nuclear spin polarization induced by breakdown of quantum Hall effectDec 20 2010We studied spatial distribution of dynamic nuclear polarization (DNP) in a Hall-bar device in a breakdown regime of the quantum Hall effect (QHE). We detected nuclear magnetic resonance (NMR) signals from the polarized nuclear spins by measuring the Hall ... More
Giant Tunable Faraday Effect in a Semiconductor Magneto-plasma for Broadband Terahertz Polarization OpticsJun 10 2012We report on a giant Faraday effect in an electron plasma in n-InSb probed via polarization-resolved terahertz (THz) time-domain spectroscopy. Polarization rotation angles and ellipticities reach as large as {\pi}/2 and 1, respectively, over a wide frequency ... More
Dynamics of fine particles due to quantized vortices on the surface of superfluid $^4$HeSep 05 2018Peculiar dynamics of a free surface of the superfluid 4He has been observed experimentally with a newly established technique utilizing a number of electrically charged fine metal particles trapped electrically at the surface by Moroshkin et al. They ... More
Microwave Absorption of Surface-State Electrons on Liquid $^3$HeMay 03 2007We have investigated the intersubband transitions of surface state electrons (SSE) on liquid $^3$He induced by microwave radiation at temperatures from 1.1 K down to 0.01 K. Above 0.4 K, the transition linewidth is proportional to the density of $^3$He ... More
High-Ampacity Power Cables of Tightly-Packed and Aligned Carbon NanotubesFeb 14 2014We characterize the current-carrying capacity (CCC), or ampacity, of highly-conductive, light, and strong carbon nanotube (CNT) fibers by measuring their failure current density (FCD) and continuous current rating (CCR) values. We show, both experimentally ... More
Ultrafast Photoinduced Softening in a III-V Ferromagnetic Semiconductor for Non-thermal Magneto-Optical RecordingMay 01 2003Mar 04 2004Through time-resolved two-color magneto-optical Kerr spectroscopy we have demonstrated that photogenerated transient carriers decrease the coercivity of ferromagnetic InMnAs at low temperatures. This transient ``softening'' persists only during the carrier ... More
The Unique Origin of Colors of Armchair Carbon NanotubesSep 11 2011Dec 09 2011The colors of suspended metallic colloidal particles are determined by their size-dependent plasma resonance, while those of semiconducting colloidal particles are determined by their size-dependent band gap. Here, we present a novel case for armchair ... More
An incompressible state of a photo-excited electron gasApr 16 2015Two dimensional electrons in a magnetic field can form new states of matter characterized by topological properties and strong electronic correlations as displayed in the integer and fractional quantum Hall states. In these states the electron liquid ... More
Femtosecond Demagnetization and Hot Hole Relaxation in Ferromagnetic GaMnAsApr 02 2008We have studied ultrafast photoinduced demagnetization in GaMnAs via two-color time-resolved magneto-optical Kerr spectroscopy. Below-bandgap midinfrared pump pulses strongly excite the valence band, while near-infrared probe pulses reveal sub-picosecond ... More
Observation of strong electron dephasing in disordered Cu$_{93}$Ge$_4$Au$_3$ thin filmsJun 20 2007We report the observation of strong electron dephasing in a series of disordered Cu$_{93}$Ge$_4$Au$_3$ thin films. A very short electron dephasing time possessing very weak temperature dependence around 6 K, followed by an upturn with further decrease ... More
Terahertz Time-Domain Magnetospectroscopy of a High-Mobility Two-Dimensional Electron GasApr 14 2007We have observed cyclotron resonance in a high-mobility GaAs/AlGaAs two-dimensional electron gas by using the techniques of terahertz time-domain spectroscopy combined with magnetic fields. From this, we calculate the real and imaginary parts of the diagonal ... More
Terahertz Dynamics of Quantum-Confined Electrons in Carbon NanomaterialsMay 28 2012Low-dimensional carbon nanostructures, such as single-wall carbon nanotubes (SWCNTs) and graphene, offer new opportunities for terahertz science and technology. Being zero-gap systems with a linear, photon-like energy dispersion, metallic SWCNTs and graphene ... More
mini-TimeCube as a Neutron Scatter CameraMar 05 2019We present Monte Carlo (MC) simulation results from a study of a compact plastic-scintillator detector suitable for imaging fast neutrons in the 1 -- 10 MeV energy range: the miniTimeCube (mTC). Originally designed for antineutrino detection, the mTC ... More
$S$ =1/2 ferromagnetic Heisenberg chain in a verdazyl-based complexMar 16 2019We present a model compound for the $S$=1/2 ferromagnetic Heisenberg chain composed of the verdazyl-based complex $[$Zn(hfac)$_2]$$[$4-Cl-$o$-Py-V-(4-F)$_2]$. $Ab$ $initio$ MO calculations indicate a predominant ferromagnetic interaction forming an $S$=1/2 ... More
Quantized escape and formation of edge channels at high Landau levelsDec 10 2012We present nonlocal resistance measurements in an ultra high mobility two dimensional electron gas. Our experiments show that even at weak magnetic fields classical guiding along edges leads to a strong non local resistance on macroscopic distances. In ... More
Synergistic Formation of Radicals by Irradiation with Both Vacuum Ultraviolet and Atomic Hydrogen: A Real-Time In Situ Electron Spin Resonance StudyJun 29 2012We report on the surface modification of polytetrafluoroethylene (PTFE) as an example of soft- and bio-materials that occur under plasma discharge by kinetics analysis of radical formation using in situ real-time electron spin resonance (ESR) measurements. ... More
Microwave-Absorption-Induced Heating of Surface State Electrons on Liquid 3HeNov 09 2007A resonance-induced change in the resistivity of the surface state electrons (SSE) exposed to the microwave (MW) radiation is observed. The MW frequency corresponds to the transition energy between two lowest Rydberg energy levels. All measurements are ... More
Resonant Correlation-Induced Optical Bistability in an Electron System on Liquid HeliumJun 30 2009We show that electrons on liquid helium display intrinsic bistability of resonant inter-subband absorption. The bistability occurs for comparatively weak microwave power. The underlying giant nonlinearity of the many-electron response results from the ... More
Nonclassical photon number distribution in a superconducting cavity under a squeezed driveFeb 20 2017Aug 25 2017A superconducting qubit in the strong dispersive regime of a circuit quantum electrodynamics system is a powerful probe for microwave photons in a cavity mode. In this regime, a qubit spectrum is split into multiple peaks, with each peak corresponding ... More
Review of Anisotropic Terahertz Material ResponseMay 09 2013Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear ... More
Above-Bandgap Magneto-optical Kerr Effect in Ferromagnetic GaMnAsJul 09 2009May 19 2010We have performed a systematic magneto-optical Kerr spectroscopy study of GaMnAs with varying Mn densities as a function of temperature, magnetic field, and photon energy. Unlike previous studies, the magnetization easy axis was perpendicular to the sample ... More
Spin bottleneck in resonant tunneling through double quantum dots with different Zeeman splittingsApr 07 2009Dec 21 2009We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g-factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels ... More
Wing structure in the phase diagram of the Ising Ferromagnet URhGe close to its tricritical point investigated by angle-resolved magnetization measurementsSep 01 2017High-precision angle-resolved dc magnetization and magnetic torque studies were performed on a single-crystalline sample of URhGe, an orthorhombic Ising ferromagnet with the $c$ axis being the magnetization easy axis, in order to investigate the phase ... More
Exciton Diamagnetic Shifts and Valley Zeeman Effects in Monolayer WS$_2$ and MoS$_2$ to 65 TeslaOct 23 2015We report circularly-polarized optical reflection spectroscopy of monolayer WS$_2$ and MoS$_2$ at low temperatures (4~K) and in high magnetic fields to 65~T. Both the A and the B exciton transitions exhibit a clear and very similar Zeeman splitting of ... More
A table-top, repetitive pulsed magnet for nonlinear and ultrafast spectroscopy in high magnetic fields up to 30 TOct 14 2013We have developed a mini-coil pulsed magnet system with direct optical access, ideally suited for nonlinear and ultrafast spectroscopy studies of materials in high magnetic fields up to 30 T. The apparatus consists of a small coil in a liquid nitrogen ... More
Ultrafast optical manipulation of ferromagnetic order in InMnAs/GaSbJul 23 2002We have performed a two-color time-resolved magneto-optical Kerr effect (MOKE) study of a ferromagnetic InMnAs/GaSb heterostructure. We observed ultrafast photo-induced changes in the MOKE signal induced by a large density of spin-polarized transient ... More
Theory of carrier dynamics and time resolved reflectivity in InMnAs/GaSb heterostructuresSep 06 2005We present detailed theoretical calculations of two color, time-resolved pump-probe differential reflectivity measurements. The experiments modeled were performed on InMnAs/GaSb heterostructures and showed pronounced oscillations in the differential reflectivity ... More
Terahertz Coherent Control of a Landau-Quantized Two-Dimensional Electron GasSep 28 2011We demonstrate coherent control of cyclotron resonance (CR) in a two-dimensional electron gas (2DEG). We use a sequence of terahertz pulses to control the amplitude of CR oscillations in an arbitrary fashion via phase-dependent coherent interactions. ... More
Anisotropic magnetic-field response of quantum critical fluctuations in Ni-doped CeCoIn5Feb 13 2019This paper demonstrates the anisotropic response of quantum critical fluctuations with respect to the direction of the magnetic field $B$ in Ni-doped CeCoIn$_5$ by measuring the magnetization $M$ and specific heat $C$. The results show that $M/B$ at $B=0.1\ ... More
Anomalous Quasiparticle Reflection from the Surface of a $^3$He-$^4$He Dilute SolutionJun 23 2017Nov 21 2017A free surface of a dilute $^3$He-$^4$He liquid mixture is a unique system where two Fermi liquids with distinct dimensions coexist: a three-dimensional (3D) $^3$He Fermi liquid in bulk and a two-dimensional (2D) $^3$He Fermi liquid at the surface. To ... More
Magneto-reflection spectroscopy of monolayer transition-metal dichalcogenide semiconductors in pulsed magnetic fieldsMar 22 2016We describe recent experimental efforts to perform polarization-resolved optical spectroscopy of monolayer transition-metal dichalcogenide semiconductors in very large pulsed magnetic fields to 65 tesla. The experimental setup and technical challenges ... More
Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal EmittersMar 14 2019Refractory nanophotonics, or nanophotonics at high temperatures, can revolutionize many applications, including data storage and waste heat recovery. In particular, nanophotonic devices made from hyperbolic materials are promising due to their nearly ... More
Terahertz magneto-spectroscopy of transient plasmas in semiconductorsSep 03 2002Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have performed picosecond time-resolved THz spectroscopy of transient carriers in semiconductors. Specifically, we measured the temporal evolution of THz transmission and reflectivity ... More
Cotunneling effects in GaAs vertical double quantum dotNov 17 2010We observed lifting of Coulomb blockade in GaAs vertical double quantum dot with low potential barriers, induced by cotunneling mechanisms at dilution fridge temperature of 10 mK. Several distinct features were observed, compared to single dot case, and ... More
Anti-ExB flow field associated with a vortex formation in a partially ionized plasmaOct 22 2004A high-density magnetized plasma has been studied for understanding of plasma dynamics in partially ionized plasmas. Ion flow field has been obtained experimentally, and is shown to be associated with a vortex formation. The most remarkable result is ... More
Direct Measurement of Cyclotron Coherence Times of High-Mobility Two-Dimensional Electron GasesMar 14 2010We have observed long-lived (~30 ps) coherent oscillations of charge carriers due to cyclotron resonance (CR) in high-mobility two-dimensional electrons in GaAs in perpendicular magnetic fields using time-domain terahertz spectroscopy. The observed coherent ... More
Rapid Scanning Terahertz Time-Domain Magnetospectroscopy with a Table-Top Repetitive Pulsed MagnetApr 22 2014We have performed terahertz time-domain magnetospectroscopy by combining a rapid scanning terahertz time-domain spectrometer based on the electronically coupled optical sampling method with a table-top mini-coil pulsed magnet capable of producing magnetic ... More
A Radio Detection Survey of Narrow-Line Seyfert 1 Galaxies using Very-Long-Baseline Interferometry at 22 GHzMar 15 2016We conducted a high-sensitivity radio detection survey for forty narrow-line Seyfert 1 (NLS1) galaxies using very-long-baseline interferometry (VLBI) at 22 GHz through phase-referencing long-time integration and using a newly developing recorder with ... More
Stick-Slip Motion of the Wigner Solid on Liquid HeliumMar 22 2016We present time-resolved transport measurements of a Wigner solid (WS) on the surface of liquid Helium confined in a micron-scale channel. At rest, the WS is `dressed' by a cloud of quantised capillary waves (ripplons). Under a driving force, we find ... More
Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser IrradiationApr 25 2005Aug 18 2005Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs reveals two distinct {\em demagnetization} processes -- fast ($<1$ ps) and slow ($\sim$100 ps). Both components diminish with increasing temperature and are absent above the Curie ... More
Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon NanotubesAug 26 2018Optical properties of single-wall carbon nanotubes (SWCNTs) for light polarized parallel to the nanotube axis have been extensively studied, whereas their response to light polarized perpendicular to the nanotube axis has not been well explored. Here, ... More
Superfluid-like TO Responses in Rotating Solid HeliumJan 25 2017The irrotational nature of superfluid helium was discovered through its decoupling from the container under rotation. Similarly, the resonant period drop of a torsional oscillator (TO) containing solid helium was first interpreted as the decoupling of ... More
Mode identification of high-quality-factor single-defect nanocavities in quantum dot-embedded photonic crystalsFeb 09 2007We investigate the quality (Q) factor and the mode dispersion of single-defect nanocavities based on a triangular-lattice GaAs photonic-crystal (PC) membrane, which contain InAs quantum dots (QDs) as a broadband emitter. To obtain a high Q factor for ... More
Stability of 1-D Excitons in Carbon Nanotubes under High Laser ExcitationsAug 30 2004Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide continuum probe, we show that interband exciton peaks in single-walled carbon nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates of the initial densities ... More
Propagating Coherent Acoustic Phonon Wavepackets in InMnAs/GaSbMay 10 2005We observe pronounced oscillations in the differential reflectivity of a ferromagnetic InMnAs/GaSb heterostructure using two-color pump-probe spectroscopy. Although originally thought to be associated with the ferromagnetism, our studies show that the ... More
Bistability and Hysteresis of Intersubband Absorption in Strongly Interacting Electrons on Liquid HeliumJan 27 2012We study nonlinear inter-subband microwave absorption of electrons bound to the liquid helium surface. Already for a comparatively low radiation intensity, resonant absorption due to transitions between the two lowest subbands is accompanied by electron ... More
Transport Measurements of Strongly-Correlated Electrons on Helium in a Classical Point-Contact DeviceMay 19 2011We present transport measurements of electrons on the surface of liquid helium in a microchannel device in which a constriction may be formed by a split-gate electrode. The surface electron current passing through the microchannel first decreases and ... More
Effect of Rotation on Elastic Moduli of Solid $^4$HeNov 12 2017We report measurements of elastic moduli of hcp solid $^4$He down to 15 mK when the samples are rotated unidirectionally. Recent investigations have revealed that the elastic behavior of solid $^4$He is dominated by gliding of dislocations and pinning ... More
Bistable Transport Properties of a Quasi-One-Dimensional Wigner Solid on Liquid Helium under Continuous DrivingAug 31 2017We investigate low-frequency fluctuations in the transport characteristics of a quasi-1D Wigner solid (WS) moving along a liquid helium substrate in response to a sinusoidal driving voltage. The fluctuations occur between distinct transport modes in which ... More
Dicke Superradiance in SolidsFeb 13 2016May 29 2016Recent advances in optical studies of condensed matter have led to the emergence of phenomena that have conventionally been studied in the realm of quantum optics. These studies have not only deepened our understanding of light-matter interactions but ... More
Magneto-Optics of Exciton Rydberg States in a Monolayer SemiconductorSep 01 2017Jan 25 2018We report 65 tesla magneto-absorption spectroscopy of exciton Rydberg states in the archetypal monolayer semiconductor WSe$_2$. The strongly field-dependent and distinct energy shifts of the 2s, 3s, and 4s excited neutral excitons permits their unambiguous ... More
Time-Integrated Evidence for Superfluorescence from Dense Electron-Hole Magneto-Plasmas in Semiconductor Quantum WellsJul 02 2006Jul 28 2009Cooperative spontaneous recombination (superfluorescence) of electron-hole plasmas in semiconductors has been a challenge to observe due to ultrafast decoherence. We argue that superfluorescence can be achieved in quantum-confined semiconductor systems ... More
Fine-Tuning of Magnetic Interactions in Organic Spin LaddersFeb 12 2014We have succeeded in synthesizing two types of new organic radical crystals 3-I-V [= 3- (3-iodophenyl)-1,5-diphenylverdazyl] and 3-Br-4-F-V [= 3-(3-bromo-4-fluorophenyl)-1,5- diphenylverdazyl]. Their crystal strucutures are found to be isomorphous to ... More