A5007066086- Physics of Superconductivity and Magnetism
- Semiconductor Quantum Structures and Devices
- Quantum and electron transport phenomena
- Terahertz technology and applications
- Spectroscopy and Quantum Chemical Studies
- Magnetic and transport properties of perovskites and related materials
- Multiferroics and related materials
- Strong Light-Matter Interactions
- Advanced Condensed Matter Physics
- Photonic and Optical Devices
- Topological Materials and Phenomena
- Superconducting and THz Device Technology
- Organic and Molecular Conductors Research
- Spectroscopy and Laser Applications
- Cold Atom Physics and Bose-Einstein Condensates
- Magnetic properties of thin films
- Solid-state spectroscopy and crystallography
- Iron-based superconductors research
- Molecular Junctions and Nanostructures
- Mechanical and Optical Resonators
- Photonic Crystals and Applications
- Quantum optics and atomic interactions
- Quantum, superfluid, helium dynamics
- Gyrotron and Vacuum Electronics Research
- Acoustic Wave Resonator Technologies
The University of Tokyo
2016-2025
Fukui Prefectural University
2018
Cryogenic Industries (United States)
2014
Japan Science and Technology Agency
2001-2011
Bunkyo University
2005-2010
Bio-oriented Technology Research Advancement Institution
2003
Resuscitation Council
2002
University of Arizona
1994
Optically manipulating superconductors In superconductors, electrons of opposite momenta pair to form a highly correlated state that manages flow without encountering any resistance. Matsunaga et al. manipulated the wavefunction these pairs in superconductor NbN with an electromagnetic pulse they transmitted through thin layer material (see Perspective by Pashkin and Leitenstorfer). The superconducting gap, which is energy needed break apart, oscillated at twice frequency pulse's electric...
Ultrafast responses of BCS superconductor Nb(1-x)Ti(x)N films in a nonadiabatic excitation regime were investigated by using terahertz (THz) pump-THz probe spectroscopy. After an instantaneous with the monocycle THz pump pulse, transient oscillation emerges electromagnetic response gap energy region. The frequency coincides asymptotic value energy, indicating appearance theoretically anticipated collective amplitude mode order parameter, namely Higgs mode. Our result opens new pathway to...
When a continuous symmetry of physical system is spontaneously broken, two types collective modes typically emerge: the amplitude and phase order-parameter fluctuation. For superconductors, mode recently referred to as ''Higgs mode'' it condensed-matter analogue Higgs boson in particle physics. scalar excitation order parameter, distinct from charge or spin fluctuations, thus does not couple electromagnetic fields linearly. This why superconductors has evaded experimental observations over...
Using terahertz (THz) pump-THz probe spectroscopy, we have investigated the dynamics of nonequilibrium BCS state in a superconducting NbN film after impulsive photoinjection high-density Bogoliubov quasiparticles. The rapidly changes within duration monocycle THz pump pulse (1.6 ps). complex optical conductivity spectrum significantly deviates from that equilibrium state. observed spectral features are qualitatively well described by effective medium theory assumes formation normal patches...
Abstract In high-energy physics, the Higgs field couples to gauge bosons and fermions gives mass their elementary excitations. Experimentally, such couplings can be inferred from decay product of boson, i.e., scalar (amplitude) excitation field. superconductors, Cooper pairs bear a close analogy Interaction between other degrees freedom provides dissipation channels for amplitude mode, which may reveal important information about microscopic pairing mechanism. To this end, we investigate...
We investigate the terahertz (THz)-pulse-driven nonlinear response in d-wave cuprate superconductor Bi_{2}Sr_{2}CaCu_{2}O_{8+x} (Bi2212) using a THz pump near-infrared probe scheme time domain. observe an oscillatory behavior of optical reflectivity that follows electric field squared and is markedly enhanced below T_{c}. The corresponding third-order effect exhibits both A_{1g} B_{1g} symmetry components, which are decomposed from polarization-resolved measurements. A comparison with BCS...
Recent advances in time-domain terahertz (THz) spectroscopy have unveiled that resonantly enhanced strong THz third-harmonic generation (THG) mediated by the collective Higgs amplitude mode occurs $s$-wave superconductors, where charge-density fluctuations (CDFs) been shown to also contribute nonlinear third-order susceptibility. It has theoretically proposed responses of and CDF exhibit essentially different polarization dependences. Here we experimentally discriminate two contributions...
We report frequency-domain degenerate four-wave mixing results on excitons in a semiconductor microcavity the strong coupling regime. The excitation is kept to ${\ensuremath{\chi}}^{(3)}$ limit. spectral response shows polarization dependence. analyze data with new model where process described as an elastic scattering of two cavity polaritons mediated by state filling effect and two-body attractive repulsive interaction between excitons. From detuning dependence, ratio constants these three...
Temperature (5--250 K) and magnetic-field (0--70 kOe) variations of the low-energy (1--10 meV) electrodynamics spin excitations have been investigated for a complete set light-polarization configurations ferroelectric magnet ${\text{DyMnO}}_{3}$ by using terahertz time-domain spectroscopy. We identify pronounced absorption continuum (1--8 with peak feature around 2 meV, which is electric-dipole active only light $E$ vector along $a$ axis. This band grows in intensity lowering temperature...
Optical Hall conductivity ${\ensuremath{\sigma}}_{xy}(\ensuremath{\omega})$ is measured from the Faraday rotation for a $\mathrm{GaAs}/\mathrm{AlGaAs}$ heterojunction quantum system in terahertz-frequency regime. The angle ($\ensuremath{\sim}$ fine-structure constant $\ensuremath{\sim}\text{ }\text{ }\mathrm{mrad}$) found to significantly deviate Drude-like behavior exhibit plateaulike structure around Landau-level filling $\ensuremath{\nu}=2$. result, which fits with expected carrier...
In multiband superconductors, multiple collective modes exist associated with the order parameters. Oscillations of amplitude and relative phase parameters are called Higgs Leggett modes, respectively. Recently, it has been suggested that nonmagnetic impurity scattering would enhance nonlinear coupling between mode an electromagnetic wave a frequency located in superconducting gap region, while its effect on is still unresolved. Here, we theoretically investigated optical response...
Higgs mode in superconductors, i.e. the collective amplitude of order parameter does not associate with charge nor spin fluctuations, therefore it couple to electromagnetic field linear response regime. On contrary this common understanding, here, we demonstrate that, if dc supercurrent is introduced into superconductor, becomes infrared active and directly observed optical conductivity measurement. We a sharp resonant peak at $\omega=2\Delta$ spectrum thin-film NbN presence supercurrent,...
Giant second-harmonic generation in the terahertz (THz) frequency range is observed a thin film of an $s$-wave superconductor NbN, where time-reversal ($\mathcal{T}$) and space-inversion ($\mathcal{P}$) symmetries are simultaneously broken by supercurrent injection. We demonstrate that phase signal flips when direction inverted; i.e., ascribed to nonreciprocal response occurs under $\mathcal{P}$ $\mathcal{T}$ symmetries. The temperature dependence SH exhibits sharp resonance, which accounted...
The recent observation of the light-induced superconducting (SC)-like transient response in $c$-axis optical conductivity far above SC transition temperature ${T}_{\mathrm{c}}$ underdoped $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ (YBCO) has attracted a great deal attention field high-${T}_{\mathrm{c}}$ superconductors. Since then, various theoretical and experimental studies have been devoted to elucidating its microscopic origin. One prominent fingerprint...
We investigated the formation dynamics of excitons and electron-hole (e-h) droplets (EHDs) in Si by using broadband terahertz time-domain spectroscopy. The indirect was studied observing their 1S-2P transition. Changes surface plasmon resonance EHDs showed a gradual condensation from homogeneous e-h plasma at densities above exciton-Mott Excitonic correlations were shown to exist prior EHD even Mott density.
The wide range optical spectra on a multiferroic prototype ${\mathrm{TbMnO}}_{3}$ have been investigated to clarify the origin of spin excitations observed in far-infrared region. We elucidate full band structure, whose high energy edge ($133\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$) exactly corresponds twice highest-lying magnon energy. Thus this absorption is clearly assigned two-magnon excitation driven by electric field light. There an overlap between and phonon ranges, where...
Magnetically-driven ferroelectric atomic displacements of the order 10$^{-3} Angstrom have been observed in orthorhombic (perovskite like) YMnO$_3$ by a single-crystal synchrotron x-ray diffraction. The refined polar structure shows characteristic bond alternation driven exchange striction staggered Mn-O-Mn arrays with $\uparrow\uparrow\downarrow\downarrow$ type ordering, giving rise to spontaneous polarization along a-axis. First-principles calculations based on Berry phase method as well...
We have investigated the highly nonlinear terahertz (THz) light-matter interaction in single-walled carbon nanotubes (SWNTs). The high-peak THz electric-field (∼0.7 MV/cm) and low effective mass of carriers result their ponderomotive energy exceeding bandgap semiconducting SWNTs. Under such an intense pulse irradiation, interband excitation that results generation excitons occurs, although photon (∼4 meV) is much smaller than gap SWNTs (∼1 eV). ultrafast dynamics this exciton process by pump...
Recent spectroscopic studies at terahertz frequencies for a variety of multiferroics endowed with both ferroelectric and magnetic orders have revealed the possible emergence new collective excitation, frequently referred to as electromagnon. It is in origin, but it becomes active response electric field component light. Here we give an overview our recent advance time-domain spectroscopy electromagnons, or electric-dipole resonances, focused on perovskite manganites—RMnO3 (R denotes...
Abstract Illumination of light on matter normally causes heating and destroys the ordered ground states. Despite this common understanding, recent advances in ultrafast sources have enabled non-thermal control quantum phases. Here, we report light-induced enhancement superconductivity a thin film an iron chalcogenide FeSe 0.5 Te , which exhibits multiple condensates associated with multi-orbital character. Upon photoexcitation, observed transient increase superfluid density as indicated by...