Ikufumi Katayama

Ikufumi Katayama
Yokohama National University · Department of Physics, Electrical and Computer Engineering

PhD, Science

About

154
Publications
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1,155
Citations

Publications

Publications (154)
Article
The compound GeCu2Te3 (GCT) has attracted considerable attention because of its several advantages for next-generation nonvolatile memories, including its higher thermal stability and lower volume change, with large optical contrast between the crystalline and amorphous phases. In this study, we demonstrate the ultrafast amorphization dynamics that...
Preprint
Full-text available
PbTe crystals have a soft transverse optical phonon mode in the terahertz frequency range, which is known to efficiently decay into heat-carrying acoustic phonons, resulting in anomalously low thermal conductivity. Here, we studied this phonon via polarization-dependent terahertz spectroscopy. We observed softening of this mode with decreasing temp...
Article
Full-text available
Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics systems with ultrastrong light-matter interactions. Their ground states are predicted to be vacuum squeezed states with suppressed quantum fluctuations owing to antiresonant terms in the Hamiltonian. However, such predictions have not been realized because antiresonant...
Article
A method to quantitatively map transient electromagnetic waveforms with atomic-spatial resolution is now possible using lightwave-driven scanning tunnelling microscopy featuring a single-molecule switch.
Article
Coupling an intense electric field of terahertz (THz) pulse to a scanning tunneling microscope (STM) has opened new avenues for conducting ultrafast electron manipulation and tracking quantum dynamics at the nanometer spatial resolution. Here we combined the THz-field-driven STM with a photon detection system and demonstrated nanospectroscopic inve...
Article
This work demonstrates terahertz (THz) line imaging that acquires broadband spectral information by combining echelon-based single-shot THz spectroscopy with high-sensitivity phase-offset electrooptic detection. An approximately 40 dB signal-to-noise ratio is obtained for a THz spectrum from a single line of the camera, with a detection bandwidth u...
Article
Full-text available
A scanning probe microscope coupled with either femtosecond laser pulses or terahertz pulses holds great promise not only for observing ultrafast phenomena but also for fabricating desirable structures at the nanoscale. In this study, we demonstrate that a few-nanometer-scale phase change can be non-thermally stored on the Ge2Sb2Te5 surface by a la...
Article
We have observed photoinduced negative optical conductivity, or gain, in the terahertz frequency range in a GaAs multiple-quantum-well structure in a strong perpendicular magnetic field at low temperatures. The gain is narrow band: it appears as a sharp peak (linewidth <0.45 meV) whose frequency shifts with applied magnetic field. The gain has a ci...
Preprint
Full-text available
Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics (QED) systems with ultrastrong light-matter interactions. Their ground states are predicted to be vacuum squeezed states with suppressed quantum fluctuations. The source of such phenomena are antiresonant terms in the Hamiltonian, yet antiresonant interactions are typic...
Article
We demonstrate spatially resolved supercontinuum spectral phase interferometry with an isolated attosecond pulse (IAP). The measured spatial-spectral interferogram over the broadband region indicates a high degree of IAP coherence in both spatial and spectral domains. In addition, the spectral-delay interferogram shows periodic temporal oscillation...
Article
Fermi level dependence of ultrafast optical responses of single-layer graphene has been investigated using sub-10-fs pump-probe spectroscopy under bias voltages. We observe the ultrafast thermalization of photoexcited carriers, whose dynamics can be modulated via bias-induced change of the Fermi level. The relaxation time and the amplitude of the e...
Preprint
We characterized spatially resolved spectral phase interferometry with an isolated attosecond pulse (IAP). The measured spatial-spectral interferogram and spectral interference fringe visibility show a high degree of IAPs spatial and spectral coherences. In addition, the characterized spectral-delay interferogram shows periodic temporal oscillation...
Preprint
Full-text available
We have observed photoinduced negative optical conductivity, or gain, in the terahertz frequency range in a GaAs multiple-quantum-well structure in a strong perpendicular magnetic field at low temperatures. The gain is narrow-band: it appears as a sharp peak (linewidth $<$0.45 meV) whose frequency shifts with applied magnetic field. The gain has a...
Article
Ionic motion significantly contributes to conductivity in devices such as memory, switches, and rechargeable batteries. In our work, we experimentally demonstrate that intense terahertz electric-field transients can be used to manipulate ions in a superionic conductor, namely Na+β-alumina. The cations trapped in the local potential minima are accel...
Article
We produce subcycle mid-infrared (MIR) pulses at a 4 MHz repetition rate via the optical rectification (OR) of sub-10 fs near-infrared pulses delivered by an optical parametric chirped pulse amplifier. The coherent MIR pulses generated in a GaSe crystal under an ultrabroadband phase-matching condition contain only 0.58–0.85 oscillation cycles withi...
Article
We report results of terahertz Faraday and Kerr rotation spectroscopy measurements on thin films of Bi1−xSbx, an alloy system that exhibits a semimetal-to-topological-insulator transition as the Sb composition x increases. By using a single-shot time-domain terahertz spectroscopy setup combined with a table-top pulsed minicoil magnet, we conducted...
Article
A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of graphene used in practical applications. Different reduction processes produce different properties in graphene, affecting the performance of the final mate...
Article
Full-text available
Metasurfaces are engineered thin surfaces comprising two-dimensional (2D) arrays of sub-wavelength spaced and sub-wavelength-sized resonators. Metasurfaces can locally manipulate the amplitude, phase, and polarization of light with high spatial resolution. In this paper, we report numerical and experimental results of a vortex-beam-generating metas...
Preprint
Full-text available
We report results of terahertz Faraday and Kerr rotation spectroscopy measurements on thin films of $\text{Bi}_{1-x}\text{Sb}_{x}$, an alloy system that exhibits a semimetal-to-topological-insulator transition as the Sb composition $x$ increases. By using a single-shot time-domain terahertz spectroscopy setup combined with a table-top pulsed mini-c...
Preprint
Metasurfaces are engineered thin surfaces comprising two dimensional (2D) arrays of sub-wavelength spaced and sub-wavelength sized resonators. Metasurfaces can locally manipulate the amplitude, phase and polarization of light with high spatial resolution. In this study, we report numerical and experimental results of a vortex-beam-generating metasu...
Article
We report on the design and performance of an echelon-based single shot visible/near-infrared spectrometer with adequate sensitivity to measure the nonlinear optical and terahertz Kerr effects in neat molecular liquids at room temperature. Useful molecular information spanning tens of picoseconds can be measured in just a few milliseconds, and the...
Article
Using a frequency-tunable optical comb generated from a Mach–Zehnder-modulator-based flat comb generator (MZ-FCG) and a nonlinear optical fiber, we demonstrated a frequency measurement of continuous terahertz wave sources with the frequency of 0.1 and 0.6 THz by an electro-optic sampling method. We clearly observed beat signals between the terahert...
Article
To acquire single-shot pump-probe waveforms for each laser pulse at a high repetition rate and high signal-to-noise ratio, we combined the photonic time-stretch technique and time-encoding method using a chirped-fiber Bragg grating (CFBG) and a grating-pair pulse compressor. By changing the pre-chirping of the probe pulse, a variable time window of...
Article
Full-text available
Using terahertz-pump and terahertz-probe spectroscopy, we investigated terahertz-induced carrier generation processes in Bi 1- x Sb x thin films. The field dependence of the terahertz-induced transmittance change indicates distinct nonlinearity related to the Zener tunneling in narrow band-gap materials.
Article
Full-text available
We characterized electronic dipole oscillations in chromium doped sapphire (Cr:Al 2 O 3 ) using Fourier transform extreme ultraviolet attosecond spectroscopy (FTXUV) combined with an isolated attosecond pulse, which reveals the electric band-structure and dephasing process in solids.
Article
Full-text available
By utilizing terahertz scanning tunneling microscopy (THz-STM) with a carrier envelope phase shifter for broadband THz pulses, we could successfully control the near-field-mediated electron dynamics in a tunnel junction with sub-cycle precision. Measurements of the phase-resolved sub-cycle electron tunneling dynamics revealed an unexpected large ca...
Conference Paper
Full-text available
We have performed time- and polarization-resolved optical-pump—terahertz-probe magnetospectroscopy measurements on a GaAs quantum well and observed narrow-band, polarization-selective THz gain, whose center frequency shifts with applied magnetic field.
Conference Paper
We successfully demonstrate the ultrafast phase-resolved and sub-cycle electron manipulation using terahertz (THz) scanning tunneling microscopy with tailor-made near fields tuned by a THz phase shifter.
Conference Paper
Terahertz time-domain spectroscopy measurements performed in pulsed, high magnetic fields reveal ultrastrong coupling between quasi-antiferromagnetic and quasi-ferromagnetic magnon modes in the canted antiferromagnet, YFeO3.
Article
Desirable control of optical properties in materials using artificial structures have been explored for decades since the development of nano- and micro fabrication techniques. While photonic crystals and plasmonics are the examples of such an approach, new concepts for designing the optically functional structures are recently arising to show rema...
Article
Terahertz-field-induced carrier generation processes were investigated in Dirac electron systems, single-crystalline bismuth antimony alloy thin films (Bi1−xSbx; 0≤x≤0.16). This investigation was performed by precisely tuning, via the substituent ratio x, the band structure of the films from that associated with a semimetal to that characteristic o...
Article
We demonstrated ultrafast optical control of multiple coherent phonons in silicon carbide (SiC) using a pulse-shaping technique combined with sub-10-fs optical pulses and a two-dimensional spatial light modulator. Because our technique produces a pulse train with the desired number of pulses and time intervals, precise manipulation of the amplitude...
Article
Here we demonstrate simultaneous measurements of the complex transmittance and birefringence using left- and right-handed circularly polarized terahertz (THz) pulses. We change the polarization of the THz pulses periodically by modulating the polarization of the pump pulses directed onto a ZnTe (111) crystal, and we convert linear to circular polar...
Article
Full-text available
One-dimensional metal-halide compounds provide model systems to investigate the manner in which coupling between elementary degrees of freedom—here, electronic and vibrational—result in instabilities that give rise to both chemical and structural rearrangements. Here, we employ “single-shot” pump-probe spectroscopy to examine a one-dimensional plat...
Article
Light-field-driven processes occurring under conditions far beyond the diffraction limit of the light can be manipulated by harnessing spatio-temporally tunable near fields. A tailor-made carrier envelope phase in a tunnel junction formed between nanogap electrodes allows precisely controlled manipulation of these processes. In particular, the char...
Article
We demonstrate that single-shot pump-probe imaging spectroscopy with an echelon mirror enables us to disclose the ferroelectric phonon-polariton dynamics across a wide temperature range from 10 K to 375 K while avoiding the photorefractive effects that appear prominently at low temperatures. The E-mode phonon-polaritons corresponding to the two tra...
Article
Full-text available
Lightwave-field-induced ultrafast electric dipole oscillation is promising for realizing petahertz (1015 Hz: PHz) signal processing in the future. In building the ultrahigh-clock-rate logic operation system, one of the major challenges will be petahertz electron manipulation accompanied with multiple frequencies. Here we study multi-petahertz inter...
Article
The gate bias dependence of excited-state relaxation dynamics in metallic single-walled carbon nanotubes (MCNTs) was investigated using pump-probe transient absorption spectroscopy coupled with electrochemical doping through an ionic liquid. The transient transmittance decayed exponentially with the pump-probe delay time, whose value could be tuned...
Article
Improved control over the electromagnetic properties of metals on a nanoscale is crucial for the development of next-generation nanoelectronics and plasmonic devices. Harnessing the terahertz (THz)-electric-field-induced nonlinearity for the motion of electrons is a promising method of manipulating the local electromagnetic properties of metals, wh...
Conference Paper
We have performed terahertz time-domain magneto-spectroscopy measurements on canted antiferromagnet YFeO3 in pulsed high magnetic fields up to 30 T, observing coherent magnon oscillations and frequency splitting.
Conference Paper
By utilizing terahertz scanning tunneling microscopy (THz-STM) with phase-controlled THz near-fields, we could successfully implement the phase-resolved sub-cycle electron dynamics in a tunnel junction.
Conference Paper
By utilizing intense terahertz (THz) pump and THz probe spectroscopy, we revealed the carrier dynamics of a semi-metallic bismuth ultrathin film, originating from the THz-induced electron acceleration and a subsequent carrier multiplication process.
Article
Full-text available
Recent advances of ultrafast spectroscopy allow the capture of an entire ultrafast signal waveform in a single probe shot, which greatly reduces the measurement time and opens the door for the spectroscopy of unrepeatable phenomena. However, most single-shot detection schemes rely on two-dimensional detectors, which limit the repetition rate of the...
Article
The ultrafast coherent manipulation of electrons using waveform-controlled laser pulses is a key issue in the development of modern electronics. Developing such an approach for a tunnel junction will provide a new platform for governing ultrafast currents on an even smaller scale, which will be indispensable for the advancement of next-generation q...
Conference Paper
Single-shot detection of a terahertz (THz) electric-field transient has been demonstrated using a high-bandwidth oscilloscope. The THz modulation was imprinted on a chirped picosecond probe pulse via an electro-optic crystal, and the probe pulse was subsequently temporally expanded to nanosecond time scales using the group velocity dispersion of a...
Conference Paper
We demonstrate that single-cycle intense terahertz (THz) pulses manipulate the motion of electrons in a single tunnel junction. By tuning the carrier-envelope phase of the THz pulses, the direction of the electron tunneling through the junction was coherently controlled either from the nanotip to the sample or vice versa. By analyzing the experimen...
Conference Paper
Broadband THz detection technique is required for high precision molecular gas spectroscopy, wireless communications, and so on. In this work, Sensitivities of electrooptic (EO) sampling method for the frequency measurement of continuous-wave terahertz (THz) sources were compared from 0.1 to 3.1 THz. By using a femtosecond fiber laser to gate the E...
Conference Paper
We demonstrate real-time mapping of high-frequency phonon-polariton dispersions up to 7 THz in ferroelectric LiNbO 3 using a single-shot spectroscopic setup with an echelon mirror. The echelon mirror provides a spatially encoded time delay for the probe pulse, and therefore, ultrafast transient behavior of materials can be detected on a single-shot...
Article
We have developed a single-shot terahertz time-domain spectrometer to perform optical pump/terahertz probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the gate beam before...
Conference Paper
In the recent progress in terahertz (THz) devices, various kinds of source devices, such as resonant tunneling diodes, quantum cascade lasers and so forth, have been developed. Frequency measurement of THz radiations, which can operate in high speed and at room-temperature, is important for development of high-performance THz source devices. Recent...
Conference Paper
We have investigated bias-voltage dependence of carrier dynamics in metallic single-walled carbon nanotubes. By tuning the Fermi energy with the bias-voltage, the carrier relaxation time becomes minimum near the Dirac point, indicating the carrier-carrier interaction.
Conference Paper
We demonstrated a new method of measuring Kerr-ultrafast waveforms using chirped femtosecond pulses, a single photodiode and an oscilloscope. This allowed thee full pump intensity dependence to bewas obtained recorded within one second.
Article
Full-text available
Dirac-like electrons in solid state have been of great interest since they exhibit many peculiar physical behaviors analogous to relativistic mechanics. Among them, carriers in graphene and surface states of topological insulators are known to behave as massless Dirac fermions with a conical band structure in the two-dimensional momentum space, whe...
Article
Full-text available
We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay ti...
Article
Full-text available
Because of their robust switching capability, chalcogenide glass materials have been used for a wide range of applications, including optical storages devices. These phase transitions are achieved by laser irradiation via thermal processes. Recent studies have suggested the potential of nonthermal phase transitions in the chalcogenide glass materia...
Article
We demonstrate the real-time observation of phonon-polariton propagation in ferroelectric LiNbO3 using a single-shot spectroscopic setup that employs an echelon mirror. The echelon mirror provides a spatially encoded time delay for the probe pulse; therefore, the ultrafast transient behavior of materials can be detected on a single-shot basis. Usin...
Article
We observed the nonlinear electron dynamics in polycrystalline gold (Au) thin films via intense terahertz spectroscopy. Under the intense terahertz wave illumination, the transmittance of Au thin film decreases, indicating that the damping constant of electrons becomes smaller due to the suppression of the grain-boundary effect on electrons induced...
Article
We observed the Drude response of photoexcited electrons in high resistivity silicon by using single-shot terahertz spectroscopy. In contrast to conventional optical-pump and terahertzprobe spectroscopy, this technique can significantly reduce the measurement time and repetition rate of pump pulses. As a result, the dynamics of long-lived photoexci...
Article
Improved control over the electromagnetic properties of metal nanostructures is indispensable for the development of next-generation integrated nanocircuits and plasmonic devices. The use of terahertz (THz)-field-induced nonlinearity is a promising approach to controlling local electromagnetic properties. Here, we demonstrate how intense THz electr...