Kenji Ikushima

Tokyo University of Agriculture and Technology | TUAT · Department of Applied Physics/Department of Biomedical Engineering

Charge-sensitive infrared phototransistors (CSIPs) based on GaAs/AlGaAs quantum well structures permit highly sensitive detection of radiation in the wavelength range of 10–50 μm. Despite this excellent sensitivity, their quantum efficiency remains limited to approximately 20%. In this study, we first developed a cryogenic measurement system for ev...

Terahertz (THz) emission from electrically biased graphene is studied under high magnetic fields. A quantum well (QW)-based charge-sensitive infrared phototransistor (CSIP) is used to detect weak THz emission from a graphene Hall bar. THz emission is clearly observed at around 5 T when the Hall voltage exceeds the corresponding Landau-level (LL) en...

Acoustically induced electric polarization and its anisotropy in soft fibrous biological tissues were investigated under wet conditions. Assuming that fibrous tissues have polar uniaxial symmetry, stress-induced polarization should occur in the direction of fiber orientation in the non-shear terms of the piezoelectric tensor. Using the acoustically...

The accumulation of photoinduced carriers at the SiO 2 /Si interface was observed via graphene transport. Chemical vapor deposition graphene was transferred to a lightly p-doped silicon substrate with a SiO 2 dielectric layer and served as a charge sensor for detecting the accumulation of photoinduced carriers at the SiO 2 /Si interface. The sample...

A measurement technique for detecting acoustically induced polarization is introduced. Ultrasonic irradiation can generate alternating electric or magnetic polarization in materials via electromechanical or magnetomechanical coupling, respectively. It follows that electromagnetic fields are often emitted to the surrounding environment when material...

A measurement technique for detecting acoustically induced polarization is reviewed. Ultrasonic irradiation can generate alternating electric or magnetic polarization in materials via electromechanical or magnetomechanical coupling, respectively, and electromagnetic fields are often emitted to the surrounding environment when materials are acoustic...

Periodic arrays of metallic nanostructures were fabricated by electron beam lithography and studied by means of spectroscopic imaging ellipsometry in the near‐infrared to ultraviolet spectral ranges. The sample consists of gold nanodisc and nanorod gratings on a silicon substrate. Spectroscopic imaging ellipsometry, allowing for the simultaneous ob...

Residual stress is one factor involved in the degradation and damage of industrial products. It is important to understand the magnitude and distribution of residual stress to maintain the integrity of a product. Magnetic measurements are a potential nondestructive method for evaluating residual stress in steel because the hysteresis properties are...

The refractive index and the extinction coefficient are usually inherent (noncontrollable) material characteristics. Recently, it was reported that the reflectivity of graphene in the mid‐infrared spectral range can be modified by an external bias. This report attracted much attention, but the controllable frequency/energy range is too narrow for p...

Acoustically stimulated electromagnetic (ASEM) waves in thin steel sheets have been investigated for flaw detection. In the ASEM wave technique, magnetization is temporally modulated at the radio frequency (rf) of the irradiated ultrasonic waves through magnetomechanical coupling. The induced rf magnetic fields are detected by a resonant coil anten...

Ultrasound irradiation makes it possible to generate alternating electric polarization through the electromechanical coupling of materials. It follows that electromagnetic fields are often emitted to the surrounding environment when materials are acoustically stimulated. We investigate the acoustically stimulated electromagnetic (ASEM) response of...

Magnetic hysteresis properties are sensitive to stress in ferromagnetic materials. This suggests that magnetic measurements are a potential method to evaluate residual stress in steel products. Nevertheless, nondestructive inspection of residual stress by using magnetic properties has been limited because bulk properties over the entire sample are...

Some mechanical property parameters of steel corrosion products require detailed examination in order to analyze cracking process of concrete with numerical models. Microstructural and micromechanical investigations on corrosion products were performed by combined analysis by scanning electron microscopy, Raman spectroscopy and nano-indentation tec...

In a two dimensional electron gas, low energy transport in presence of a magnetic field occurs in chiral 1D channels located on the edge of the sample. In the AC description of quantum transport, the emittance determines the amplitude of the imaginary part of the admittance, whose sign and physical meaning are determined by the sample topology: a H...

The signal of acoustically stimulated electromagnetic (ASEM) response have been investigated in steel. In the ASEM method, ultrasonic and electromagnetic techniques are used. Magnetization is modulated with the radio frequency (RF) of irradiated ultrasonic waves through magnetomechanical coupling. The signal amplitude of ASEM waves is determined by...

Ultrasonic irradiation induces alternating electromagnetic polarization through electro- or magneto-mechanical coupling. It follows that electromagnetic fields are generated from a variety of materials when they are acoustically stimulated. In this paper, the acoustically stimulated electromagnetic response is investigated in biomedical tissues tha...

The signal amplitude and the phase of acoustically stimulated electromagnetic (ASEM) response have been investigated in steel. In the ASEM method, magnetization is temporally modulated with the radio frequency (rf) of irradiated ultrasonic waves through magnetomechanical coupling. The first-harmonic components of the induced rf dipolar magnetic fie...

The characteristics of a charge-sensitive infrared phototransistor (CSIP) based on a GaAs/AlGaAs multiple quantum-well (QW) structure are studied under a magnetic field. In the CSIP, the upper QWs serve as a floating gate that is charged by photoexcitation. The photoinduced charges are detected using the resistance of the lowest QW conducting chann...

In recent years, the number of old bridges has remarkably increased in Japan. A periodic monitoring of them is necessary in order to confirm their security. This monitoring can lead to early warnings and prediction of potential problems and help in the planning of the necessary maintenance interventions and enables the damage assessment after earth...

We have developed a hybrid quantum Hall midinfrared (QHMIR)–quantum Hall far-infrared (QHFIR) photodetector by the use of graphene-GaAs/(Al,Ga)As–layered composite material. Both MIR and FIR photoresistance are observed in a single chip by utilizing cyclotron resonance in the quantum Hall regimes of graphene and two-dimensional electron gas (2DEG)...

Single photon detection is now realized by utilizing semiconductor quantum structures in a wide range of the terahertz (THz) region between submillimeter-wave to MIR light. In this paper, we provide THz photon-counting techniques and its applications to THz microscopy and on-chip THz detection for studies of semiconductor quantum transport.

Recent progress combining solid-state physics with quantum optics has opened up exciting possibilities for generating quantum optical phenomena in the integrated circuits [1, 2]. Given the trade-off between photon energy and wavelength, the spatial and energy scale in the terahertz (THz) region (wavelengths of 100 µm, photon energies of 10 meV) may...

Magnetic sensing is used for nondestructive evaluation (NDE) of steel products or infrastructures. In this paper, we report a unique magnetic sensing method through the detection of acoustically stimulated electromagnetic (ASEM) response. In this method, magnetization is temporally modulated by ultrasonic irradiation through magnetomechanical coupl...

Magnetic hysteresis loops are measured by ultrasonic techniques and used in visualizing the magnetic-flux distribution in a steel plate. The piezomagnetic coefficient determines the amplitude of acoustically stimulated electromagnetic (ASEM) fields, yielding the hysteresis behavior of the intensity of the ASEM response. By utilizing the high corres...

In recent years, the number of old concrete bridges has remarkably increased in Japan. A periodic monitoring of them is necessary in order to confirm their security. This monitoring can lead to early warnings and prediction of potential problems and helps in the planning of the necessary maintenance interventions and enables the damage assessment a...

Session 14 92, Martinique, France

Pisa, Italy,

28aAW-9, Tokai University

28aAW-8, Tokai University

We demonstrate single photon counting of terahertz (THz) waves transmitted from a local THz point source through a coplanar two-wire waveguide on a GaAs/AlGaAs single heterostructure crystal. In the electrically driven all-in-one chip, quantum Hall edge transport is used to achieve a noiseless injection current for a monochromatic point source of T...

26pDD-5, Tokushima University,

18pFB-10, Yokohama National University,

Tu4-32 Kyoto, Japan

We present ultrasonic techniques for magnetic measurements. Acoustically modulated magnetization is investigated with sensitive rf detection by narrowband loop antennas. Magnetization on the surface of ferromagnetic metals is temporally modulated with the rf frequency of the irradiated ultrasonic waves, and the near-field components emitted from th...

28pPSA-4, Hiroshima University

A variety of piezoelectric and magnetic materials are studied through acoustically stimulated electromagnetic (ASEM) response. The ASEM signals are found in polycrystalline plastic materials, ferrite magnets, and a biological tissue of bone as well as single-crystalline GaAs. Since ASEM signals will be canceled in amorphous or randomly oriented pol...

Two types of passive infrared microscopes with micro/nano scale resolution are developed. One is used for surface studies of solids with near-field techniques. The other is for solution measurements with a solid immersion lens. Modulation techniques to extract net signals from background radiation are introduced in both microscope systems.

Photon emission caused by quantum electron transport has been found in the quantum Hall effect regime through photon-counting THz microscopy. The imaging reveals that Landau-level emission occurs at the confluence of unequally occupied edge channels in the quantum Hall effect plateau (filling factor ν=4) when a potential barrier across the Hall bar...

A completed on-chip terahertz system is implemented on a quantum Hall effect device fabricated from a GaAs/AlGaAs single heterostructure crystal. Terahertz photons, emitted from an edge-channel confluence, are transmitted along a coplanar waveguide and subsequently counted by a quantum-dot single photon detector fabricated on the same chip. This te...

Photon counting method is indispensable in visible/near-infrared optical measurements for detecting extremely weak radiation. The method, however, has been inaccessible in terahertz region, where the photon energies are more than 100 times smaller and catching individual photons is difficult. Here we review photon counting measurements of terahertz...

Photon counting method is indispensable in visible/near-infrared optical measurements for detecting extremely weak radiation. The method, however, has been inaccessible in terahertz region, where the photon energies are more than 100 times smaller and catching individual photons is difficult. Here we review recent development of single terahertz ph...

An on-chip terahertz measurement has been performed to investigate photon generation due to electrons injected by quantum Hall edge channels. In this device configuration, terahertz waves emitted from a quantum Hall effect device are transmitted to a quantum-dot single photon detector (fabricated on the same chip) via a coplanar waveguide. Photon g...

17O-NMR have been performed to investigate the order parameters in actinide dioxides. In the antiferro-magnetic ordered state of UO2, magnetic dipole and electric quadrupole order parameters have been extracted individually through the microscopic hyperfine interactions with 17O nuclei. We have also detected the development of the quadrupole order...

We report THz radiation originating from encounter of quantum-Hall edge states. The measurements are implemented by using a photon-counting microscope with quantum-dot single THz-photon detectors. Inter-Landau-level photon emission is found to occur on the confluence of unequally populated edge states in a quantum-Hall effect plateau (filling facto...

Unequally populated edge channels in the quantum Hall effect regime are visualized through terahertz emissions originating from the inter-Landau-level optical transition. Terahertz emission in Hall bars is imaged in transition regions below and above the filling factor of = 2. The image is remarkably different as 2 or 2, signaling the absence or th...

O17 NMR measurements have been performed on a series of the actinide dioxides, UO2, NpO2 and PuO2. Although the O17 NMR spectra in these materials are similar at higher temperatures, the low-temperature spectra present are significantly different. In UO2 we have observed a wide spectrum, forming a rectangular shape below TN=30 K. In NpO2, on the ot...

THz photon-counting microscope is developed with quantum-dot single photon detectors. The photon detector is incorporated into a scanning confocal optical system which consists of aplanatic Si-hyperhemisphere lenses. A spatial resolution of 0.05 mm is achieved for a free space wavelength of 0.13 mm. We use the microscope to probe extremely weak int...

Electromagnetomechanical response of materials is detected through electromagnetic radiation induced by ultrasound waves. Target specimens are placed in the focusing zone of the ultrasound waves at a distance of ∼ 60 mm from an acoustic generator. The radiation is picked up by a narrow-band loop antenna tuned to the ultrasound frequency. Due to the...

Recent studies of cyclotron emission microscopy on quantum Hall related states are reported. The topics include non-equilibrium between edge and bulk states, current-induced breakdown of the quantum Hall effect, and the emission threshold at hot spots. Experimental method of scanning-type terahertz microscopes developed towards photon-counting leve...

A terahertz (THz) micro spectroscope is developed, in which the frequency of extremely weak THz radiation is resolved by scanning the magnetic field for a quantum Hall detector. The electron density of the detectors is controlled by the backgate biasing, so that the detector sensitivity is calibrated over a spectral range studied. Reliable spectral...

Spectroscopy of local cyclotron emission from the hot spots is carried out on a GaAs/AlGaAs heterostructure two-dimensional electron gas system at B=6 T (ν=2.5) by applying a terahertz scanning microscope. The spectra of CE at the current entry and exit corners (hot spots) are remarkably broadened towards lower frequencies with increasing I up to 3...

Photon-counting imaging of terahertz radiation is demonstrated with a spatial resolution of 50 mu m for a free-space wavelength of 132 mu m by incorporating a quantum-dot single photon detector into a scanning confocal optical system. Terahertz radiation of 10(-19)-10(-16) W or 10(2)-10(5) photons/s is imaged. Applying the microscope to the study o...

Spectroscopic studies are carried out on the cyclotron emission from the hot spots of GaAs∕AlGaAs two-dimensional electron gas systems in a quantum Hall regime at B=6.0 T (ν=2.5) and 7.5 T (ν=2.0) at T=4.2 K by applying a terahertz scanning microscope. The spectra at the current entry and exit corners (hot spots) are remarkably broadened towards lo...

We review our recent 17O NMR results on NpO 2. The compound is suggested to exhibit a magnetic octupolar phase transition at T 0=26 K. From the temperature dependence of 17O- NMR spectrum, the occurrence of two inequivalent oxygen sites has been confirmed below T 0. Furthermore, a dramatic dependence of nuclear spin-lattice relaxation rates on appl...

Coherent control of local nuclear spins has been demonstrated based on a pulsed NMR in a quantum-Hall device. Compared to standard NMR measurements, the present work is distinguished by (39.1) its efficient initialization of nuclear-spin state via edge channels, (2) the local controllability of nuclear spins in a well-defined narrow region along th...

Photon-counting microscopy imaging in the terahertz (THz) region has been realized with a resolution of 0.05mm for a free space wavelength of 0.13mm. The system incorporates quantum-dot photon detectors into a scanning confocal optical microscope. Minimal requirements for practical application have been fulfilled by improving the operation speed of...

Edge channels formed by spin‐split Landau levels in quantum Hall electron systems are demonstrated to be a unique tool to control and detect nuclear spins. Nuclear spins along the edge channels are strongly polarized through the hyperfine interaction. The nuclear spins evolve coherently during a pulsed‐mode application of RF magnetic field generate...

Non‐equilibrium edge states in a transition region between quantum Hall states (filling factor 2<v<3) have been visualized through cyclotron emission measured by using a recent developed scanning terahertz microscope. Cyclotron emission occurs in a narrow region along one sample boundary at large currents of more than 20 μA even though characterist...

We have succeeded in resolving a 235U antiferromagnetic nuclear magnetic resonance (AFNMR) signal using 235U-enriched samples of USb2. The uranium hyperfine field and coupling constant estimated for this compound are consistent with those from other experiments. This is the first reported observation of 235U NMR in conducting host material.

A GaAs/AlGaAs quantum dot THz detector is incorporated in a confocal scanning THz microscope, realizing photon counting THz imaging of extremely weak cyclotron emission in quantum Hall devices.

We have utilized the electron–nuclear spin interaction in quantum-Hall edge channels for manipulating local nuclear spins in semiconductors. Nuclear spins in a limited region along spin-resolved quantum-Hall edge channels are strongly polarized through the hyperfine interaction. Quantum states of the nuclear spins evolve coherently during a pulsed-...

A local probing technique of cyclotron emission is applied to image nonequilibrium electrons generated along edge channels in quantum Hall conductors. In a lower-magnetic field region of a quantum Hall state plateau (filling factor 2<nu), cyclotron emission is found to occur along the boundary of a conductor on the side of lower potential (with pos...

Direct AFNMR studies of U-235 as well as of Sb-121 and Sb-121 nuclear spins have been carried out in the antiferromagnetic state of USb2. The central (+/-1/2) U-235 peak found at 217.2MHz passes several identification tests, including the expected very low rate of broadening in an applied field. The U-235 hyperfine constant found, 147 T/mu(B), is w...

We demonstrate coherent control of local nuclear spins in semiconductor devices. Nuclear spins in a limited region along spin-resolved quantum-Hall edge channels are strongly polarized through the hyperfine interaction. Quantum states of the nuclear spins evolve coherently during a pulsed-mode application of RF magnetic field generated by a built-i...

The current state of highly sensitive terahertz imaging microscopes is reported in the context of applications for cyclotron emission studies of quantum Hall devices. Without external excitation other than the transport current, the microscope maps the distribution of nonequilibrium electrons generated in quantum devices by detecting weak cyclotron...

We develop a highly sensitive scanning far-infrared (FIR) microscope, which consists of a silicon solid immersion lens that probes FIR and a condenser lens that focuses the FIR onto a small quantum Hall detector (400 μm×400 μm). The solid immersion lens is in contact with the backside of a Hall bar sample, which is moved with a mechanical XY stage....

A highly-sensitive scanning far-infrared (FIR) microscope is developed. The microscope consists of a silicon solid immersion lens that probes FIR and a condenser lens that focuses the FIR onto a small and highly-sensitive quantum Hall detector. The solid immersion lens is in contact with a sample, which is moved with a mechanical stage. The microsc...

We demonstrate pulsed-mode control of nuclear-spin polarization in integer quantum Hall systems. Nuclear spins in a limited region along edge channels of a quantum Hall conductor are initially polarized through the hyperfine interaction with electron spins. The initialized nuclear-spin polarization is then manipulated with pulsed nuclear magnetic r...

Coherent control of local nuclear spins in a solid-state device is demonstrated. By unequally populating spin-resolved quantum-Hall edge channels, nuclear spins in a limited region along the edge channels are strongly polarized via the hyperfine interaction. Pulsed rf magnetic fields, generated by a built-in micrometal strip, cause the nuclear-spin...

We demonstrate coherent control of local nuclear spins in a solid-state device. Nuclear spins in a limited region along spin-resolved quantum-Hall edge channels are strongly polarized through the hyperfine interaction. Quantum states of the nuclear spins evolve coherently during a pulsed-mode application of radio frequency magnetic field generated...

Microscopic magnetic properties of a uraniun intermetallic compound, UGa3 (), have been investigated by the 69Ga and 71Ga NMR/NQR measurements. We found a drastic temperature (T-) dependence of the NQR spectrum near TN, in which a single 69Ga NQR line of 19.8 MHz in the paramagnetic state rapidly vanishes at 70 K and a double peak appears at 17.2 a...

A nuclear magnetic resonance (NMR) study is reported for a 5f-cooperative Jahn-Teller (JT) system with antiferromagnetic ordering, UO2, where we have performed magnetic actinide (235U) as well as nonmagnetic ligand (17O) NMR studies in a 5f-electron system. The observed 235U hyperfine interaction is consistent with an axially symmetric 5f-wave-func...

A nuclear magnetic resonance (NMR) study is reported for a 5f-cooperative Jahn-Teller (JT) system with antiferromagnetic ordering, UO2, where we have performed magnetic actinide (235U) as well as nonmagnetic ligand (17O) NMR studies in a 5f-electron system. The observed 235U hyperfine interaction is consistent with an axially symmetric 5f-wave-func...

The 171Yb nuclear magnetic resonance (NMR) is observed below 10 K in the single crystal of the Kondo semiconductor YbB12 with the large shift of 66%. The hyperfine coupling constant of 115 T/μB agrees with the calculated value for the state of free Yb3+ ions, indicating that the the magnetic susceptibility at the low-temperature (T) limit is the Va...

A typical hyperfine structure of U4+ ions is obtained by the 235U NMR in the antiferromagnetic state of UO2. The nuclear electric quadrupole interaction indicates that the 5f-wave function in the cubic crystalline field is reduced to the axial symmetry below TN. The nuclear spin-lattice relaxation rate at both uranium and oxygen sites shows a T7-li...

The validity of scaling has been straightforwardly investigated in CeRhSb and CeNiSn through the high-pressure studies on the nuclear spin-lattice relaxation rate T1-1. A universal curve with a characteristic temperature in (T1T)-1, independent of the applied pressures about 1 GPa, is observed over a broad temperature range including the formation...

The 238U Mössbauer effect of UO2 has been investigated in the temperature range from 5.4 K to 280 K. Nuclear Zeeman splitting of the 238U nucleus in antiferromagnetic UO2 at 5.4 K is 59.1±3.9 mm s-1 and corresponds to the value of 252.3±0.5 T obtained by the 235U pulsed NMR technique. The nuclear magnetic moment of the first excited state (I=2+) of...

The 235U (I=7/2) NMR for magnetic uranium sites with 5f-electronshas been first observed in the antiferromagnetic state of UO2.The hyperfine field is estimated to be 252.3 ± 0.5 T.Well articulated quadrupole splittings have also been observedwith |e2qQ(3 cos2theta-1)/h| = 392 ±11 MHz. This indicates the presence of an electric field gradient produc...

The 61Ni spin-lattice relaxation rate,61T1-1, and the Knight shift of a 91% 61Ni enrichedsample of LuNi2B2C have been measured in the normal state.It was found that 61(T1T)-1 shows a Curie-Weiss like behavior,while the Knight shift has a slight temperature dependence.The hyperfine coupling constant is estimated to be 61A=-16 kOe/µ B, which is an or...