Hisashi Sato

Hisashi Sato
Nippon Telegraph and Telephone · NTT Basic Research Laboratories

PhD

About

91
Publications
8,129
Reads
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2,399
Citations
Additional affiliations
April 2016 - present
NTT Basic Research Laboratories
Position
  • Researcher
October 2003 - March 2016
NTT Basic Research Laboratories
Position
  • Senior Researcher
April 2001 - September 2003
NTT Network Innovation Laboratories
Position
  • Senior Researcher

Publications

Publications (91)
Article
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We revealed a mechanism of hole doping into hydrogen (H) terminated diamond by the adsorption of inorganic molecules, based on first-principle calculation. Electron transfer from H-terminated diamond to adsorbate molecules was found in the case that the energy level of unoccupied molecular orbitals in an adsorbate molecule is below or around the va...
Article
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NO2 exposure drastically increases the hole concentration on the surface of hydrogen (H)-terminated diamond. When the NO2 gas concentration is higher than 300 ppm, the saturated hole sheet concentration ps stays the same. Therefore, the ps value is regarded as the high limit of the concentration of holes on H-terminated diamond surface, ps,max. In...
Article
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The hole channel of hydrogen (H)-terminated diamond surface can be linked to adsorption of a specific gas species on the surface. O3, NO2, NO, and SO2 were identified as adsorbates, which induce holes on the H-terminated diamond surface. During NO2 adsorption, hole sheet concentration, ps, saturated at a certain value, however, in the NO2 gas conce...
Article
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Using nitrogen-dioxide (NO2) adsorption treatment and Al2O3 passivation technique, we improved drain current (IDS) of hydrogen-terminated (H-terminated) diamond field-effect transistors (FETs). The Al2O3 passivation layer also serves as a gate-insulator in a gate region. Maximum IDS (IDSmax) of �1.35A/mm was obtained for the diamond FETs with NO2 a...
Article
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Using the NO2 adsorption and Al2O3 passivation technique, we improved the thermal stability of hydrogen terminated diamond field-effect transistors (FETs) and then demonstrated stable operation at 200 ◦C in a vacuum for the first time. At 200 ◦C, the drain current IDS of a passivated diamond FET remained constant for at least more than 2 h. No degr...
Article
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We investigated hole sheet concentration and mobility during NO2 or O3 adsorption/desorption on H-terminated diamond surface with a hole sheet concentration (ps) of ~ 1 × 1014 cm− 2. During NO2 adsorption, ps first increased with time and eventually saturated. When the NO2 gas concentration increased in a range of < 300 ppm, the saturated value of...
Article
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We have established an atomic-layer-deposited Al2O3 overlayer deposition method, which makes the H-surface-terminated p-type channel diamond surface thermally stable and completely keeps the concentration and mobility high even at 150 °C. In a range from 230 to 500 K, the mobility is proportional to the inverse of temperature showing a property cha...
Chapter
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Although high-Tc superconductivity has been reported for several different material families, as exemplified by MgB2 and iron-based compounds, the record in Tc is held by cuprate superconductors. The electronic phase diagram of the cuprates, however, remains enigmatic and is still a key ingredient to understand the mechanism of high-Tc superconduct...
Article
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I report measurement results of the temperature dependence of electrical resistivity for the compressively strained (0 0 1)-oriented films of La2−xSrxCuO4, which show values of the superconducting transition temperature (Tc) higher than those for bulk materials. A comparison of the results for the films to those for bulk suggests that the number de...
Article
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The temperature dependence of resistivity was measured for (001), (100) and (110)-oriented La1.85Sr0.15Cu4 (LSCO) thin films with thickness between 1 and 90nm on LaSrAlO4 (LSAO) substrates. As thickness increases, superconductivity appears for (001) films at 3nm, whereas it appears for (100) and (110) films at 23nm. The difference is explained by c...
Article
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We prepared various MgO substrates cut from various ingots with different impurity-Ca concentrations and deposited NdBa2Cu3O7-delta (NBCO) thin-films on them by using molecular beam epitaxy (MBE). As a result, we found that the room temperature resistivity (rho(RT)) of NBCO thin-films and the Ca concentration in an MgO substrate are quantitatively...
Article
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For possible application to microwave filters, we examined high-quality superconducting films of NdBa2Cu3O7 (NBCO), whose Tc is higher than that for YBa2Cu3O7 (YBCO). We fabricated bandpass filters on NBCO films and characterized them with measurements of the scattering parameters and third-order intermodulation. The results indicate that utilizing...
Article
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We have grown NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} films under silver atomic flux by molecular-beam epitaxy, which show a drastic improvement in microstructure and also crystallinity leading to a 30% enhancement in critical current density. The most remarkable point is that the final film is free from silver. The key to our process in achieving a s...
Article
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Many microwave applications of high temperature superconductors require double-sided films on substrates with diameters larger than 2 inches. Although there are different techniques for the growth of fair quality superconductor films, there exists a need for further improvement in quality, uniformity, reproducibility and scalability in order to mee...
Article
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Compressive (or expansive) epitaxial strain was induced in (001)-oriented La-214 thin films. For the compressed films of La2−xSrxCuO4+δ and La2−xBaxCuO4+δ on LaSrAlO4 substrates, the superconducting transition temperature (Tc) reached 44 K and 47 K, respectively, with δ ∼ 0. When both films had δ > 0, Tc reached 49 K. These values are higher than t...
Article
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An important barrier to the application of high-temperature superconducting microwave filters is their power-handling capability. To clarify the key parameters for improving the power-handling capability of rf filters based on high-temperature superconductors with microstrip structures, we synthesize bandpass filters with different layouts using se...
Article
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A major barrier to the application of high-temperature superconducting microwave filters is their power-handling capability. To clarify the key parameters for improving the power-handling capability of rf (radio frequency) filters based on high-temperature superconductors with microstrip structures, we synthesized bandpass filters with different la...
Chapter
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The insufficient power-handling capability of high-temperature superconducting microwave filters has been a serious barrier to their application. To clarify the key parameters for improving the power-handling capability of RF filters based on high-temperature superconductors (HTSs) with microstrip structures, we synthesized bandpass filters with di...
Article
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We investigated current–voltage characteristics (IVCs) of intrinsic Josephson junctions (IJJs) for c-axis oriented La1.85Sr0.15CuO4 thin films. We fabricated IJJs with two kinds of structures. One was a mesa structure with a junction area of 22–194 μm2 fabricated by using conventional photolithography and Ar-ion milling, and the other was a microbr...
Article
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We present the transport properties of the low-temperature normal-state for strained La2−xSrxCuO4 (LSCO) films achieved by suppressing superconductivity with high magnetic fields up to 50 T. Systematic measurements were performed on six MBE grown films with three different doping levels (underdope, optimumdope, and overdope) and also with either co...
Article
Cuprates with a K2NiF4 structure are prototypes of p-type high-Tc superconductors and may provide a good opportunity for understanding the relationship between structure and Tc. However, until now they have all been La-based compounds, which limits the structural parameter range. Recently, by means of molecular beam epitaxy (MBE) and subsequent ozo...
Article
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We report the magnetic imaging for underdoped and optimally-dopedLa2−x Srx CuO4 (LSCO) thin films on single substrates and nearly optimallydoped YBa2Cu3O7−x (YBCO) thin films on tricrystal substrates in the temperature range both below and above T c using scanning SQUID microscopy. Below T c, clear integer- and half-integer quantized vortices were...
Article
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To elucidate the key parameters for improving the power-handling capability of rf filters of high-temperature superconductors with microstrip structures, we synthesize bandpass filters with different layouts using several kinds of thin film high-temperature superconductors, and perform third-order intermodulation measurements on them. The third-ord...
Article
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The lanthanide (Ln) copper oxides of the general chemical formula Ln2CuO4 take two different crystal structures: K2NiF4(T) and Nd2CuO4(T'). La2CuO4 takes the T structure by high-temperature bulk processes. The "thermal expansion mismatch" between the La-O and Cu-O bonds predicts that the T' phase of La2CuO4 can be stabilized at synthesis temperatur...
Article
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We report high-field magnetotransport properties of strained La1.85Sr0.15CuO4 (LSCO) thin films. The measurements were performed on two LSCO films with identical chemical composition but with different epitaxial strain. One film was compressively strained in plane, and had Tc∼44 K. The other film was strained in the opposite way, and had Tc∼26 K. T...
Article
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We present our recent studies of high-Tc superconductors in very high pulsed magnetic fields exceeding 100T (megagauss fields). In YBa2Cu3O7−δ, the super to normal transition was observed in transport measurements for B∥c under short pulse fields up to 120T. A plot of the upper critical field Hc2 as a function of temperature demonstrates that the c...
Article
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Magnetic images of high-Tc La1.85Sr0.15CuO4 (LSCO) and YBa2Cu3O7-y (YBCO) thin films near optimal doping observed by scanning superconducting quantum interference device (SQUID) microscopy are presented in the temperature range both below and above the transition temperature Tc. While the quantized vortices were observable below Tc, local diamagnet...
Article
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We performed high-field magnetotransport experiments up to 50 T on strained La1.85Sr0.15CuO4 films. Two films with different strain, one expansively strained with Tc ~ 26 K and the other compressively strained with Tc ~ 44 K, show a striking contrast in the normal-state transport: the former has a prominent low-temperature upturn while the latter h...
Article
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For growth of high-quality epitaxial thin films of high-temperature superconductors (HTSCs), it is essential to choose appropriate substrates. For a thin film of La2−xMxCuO4 (M=Ba, Sr), the superconducting transition temperature (Tc) is modified by the strain due to the lattice mismatch between the film and the substrate. For the compressively stra...
Article
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The photon energy dependence of the optical Cooper pair breaking rate (CPBR) is studied for compressibly strained La1.85Sr0.15CuO4 (LSCO) films and YBa2Cu2.92Zn0.08O7-δ (YBCZO) thin films, and compared to that in YBa2Cu3O7-δ (YBCO). Unlike YBCO, the CPBR for LSCO does not show an obvious photon energy dependence. In YBCZO, the CPBR shows a strong e...
Article
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It is well established that the order parameter symmetry in the hole doped high-temperature superconductors (HTS) is of d-wave type. In contrast, there is growing experimental evidence for a s-wave type symmetry in the electron doped cuprate superconductors. We present tunneling spectra and measurements of the London penetration depth, both support...
Article
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This paper reviews the MBE-synthesis and structural characterization of a new superconducting barium cuprate Ba2CuO4−δ (Tc≤90 K). The keys to the successful synthesis of this superconductor are (1) the preparation of Ba2CuO3 in a CO2/H2O-free environment and (2) structural transformation from insulating Ba2CuO3 with 1D CuO chains to superconducting...
Article
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We have measured the temperature dependence of the change Δλab(T)=λab(T)−λab(T=0) of the in-plane London penetration depth λab in the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4−y (NCCO). An anomalous temperature dependence below about 4 K is observed. In contrast to the expected monotonous decrease of λab(T) with decreasing temperature,...
Article
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It is well established that the order parameter symmetry in the hole-doped high-temperature superconductors (HTS) is of d-wave type. For the electron-doped HTS one could expect to find the same order parameter symmetry because both systems have the copper oxygen planes in common. However, our experiments based on bicrystal grain boundary junctions...
Article
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Compressive and expansive strain was induced into La2-xBaxCuO4+delta thin films with x=0-0.35 on LaSrAlO4 and SrTiO3 substrates, respectively. For the compressed films, the superconducting transition temperature (Tc) reached 44 K with delta~0 and 49 K with delta>0, and the Tc-x phase diagram did not show a local minimum at x~0.125, the so-called ``...
Article
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In this article, we point out the key issue to fabricate high-Tc tunnel junctions on the basis of our recent systematic photoemission studies on MBE grown films. As a general feature for cuprates, the CuO bond is weak. Therefore, the redox reaction easily occurs at the interface between the cuprate surface and overlayers. This causes significant o...
Article
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We have grown (001)-oriented thin films of La2-xSrxCuOy with strontium composition x=0-2 by reactive coevaporation and characterized them by x-ray-diffraction and resistivity measurements. A systematical change in the c-axis length indicates that single-phase films were obtained for the whole compositional range. The films with the oxygen compositi...
Article
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We have measured the temperature dependence of the change Δλab(T)=λab(T)−λab(T=0) of the in-plane London penetration depth λab in the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4−y (NCCO). An anomalous temperature dependence below about 4K is observed. In contrast to the expected monotonous decrease of λab(T) with decreasing temperature,...
Article
Full-text available
Lattice-mismatch strain was induced in (001)-oriented thin films of La-214 superconducting oxides. For the compressed films of La2-xSrxCuO4 and La2-xBaxCuO4 on LaSrAlO4 substrates, the superconducting transition temperature (Tc) reached 44 K and 47 K, respectively, which are higher than the values for bulk samples. Moreover, the Tc-x phase diagram...
Chapter
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It has been well established that the carrier concentration is one of the key parameters govering the superconducting transition temperature (Tc) in cuprate high-Tc superconductors (HTSCs). In the La-214 system, which includes La2-xSrxCuO4+d (LSCO) and La2-xBaxCuO4+d (LBCO), the carrier concentration is easily controlled to a wide extent by cation...
Article
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Compressive (or expansive) epitaxial strain was induced in (001)-oriented La-214 thin films. For the compressed films of La2-xSrxCuO4+d and La2_xBaxCuO4+d on LaSrAIO4 substrates, the superconducting transition temperature (Tc) reached 44 K and 47 K, respectively, with d around 0. When both films had d > 0, Tc reached 49 K. These values are higher t...
Article
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We have measured the temperature dependence of the in-plane London penetration depth lambdaab\(T\) and the maximum Josephson current Ic\(T\) using bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4-y. In contrast to the usual monotonous decrease (increase) of lambdaab\(T\) [ Ic\(T\)] with decr...
Article
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The study of the detailed influence of the order parameter (OP) symmetry on the properties of high temperature superconducting (HTS) Josephson junctions still is a key issue. Whereas the hole doped HTS such as YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO), Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO), or La/sub 1.85/Sr/sub 0.15/CuO/sub 4-/spl d...
Article
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The temperature dependence of the resistivity ρ(T) and the thermoelectric power α(T) have been measured under hydrostatic pressure on a single-crystal film of La1.85Sr0.15CuO4 deposited on a LaSrAlO4 substrate. The compressive biaxial stress built into the film raises Tc at ambient pressure. Tc increased with pressure P<3.3 kbar, but saturated at a...
Chapter
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The influence of the order parameter (OP) symmetry on the transport properties of high-T c grain boundary Josephson junctions has been studied. While the hole doped high temperature superconductors (HTS) are known to have a d-wave type OP, there is significant evidence that the electron doped material Nd1.85Ce0.15CuO4-y (NCCO) has a s-wave symmetry...
Article
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This paper describes our recent progress in MBE growth and the surface/interface investigation of high-Tc superconducting films. The careful XPS analyses of the in-situ surface and interface reaction for MBE grown (Nd,Ce)2CuO4 films demonstrate that correct oxygen stoichiometry is the most crucial issue in preparing high-quality films and improving...
Article
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This paper reports a systematic study on the homoepitaxial growth of SrTiO3(001) conducted using reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) in order to improve our understanding of the basic processes in the epitaxial growth of perovskite thin films. Under certain growth conditions, the homoepitaxial growt...
Article
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We have studied the electric transport properties of symmetrical [001] tilt Nd <sub> 1.85 </sub> Ce <sub> 0.15 </sub> CuO <sub>4-y</sub> (NCCO) bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO <sub> 3 </sub> bicrystal substrates with misorientation angles of 24° and 36.8°. The superconducting properties of the NCCO GBJs are s...
Article
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We have performed a detailed study of the tunneling spectra of bicrystal grain boundary junctions (GBJs) fabricated from the HTS YBCO, BSCCO, LSCO, and NCCO. In all experiments the tunneling direction was along the CuO planes. With the exception of NCCO, for all materials a pronounced zero bias conductance peak was observed which decreases with inc...
Article
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The growth of (La,Sr)2CuO4 and (Nd,Ce)2CuO4 thin films by reactive coevaporation is reviewed. By (1) careful adjustment of the cation stoichiometry, (2) optimum oxidation, and (3) appropriate choice of substrates, we have successfully grown c-axis and non-c-axis oriented high-quality thin films of (La,Sr)2CuO4 and (Nd,Ce)2CuO4. The key points for t...
Article
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This paper reports on the stability of a Nd1.85Ce0.15CuO4 (NCCO) surface investigated by reflection high-energy electron diffraction (RHEED) and photoemission spectroscopy. Experiments were performed on an “intrinsic” surface prepared by molecular beam epitaxy (MBE). Ex situ observation of the time evolution of the MBE-grown NCCO surface showed tha...
Article
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Nd1.85Ce0.15CuO4 (NCCO) surfaces and metal (Au, Ag, and Pb)/NCCO interfaces have been extensively investigated by x-ray and ultraviolet photoelectron spectroscopies using films grown by molecular beam epitaxy (MBE). The photoelectron spectra obtained in situ on the surfaces of MBE-grown NCCO films are free from any dirt peak and show a fine structu...
Article
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Ndl.85CeO.l5Cu04 (NCCO) surfaces and PblNCCO interfaces have been extensively investigated by X-ray / ultraviolet spectroscopies and tunnel spectroscopy using films grown by MBE. The photoelectron spectra obtained in-situ on the surfaces ofMBE-grown NCCO films are free from any dirt peak, and make feasible the first systematic investigation of the...