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Y. Onishi

Publications and source records attributed to Y. Onishi.

15 recordsLinked to original sources
arXiv2022

Pure nematic quantum critical point accompanied by a superconducting dome

When a symmetry-breaking phase of matter is suppressed to a quantum critical point (QCP) at absolute zero, quantum-mechanical fluctuations proliferate. Such fluctuations can lead to unconventional superconductivity, as evidenced by the superconducting domes often found near magnetic QCPs in correlated materials. However, it remains unclear whether this superconductivity mechanism holds for QCPs of the electronic nematic phase, characterized by rotational symmetry breaking. Here, we demonstrate from systematic elastoresistivity measurements that nonmagnetic FeSe$_{1-x}$Te$_{x}$ exhibits an electronic nematic QCP showing diverging nematic susceptibility. This finding establishes two nematic QCPs in FeSe-based superconductors with contrasting accompanying phase diagrams. In FeSe$_{1-x}$Te$_{x}$, a superconducting dome is centered at the QCP, whereas FeSe$_{1-x}$S$_{x}$ shows no QCP-associated enhancement of superconductivity. We find that this difference is related to the relative strength of nematic and spin fluctuations. Our results in FeSe$_{1-x}$Te$_{x}$ present the first case in support of the superconducting dome being associated with the pure nematic QCP.

cond-mat.supr-con↗
arXiv2018

MIRIS observation of near-infrared diffuse Galactic light

We report near-infrared (IR) observations of high Galactic latitude clouds to investigate diffuse Galactic light (DGL), which is starlight scattered by interstellar dust grains. The observations were performed at $1.1$ and $1.6\,\rm{μm}$ with a wide-field camera instrument, the Multi-purpose Infra-Red Imaging System (MIRIS) onboard the Korean satellite STSAT-3. The DGL brightness is measured by correlating the near-IR images with a far-IR $100\,\rm{μm}$ map of interstellar dust thermal emission. The wide-field observation of DGL provides the most accurate DGL measurement achieved to date. We also find a linear correlation between optical and near-IR DGL in the MBM32 field. To study interstellar dust properties in MBM32, we adopt recent dust models with or without $\rm{μm}$-sized very large grains and predict the DGL spectra, taking into account reddening effect of interstellar radiation field. The result shows that observed color of the near-IR DGL is closer to the model spectra without very large grains. This may imply that dust growth in the observed MBM32 field is not active owing to its low density of interstellar medium.

astro-ph.GA↗
arXiv2016

A measurement of the time profile of scintillation induced by low energy gamma-rays in liquid xenon with the XMASS-I detector

We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832 kg liquid xenon scintillation detector. Decay time constant was derived from a comparison of scintillation photon timing distributions between the observed data and simulated samples in order to take into account optical processes such as absorption and scattering in liquid xenon. Calibration data of radioactive sources, $^{55}$Fe, $^{241}$Am, and $^{57}$Co were used to obtain the decay time constant. Assuming two decay components, $τ_1$ and $τ_2$, the decay time constant $τ_2$ increased from 27.9 ns to 37.0 ns as the gamma-ray energy increased from 5.9 keV to 122 keV. The accuracy of the measurement was better than 1.5 ns at all energy levels. A fast decay component with $τ_1 \sim 2$ ns was necessary to reproduce data. Energy dependencies of $τ_2$ and the fraction of the fast decay component were studied as a function of the kinetic energy of electrons induced by gamma-rays. The obtained data almost reproduced previously reported results and extended them to the lower energy region relevant to direct dark matter searches.

physics.ins-det↗
arXiv2016

Direct dark matter search by annual modulation in XMASS-I

A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP-nucleon cross section 4.3$\times$10$^{-41}$cm$^2$ at 8 GeV/c$^2$ was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c$^2$ range at $\sim$10$^{-40}$cm$^2$. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/$γ$ events, showed a slight negative amplitude. The $p$-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. we obtained 90\% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.

astro-ph.CO↗
arXiv2016

Search for two-neutrino double electron capture on $^{124}$Xe with the XMASS-I detector

Double electron capture is a rare nuclear decay process in which two orbital electrons are captured simultaneously in the same nucleus. Measurement of its two-neutrino mode would provide a new reference for the calculation of nuclear matrix elements whereas observation of its neutrinoless mode would demonstrate lepton number violation. A search for two-neutrino double electron capture on $^{124}$Xe is performed using 165.9 days of data collected with the XMASS-I liquid xenon detector. No significant excess above background was observed and we set a lower limit on the half-life as $4.7 \times 10^{21}$ years at 90% confidence level. The obtained limit has ruled out parts of some theoretical expectations. We obtain a lower limit on the $^{126}$Xe two-neutrino double electron capture half-life of $4.3 \times 10^{21}$ years at 90% confidence level as well.

nucl-ex↗
arXiv2016

First Detection of Galactic Latitude Dependence of Near-Infrared Diffuse Galactic Light from DIRBE Reanalysis

Observational study on near-infrared (IR) scattering properties of interstellar dust grains has been limited due to its faintness. Using all-sky maps obtained from Diffuse Infrared Background Experiment (DIRBE), we investigate the scattering property from diffuse Galactic light (DGL) measurements at 1.25, 2.2, and 3.5 μm in addition to our recent analyses of diffuse near-IR emission (Sano et al. 2015; Sano et al. 2016). As a result, we first find that the intensity ratios of near-IR DGL to 100 μm emission increase toward low Galactic latitudes at 1.25 and 2.2 μm. The derived latitude dependence can be reproduced by a scattered light model of interstellar dust with a large scattering asymmetry factor g = of $0.8^{+0.2}_{-0.3}$ at 1.25 and 2.2 μm, assuming an infinite Galaxy disk as an illuminating source. The derived asymmetry factor is comparable to the values obtained in the optical, but several times larger than that expected from a recent dust model. Since possible latitude dependence of ultraviolet-excited dust emission at 1.25 and 2.2 μm would reduce the large asymmetry factor to the reasonable value, our result may indicate the first detection of such an additional emission component in the diffuse interstellar medium.

astro-ph.GA↗
arXiv2015

Measurements of the mean diffuse galactic light spectrum in the 0.95 μm to 1.65 μm band from CIBER

We report measurements of the Diffuse Galactic Light (DGL) spectrum in the near-infrared, spanning the wavelength range 0.95-1.65 μm by the Cosmic Infrared Background ExpeRiment (CIBER). Using the low-resolution spectrometer (LRS) calibrated for absolute spectro-photometry, we acquired long-slit spectral images of the total diffuse sky brightness towards four high-latitude fields spread over four sounding rocket flights. To separate the DGL spectrum from the total sky brightness, we correlated the spectral images with a 100 μm intensity map, which traces the dust column density in optically thin regions. The measured DGL spectrum shows no resolved features and is consistent with other DGL measurements in the optical and at near-infrared wavelengths longer than 1.8 μm. Our result implies that the continuum is consistently reproduced by models of scattered starlight in the Rayleigh scattering regime with a few large grains.

astro-ph.GA↗
arXiv2014

Search for bosonic superweakly interacting massive dark matter particles with the XMASS-I detector

Bosonic superweakly interacting massive particles (super-WIMPs) are a candidate for warm dark matter. With the absorption of such a boson by a xenon atom these dark matter candidates would deposit an energy equivalent to their rest mass in the detector. This is the first direct detection experiment exploring the vector super-WIMPs in the mass range between 40 and 120 keV. Using 165.9 days of data no significant excess above background was observed in the fiducial mass of 41 kg. The present limit for the vector super-WIMPs excludes the possibility that such particles constitute all of dark matter. The absence of a signal also provides the most stringent direct constraint on the coupling constant of pseudoscalar super-WIMPs to electrons. The unprecedented sensitivity was achieved exploiting the low background at a level $10^{-4}$ kg$^{-1}$keV$_{ee}^{-1}$day$^{-1}$ in the detector.

astro-ph.CO↗
arXiv2014

Search for inelastic WIMP nucleus scattering on $^{129}$Xe in data from the XMASS-I experiment

A search for inelastic scattering of Weakly Interacting Massive Particles (WIMPs) on the isotope $^{129}$Xe was done in data taken with the single phase liquid xenon detector XMASS at the Kamioka Observatory. Using a restricted volume containing 41 kg of LXe at the very center of our detector we observed no significant excess of events in 165.9 days of data. Our background reduction allowed us to derive our limits without explicitly subtracting the remaining events which are compatible with background expectations and derive for e.g. a 50 GeV WIMP an upper limit for its inelastic cross section on $^{129}$Xe nuclei of 3.2 pb at the 90% confidence level.

astro-ph.CO↗
arXiv2013

Search for solar axions in XMASS, a large liquid-xenon detector

XMASS, a low-background, large liquid-xenon detector, was used to search for solar axions that would be produced by bremsstrahlung and Compton effects in the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent limit on the coupling for mass $\ll$ 1keV is $|g_{aee}|< 5.4\times 10^{-11}$ (90% C.L.), which is a factor of two stronger than the existing experimental limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are 1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced the most stringent limit, which is better than that previously derived from astrophysical arguments regarding the Sun to date.

astro-ph.CO↗
arXiv2013

Light WIMP search in XMASS

A search for light dark matter using low-threshold data from the single phase liquid xenon scintillation detector XMASS, has been conducted. Using the entire 835 kg inner volume as target, the analysis threshold can be lowered to 0.3 keVee (electron-equivalent) to search for light dark matter. With low-threshold data corresponding to a 5591.4 kg$\cdot$day exposure of the detector and without discriminating between nuclear-recoil and electronic events, XMASS excludes part of the parameter space favored by other experiments.

astro-ph.CO↗
arXiv2013

XMASS detector

The XMASS project aims to detect dark matter, pp and $^{7}$Be solar neutrinos, and neutrinoless double beta decay using ultra pure liquid xenon. The first phase of the XMASS experiment searches for dark matter. In this paper, we describe the XMASS detector in detail, including its configuration, data acquisition equipment and calibration system.

physics.ins-det↗
arXiv2011

Abelian functions associated with genus three algebraic curves

We develop the theory of Abelian functions associated with algebraic curves. The growth in computer power and an advancement of efficient symbolic computation techniques has allowed for recent progress in this area. In this paper we focus on the genus three cases, comparing the two canonical classes of hyperelliptic and trigonal curves. We present new addition formulae, derive bases for the spaces of Abelian functions and discuss the differential equations such functions satisfy.

math.AG↗
arXiv2000

Enhanced Valence Fluctuations Caused by f-c Coulomb Interaction in Ce-Based Heavy Electrons: Possible Origin of Pressure-Induced Enhancement of Superconducting Transition Temperature in \Ge and Related Compounds

Properties of an extended periodic Anderson model with the f-c Coulomb interaction $\Ufc$ is studied as a model for \Ge and related compounds which is cosidered to exhibit a sharp valence change under pressure. The problem is treated by extending the {\it slave-boson} and large-N expansion method to treat the present system. It is shown that, as the f-level $ε_{\rm f}$ is increased relative to the Fermi level, the sharp valence change is caused by the effect of $\Ufc$ with moderate strength of the order of the bandwith of conduction electrons. The superconducting transition temperature $T_\rc$ due to the valence-fluctuation exchange is estimated on the slave-boson fluctuation approximation. In the model with spherical Fermi surface, $T_\rc$ exhibits sharp peak as a function of $ε_{\rm f}$, simulating the effect of pressure, for the d-wave pairing channel.

cond-mat.str-el↗