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H. Hosono

Publications and source records attributed to H. Hosono.

At least 19 recordsLinked to original sources
arXiv2026

Relationship between local hydride ion dynamics and ionic conductivity in LaH$_{3-2x}$O$_x$ inferred from muon study

We performed muon spin rotation and relaxation ($\mu$SR) experiments to investigate the microscopic mechanism behind the high ionic conductivity ($\sigma$) exhibited by hydride (H$^-$) ions in lanthanum hydroxide LaH$_{3-2x}$O$_x$. The $\mu$SR spectra observed at 5--300 K in a sample with $x\approx0.25$ consist primarily of two components which are attributed to muons occupying tetrahedral (Tet) and octahedral (Oct) sites common to H$^-$. The spectra also indicate that muons at the Oct sites (Mu$_{\rm O}$) appear nearly stationary in the time scale of $\mu$SR ($\sim$10$^{-5}$ s), whereas those at the Tet sites (Mu$_{\rm T}$) are subject to the fluctuating local fields. The cusp-like peak in the fluctuation rate around 160 K and the decrease in linewidth at higher temperatures probed by Mu$_{\rm T}$ suggest that the jump motion of both Mu$_{\rm T}$ (via the vacant Oct sites) and surrounding Oct-site H$^-$ contributes to spin relaxation and that the fluctuation frequency is widely distributed. These results indicate that the implanted Mu behave as Mu$^-$ and that the jump motion of Mu$^-$/H$^-$ is restricted by the availability of nearby vacant sites. On the other hand, the activation energy for the jump is estimated to be 0.11(3) eV, which is significantly different from $\sim$1.3 eV evaluated from the temperature dependence of $\sigma$ at high temperatures ($\gtrsim400$ K). In our attempt to resolve this discrepancy, we discuss problems inherent in interpreting $\sigma$ using the Arrhenius equation, and demonstrate that the behavior of H$^-$ ions can be better explained as a viscous fluid exhibiting a glass transition.

cond-mat.mtrl-sci↗
arXiv2024

Discovery of an Antiferromagnetic Topological Nodal-line Kondo Semimetal

The symbiosis of strong interactions, flat bands, topology and symmetry has led to the discovery of exotic phases of matter, including fractional Chern insulators, correlated moir\'e topological superconductors, and Dirac and Weyl semimetals. Correlated metals, such as those present in Kondo lattices, rely on the screening of local moments by a sea of non-magnetic conduction electrons. Here, we report on a unique topological Kondo lattice compound, CeCo2P2, where the Kondo effect - whose existence under the magnetic Co phase is protected by PT symmetry - coexists with antiferromagnetic order emerging from the flat bands associated with the Co atoms. Remarkably, this is the only known Kondo lattice compound where magnetic order occurs in non-heavy electrons, and puzzlingly, at a temperature significantly higher than that of the Kondo effect. Furthermore, at low temperatures, the emergence of the Kondo effect, in conjunction with a glide-mirror-z symmetry, results in a nodal line protected by bulk topology near the Fermi energy. These unusual properties, arising from the interplay between itinerant and correlated electrons from different constituent elements, lead to novel quantum phases beyond the celebrated topological Kondo insulators and Weyl Kondo semimetals. CeCo2P2 thus provides an ideal platform for investigating narrow bands, topology, magnetism, and the Kondo effect in strongly correlated electron systems.

cond-mat.str-el↗
arXiv2024

Exploring Superconductivity in Ba$_{3}$Ir$_{4}$Ge$_{16}$: Experimental and Theoretical Insights

We explore both experimental and theoretical aspects of the superconducting properties in the distinctive layered caged compound, Ba$_{3}$Ir$_{4}$Ge$_{16}$. Our approach integrates muon spin rotation and relaxation ($μ$SR) measurements with magnetization and heat capacity experiments, accompanied by first-principle calculations. The compound's bulk superconductivity is unequivocally established through DC magnetization measurements, revealing a critical temperature ($T_\mathrm{C}$) of 5.7 K. A noteworthy characteristic observed in the low-temperature superfluid density is its saturating behavior, aligning with the features typical of conventional Bardeen-Cooper-Schrieffer (BCS) superconductors. The assessment of moderate electron-phonon coupling superconductivity is conducted through transverse field $μ$SR measurements, yielding a superconducting gap to $T_\mathrm{C}$ ratio ($2Δ(0)/k_\mathrm{B}T_\mathrm{C}$) of 4.04, a value corroborated by heat capacity measurements. Crucially, zero field $μ$SR measurements dismiss the possibility of any spontaneous magnetic field emergence below $T_\mathrm{C}$, highlighting the preservation of time-reversal symmetry. Our experimental results are reinforced by first-principles density functional calculations, underscoring the intricate interplay between crystal structure and superconducting order parameter symmetry in polyhedral caged compounds. This comprehensive investigation enhances our understanding of the nuanced relationship between crystal structure and superconductivity in such unique compounds.

cond-mat.supr-con↗
arXiv2024

Ir-Sb Binary System: Unveiling Nodeless Unconventional Superconductivity Proximate to Honeycomb-Vacancy Ordering

Vacancies play a crucial role in solid-state physics, but their impact on materials with strong electron-electron correlations has been underexplored. A recent study on the Ir-Sb binary system, Ir$_{16}$Sb$_{18}$ revealed a novel extended buckled-honeycomb vacancy (BHV) order. Superconductivity is induced by suppressing the BHV ordering through high-pressure growth with excess Ir atoms or isovalent Rh substitution, although the nature of superconducting pairing has remained unexplored. Here, we conduct muon spin rotation experiments probing the temperature-dependence of the effective magnetic penetration depth $λ_{eff}\left(T\right)$ in Ir$_{1-δ}$Sb (synthesized at 5.5 GPa with $T_{\rm c}$ = 4.2 K) and ambient pressure synthesized optimally Rh-doped Ir$_{1-x}$Rh$_{x}$Sb ($x$=0.3, $T_{\rm c}$ = 2.7 K). The exponential temperature dependence of the superfluid density $n_{\rm s}$/m$^{*}$ at low temperatures indicates a fully gapped superconducting state in both samples. Notably, the ratio of $T_{\rm c}$ to the superfluid density is comparable to previously measured unconventional superconductors. A significant increase in $n_{\rm s}$/m$^{*}$ in the high-pressure synthesized sample correlates with $T_{\rm c}$, a hallmark feature of unconventional superconductivity. We further demonstrate a similar effect induced by chemical pressure (Rh substitution) and hydrostatic pressure in Ir$_{1-x}$Rh$_{x}$Sb, highlighting that the dome-shaped phase diagram is a fundamental feature of the material. These findings underscore the unconventional nature of the observed superconductivity, and classifies IrSb as the first unconventional superconducting parent phase with ordered vacancies.

cond-mat.supr-con↗
arXiv2023

Local electronic structure of dilute hydrogen in $β$-Ga$_2$O$_3$ probed by muons

The local electronic structure of muons (Mu) as dilute pseudo-hydrogen in single-crystalline $β$-Ga$_2$O$_3$ has been studied by the muon spin rotation/relaxation ($μ$SR). High-precision measurements over a long time range of $\sim$25 $μ$s have clearly identified two distinct Mu states: a quasi-static Mu (Mu$_1$) and fast-moving Mu (Mu$_2$). By comparing this result with predictions from the recently established ambipolarity model, these two states are respectively attributed to the relaxed-excited states associated with the donor ($E^{+/0}$) and acceptor ($E^{-/0}$) levels predicted by density functional theory (DFT) calculations for the interstitial H. Furthermore, the local electronic structure of Mu$_1$ is found to be an OMu-bonded state with three-coordinated oxygen. The structure is almost identical with the thermal equilibrium state of H, and it is found to function as an electron donor. The other Mu$_2$ is considered to be in the hydride state (Mu$^-$) from the ambipolarity model, suggesting that it is in fast diffusion motion through the short-lived neutral state due to the charge exchange reaction with conduction electrons (Mu$^0+e^-\rightleftarrows$Mu$^-$).

cond-mat.mtrl-sci↗
arXiv2022

Ambipolar Property of Isolated Hydrogen in Oxide Materials Revealed by Muon

The study on the electronic state of muon as pseudo-hydrogen (represented by the elemental symbol Mu) has long been appreciated as one of the few methods to experimentally access the electronic state of dilute hydrogen (H) in semiconductors and dielectrics. Meanwhile, theoretical predictions on the electronic state of H in these materials by first-principles calculations using density functional theory (DFT) do not always agree with the observed states of Mu, standing as an obstacle to integrating the findings of both Mu and H. In this paper, we provide resolution to this problem by a semi-quantitative model that enables systematic understanding of the electronic states of Mu in most oxides.

cond-mat.mtrl-sci↗
arXiv2022

$s$-wave superconductivity in the noncentrosymmetric W$_3$Al$_2$C superconductor: An NMR study

We report on a microscopic study of the noncentrosymmetric superconductor W$_3$Al$_2$C (with $T_c$ = 7.6 K), mostly by means of $^{27}$Al- and $^{13}$C nuclear magnetic resonance (NMR). Since in this material the density of states at the Fermi level is dominated by the tungsten's 5$d$ orbitals, we expect a sizeable spin-orbit coupling (SOC) effect. The normal-state electronic properties of W$_3$Al$_2$C resemble those of a standard metal, but with a Korringa product $1/(T_{1}T)$ significantly smaller than that of metallic Al, reflecting the marginal role played by $s$-electrons. In the superconducting state, we observe a reduction of the Knight shift and an exponential decrease of the NMR relaxation rate $1/T_1$, typical of $s$-wave superconductivity. This is further supported by the observation of a small but distinct coherence peak just below $T_c$ in the $^{13}$C NMR relaxation-rate, in agreement with the fully-gapped superconducting state inferred from the electronic specific-heat data well below $T_c$. The above features are compared to those of members of the same family, in particular, Mo$_3$Al$_2$C, often claimed to exhibit unconventional superconductivity. We discuss why, despite the enhanced SOC, W$_3$Al$_2$C does not show spin-triplet features in its superconducting state and consider the broader consequences of our results for noncentrosymmetric superconductors in general.

cond-mat.supr-con↗
arXiv2021

Anomalous diamagnetism of electride electrons in transition metal silicides

Intermetallic silicide compounds, LaScSi and Y$_5$Si$_3$, known for being hydrogen (H) storage materials, are drawing attention as candidates for electrides in which anions are substituted by unbound electrons. It is inferred from a muon spin rotation experiment that the local field at the muon site (which is the same site as that for H) in these compounds exhibits a large negative shift under an external magnetic field, which is mostly independent of temperature. Such anomalous diamagnetism signals a unique property of electride electrons associated with transition metals. Moreover, the diamagnetic shift decreases with increasing H content, suggesting that the electride electrons existing coherently in the hollow interstitial positions are adsorbed by H to form hydride ions (H$^-$)

cond-mat.mtrl-sci↗
arXiv2020

Superconducting gap symmetry of the noncentrosymmetric superconductor W3Al2C

A detailed zero-field and transverse-field muon spin relaxation/rotation ($μ$SR) experiemnts have been carried out on the recently discovered non-centrosymmetric superconductor W$_3$Al$_2$C to speculate about its superconducting ground state. Bulk nature of superconductivity below 7.6 K is confirmed through magnetization measurements. No change in the $μ$SR spectra collected above and below $T_c$ is visible, ruling out the possibility of spontaneous magnetic field below $T_c$. This confirms that time-reversal symmetry is preserved for W$_3$Al$_2$C upon entering in the superconducting ground state. Temperature dependent superfluid density [$ρ_s(T)$], which directly reflects the superconducting gap symmetry is obtained by the analysis of spectra obtained from the transverse-field $μ$SR experiments. Despite a non-centrosymmetric structure, W$_3$Al$_2$C adopts a fully gaped spin-singlet superconducting ground state with a zero temperature value of gap $Δ_0$ = 1.158(8) meV with gap-to-$T_c$ ratio 2$Δ_0/k_BT_c\approx$3.54, classifying this material as a weakly-coupled superconductors.

cond-mat.supr-con↗
arXiv2020

Magnetism driven by strong electronic correlation in the heavily carrier-doped iron oxypnictide LaFeAsO$_{0.49}$H$_{0.51}$

The magnetism of the second antiferromagnetic phase (AF2) arising in the iron-based LaFeAsO$_{1-x}$H$_{x}$ superconductor for $x\gtrsim0.4$ was investigated by muon spin rotation measurements under hydrostatic pressure up to 2.6 GPa. The Néel temperature ($T_{\rm N}$) obtained for a sample with $x=0.51$ exhibits considerably greater sensitivity to pressure than that in the pristine antiferromagnetic phase (AF1, $x\lesssim0.06$). Moreover, while the AF1 phase is always accompanied by the structural transition (from tetragonal to orthorhombic) at a temperature ($T_{\rm s}$) which is slightly higher than $T_{\rm N}$, the AF2 phase prevails at higher pressures above $\sim$1.5 GPa where the structural transition is suppressed ($T_{\rm s}=0$). These features indicate that the microscopic origin of the AF2 phase is distinct from that of AF1, suggesting that electronic correlation plays important role in the former phase. We argue that the orbital-selective Mott transition is a plausible scenario to account for the observed pressure dependence of $T_{\rm N}$ and $T_{\rm s}$ in the AF2 phase.

cond-mat.str-el↗
arXiv2019

Electronic structure of interstitial hydrogen in In-Ga-Zn-O semiconductor simulated by muon

We report on the local electronic structure of interstitial muon (Mu) as pseudo-hydrogen in In-Ga-Zn oxide (IGZO) semiconductor studied by muon spin rotation/relaxation ($μ$SR) experiment. In polycrystalline (c-) IGZO, it is inferred that Mu is in a diamagnetic state, where the $μ$SR time spectra under zero external field is perfectly described by the Gaussian Kubo-Toyabe relaxation function with the linewidth $Δ$ serving as a sensitive measure for the random local fields from In/Ga nuclear magnetic moments. The magnitude of $Δ$ combined with the density functional theory calculations for H (to mimic Mu) suggests that Mu occupies Zn-O bond-center site (Mu$_{\rm BC}$) similar to the case in crystalline ZnO. This implies that the diamagnetic state in c-IGZO corresponds to Mu$_{\rm BC}^+$, thus serving as an electron donor. In amorphous (a-) IGZO, the local Mu structure in as-deposited films is nearly identical with that in c-IGZO, suggesting Mu$_{\rm BC}^+$ for the electronic state. In contrast, the diamagnetic signal in heavily hydrogenated a-IGZO films exhibits the Lorentzian Kubo-Toyabe relaxation, implying that Mu accompanies more inhomogeneous distribution of the neighboring nuclear spins that may involve Mu$^-$H$^-$-complex state in an oxygen vacancy.

cond-mat.mtrl-sci↗
arXiv2018

Electronic correlation in the quasi-two-dimensional electride Y$_2$C

Magnetic properties of the electride compound Y$_2$C were investigated by muon spin rotation and magnetic susceptibility on two samples with different form (poly- and single-crystalline), to examine the theoretically-predicted Stoner ferromagnetism for the electride bands. There was no evidence of static magnetic order in both samples even at temperatures down to 0.024 K. For the poly-crystalline sample, the presence of a paramagnetic moment at Y sites was inferred from the Curie-Weiss behavior of the muon Knight shift and susceptibility, whereas no such tendency was observed in the single-crystalline sample. These observations suggest that the electronic ground state of Y$_2$C is at the limit between weak-to-strong electronic correlation, where onsite Coulomb repulsion is sensitive to a local modulation of the electronic state or a shift in the Fermi level due to the presence of defects/impurities.

cond-mat.mtrl-sci↗
arXiv2016

Experimental evidence of $T_c$ enhancement without the influence of spin fluctuations: NMR study on LaFeAsO_{1-x}H_x under a pressure of 3.0 GPa

The electron-doped high-transition-temperature (T_c) iron-based pnictide superconductor LaFeAsO_{1-x}H_x has a unique phase diagram: superconducting (SC) double domes are sandwiched by antiferromagnetic phases at ambient pressure and they turn to a single dome with a maximum T_c that exceeds 45K at a pressure of 3.0 GPa. We studied whether spin fluctuations are involved in increasing T_c under a pressure of 3.0 GPa by using ^{75}As nuclear magnetic resonance (NMR) technique. The ^{75}As-NMR results for the powder samples show that T_c increases up to 48 K without the influence of spin fluctuations. The fact indicates that spin fluctuations are not involved in raising T_c, which implies that other factors, such as orbital degrees of freedom, may be important for achieving a high T_c of almost 50 K.

cond-mat.supr-con↗
arXiv2016

Multiple-pseudogap phases in hydrogen-doped LaFeAsO system

The low energy electronic structure of LaFeAsO1-xHx (0.0 < x < 0.60), the system which exhibits two superconducting domes in its phase diagram, is investigated by utilizing the laser photoemission spectroscopy. From the precise temperature-dependent measurement of the spectra near the Fermi level, we find the suppression of the density of states with cooling, namely the pseudogap formation, for all doping range. The pseudogap in the low x range (i.e. the first superconducting dome regime) gets suppressed with increasing x, more or less similarly to the previous results in F-doped LaFeAsO system. On the other hand, the pseudogap behavior in the second superconducting dome regime at high-x becomes stronger with increasing the H-doping level. The systematic doping dependence shows that the pseudogap is enhanced toward the both ends of the phase diagram where the different types of antiferromagnetic order exist.

cond-mat.supr-con↗
arXiv2016

Cage Electron-Hydroxyl Complex State as Electron Donor in Mayenite

It is inferred from the chemical shift of muon spin rotation ($μ$SR) spectra that muons implanted in pristine (fully oxidized) mayenite, [Ca$_{12}$Al$_{14}$O$_{32}]^{2+}$[$\square_5$O$^{2-}$] (C12A7, with $\square$ referring to the vacant cage), are bound to O$^{2-}$ at the cage center to form OMu$^-$ (where Mu represents muonium, a muonic analog of the H atom). However, an isolated negatively charged state (Mu$^-$, an analog of H$^-$) becomes dominant when the compound approaches the state of electride [Ca$_{12}$Al$_{14}$O$_{32}]^{2+}$[$\square_4$2e$^{-}$] as a result of the reduction process. Moreover, the OMu$^-$ state in the pristine specimen exhibits depolarization of paramagnetic origin at low temperatures (below $\sim$30~K), indicating that OMu$^-$ accompanies a loosely bound electron in the cage that can be thermally activated. This suggests that interstitial muons (and hence H) forming a "cage electron-hydroxyl" complex can serve as electron donors in C12A7.

cond-mat.mtrl-sci↗
arXiv2015

Quantum critical behavior in heavily doped LaFeAsO$_{1-x}$H$_x$ pnictide superconductors analyzed using nuclear magnetic resonance

We studied the quantum critical behavior of the second antiferromagnetic (AF) phase in the heavily electron-doped high-$T_c$ pnictide, LaFeAsO$_{1-x}$H$_x$ by using $^{75}$As and $^{1}$H nuclear-magnetic-resonance (NMR) technique. In the second AF phase, we observed a spatially modulated spin-density-wave-like state up to $x$=0.6 from the NMR spectral lineshape and detected a low-energy excitation gap from the nuclear relaxation time $T_1$ of $^{75}$As. The excitation gap closes at the AF quantum critical point (QCP) at $x \approx 0.49$. The superconducting (SC) phase in a lower-doping regime contacts the second AF phase only at the AF QCP, and both phases are segregated from each other. The absence of AF critical fluctuations and the enhancement of the in-plane electric anisotropy are key factors for the development of superconductivity.

cond-mat.supr-con↗
arXiv2014

Crossover between magnetism and superconductivity in low H-doped LaFeAsO

By a systematic study of the hydrogen-doped LaFeAsO system by means of dc resistivity, dc magnetometry, and muon-spin spectroscopy we addressed the question of universality of the phase diagram of rare-earth-1111 pnictides. In many respects, the behaviour of LaFeAsO_(1-x)H_(x) resembles that of its widely studied F-doped counterpart, with H^- realizing a similar (or better) electron-doping in the LaO planes. In a x = 0.01 sample we found a long-range SDW order with T_n = 119 K, while at x = 0.05 the SDW establishes only at 38 K and, below T_c = 10 K, it coexists at a nanoscopic scale with bulk superconductivity. Unlike the abrupt M-SC transition found in the parent La-1111 compound, the presence a crossover region makes the H-doped system qualitatively similar to other Sm-, Ce-, or Nd-1111 families.

cond-mat.supr-con↗