S. Hosoya

Bio: S. Hosoya is an academic researcher from University of Yamanashi. The author has contributed to research in topics: Neutron scattering & Superconductivity. The author has an hindex of 11, co-authored 22 publications receiving 1199 citations.

Doping dependence of the spatially modulated dynamical spin correlations and the superconducting-transition temperature in La 2-x Sr x CuO 4

Abstract: Systematic low-energy neutron-scattering studies have been performed on float-zone-grown single crystals of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ with $x$ extending from zero doping, $x=0$, to the overdoped, weakly superconducting regime, $x=025$ For $x$ beyond a critical doping value of ${x}_{c}\ensuremath{\approx}005$ the low-energy spin-fluctuation peak position shifts from ($\frac{1}{2}$, $\frac{1}{2}$) to ($\frac{1}{2}$\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}, $\frac{1}{2}$), and ($\frac{1}{2}$, $\frac{1}{2}$\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}); ${x}_{c}$ also represents the onset concentration for superconductivity For $006l~xl~012$ the incommensurability $\ensuremath{\delta}$ follows approximately the quantitative relation $\ensuremath{\delta}=x$ However, beyond $x\ensuremath{\approx}012$ the incommensurability tends to saturate around $\ensuremath{\delta}\ensuremath{\approx}1/8$ The superconducting-transition temperature ${T}_{c}(x)$ for stoichiometric samples at a given doping scales linearly with $\ensuremath{\delta}$ up to the optimal doping value of $x$ The peak momentum width of the spin fluctuations at low energies is small throughout the superconducting concentration region except in the strongly overdoped region An anomalously small width is observed for $x=\frac{1}{8}$ The incommensurate spatial modulation is found to be robust with respect to pair-breaking effects that lower ${T}_{c},$ such as deoxygenation of the sample or replacement of Cu by Zn

Direct Observation of a Magnetic Gap in Superconducting La 1.85 Sr 0.15 CuO 4 ( T c = 37.3 K )

Abstract: Neutron inelastic scattering experiments have been performed on homogeneous single crystals of ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$ with ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}37.3$ K (at onset), higher than any previously studied single crystals. The temperature dependence of the low energy incommensurate peak intensity at $(\ensuremath{\pi}(1\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}),\ensuremath{\pi})$ and $(\ensuremath{\pi},\ensuremath{\pi}(1\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}))$ exhibits a pronounced maximum near ${T}_{c}$. In contrast to the results reported on lower ${T}_{c}$ crystals, the intensity below 3.5 meV dramatically decreases as the temperature decreases below ${T}_{c}$, vanishing into the background below $\ensuremath{\sim}15$ K. The behavior is consistent with predictions based on a ${d}_{{x}^{2}{\ensuremath{-}y}^{2}}$ superconducting order parameter.

Reduction of Ordered Moment and Néel Temperature of Quasi-One-Dimensional Antiferromagnets Sr 2 CuO 3 and Ca 2 CuO 3

Abstract: We report elastic neutron diffraction and muon spin relaxation ( $\ensuremath{\mu}\mathrm{SR}$) measurements of the quasi-one-dimensional antiferromagnets ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ and ${\mathrm{Ca}}_{2}{\mathrm{CuO}}_{3}$, which have extraordinarily reduced ${T}_{N}/J$ ratios. We observe almost resolution-limited antiferromagnetic Bragg reflections in ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ and obtain a reduced ordered moment size of $\ensuremath{\sim}0.06{\ensuremath{\mu}}_{\mathrm{B}}$. We find that the ratio of ordered moment size $\ensuremath{\mu}({\mathrm{Ca}}_{2}{\mathrm{CuO}}_{3})/\ensuremath{\mu}({\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.5(1)$ roughly scales with their N\'eel temperatures, which suggests that the ordered moment size of quasi-one-dimensional antiferromagnets decreases continuously in the limit of vanishing interchain interactions.

An Overall Energy Spectrum of Magnetic Fluctuations in the Superconducting La1.85Sr0.15CuO4

Abstract: High-energy pulsed neutron inelastic scattering experiments have been performed using single crystals of La 1.85 Sr 0.15 CuO 4 to study magnetic fluctuations in the superconducting phase. A peak centered at the reciprocal point (π,π) is well defined below around 120 meV and rapidly damped beyond this energy. However, the \lq\lqbackground-subtracted” scattering intensities indicate that magnetic signals remain up to around 300 meV. These data combined with the results obtained by triple-axis neutron scattering experiments provide the first overall energy spectrum of the dynamical susceptibility in La 1.85 Sr 0.15 CuO 4 . The obtained spectrum is much wider than that of YBa 2 Cu 3 O 7- d ( d ∼0).

Doping a Mott insulator: Physics of high-temperature superconductivity

Abstract: This article reviews the physics of high-temperature superconductors from the point of view of the doping of a Mott insulator. The basic electronic structure of cuprates is reviewed, emphasizing the physics of strong correlation and establishing the model of a doped Mott insulator as a starting point. A variety of experiments are discussed, focusing on the region of the phase diagram close to the Mott insulator (the underdoped region) where the behavior is most anomalous. The normal state in this region exhibits pseudogap phenomenon. In contrast, the quasiparticles in the superconducting state are well defined and behave according to theory. This review introduces Anderson's idea of the resonating valence bond and argues that it gives a qualitative account of the data. The importance of phase fluctuations is discussed, leading to a theory of the transition temperature, which is driven by phase fluctuations and the thermal excitation of quasiparticles. However, an argument is made that phase fluctuations can only explain pseudogap phenomenology over a limited temperature range, and some additional physics is needed to explain the onset of singlet formation at very high temperatures. A description of the numerical method of the projected wave function is presented, which turns out to be a very useful technique for implementing the strong correlation constraint and leads to a number of predictions which are in agreement with experiments. The remainder of the paper deals with an analytic treatment of the $t\text{\ensuremath{-}}J$ model, with the goal of putting the resonating valence bond idea on a more formal footing. The slave boson is introduced to enforce the constraint againt double occupation and it is shown that the implementation of this local constraint leads naturally to gauge theories. This review follows the historical order by first examining the U(1) formulation of the gauge theory. Some inadequacies of this formulation for underdoping are discussed, leading to the SU(2) formulation. Here follows a rather thorough discussion of the role of gauge theory in describing the spin-liquid phase of the undoped Mott insulator. The difference between the high-energy gauge group in the formulation of the problem versus the low-energy gauge group, which is an emergent phenomenon, is emphasized. Several possible routes to deconfinement based on different emergent gauge groups are discussed, which leads to the physics of fractionalization and spin-charge separation. Next the extension of the SU(2) formulation to nonzero doping is described with a focus on a part of the mean-field phase diagram called the staggered flux liquid phase. It will be shown that inclusion of the gauge fluctuation provides a reasonable description of the pseudogap phase. It is emphasized that $d$-wave superconductivity can be considered as evolving from a stable U(1) spin liquid. These ideas are applied to the high-${T}_{c}$ cuprates, and their implications for the vortex structure and the phase diagram are discussed. A possible test of the topological structure of the pseudogap phase is described.

Angle-resolved photoemission studies of the cuprate superconductors

Abstract: The last decade witnessed significant progress in angle-resolved photoemission spectroscopy (ARPES) and its applications. Today, ARPES experiments with 2-meV energy resolution and $0.2\ifmmode^\circ\else\textdegree\fi{}$ angular resolution are a reality even for photoemission on solids. These technological advances and the improved sample quality have enabled ARPES to emerge as a leading tool in the investigation of the high-${T}_{c}$ superconductors. This paper reviews the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds, with the purpose of providing an updated summary of the extensive literature. The low-energy excitations are discussed with emphasis on some of the most relevant issues, such as the Fermi surface and remnant Fermi surface, the superconducting gap, the pseudogap and $d$-wave-like dispersion, evidence of electronic inhomogeneity and nanoscale phase separation, the emergence of coherent quasiparticles through the superconducting transition, and many-body effects in the one-particle spectral function due to the interaction of the charge with magnetic and/or lattice degrees of freedom. Given the dynamic nature of the field, we chose to focus mainly on reviewing the experimental data, as on the experimental side a general consensus has been reached, whereas interpretations and related theoretical models can vary significantly. The first part of the paper introduces photoemission spectroscopy in the context of strongly interacting systems, along with an update on the state-of-the-art instrumentation. The second part provides an overview of the scientific issues relevant to the investigation of the low-energy electronic structure by ARPES. The rest of the paper is devoted to the experimental results from the cuprates, and the discussion is organized along conceptual lines: normal-state electronic structure, interlayer interaction, superconducting gap, coherent superconducting peak, pseudogap, electron self-energy, and collective modes. Within each topic, ARPES data from the various copper oxides are presented.

Doping a Mott Insulator: Physics of High Temperature Superconductivity

Abstract: This article reviews the effort to understand the physics of high temperature superconductors from the point of view of doping a Mott insulator. The basic electronic structure of the cuprates is reviewed, emphasizing the physics of strong correlation and establishing the model of a doped Mott insulator as a starting point. A variety of experiments are discussed, focusing on the region of the phase diagram close to the Mott insulator (the underdoped region) where the behavior is most anomalous. We introduce Anderson's idea of the resonating valence bond (RVB) and argue that it gives a qualitative account of the data. The importance of phase fluctuation is discussed, leading to a theory of the transition temperature which is driven by phase fluctuation and thermal excitation of quasiparticles. We then describe the numerical method of projected wavefunction which turns out to be a very useful technique to implement the strong correlation constraint, and leads to a number of predictions which are in agreement with experiments. The remainder of the paper deals with an analytic treatment of the t-J model, with the goal of putting the RVB idea on a more formal footing. The slave-boson is introduced to enforce the constraint of no double occupation. The implementation of the local constraint leads naturally to gauge theories. We give a rather thorough discussion of the role of gauge theory in describing the spin liquid phase of the undoped Mott insulator. We next describe the extension of the SU(2) formulation to nonzero doping. We show that inclusion of gauge fluctuation provides a reasonable description of the pseudogap phase.

Transport in proton conductors for fuel-cell applications: simulations, elementary reactions, and phenomenology.

Abstract: 1. Introduction 46372. Theoretical Methodologies and Simulation Tools 46402.1. Ab Initio Quantum Chemistry 46412.2. Molecular Dynamics 46422.2.1. Classical Molecular Dynamics and MonteCarlo Simulations46432.2.2. Empirical Valence Bond Models 46442.2.3. Ab Initio Molecular Dynamics (AIMD) 46452.3. Poisson−Boltzmann Theory 46452.4. Nonequilibrium Statistical Mechanical IonTransport Modeling46462.5. Dielectric Saturation 46473. Transport Mechanisms 46483.1. Proton Conduction Mechanisms 46483.1.1. Homogeneous Media 46483.1.2. Heterogeneous Systems (ConfinementEffects)46553.2. Mechanisms of Parasitic Transport 46613.2.1. Solvated Acidic Polymers 46613.2.2. Oxides 46654. Phenomenology of Transport inProton-Conducting Materials for Fuel-CellApplications46664.1. Hydrated Acidic Polymers 46664.2. PBI−H

How to detect fluctuating stripes in the high-temperature superconductors

Abstract: This article discusses fluctuating order in a quantum disordered phase proximate to a quantum critical point, with particular emphasis on fluctuating stripe order. Optimal strategies are derived for extracting information concerning such local order from experiments, with emphasis on neutron scattering and scanning tunneling microscopy. These ideas are tested by application to two model systems---an exactly solvable one-dimensional (1D) electron gas with an impurity, and a weakly interacting 2D electron gas. Experiments on the cuprate high-temperature superconductors which can be analyzed using these strategies are extensively reviewed. The authors adduce evidence that stripe correlations are widespread in the cuprates. They compare and contrast the advantages of two limiting perspectives on the high-temperature superconductor: weak coupling, in which correlation effects are treated as a perturbation on an underlying metallic (although renormalized) Fermi-liquid state, and strong coupling, in which the magnetism is associated with well-defined localized spins, and stripes are viewed as a form of micro phase separation. The authors present quantitative indicators that the latter view better accounts for the observed stripe phenomena in the cuprates.