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T. Ito

Publications and source records attributed to T. Ito.

At least 73 records · Page 4Linked to original sources
arXiv2009

Crystalline electric field effects in Ce 3$d$ core-level spectra of heavy-fermion systems: Hard X-ray photoemission spectroscopy on CeNi$_{1-x}$Co$_x$Ge$_2$

High-resolution hard X-ray photoemission measurements have been performed to clarify the electronic structure originating from the strong correlation between electrons in bulk Ce 3$d$ core-level spectra of CeNi$_{1-x}$Co$_x$Ge$_2$ (0 $\leq$ $x$ $\leq$ 1). In the Ce 3$d_{5/2}$ core-level spectra, the variation of satellite structures ($f^2$ peaks) shows that the hybridization strength between Ce 4$f$- and conduction electrons gradually increases with Co concentration in good agreement with the results of Ce 3$d-4f$ and 4$d-4f$ resonant photoemission spectroscopies. Particularly, in Ce 3$d_{3/2}$ core-level spectra, the multiplet structures of $f^1$ peaks systematically change with the degeneracy of $f$-states which originates from crystalline electric field effects.

cond-mat.str-el↗
arXiv2008

Electronic inhomogeneity in EuO: Possibility of magnetic polaron states

We have observed the spatial inhomogeneity of the electronic structure of a single-crystalline electron-doped EuO thin film with ferromagnetic ordering by employing infrared magneto-optical imaging with synchrotron radiation. The uniform paramagnetic electronic structure changes to a uniform ferromagnetic structure via an inhomogeneous state with decreasing temperature and increasing magnetic field slightly above the ordering temperature. One possibility of the origin of the inhomogeneity is the appearance of magnetic polaron states.

cond-mat.str-el↗
arXiv2008

Effect of Structural Parameters on Superconductivity in Fluorine-Free LnFeAsO1-y (Ln=La,Nd)

The crystal structure of LnFeAsO$_{1-y}$ (Ln = La, Nd) has been studied by the powder neutron diffraction technique. The superconducting phase diagram of NdFeAsO$_{1-y}$ is established as a function of oxygen content which is determined by Rietveld refinement. The small As-Fe bond length suggests that As and Fe atoms are connected covalently. FeAs$_4$-tetrahedrons transform toward a regular shape with increasing oxygen deficiency. Superconducting transition temperatures seem to attain maximum values for regular FeAs$_4$-tetrahedrons.

cond-mat.supr-con↗
arXiv2008

Absence of time reversal symmetry breaking in La_{2-x}Sr_{x}CuO_{4}

We have performed zero-field muon spin rotation measurements on single crystals of La_{2-x}Sr_{x}CuO_{4} to search for spontaneous currents in the pseudo-gap state. By comparing measurements on materials across the phase diagram, we put strict upper limits on any possible time-reversal symmetry breaking fields that could be associated with the pseudo-gap. Comparison between experimental limits and proposed circulating current states effectively eliminates the possibility that such states exist in this family of materials.

cond-mat.supr-con↗
arXiv2008

Mesoscopic Phase Coherence in a Quantum Spin Fluid

Mesoscopic quantum phase coherence is important because it improves the prospects for handling quantum degrees of freedom in technology. Here we show that the development of such coherence can be monitored using magnetic neutron scattering from a one-dimensional spin chain Y2BaNiO5, a quantum spin fluid where no classical, static magnetic order is present. In the cleanest samples, the quantum coherence length is 20 nm, almost an order of magnitude larger than the classical antiferromagnetic correlation length of 3 nm. We also demonstrate that the coherence length can be modified by static and thermally activated defects in a quantitatively predictable manner.

cond-mat.str-el↗
arXiv2007

Polarized structure functions of nucleons and nuclei

We determine the quark distributions and structure functions for both unpolarized and polarized DIS of leptons on nucleons and nuclei. The scalar and vector mean fields in the nucleus modify the motion of the quarks inside the nucleons. By taking into account this medium modification, we are able to reproduce the experimental data on the unpolarized EMC effect, and to make predictions for the polarized EMC effect. We discuss examples of nuclei where the polarized EMC effect could be measured. We finally present an extension of our model to describe fragmentation functions.

nucl-th↗
arXiv2007

Apollo asteroids (1566) Icarus and 2007 MK6: Icarus family members?

Although it is more complicated to search for near-Earth object (NEO) families than main belt asteroid (MBA) families, since differential orbital evolution within a NEO family can cause current orbital elements to drastically differ from each other, we have found that Apollo asteroids (1566) Icarus and the newly discovered 2007 MK6 are almost certainly related. Specifically, their orbital evolutions show a similar profile, time shifted by only ~1000 yr, based on our time-lag theory. The dynamical relationship between Icarus and 2007 MK6 along with a possible dust band, the Taurid-Perseid meteor swarm, implies the first detection of an asteroidal NEO family, namely the "Icarus asteroid family".

astro-ph↗
arXiv2005

Muon Spin Relaxation Studies of Magnetic-Field-Induced Effects in High-$T_{c}$ Superconductors

Muon spin relaxation ($μ$SR) measurements in high transverse magnetic fields ($\parallel \hat c$) revealed strong field-induced quasi-static magnetism in the underdoped and Eu doped (La,Sr)$_{2}$CuO$_{4}$ and La$_{1.875}$Ba$_{0.125}$CuO$_{4}$, existing well above $T_{c}$ and $T_{N}$. The susceptibility-counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards $T \sim 25$ K. No field-induced magnetism was detected in overdoped La$_{1.81}$Sr$_{0.19}$CuO$_{4}$, optimally doped Bi2212, and Zn-doped YBa$_{2}$Cu$_{3}$O$_{7}$.

cond-mat.supr-con↗
arXiv2005

Temperature dependent Luttinger surfaces

The Luttinger surface of an organic metal (TTF-TCNQ), possessing charge order and spin-charge separation, is investigated using temperature dependent angle-resolved photoemission spectroscopy. The Luttinger surface topology, obtained from momentum distribution curves, changes from quasi-2D(dimensional) to quasi-1D with temperature. The high temperature quasi-2D surface exhibits 4$k_F$ charge-density-wave (CDW) superstructure in the TCNQ derived holon band, in the absence of 2$k_F$ order. Decreasing temperature results in quasi-1D nested 2$k_F$ CDW order in the TCNQ spinon band and in the TTF surface. The results establish the link in momentum-space between charge order and spin-charge separation in a Luttinger liquid.

cond-mat.str-el↗
arXiv2005

The origin of the phase separation in partially deuterated $κ$-(ET)$_2$Cu[N(CN)$_2$]Br studied by infrared magneto-optical imaging spectroscopy

The direct observation of the phase separation between the metallic and insulating states of 75 %-deuterated $κ$-(ET)$_2$Cu[N(CN)$_2$]Br ($d33$) using infrared magneto-optical imaging spectroscopy is reported, as well as the associated temperature, cooling rate, and magnetic field dependencies of the separation. The distribution of the center of spectral weight ($< ω>$) of $d33$ did not change under any of the conditions in which data were taken and was wider than that of the non-deuterated material. This result indicates that the inhomogenity of the sample itself is important as part of the origin of the metal - insulator phase separation.

cond-mat.str-el↗
arXiv2004

Effects of hole-doping on the magnetic ground state and excitations in the edge-sharing CuO$_2$ chains of Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$

Neutron scattering experiments were performed on the undoped and hole-doped Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$, which consists of ferromagnetic edge-sharing CuO$_2$ chains. It was previously reported that in the undoped Ca$_2$Y$_2$Cu$_5$O$_{10}$ there is an anomalous broadening of spin-wave excitations along the chain, which is caused mainly by the antiferromagnetic interchain interactions [Matsuda $et$ $al.$, Phys. Rev. B 63, 180403(R) (2001)]. A systematic study of temperature and hole concentration dependencies of the magnetic excitations shows that the magnetic excitations are softened and broadened with increasing temperature or doping holes irrespective of $Q$ direction. The broadening is larger at higher $Q$. A characteristic feature is that hole-doping is much more effective to broaden the excitations along the chain. It is also suggested that the intrachain interaction does not change so much with increasing temperature or doping although the anisotropic interaction and the interchain interaction are reduced. In the spin-glass phase ($x$=1.5) and nearly disordered phase ($x$=1.67) the magnetic excitations are much broadened in energy and $Q$. It is suggested that the spin-glass phase originates from the antiferromagnetic clusters, which are caused by the hole disproportionation.

cond-mat.str-el↗
arXiv2004

Specific heat study of spin-structural change in pyrochlore Nd$_2$Mo$_2$O$_7$

By measurements of specific heat, we have investigated the magnetic field ($H$) induced spin-structural change in Nd$_2$Mo$_2$O$_7$ that shows spin-chirality-related magneto-transport phenomena. A broad peak around 2 K caused by the ordering of 2-in 2-out structure of the Nd moments at zero $H$ shifts to the lower temperature ($T$) up to around 3 T and then to the higher $T$ above around 3 T with increasing $H$ for all the direction of $H$. This is due to the crossover from antiferromagnetic to ferromagnetic arrangement between the Nd and Mo moments. While the peak $T$ increases monotonically above 3 T for $H$//[100], another peak emerges around 0.9 K at 12 T for $H$//[111], which is ascribed to the ordering of 3-in 1-out structure. For $H$//[110], a spike like peak is observed at around 3 T, which is caused perhaps by some spin flip transition.

cond-mat.str-el↗
arXiv2004

Expansion of Vortex Cores by Strong Electronic Correlation in La$_{2-x}$Sr$_x$CuO$_4$ at Low Magnetic Induction

The vortex core radius \rv, defined as the peak position of the supercurrent around the vortex, has been determined by muon spin rotation measurements in the mixed state of \lscox for $x=0.13$, 0.15, and 0.19. At lower doping (x=0.13 and 0.15), \rv(T) increases with decreasing temperature T, which is opposite to the behavior predicted by the conventional theory. Moreover, \rv(T\to0) is significantly larger than the Ginsburg-Landau coherence length determined by the upper critical field, and shows a clear tendency to decrease with increasing the doping x. These features can be qualitatively reproduced in a microscopic model involving antiferromagnetic electronic correlations.

cond-mat.supr-con↗
arXiv2003

Two dimensional nature of superconductivity in intercalated layered systems Li$_{x}$HfNCl and Li$_{x}$ZrNCl: muon spin relaxation and magnetization measurements

We report muon spin relaxation ($μ$SR) and magnetization measurements, together with synthesis and characterization, of the Li-intercalated layered superconductors Li$_{x}$HfNCl and Li$_{x}$ZrNCl with/without co-intercalation of THF (tetrahydrofuran) or PC (propylene carbonate). The 3-dimensional (3-d) superfluid density $n_{s}/m^{*}$ (superconducting carrier density / effective mass), as well as the two dimensional superfluid density $n_{s2d}/m^{*}_{ab}$ (2-dimensional (2-d) area density of superconducting carriers / ab-plane effective mass), have been derived from the $μ$SR results of the magnetic-field penetration depth $λ_{ab}$ observed with external magnetic field applied perpendicular to the 2-d honeycomb layer of HfN / ZrN. In a plot of $T_{c}$ versus $n_{s2d}/m^{*}_{ab}$, most of the results lie close to the linear relationship found for underdoped high-$T_{c}$ cuprate (HTSC) and layered organic BEDT superconductors. In Li$_{x}$ZrNCl without THF intercalation, the superfluid density and $T_{c}$ for $x$ = 0.17 and 0.4 do not show much difference, reminiscent of $μ$SR results for some overdoped HTSC systems. Together with the absence of dependence of $T_{c}$ on average interlayer distance among ZrN / HfN layers, these results suggest that the 2-d superfluid density $n_{s2d}/m^{*}_{ab}$ is a dominant determining factor for $T_{c}$ in the intercalated nitride-chloride systems. We also report $μ$SR and magnetization results on depinning of flux vortices, and the magnetization results for the upper critical field $H_{c2}$ and the penetration depth $λ$. Reasonable agreement was obtained between $μ$SR and magnetization estimates of $λ$. We discuss the two dimensional nature of superconductivity in the nitride-chloride systems based on these results.

cond-mat.supr-con↗
arXiv2003

Muon Spin Relaxation and Susceptibility Studies of Pure and Doped Spin 1/2 Kagomé-like system (Cu$_x$Zn$_{1-x}$)$_{3}$V$_{2}$O$_7$(OH)$_{2}$ 2H$_2$O

Muon spin relaxation ($μ$SR) and magnetic susceptibility measurements have been performed on the pure and diluted spin 1/2 kagomé system (Cu$_x$Zn$_{1-x}$)$_{3}$V$_{2}$O$_7$(OH)$_{2}$ 2H$_2$O. In the pure $x=1$ system we found a slowing down of Cu spin fluctuations with decreasing temperature towards $T \sim 1$ K, followed by slow and nearly temperature-independent spin fluctuations persisting down to $T$ = 50 mK, indicative of quantum fluctuations. No indication of static spin freezing was detected in either of the pure ($x$=1.0) or diluted samples. The observed magnitude of fluctuating fields indicates that the slow spin fluctuations represent an intrinsic property of kagomé network rather than impurity spins.

cond-mat.str-el↗
arXiv2003

Electronic correlation in the infrared optical properties of the quasi two dimensional $κ$-type BEDT-TTF dimer system

The polarized optical reflectance spectra of the quasi two dimensional organic correlated electron system $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]$Y$, $Y =$ Br and Cl are measured in the infrared region. The former shows the superconductivity at $T_{\rm c} \simeq$ 11.6 K and the latter does the antiferromagnetic insulator transition at $T_{\rm N} \simeq$ 28 K. Both the specific molecular vibration mode $ν_{3}(a_{g})$ of the BEDT-TTF molecule and the optical conductivity hump in the mid-infrared region change correlatively at $T^{*} \simeq$ 38 K of $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br, although no indication of $T^{*}$ but the insulating behaviour below $T_{\rm ins} \simeq$ 50-60 K are found in $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl. The results suggest that the electron-molecular vibration coupling on the $ν_{3}(a_{g})$ mode becomes weak due to the enhancement of the itinerant nature of the carriers on the dimer of the BEDT-TTF molecules below $T^{*}$, while it does strong below $T_{\rm ins}$ because of the localized carriers on the dimer. These changes are in agreement with the reduction and the enhancement of the mid-infrared conductivity hump below $T^{*}$ and $T_{\rm ins}$, respectively, which originates from the transitions between the upper and lower Mott-Hubbard bands. The present observations demonstrate that two different metallic states of $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br are regarded as {\it a correlated good metal} below $T^{*}$ including the superconducting state and {\it a half filling bad metal} above $T^{*}$. In contrast the insulating state of $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl below $T_{\rm ins}$ is the Mott insulator.

cond-mat.supr-con↗
arXiv2002

Structure of end states for a Haldane Spin Chain

Inelastic neutron scattering was used to probe edge states in a quantum spin liquid. The experiment was performed on finite length antiferromagnetic spin-1 chains in Y_2BaNi_{1-x}Mg_xO_5. At finite fields, there is a Zeeman resonance below the Haldane gap. The wave vector dependence of its intensity provides direct evidence for staggered magnetization at chain ends, which decays exponentially towards the bulk (xi = 8(1) at T=0.1K). Continuum contributions to the chain end spectrum indicate inter-chain-segment interactions. We also observe a finite size blue shift of the Haldane gap.

cond-mat.str-el↗