arXiv subjects

Y. Matsushita

Publications and source records attributed to Y. Matsushita.

17 recordsLinked to original sources

arXiv2024

Nano-scale dynamics of hydrogen in VO$_{2}$ studied by $μ$SR

Hydrogen dynamics in the nanoscale region of VO$_{2}$ was investigated by muon spin rotation/relaxation ($μ$SR) technique. Positively charged muon acts as a light radioisotope of proton and can be used as a probe to explore the inside of materials from an atomic perspective. By analyzing the muon hopping rate and the spatial distribution of the $^{51}$V nuclear magnetic moments, we have identified two types of diffusion paths in VO$_{2}$ (via oxygen-muon bonds or defects) and the potential of a high diffusion coefficient in the 10$^{-10}$ cm$^{2}$/s range at ambient temperature. Our results provide valuable information for developing hydrogen-driven VO$_{2}$--related electronic devices.

cond-mat.mtrl-sci↗

arXiv2020

Magnetically driven loss of centrosymmetry in metallic Pb2CoOsO6

We report magnetic, transport, neutron diffraction, and muon spin rotation data showing that Pb$_2$CoOsO$_6$, a newly synthesized metallic double-perovskite with a centrosymmetric space group at room temperature, exhibits a continuous second-order phase transition at 45 K to a magnetically ordered state with a non-centrosymmetric space group. The absence of inversion symmetry is very uncommon in metals, particularly metallic oxides. In contrast to the recently reported ferroelectric-like structural transition in LiOsO$_3$, the phase transition in Pb$_2$CoOsO$_6$ is driven by a long-range collinear antiferromagnetic order, with propagation vector $\textbf{k} = (\frac{1}{2},0,\frac{1}{2})$, which relieves the frustration associated with the symmetry of themagnetic exchanges. This magnetically-driven loss of inversion symmetry represents a new frontier in the search for novel metallic behavior.

cond-mat.str-el↗

arXiv2018

Metallic Spin Liquid-like Behavior of LiV$_2$O$_4$

LiV$_2$O$_4$ spinel is known to exhibit heavy fermion-like behavior below a characteristic temperature $T_K\simeq 20$ K, while it preserves a paramagnetic state down to $T\sim10^{-2}$ K due to geometrical frustration. Here, it is shown that the dynamical spin susceptibility $χ({\bf q},ω)$ in LiV$_2$O$_4$ exhibits anomalous duality which is modeled as a sum of itinerant ($χ_{\rm F}$) and local ($χ_{\rm L}$) components,and that the local spin dynamics inferred from $χ_{\rm L}({\bf q},ω)$ is qualitatively different from that expected from time-averaged bulk properties. The anomaly coexists with the marginal Fermi liquid behavior inferred from the $-\ln T$ dependence of the electronic specific heat over a wide temperature range below $T_K$. We argue that such unusual properties of LiV$_2$O$_4$ can be attributed to the putative metallic spin liquid state emerging near the quantum critical point between spin glass and Fermi liquid states.

cond-mat.str-el↗

arXiv2016

Rotational symmetry breaking in the topological superconductor Sr$_x$Bi$_2$Se$_3$ probed by upper-critical field experiments

Recently it was demonstrated that Sr intercalation provides a new route to induce superconductivity in the topological insulator Bi$_2$Se$_3$. Topological superconductors are predicted to be unconventional, with mixed even and odd parity Cooper pairs states. An adequate probe to test for unconventional superconductivity is the upper critical field, $B_{c2}$. For a standard BCS layered superconductor $B_{c2}$ shows an anisotropy when the magnetic field is applied parallel and perpendicular to the layers, but is isotropic when the field is rotated in the plane of the layers. Here we report measurements of the upper critical field of superconducting Sr$_x$Bi$_2$Se$_3$ crystals ($T_c = 3.0$~K). Surprisingly, field-angle dependent magnetotransport measurements reveal a large anisotropy of $B_{c2}$ when the magnet field is rotated in the basal plane. The large two-fold anisotropy, while six-fold is anticipated, cannot be explained with the Ginzburg-Landau anisotropic effective mass model or flux flow induced by the Lorentz force. The rotational symmetry breaking of $B_{c2}$ indicates unconventional superconductivity with an odd-parity polarized triplet Cooper pair state ($Δ_4$-pairing) recently proposed for rhombohedral topological superconductors, or might have a structural nature, such as self-organized stripe ordering of Sr atoms.

cond-mat.supr-con↗

arXiv2012

Simultaneous Superconducting and Antiferroquadrupolar Transitions in PrRh$_{2}$Zn$_{20}$

Superconducting and antiferroquadrupolar (AFQ) transitions in a Pr-based compound PrRh2Zn20 have been found to occur simultaneously at Tc=TQ=0.06 K. The superconducting transition manifests itself by zero resistance and large diamagnetic susceptibility. The specific heat exhibits a Schottky anomaly peaking at 14 K and magnetization curves measured at 2 K show anisotropic behaviors. The analysis of these data indicates that the crystalline electric field (CEF) ground state of the trivalent Pr ion is the non-Kramers Gamma3 doublet with the quadrupolar degrees of freedom. A sharp peak in the specific heat at 0.06 K has been attributed not to the superconducting transition but to the AFQ transition because the ordering temperature TQ decreases in B || [100] but increases in B || [110] and B || [111] with increasing B up to 6 T. This anisotropic behavior of TQ(B) can be well explained by a two-sublattice mean-field calculation, which corroborates the AFQ ordered state below TQ. The entropy release at TQ is only 10% of Rln2 expected for the Gamma3 doublet, suggesting possible interplay between the quadrupolar degrees of freedom and the superconductivity.

cond-mat.str-el↗

arXiv2011

Sr3Co2O6: a possible frustrated spin-chain material

A dense phase of a post-layered perovskite Sr3Co2O6 was created by a high-pressure and high-temperature synthetic route and quenched to ambient conditions. The structure of Sr3Co2O6 was determined by synchrotron X-ray powder diffraction. Sr3Co2O6 crystallizes in the K4CdCl6-type structure (an infinite chain-type structure), which is 6% denser than the known, iso-compositional layered perovskite Sr3Co2O7-d (d~1). The K4CdCl6-type Sr3Co2O6 shows complex magnetic behavior reflecting the spin-chain nature as well as the analogue oxides Ca3Co2O6 and Ca3CoRhO6, whose microscopic magnetic origin is still highly debated.

cond-mat.str-el↗

arXiv2010

Large decrease in the critical temperature of superconducting LaFeAsO0.85 compounds doped with 3% atomic weight of nonmagnetic Zn impurities

We observed a large decrease of Tc by no more than 3 at.% of Zn doped to the optimized superconductor LaFeAsO0.85 (Tc = 26 K), confirmed by measurements of electrical resistivity, magnetic susceptibility, specific heat, Mössbauer spectroscopy, Hall coefficient, and an electron probe micro-analysis. The rate ~9 K/% is remarkably higher than observations regarding nonmagnetic impurities. The Tc suppression is likely due to pair-breaking caused by scatterings associated with highly localized electronic state of Zn doped into the Fe2As2 layer. If this is true, the Zn result well accords with the theoretical prediction that suggests a sign reversal s-wave pairing model for the Fe pnictide superconductors, unlike other nonmagnetic impurity results.

cond-mat.supr-con↗

arXiv2009

Drastic suppression of the superconductivity of LaFeAsO0.85 by a nonmagnetic impurity

We observed a drastic Tc suppression caused by no more than 3 at.% of Zn doped to the optimized superconductor LaFeAsO0.85 (Tc = 26 K). The electrical resistivity and magnetic susceptibility measurements suggested that it is likely due to impurity scatterings rather than losing the metallic nature, seeming to support the s+/- pairing model proposed for the Fe pnictide superconductor.

cond-mat.supr-con↗

arXiv2009

Evidence for a charge Kondo effect in Pb(1-x)Tl(x)Te from measurements of thermoelectric power

We report measurements of the thermoelectric power (TEP) for a series of Pb(1-x)Tl(x)Te crystals with x = 0.0 to 1.3%. Although the TEP is very large for x = 0.0, using a single band analysis based on older work for dilute magnetic alloys we do find evidence for a Kondo contribution of 11 - 18 uV/K. This analysis suggests that Tk is ~ 50 - 70 K, a factor 10 higher than previously thought.

cond-mat.str-el↗

arXiv2009

Superconducting properties of the oxygen-vacant iron oxyarsenide TbFeAsO1-x from underdoped to overdoped compositions

A wide-range doping was achieved by a high-pressure method for TbFeAsO1-x from "under doped" to "over doped" superconducting compositions throughout the optimized superconductivity (Tc of 44 K). Tc vs. lattice constant shows a dome-shaped feature, while Tc vs. the lattice constant likely follows a unique empirical curve over the doping range. The relatively large amount of oxygen vacancies up to 0.3 per the formula unit was introduced possibly because of the smaller replacement Tb than the other Ln (rare-earth element) in the LnFeAsO1-x system.

cond-mat.supr-con↗

arXiv2008

New structural and magnetic aspects of the nanotube system Na2V3O7

We present new experimental results of low temperature x-ray synchrotron diffraction, neutron scattering and very low temperature (mK-range) bulk measurements on the nanotube system ${\tube}$. The crystal structure determined from our data is similar to the previously proposed model (P. Millet {\it et al.} J. Solid State Chem. $\bf{147}$, 676 (1999)), but also deviates from it in significant details. The structure comprises nanotubes along the c-axis formed by stacking units of two V-rings buckled in the $ab$-plane. The space group is P$\bar{3}$ and the composition is nonstoichiometric, Na(2-x)V3O7, x=0.17. The thermal evolution of the lattice parameters reveals anisotropic lattice compression on cooling. Neutron scattering experiments monitor a very weak magnetic signal at energies from -20 to 9 meV. New magnetic susceptibility, specific heat measurements and decay of remanent magnetization in the 30 mK - 300 mK range reveal that the previously observed transition at ~76 mK is spin-glass like with no long-range order. Presented experimental observations do not support models of isolated clusters, but are compatible with a model of odd-legged S=1/2 spin tubes possibly segmented into fragments with different lengths.

cond-mat.str-el↗

arXiv2008

Synthesis and superconducting properties of the iron oxyarsenide TbFeAsO0.85

The iron oxyarsenide TbFeAsO0.85 was synthesized by a high-pressure method. A high-quality polycrystalline sample was obtained and characterized by measurements of magnetic susceptibility and electrical resistivity. Bulk superconductivity with Tc of 42 K was clearly established without an F doping usually conducted to tune on superconductivity in the iron oxypnictide.

cond-mat.supr-con↗

arXiv2006

Superconducting properties of Tl-doped PbTe

Tl-doped PbTe (Pb_{1-x}Tl_{x}Te) is an anomalous superconductor with a remarkably high maximum T_c value given its relatively low carrier concentration. Here, we present results of systematic measurements of superconducting parameters for this material, for Tl concentrations up to x = 1.4%. We find that it is a Type II, weak-coupled BCS superconductor in the dirty limit and discuss implications for the applicability of the charge Kondo model recently proposed to account for superconductivity in this system.

cond-mat.supr-con↗

arXiv2005

Staggered magnetism in LiV$_2$O$_4$ at low temperatures probed by the muon Knight shift

We report on the muon Knight shift measurement in single crystals of LiV2O4. Contrary to what is anticipated for the heavy-fermion state based on the Kondo mechanism, the presence of inhomogeneous local magnetic moments is demonstrated by the broad distribution of the Knight shift at temperatures well below the presumed "Kondo temperature" ($T^*\simeq 30$ K). Moreover, a significant fraction ($\simeq10$ %) of the specimen gives rise to a second component which is virtually non-magnetic. These observations strongly suggest that the anomalous properties of LiV2O4 originates from frustration of local magnetic moments.

cond-mat.str-el↗

arXiv2005

Evidence for charge Kondo effect in superconducting Tl-doped PbTe

We report results of low-temperature thermodynamic and transport measurements of Pb_{1-x}Tl_{x}Te single crystals for Tl concentrations up to the solubility limit of approximately x = 1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T_K ~ 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high T_c values.

cond-mat.str-el↗

arXiv2004

Magnetic behavior of spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, from heat capacity and ac susceptibility studies

Heat-capacity (C) and ac susceptibility measurements have been performed on the spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, to establish their magnetic behavior and to explore whether there are magnetic frustration effects due to antiferromagnetic coupling of the chains arranged in a triangular fashion. While the paramagnetic Curie temperatures have been known to be large with a negative sign, as though antiferromagnetic interaction is very strong, the results establish that (i) the former apparently undergoes inhomogeneous magnetic ordering only around 15 K, however without spin-glass anomalies, and (ii) the latter orders antiferromagnetically at a relatively low temperature (17 K). Thus, the magnetic frustration manifests differently in these compounds.

cond-mat.str-el↗

arXiv2004

New Pyrochlore Oxide Superconductor RbOs2O6

We report the discovery of a new pyrochlore oxide superconductor RbOs2O6. The compound crystallizes in the same beta-pyrochlore structure as the recently discovered superconductor KOs2O6, where Os atoms form a corner-sharing tetrahedral network called the pyrochlore lattice with Rb or K atoms in the cage. Resistivity, magnetic susceptibility and specific heat measurements on polycrystalline samples evidence a bulk superconductivity with Tc = 6.3 K.

cond-mat.supr-con↗