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Objective To determine the feasibility of three-dimensional conformal radiation therapy for canine aortic body tumours. Materials and methods Medical records of dogs that had undergone three-dimensional conformal radiation therapy with presumptive diagnosis of aortic body tumour were reviewed for clinical characteristics, treatment modality and outcomes. Results Eight dogs were diagnosed with aortic body tumour and were treated with three-dimensional conformal radiation therapy. One dog had proliferation of a mass in the right atrium during treatment and died of respiratory distress. Another dog did not undergo follow-up CT to evaluate the treatment response due to the increased blood urea nitrogen values. The remaining 6 dogs were included in the case series. Radiotherapy was performed using a median dose per fraction of 7 Gy (3.3-7.14 Gy), a median of seven divided doses (7-15) and a total median dose of 49 Gy (45-50 Gy). The median number of CT scans during the follow-up period was 5 (range: 3-8 times). CT revealed acute side effects in four dogs-grade 1 effects related to the lung (n = 4) and skin (n = 2). Self-limiting or asymptomatic late side effects (grade 1 lung-related effect) were observed in three dogs. After therapy, one dog demonstrated a complete response, another demonstrated a partial response and the disease remained stable in four animals. The median follow-up period was 514.5 (235-1219) days. After three-dimensional conformal radiation therapy, the aortic body tumour reduced gradually over time without regrowth in all these 6 dogs. Clinical significance In this small case series, aortic body tumours responded to three-dimensional conformal radiation therapy. Transient and self-limiting side effects of the treatments were common. Further controlled studies are required to prove the effectiveness and the safety of this intervention.

One of the most significant issues for superconductivity is clarifying the momentum-dependent superconducting gap Δ(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{k}}$$\end{document}k), which is closely related to the pairing mechanism. To elucidate the gap structure, it is essential to investigate Δ(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{k}}$$\end{document}k) in as many different physical quantities as possible and to crosscheck the results obtained in different methods with each other. In this paper, we report a combinatorial investigation of the superfluid density and the flux-flow resistivity of iron-pnictide superconductors; LiFeAs and BaFe2(As1−xPx)2 (x = 0.3, 0.45). We evaluated Δ(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{k}}$$\end{document}k) by fitting these two-independent quantities with a two-band model simultaneously. The obtained Δ(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{k}}$$\end{document}k) are consistent with the results observed in angle-resolved photoemission spectroscopy (ARPES) and scanning-tunneling spectroscopy (STS) studies. We believe our approach is a powerful method for investigating Δ(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\boldsymbol{k}}$$\end{document}k) because it does not require a sample with clean surface unlike ARPES and STS experiments, or a rotational magnetic-field system for direct measurements of the angular dependence of thermodynamic quantities.

A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling, and Hund's coupling energy in 2D van der Waals (vdW) material produces a novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe_{3} provides a promising platform to simultaneously manipulate the magnetic and electrical properties for potential device implementation using few nanometers thick materials. Here, we show a continuous tuning of magnetic and electrical properties of a CrGeTe_{3} single crystal using pressure. With application of pressure, CrGeTe_{3} transforms from a ferromagnetic insulator with Curie temperature T_{C}∼66 K at ambient condition to a correlated 2D Fermi metal with T_{C} exceeding ∼250 K. Notably, absence of an accompanying structural distortion across the insulator-metal transition (IMT) suggests that the pressure induced modification of electronic ground states is driven by electronic correlation furnishing a rare example of bandwidth-controlled IMT in a vdW material.

A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling, and Hund's coupling energy in 2D van der Waals (vdW) material produces a novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe_{3} provides a promising platform to simultaneously manipulate the magnetic and electrical properties for potential device implementation using few nanometers thick materials. Here, we show a continuous tuning of magnetic and electrical properties of a CrGeTe_{3} single crystal using pressure. With application of pressure, CrGeTe_{3} transforms from a ferromagnetic insulator with Curie temperature T_{C}∼66 K at ambient condition to a correlated 2D Fermi metal with T_{C} exceeding ∼250 K. Notably, absence of an accompanying structural distortion across the insulator-metal transition (IMT) suggests that the pressure induced modification of electronic ground states is driven by electronic correlation furnishing a rare example of bandwidth-controlled IMT in a vdW material.

We discovered superconductivity at 4.8 K in the hexagonal layered compound La2IRu2 comprising a triangular lattice of the La and a honeycomb lattice of the Ru atoms. First-principles calculations reveal a two-dimensional band structure made up of La 5d and Ru 4d electrons and formal oxidation states +1.5 for the La and the uncommon oxidation state −1 for the Ru atoms. The temperature dependence of the specific heat indicates fully gapped superconductivity. Nevertheless, the upper critical field of this compound violates the Pauli limit. We argue that the high upper critical field is ascribed to an antisymmetric spin–orbit coupling in the unique multilayer structure.

This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI (Grants No. 24224010, No. 15K13523, No. JP15H05852, No. JP15K21717,, No. 17H01140, No. 18H01162, and No. 17J05243), JSPS Core-to-Core Program (A) Advanced Research Networks, and the Alexander von Humboldt Foundation. S.S. acknowledges financial support by JSPS and the Materials Education program for the future leaders in Research, Industry, and Technology (MERIT). In Dirac semimetals, interband mixing has been known theoretically to give rise to a giant orbital diamagnetism when the Fermi level is close to the Dirac point. In Bi1−xSbx and other Dirac semimetals, an enhanced diamagnetism in the magnetic susceptibility χ has been observed and interpreted as a manifestation of such giant orbital diamagnetism. Experimentally proving their orbital origin, however, has remained challenging. The cubic antiperovskite Sr3PbO is a three-dimensional Dirac electron system and shows the giant diamagnetism in χ as in the other Dirac semimetals. 207Pb NMR measurements are conducted in this study to explore the microscopic origin of diamagnetism. From the analysis of the Knight shift K as a function of χ and the relaxation rate T1–1 for samples with different hole densities, the spin and the orbital components in K are successfully separated. The results establish that the enhanced diamagnetism in Sr3PbO originates from the orbital contribution of Dirac electrons, which is fully consistent with the theory of giant orbital diamagnetism. Publisher PDF

SmS, a prototypical intermediate valence compound, has been studied by performing high-pressure nuclear magnetic resonance measurements on a $^{33}\mathrm{S}$-enriched sample. The observation of an additional signal below 15--20 K above a nonmagnetic-magnetic transition pressure ${P}_{\mathrm{c}2}\ensuremath{\approx}2$ GPa gives evidence of a magnetic transition. The absence of a Curie term in the Knight shift near ${P}_{\mathrm{c}2}$ indicates that the localized character of $4f$ electrons is entirely screened and the mechanism of the magnetic ordering is not described within a simple localized model. Simultaneously, the line shape in the magnetically ordered state is incompatible with a spin density wave order. These suggest that the magnetic order in SmS may require an understanding beyond the conventional framework for heavy fermions. The fact that hyperfine fields from the ordered moments cancel out at the S site leads us to a conclusion that the ordered phase has a type II antiferromagnetic structure.

H${}_{3}$LiIr${}_{2}$O${}_{6}$ shows no magnetic order down to lowest temperatures, raising hopes for a true Kitaev spin liquid. Its structure reveals H bonds between honeycomb layers and theory has proposed hydrogen disorder to affect the magnetic exchange. Using dielectric spectroscopy, the authors report here dipolar relaxations in H${}_{3}$LiIr${}_{2}$O${}_{6}$ and D${}_{3}$LiIr${}_{2}$O${}_{6}$, mirroring the dynamics of protons or deuterons within the double-well potentials of the H bonds. Under cooling, thermal activation crosses over into quantum tunneling, establishing a quantum paraelectric state with quasistatic disorder. This supports the realization of the long-pursued Kitaev spin liquid.

A powder sample of pure H3LiIr2O6 was synthesized from α-Li2IrO3 powder by a soft chemical replacement of Li+ with H+. The crystal structure of H3LiIr2O6 consists of sheets of edge sharing LiO6- and IrO6-octahedra forming a honeycomb network with layers stacked in a monoclinic distorted HCrO2 type pattern. Heavy stacking faulting of the sheets is indicated by anisotropic peak broadening in the X-ray powder diffraction (XRPD) pattern. The ideal, faultless crystal structure was obtained by a Rietveld refinement of the laboratory XRPD pattern while using the LiIr2O63--layers of α-Li2IrO3 as a starting model. The low radial distances of the PDF function, derived from synchrotron XRPD data, as constraints to stabilize the structural refinement. DIFFaX-simulations, structural considerations, high radial distances of the PDF function and a Rietveld compatible global optimization of a supercell were employed to derive a suitable faulting model and to refine the microstructure using the experimental data. We assumed that the overall stacking pattern of the layers in the structure of H3LiIr2O6 is governed by interlayer O-HO contacts. From the constitution of the layers, different stacking patterns with similar amounts of strong O-HO contacts are considered. Random transitions among these stacking patterns can occur as faults in the crystal structure of H3LiIr2O6, which quantitatively describe the observed XRPD.

We discovered superconductivity at 4.8 K in the hexagonal layered compound La

We have measured anisotropic electrical resistivity of quasi-one-dimensional Ta2NiSe5 single crystals under pressure. While the in-plane anisotropy is almost pressure independent, the inter-plane one greatly decreases at P c ∼ 3 GPa accompanied by a pressure-induced semiconductor-semimetal transition. Nevertheless, a similar anomaly in the temperature dependence of in-plane anisotropy has been observed in each phase. This anomaly in the low-pressure phase below P c is regarded as an excitonic transition, and thus both of these anomalies are suppressed with increasing pressure. These results suggest that the suppression of the excitonic binding energy with pressure is caused by the increase of free carrier densities and the inter-plane conductivity.

Novel topological phenomena are anticipated for three-dimensional (3D) Dirac electrons. The magnetotransport properties of cubic ${\mathrm{Sr}}_{3}\mathrm{PbO}$ antiperovskite, theoretically proposed to be a 3D massive Dirac electron system, are studied. The measurements of Shubnikov--de Haas oscillations and Hall resistivity indicate the presence of a low density ($\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$) of holes with an extremely small cyclotron mass of $0.01--0.06{m}_{e}$. The magnetoresistance $\mathrm{\ensuremath{\Delta}}{\ensuremath{\rho}}_{xx}(B)$ is linear in magnetic field $B$ with the magnitude independent of temperature. These results are fully consistent with the presence of 3D massive Dirac electrons in ${\mathrm{Sr}}_{3}\mathrm{PbO}$. The chemical flexibility of the antiperovskites and our findings in the family member ${\mathrm{Sr}}_{3}\mathrm{PbO}$ point to their potential as a model system in which to explore exotic topological phases.

Spin-orbit coupling of as large as a half eV for electrons in $5d$ orbitals often gives rise to the formation of spin-orbital entangled objects, with the effective total angular momentum ${J}_{\mathrm{eff}}$. Of particular interest are the ${J}_{\mathrm{eff}}=3/2$ states realized in $5{d}^{1}$ transition metal ions surrounded by an anion octahedron. The pure ${J}_{\mathrm{eff}}=3/2$ quartet does not have any magnetic dipolar moment $(\ensuremath{\langle}M\ensuremath{\rangle}=0)$ but hosts hidden pseudodipolar moments accompanied by charge quadrupoles and magnetic octupoles. $\mathrm{C}{\mathrm{s}}_{2}\mathrm{TaC}{\mathrm{l}}_{6}$ and $\mathrm{R}{\mathrm{b}}_{2}\mathrm{TaC}{\mathrm{l}}_{6}$ are correlated insulators with $5{d}^{1}\mathrm{T}{\mathrm{a}}^{4+}$ ions in a regular Cl octahedron. Here we demonstrate that these Ta chlorides indeed have a substantially suppressed effective magnetic dipolar moment of $\ensuremath{\sim}0.2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$. Two phase transitions are observed at low temperatures that are not pronounced in the magnetization but accompanied with large electronic entropy of \ensuremath{\sim}R ln4. We ascribe the two transitions to the ordering of hidden multipoles.

Field-swept 33 S NMR spectra of a cyclic octaatomic molecule of elemental sulfur, α-S 8 , are presented. The spectra were acquired at a Larmor frequency of 16.2 MHz and using a superconducting magnet at between 6.32 and 0.50 T. Methods were developed for analyzing the field-swept 33 S NMR spectra in which both Zeeman and quadrupole interactions were dominant. The quadrupole coupling constant, C Q , and the asymmetry parameter, η Q , for α-S 8 were found to be 43.68 MHz and 0.57, respectively. T 1 measurements of α-S 8 were conducted using the nuclear quadrupole resonance signals, and the activation energy was determined to be 54(1) kJ mol −1 from these T 1 measurements. The molecular motion was assigned to ring-puckering of α-S 8 molecules within the crystal structure.

We examined the electrical resistivity ($\ensuremath{\rho}$) of antiferromagnetic (AFM) Kondo semiconductors $\mathrm{Ce}({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}$)${}_{2}{\mathrm{Al}}_{10}$ ($x=0$ and 0.1) under pressure in order to obtain information on the electronic states under pressure, especially near the critical pressure (${P}_{\mathrm{c}}$) from the AFM ordered state to the paramagnetic one, where the $\mathrm{Ce}\text{\ensuremath{-}}4f$ electron character is a more localized state in $x=0.1$ than in $x=0$. From the results, nearly the same ${P}_{\mathrm{c}}$ was obtained; ${P}_{\mathrm{c}}\ensuremath{\sim}4.7$ and 4.5 GPa in $x=0$ and 0.1, respectively. In both samples, the Kondo semiconducting increase of $\ensuremath{\rho}$ is observed up to $P\ensuremath{\sim}3$ GPa, above which, however, the increase disappears and a broad maximum appears at high temperatures. Below the maximum, $\ensuremath{\rho}$ exhibits a metallic decrease with decreasing temperature down to the AFM transition temperature ${T}_{0}$, suggesting that the $c\text{\ensuremath{-}}f$ hybridization gap could be not necessary to form the unusual AFM order. We also examined pressure effects on the magnetic susceptibility $\ensuremath{\chi}$ of both samples up to $P\ensuremath{\sim}2$ GPa, and found that $\ensuremath{\chi}$ along the easy axis is strongly suppressed by pressure in both samples. In $x=0$, the broad maximum just above ${T}_{0}$ shifts to high temperatures with increasing pressure. On the other hand, for $x=0.1$, a clear cusp at ${T}_{0}$ remains sharp and no broad peak appears at least up to 2 GPa. Such a difference in the pressure response of $\ensuremath{\chi}$ could originate from the difference in the electronic state between $x=0$ and 0.1.

A powder sample of pure H

The honeycomb lattice is one of the simplest lattice structures. Electrons and spins on this simple lattice, however, often form exotic phases with non-trivial excitations. Massless Dirac fermions can emerge out of itinerant electrons, as demonstrated experimentally in graphene, and a topological quantum spin liquid with exotic quasiparticles can be realized in spin-1/2 magnets, as proposed theoretically in the Kitaev model. The quantum spin liquid is a long-sought exotic state of matter, in which interacting spins remain quantum-disordered without spontaneous symmetry breaking. The Kitaev model describes one example of a quantum spin liquid, and can be solved exactly by introducing two types of Majorana fermion. Realizing a Kitaev model in the laboratory, however, remains a challenge in materials science. Mott insulators with a honeycomb lattice of spin-orbital-entangled pseudospin-1/2 moments have been proposed, including the 5d-electron systems α-Na2IrO3 (ref. 5) and α-Li2IrO3 (ref. 6) and the 4d-electron system α-RuCl3 (ref. 7). However, these candidates were found to magnetically order rather than form a liquid at sufficiently low temperatures, owing to non-Kitaev interactions. Here we report a quantum-liquid state of pseudospin-1/2 moments in the 5d-electron honeycomb compound H3LiIr2O6. This iridate does not display magnetic ordering down to 0.05 kelvin, despite an interaction energy of about 100 kelvin. We observe signatures of low-energy fermionic excitations that originate from a small number of spin defects in the nuclear-magnetic-resonance relaxation and the specific heat. We therefore conclude that H3LiIr2O6 is a quantum spin liquid. This result opens the door to finding exotic quasiparticles in a strongly spin-orbit-coupled 5d-electron transition-metal oxide.

Bulk Dirac electron systems have attracted strong interest for their unique magnetoelectric properties as well as their close relation to topological (crystalline) insulators. Recently, the focus has been shifting toward the role of magnetism in stabilizing Weyl fermions as well as chiral surface states in such materials. While a number of nonmagnetic systems are well known, experimental realizations of magnetic analogs are a key focus of current studies. Here, we report on the physical properties of a large family of inverse perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) in which we are able to not only stabilize 3D Dirac electrons at the Fermi energy but also chemically control their properties. In particular, it is possible to introduce a controllable Dirac gap, change the Fermi velocity, tune the anisotropy of the Dirac dispersion, and—crucially—introduce complex magnetism into the system. This family of compounds therefore opens up unique possibilities for the chemical control and systematic investigation of the fascinating properties of such topological semimetals.Bulk Dirac electron systems have attracted strong interest for their unique magnetoelectric properties as well as their close relation to topological (crystalline) insulators. Recently, the focus has been shifting toward the role of magnetism in stabilizing Weyl fermions as well as chiral surface states in such materials. While a number of nonmagnetic systems are well known, experimental realizations of magnetic analogs are a key focus of current studies. Here, we report on the physical properties of a large family of inverse perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) in which we are able to not only stabilize 3D Dirac electrons at the Fermi energy but also chemically control their properties. In particular, it is possible to introduce a controllable Dirac gap, change the Fermi velocity, tune the anisotropy of the Dirac dispersion, and—crucially—introduce complex magnetism into the system. This family of compounds therefore opens up unique possibilities for the chemical control and systematic investigat...

We measured the surface impedance of NaFe 1− x Co x As ( x ≈ 0.03, optimally doped) single crystals under finite magnetic fields. At low temperatures ( T T c ), the penetration depth of these crystals was increased as λ ( T ) − λ (0) = A × T n with an exponent n ≈ 2, indicating the realization of the gapless superconductivity. The flux-flow resistivity, ρ f , behaved similarly to the Bardeen–Stephen prediction, ρ f / ρ n = B / B c 2 . However, the electronic state inside the vortex core was not so dirty. By comparing the results with those of LiFeAs 1− x P x and SrFe 2 (As 0.7 P 0.3 ) 2 , it has been clarified that the gap anisotropy dominates the gradient of ρ f ( B ).

The flux-flow resistivity and the electronic state inside the vortex core in single crystals of LiFe(As, P) were investigated by microwave-surface impedance. The flux-flow resistivity of these materials increase linearly with the magnetic field, and it is consistent with an isotropic gap nature of materials. However, the gradient is larger than theoretical predictions for superconductors with isotropic gap structure. It is probably the consequence of multiple-bands nature of these materials. We also found that the materials have the moderately clean core, and the mean free path of the quasi-particle inside the vortex core is much shorter than that outside the core, and rather comparable to the core radius. We believe that this is a novel and a universal feature of all superconductors.

``Strange metal phases'', displaying strong deviations from Fermi liquid theory, are discussed in the context of cuprates, itinerant magnets, or heavy-fermion metals. Several Yb-based materials, e.g., $\ensuremath{\beta}$-YbAlB${}_{4}$ or the Au-Al-Yb quasicrystal, display $T$/$B$ scaling of magnetic and thermodynamic properties. This has been taken as evidence for zero-field quantum criticality without requirement to fine-tune composition and pressure. However, it appears unlikely that materials are accidentally located at such a special point in multidimensional phase space. In this paper, the authors demonstrate by a thermodynamic study on the new Kondo lattice compound YbCo${}_{2}$Ge${}_{4}$ that $T$/$B$ scaling and a divergence of the magnetic Gr\"uneisen parameter can arise without a quasiparticle mass divergence and in the absence of zero-field quantum criticality. They discuss alternative scenarios for such strange metal behavior.

We study microwave surface impedance measurements of LiFeAs, LiFe(As,P) and FeSe1−xTex single crystals. The in-plane penetration depths of LiFeAs and LiFe(As,P) depend on temperature exponentially at low temperatures, which is a strong indication that these two materials have the nodeless superconducting gap. The temperature dependence of the superfluid density indicates that LiFeAs and LiFe(As,P) are multi-gap superconductors with at least two isotropic gaps. In FeSe1−xTex, on the other hand, the quadratic temperature dependence of the in-plane penetration depth appears, which indicates the existence of some sort of quasiparticle excitations. In addtion, the real part of the microwave conductivity exhibits a large enhancement below Tc in all three materials, which results from the increase of the quasiparticle relaxation time, τ, below Tc.

Frequency-swept solid-state 33 S nuclear magnetic resonance (NMR) spectra of a 33 S-enriched organosulfur compound, [ 33 S]-diphenyl disulfide, are presented. The NMR spectra were acquired at extremely low magnetic fields, 0.06 and 0.10 T, which correspond to Larmor frequencies of 0.1959 and 0.3265 MHz, respectively. The quadrupole coupling constant, C Q , and the asymmetry parameter, η Q , for [ 33 S]-diphenyl disulfide were found to be C Q = 43.3 ± 1.9 MHz and η Q = 0.70 ± 0.20, respectively. T 1 measurements of [ 33 S]-diphenyl disulfide were performed between 60 and 300 K using nuclear quadrupole resonance signals, and a compromise observation temperature was found to be 300 K. Quantum chemical calculations were performed and the results demonstrated that the quadrupole frequencies and C Q values were highly sensitive to the changes in dihedral angles of disulfide bonds.

We report electrical resistivity, ac magnetic susceptibility, and x-ray absorption spectroscopy measurements of intermediate valence ${\mathrm{YbNi}}_{3}{\mathrm{Ga}}_{9}$ under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below ${P}_{c}\ensuremath{\sim}9\text{ }\text{ }\mathrm{GPa}$ where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

111 Cd NMR measurements have been performed in the superconducting (SC) state of the pyrochlore Cd 2 Re 2 O 7 at T c ∼1 K, and in a field of less than 3 kOe below T c . The upper critical field at 0.1 K has been determined to be 4 kOe from in situ measurements of the ac susceptibility. A reduction of the Knight shift in the SC state is confirmed. The present results provide strong evidence that this compound has a singlet SC pairing symmetry.

In the s -wave superconductor LaRu 4 P 12 ( T c =7.2 K), a clear Redfield pattern was observed below T c , which arises from a triangular lattice. We observed distinct frequency dependence of the spin–lattice relaxation rate 1/ T 1 in the vortex state in contrast to the normal state. In addition, from the T -dependence of 1/ T 1 T measured at different frequencies, 1/ T 1 T at the vortex core is considered to be greater than that in the normal state, indicating that the LDOS in the vortex core region is higher than that in the normal state. This enhancement of the LDOS in the core region can be understood in terms of the bound states inside a vortex core.

We have measured 101 Ru Knight shift ( 101 K) in the spin triplet superconductor Sr 2 RuO 4 in various magnetic fields applied parallel and perpendicular to the RuO 2 plane to determine the spin direction of the Cooper pair. We measured temperature dependence of 101 K in 0.15 and 0.055 T parallel to the RuO 2 plane using nuclear-quadrupole-resonance (NQR) technique. We found that 101 K is invariant with temperature in both fields on passing through the superconducting (SC) transition temperature. These results indicate that the spin susceptibility parallel to the RuO 2 plane does not change in the field greater than 0.055 T, suggesting that the SC d-vector is along the c-axis when the magnetic field greater than 0.055 T is applied along to the RuO 2 plane. The possible spin state in magnetic fields is discussed on the basis of the Knight-shift measurements so far.

Fractionalization-the breaking up of an apparently indivisible microscopic degree of freedom-is one of the most counterintuitive phenomena in many-body physics. Here we study its most fundamental manifestation in spin ice, the only known fractionalized magnetic compound in 3D: we directly visualize the 1/r(2) magnetic Coulomb field of monopoles that emerge as the atomic magnetic dipoles fractionalize. We analyze the internal magnetic field distribution, relevant for local experimental probes. In particular, we present new zero-field NMR measurements that exhibit excellent agreement with the calculated line shapes, noting that this experimental technique can in principle measure directly the monopole density in spin ice. The distribution of field strengths is captured by a simple analytical form that exhibits a low density of low-field sites-in apparent disagreement with reported muon spin rotation results. Counterintuitively, the density of low-field locations decreases as the local ferromagnetic correlations imposed by the ice rules weaken.

We measured the microwave surface impedances and obtained the superfluid density and flux flow resistivity in single crystals of a phosphor-doped iron-based superconductor SrFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ single crystals ($x=0.30$, ${T}_{c}=25\phantom{\rule{4pt}{0ex}}\mathrm{K}$). At low temperatures, the superfluid density, ${n}_{s}(T)/{n}_{s}(0)$, obeys a power law, ${n}_{s}(T)/{n}_{s}(0)=1\ensuremath{-}C{(T/{T}_{c})}^{n}$, with a fractional exponent of $n=1.5$--1.6. The flux flow resistivity was significantly enhanced at low magnetic fields. These features are consistent with the presence of line nodes on at least one band and modulated nodeless gap with deep minimum on the same bands and/or other bands. The remarkable difference observed in the superconducting gap structure between SrFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ and BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ in our experiments is important for clarifying the mechanism of iron-based superconductivity in the 122 system.

We investigate vortices in LiFeAs using scanning tunneling microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting gaps without detectable spectral weight near the Fermi energy, evidencing fully-gapped multi-band superconductivity. We image vortices in a wide field range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi energy. A quasi-hexagonal vortex lattice at low field contains domain boundaries which consist of alternating vortices with unusual coordination numbers of 5 and 7. With increasing field, the domain boundaries become ill-defined, resulting in a uniformly disordered vortex matter. Tunneling spectra taken at the vortex center are characterized by a sharp peak just below the Fermi energy, apparently violating particlehole symmetry. The image of each vortex shows energy-dependent 4-fold anisotropy which may be associated with the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing temperature and becomes smaller than the coherence length estimated from the upper critical field. This is direct evidence of the Kramer-Pesch effect expected in a clean superconductor., 9 pages, 7 figures

LiFeAs is one of the iron-based superconductors having multiple gaps with the possible sign reversal. To clarify how those novel natures affect the energy dissipation of magnetic vortices, we investigated the microwave surface impedance of LiFeAs single crystals under finite magnetic fields. The flux-flow resistivity enhanced rapidly at low magnetic fields, which is similar to the case of MgB$_{2}$. This is probably the consequence of the multiple-gap nature and the gap anisotropy. This suggest that the sign-reversal is not important for the flux-flow even for multiple-gap superconductors. As for the electronic state, the vortex core of LiFeAs turned out to be "moderately clean". Furthermore, the mean free path inside the vortex core was much shorter than that outside, and was close to the core radius. These results strongly suggest a process specific to the core boundary is important for a scattering mechanism inside the vortex core., 5 pages, 4 figures

We report on the upper critical field B_c2 of a superconducting LiFeAs single crystal with T_c~16 K, determined from magnetic torque measurements in dc-magnetic fields up to 35 T and at temperatures down to 0.3 K. B_c2 at 0.3 K is obtained to be 26.4 T and 15.5 T for the applied field B_a||ab and B_a||c, respectively. The anisotropy parameter $\Gamma$=$B_c2^ab / B_c2^c$ is ~ 3 at T_c and decreases to 1.7 as $T \rightarrow 0$, showing rather isotropic superconductivity. While B_c2 is orbitally-limited for B_a||c, the spin-paramagnetic effect is evident in the temperature dependence of B_c2 for B_a||ab, Comment: 4 pages, 4 figures, revised version to be published in J. Phys. Soc. Jpn. as a letter article

We report results of 23Na and 75As nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of stoichiometric NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic structural phase transition at T_O = 57 K and an antiferromagnetic (AF) transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate near T_AF shows significant anisotropy, indicating that the critical slowing down of stripe-type AF fluctuations are strongly anisotropic in spin space. The NMR spectra at low enough temperatures consist of sharp peaks showing a commensurate stripe AF order with a small moment \sim 0.3 muB. However, the spectra just below T_AF exhibits highly asymmetric broadening pointing to an incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs shows a certain similarity to the behavior of SrFe2As2 under high pressure., 5 pages, 5 figures, revised version to appear in J. Phys. Soc. Jpn

We report results of microwave surface impedance measurements of LiFeAs single crystals. The in-plane penetration depth depends on temperature exponentially at low temperatures, which strongly suggests that this material has the nodeless superconducting gap. The temperature dependence of the superfluid density indicates that LiFeAs is a multi-gap superconductor with at least two isotropic gaps. In addtion, the real part of the microwave conductivity exhibits a large enhancement below $T_\mathrm{c}$, indicating that the quasi-particle relaxation time, $\tau$, increases rapidly below $T_\mathrm{c}$. We believe that this enhancement is rather common to all superconductors where an inelastic scattering is dominant above $T_\mathrm{c}$, irrespective of the strength of the electron correlation., Comment: 13 pages, 3 figures

We report a novel superconducting (SC) and antiferromagnetic (AF) hybrid state in ${\mathrm{SrFe}}_{2}{\mathrm{As}}_{2}$ revealed by $^{75}\mathrm{As}$ nuclear magnetic resonance (NMR) experiments on a single crystal under highly hydrostatic pressure up to 7 GPa. The NMR spectra at 5.4 GPa indicate simultaneous development of the SC and AF orders below 30 K. The nuclear spin-lattice relaxation rate in the SC domains shows a substantial residual density of states, suggesting proximity effects due to the spontaneous formation of a nanoscale SC-AF hybrid structure. This entangled behavior is a remarkable example of a self-organized heterogeneous structure in a clean system.

We report results of 75As nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of SrFe2As2. The NMR spectra clearly show sharp first-order antiferromagnetic (AF) and structural transitions occurring simultaneously. The behavior in the vicinity of the transition is compared with our previous study on BaFe2As2. No significant difference was observed in the temperature dependence of the static quantities such as the AF splitting and electric quadrupole splitting. However, the results of the NMR relaxation rate revealed difference in the dynamical spin fluctuations. The stripe-type AF fluctuations in the paramagnetic state appear to be more anisotropic in BaFe2As2 than in SrFe2As2., 4 pages, 5 figures; discussion revised; accepted for publication in J. Phys. Soc. Jpn

We have performed nuclear quadrupole resonance (NQR) experiments on $^{47}\text{T}\text{i}$ nuclei in ${\text{Dy}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ in the temperature range of 70--300 K in order to investigate the dynamics of $4f$ electrons with strong Ising anisotropy. A significant change in the NQR frequency with temperature was attributed to the variation of the quadrupole moment of $\text{Dy}\text{ }4f$ electrons. A quantitative account was given by the mean-field analysis of the quadrupole-quadrupole (Q-Q) interaction in the presence of the crystalline-electric-field splitting. The magnitude and the temperature dependence of the nuclear spin-lattice relaxation rate were analyzed, including both the spin-spin and the Q-Q interactions. The results indicate that these two types of interaction contribute almost equally to the fluctuation of Dy magnetic moments.

We have performed $^{69,71}\mathrm{Ga}$ nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and muon spin rotation and resonance on the quasi-two-dimensional antiferromagnet $\mathrm{Ni}{\mathrm{Ga}}_{2}{\mathrm{S}}_{4}$, in order to investigate its spin dynamics and magnetic state at low temperatures. Although there exists only one crystallographic site for Ga in $\mathrm{Ni}{\mathrm{Ga}}_{2}{\mathrm{S}}_{4}$, we found two distinct Ga signals by NMR and NQR. The origin of the two Ga signals is not fully understood, but possibly due to stacking faults along the $c$ axis which induce additional broad Ga NMR and NQR signals with different local symmetries. We found the spin freezing occurring at ${T}_{\mathrm{f}}$, at which the specific heat shows a maximum, from a clear divergent behavior of the nuclear spin-lattice relaxation rate $1∕{T}_{1}$ and nuclear spin-spin relaxation rate $1∕{T}_{2}$ measured by Ga-NQR as well as the muon spin relaxation rate $\ensuremath{\lambda}$. The main sharp NQR peaks exhibit a stronger tendency of divergence, compared with the weak broader spectral peaks, indicating that the spin freezing is intrinsic in $\mathrm{Ni}{\mathrm{Ga}}_{2}{\mathrm{S}}_{4}$. The behavior of these relaxation rates strongly suggests that the Ni spin fluctuations slow down towards ${T}_{\mathrm{f}}$, and the temperature range of the divergence is anomalously wider than that in a conventional magnetic ordering. A broad structureless spectrum and multicomponent ${T}_{1}$ were observed below $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, indicating that a static magnetic state with incommensurate magnetic correlations or inhomogeneously distributed moments is realized at low temperatures. However, the wide temperature region between $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{f}}$, where the NQR signal was not observed, suggests that the Ni spins do not freeze immediately below ${T}_{\mathrm{f}}$, but keep fluctuating down to $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with the MHz frequency range. Below $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, all components of $1∕{T}_{1}$ follow a ${T}^{3}$ behavior. We also found that $1∕{T}_{1}$ and $1∕{T}_{2}$ show the same temperature dependence above ${T}_{\mathrm{f}}$ but different temperature dependence below $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These results suggest that the spin dynamics is isotropic above ${T}_{\mathrm{f}}$, which is characteristic of the Heisenberg spin system, and becomes anisotropic below $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

We report a site-separated $^{17}\mathrm{O}$ NMR study of the layered perovskite ruthenate ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$, which exhibits nearly two-dimensional transport properties and itinerant metamagnetism at low temperatures. The local hole occupancies and the spin densities in the oxygen $2p$ orbitals are obtained by means of tight-binding analyses of electric field gradients and anisotropic Knight shifts. These quantities are compared with two other layered perovskite ruthenates: the two-dimensional paramagnet ${\mathrm{Sr}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$ and the three-dimensional ferromagnet $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_{3}$. The hole occupancies at the oxygen sites are very large, about one hole per ruthenium atom. This is due to the strong covalent character of the Ru-O bonding in this compound. The magnitude of the hole occupancy might be related to the rotation or tilt of the $\mathrm{Ru}{\mathrm{O}}_{6}$ octahedra. The spin densities at the oxygen sites are also large, 20%--40% of the bulk susceptibilities, but in contrast to the hole occupancies, the spin densities strongly depend on the dimensionality. This result suggests that the density of states at the oxygen sites plays an essential role for the understanding of the complex magnetism found in the layered perovskite ruthenates.

The linewidth of the Ru nuclear quadrupole resonance (NQR) spectrum was measured in the superconducting state of Sr2RuO4 in order to search for the spontaneous field at the Ru site. We considered that the large hyperfine field would be expected at the Ru site in the superconducting state if the spontaneous field revealed by the μSR measurement originated from the nonzero spin moment. The linewidth of the spectrum is unchanged within an experimental error, which gives that the maximum value of the spontaneous field at the Ru nucleus site is less than 5 G if any. Our result suggests that the spontaneous field originates from the orbital component of the spin‐triplet pairs.