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High-quality single crystals are essentially needed for the investigation of the novel bulk properties of unconventional superconductors. The availability of such crystals grown by the floating-zone method has helped to unveil the unconventional superconductivity of the layered perovskite Sr$_2$RuO$_4$, which is considered as a strong candidate of a topological spin-triplet superconductor. Yet, recent progress of investigations urges further efforts to obtain ultimately high-quality crystalline samples. In this paper, we focus on the method of preparation of feed rods for the floating-zone melting and report on the improvements of the crystal growth. We present details of the improved methods used to obtain crystals with superconducting transition temperatures $T_\mathrm{c}$ that are consistently as high as 1.4 K, as well as the properties of these crystals., 9 pages, 6 figures

The Ce atoms in CeIrSn form a quasikagome lattice in the hexagonal $c$ plane. Our single-crystal x-ray diffraction analysis has confirmed the absence of superstructure in the ZrNiAl-type structure. Motivated by the recent observation of quantum critical behaviors in the isostructural and isoelectronic compound CeRhSn, we have studied low-temperature properties of single-crystalline samples of CeIrSn by measuring the electrical resistivity, magnetic susceptibility $\ensuremath{\chi}$, magnetization $M$, and specific heat $C$ down to 0.05 K. Our study does not show evidence of a long-range magnetic ordering down to the lowest temperature. The $\ensuremath{\chi}(T)$ data show an Ising character, ${\ensuremath{\chi}}_{c}\ensuremath{\gg}{\ensuremath{\chi}}_{a}$, and power-law behaviors at low temperatures: ${\ensuremath{\chi}}_{c}\ensuremath{\propto}{T}^{\ensuremath{-}0.8}$ and ${\ensuremath{\chi}}_{a}\ensuremath{\propto}{T}^{\ensuremath{-}0.6}$. When external field $B$ is applied along the $a$ axis, both $M(B)$ and $C(B)/T$ exhibit metamagnetic anomalies at 5.5 T, which resemble those observed in CeRhSn at 3.5 T. We attribute the metamagnetic crossover under in-plane magnetic fields to the alleviation of magnetic frustration inherent in the quasikagome Ising Kondo lattice.

Resistance and magnetic torque measurements are reported in a layered organic superconductor, $\ensuremath{\beta}''\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{4}[({\mathrm{H}}_{3}\mathrm{O})\mathrm{Ga}{({\mathrm{C}}_{2}{\mathrm{O}}_{4})}_{3}]{\mathrm{C}}_{6}{\mathrm{H}}_{5}{\mathrm{NO}}_{2}$ with ${T}_{c}=4.8$ K, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. Because of the large anion between the BEDT-TTF conducting layers, the superconductivity of this salt is highly anisotropic. In magnetic fields parallel to the conducting layers for $T=0.4$ K, the magnetic torque shows a large diamagnetic signal associated with hysteresis up to $\ensuremath{\sim}21$ T, suggesting the upper critical field ${H}_{c2}\ensuremath{\gtrsim}21$ T at 0.4 K. The large reduction of the diamagnetic signal is observed above 16 T, which shows a Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) phase transition. For $T=0.5$ K, the interlayer resistance has nonzero value in a wide field region up to ${H}_{c2}$, arising from the Josephson vortex dynamics. Successive dips in the second derivative curves of the resistance are observed between 16 T and ${H}_{c2}$, which are ascribed to the commensurability effect between the Josephson vortex lattice and the order parameter oscillation of the FFLO phase. The commensurability effect is observed only in nearly parallel fields, showing that the FFLO phase is stable in a very limited field angle region. The temperature-field phase diagram is determined.

The strongly correlated insulator Ca2RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K-edge resonant inelastic x-ray scattering study of the antiferromagnetic Mott insulating state of Ca2RuO4. A set of low-energy (about 80 and 400 meV) and high-energy (about 1.3 and 2.2 eV) excitations are reported, which show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modeling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveils the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by Hund’s coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca2RuO4.

We report single-crystal growth of a perovskite ruthenate SrRuO3 by the floating-zone method using an infrared image furnace. By employing a cold trap for the growth, we prevented the evaporated RuO2 from coating the inner surface of a quartz tube and were thereby able to maintain a stable molten zone during the growth. Powder X-ray and Laue diffraction measurements confirmed the quality of the grown single crystal. The crystal was cut into a 1.4 mm × 1.4 mm × 3.0 mm rectangle that was characterized by magnetic susceptibility, magnetization, and specific heat measurements. The crystal showed a ferromagnetic transition with a Curie temperature of 163.5 K, and the coercive field was as low as 0.004 T. The residual resistivity was 1.05 μΩ cm, corresponding to a residual resistivity ratio of 192. These results indicate that the grown crystal is high-quality. Electrical resistivity measurements show temperature-squared behavior, revealing that a Fermi-liquid-like electron–electron scattering is dominant. Toget...

CeRhSn with a quasikagome lattice of Ce atoms in the hexagonal $c$ plane has been expected to be in close vicinity to a zero-field quantum criticality derived from magnetic frustration. We have studied how the ground state changes with substitution of Pd for Rh in $\mathrm{CeR}{\mathrm{h}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{d}}_{x}\mathrm{Sn}$ $(x\ensuremath{\le}0.75)$ by measuring the specific heat $C$, magnetic susceptibilities ${\ensuremath{\chi}}_{\mathrm{dc}}$ and ${\ensuremath{\chi}}_{\mathrm{ac}}$, magnetization $M$, electrical resistivity \ensuremath{\rho}, and magnetoresistance. For $x=0$, the field dependence of ${\ensuremath{\chi}}_{\mathrm{ac}}$ at $T=0.03\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ shows a peak at $B\ensuremath{\parallel}a=3.5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, confirming the spin-flop crossover in the field applied along the hard axis. The temperature dependence of ${\ensuremath{\chi}}_{\mathrm{ac}}$ shows a broad maximum at 0.1 K whereas $C/T$ continues to increase down to 0.08 K. For $x\ensuremath{\geqq}0.1,\ensuremath{\rho}(T)$ is dominated by incoherent Kondo scattering and both $C/T$ and ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$ exhibit peaks, indicating the development of an antiferromagnetic order. The ordering temperature rises to 2.5 K as $x$ is increased to 0.75. Our results indicate that the ground state in the quasikagome Kondo lattice $\mathrm{CeR}{\mathrm{h}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{d}}_{x}\mathrm{Sn}$ leaves the quantum critical point at $x=0$ with increasing $x$ as a consequence of suppression of both the magnetic frustration and Kondo effect.

Twenty-two new lanthanide tellurite sulfates with five distinct structures, Ln2(Te2O5)(SO4)2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb; LnTeSO-1), Ho3(TeO3)2(SO4)2(OH)(H2O) (LnTeSO-2), Ln2TeO3(SO4)2(H2O)2 (Ln = Dy, Ho, Er; LnTeSO-3), Ln2(Te2O5)(SO4)2 (Ln = Er, Tm, Yb, Lu; LnTeSO-4), and Ln2(Te4O10)(SO4) (Ln = Gd, Dy, Ho, Er, Tm, Yb; LnTeSO-5), have been prepared and characterized. The topologies of LnTeSO-1, LnTeSO-2, LnTeSO-3, LnTeSO-4, and LnTeSO-5 are substantially different with respect to the connectivity between Ln polyhedra and the coordination environments of the lanthanide ions. For the first four topologies, the dimensionality changes from layered (LnTeSO-1) to chains (LnTeSO-2) to tetramers (LnTeSO-3) and finally to a monomer (LnTeSO-4). The coordination numbers of lanthanides decrease from nine (LnTeSO-1) to eight (LnTeSO-2 and LnTeSO-3) to seven and six (LnTeSO-4). We attribute the transitions to a decrease in the ionic radii of the 4f ions. Magnetic susceptibility measurements reveal no evidence for long-range magnetic ordering in these materials. However, diverse short-range magnetic correlations were observed within LnTeSO-1.

Magnetic torque measurements using a microcantilever have been performed to investigate the superconducting phase of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ down to 40 mK. For high-quality single crystals with the transition temperature $({T}_{\mathrm{c}})$ of 1.48--1.49 K, an abrupt jump of the torque signal is found near 1.5 T in field parallel to the conducting ${\mathrm{RuO}}_{2}$ planes below $\ensuremath{\sim}0.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The jump corresponds to the first order transition recently revealed by magnetocaloric and magnetization measurements [Yonezawa et al., Phys. Rev. Lett. 110, 077003 (2013); Kittaka et al., Phys. Rev. B 90, 220502(R) (2014)]. Furthermore, weak diamagnetic and irreversible signals are found to persist above the first order transition up to 1.85 T. The result indicates the presence of a subphase boundary separating low- and high-field phases in the superconducting phase. The high-field subphase disappears when the field is tilted from the conducting planes only by a few degrees. Quantum oscillation measurements are also reported to clarify the strong sample-quality dependence of the high-field subphase.

The resistivity $\rho$ and Hall resistivity $\rho_H$ are measured on FeSe at pressures up to $P$ = 28.3 kbar in magnetic fields up to $B$ = 14.5 T. The $\rho(B)$ and $\rho_H(B)$ curves are analyzed with multicarrier models to estimate the carrier density and mobility as a function of $P$ and temperature ($ T\leqslant$ 110 K). It is shown that the pressure-induced antiferromagnetic transition is accompanied by an abrupt reduction of the carrier density and scattering. This indicates that the electronic structure is reconstructed significantly by the antiferromagnetic order., Comment: 6 pages, 5 figures + SM ( 2 pages, 2 figures)

The gap structure of Sr$_2$RuO$_4$, which is a longstanding candidate for a chiral p-wave superconductor, has been investigated from the perspective of the dependence of its specific heat on magnetic field angles at temperatures as low as 0.06 K ($\sim 0.04T_{\rm c}$). Except near $H_{\rm c2}$, its fourfold specific-heat oscillation under an in-plane rotating magnetic field is unlikely to change its sign down to the lowest temperature of 0.06 K. This feature is qualitatively different from nodal quasiparticle excitations of a quasi-two-dimensional superconductor possessing vertical lines of gap minima. The overall specific-heat behavior of Sr$_2$RuO$_4$ can be explained by Doppler-shifted quasiparticles around horizontal line nodes on the Fermi surface, whose in-plane Fermi velocity is highly anisotropic, along with the occurrence of the Pauli-paramagnetic effect. These findings, in particular, the presence of horizontal line nodes in the gap, call for a reconsideration of the order parameter of Sr$_2$RuO$_4$., Comment: 5 pages, 3 figures (main text) + 3 pages, 3 figures (supplemental material), accepted for publication in J. Phys. Soc. Jpn

We examine the low temperature states of two transition metal compounds: (i) NbFe 2 is poised on the threshold of ferromagnetism and can be pushed into a spin-aligned state at low temperature by modifying the composition slightly. Stoichiometric NbFe 2 has been reported as a rare example of low-temperature spin density wave order in a d-metal system. We have used pressure, field and composition tuning to examine the phase diagram of NbFe 2 . Near the quantum critical point, we find distinct non-Fermi liquid forms of the resistivity and heat capacity, whereas we observe strong, hysteretic magnetoresistance effects deep in the ordered phase. (ii) Ca 3 Ru 2 O 7 undergoes first a magnetic transition (T N = 56 K) and then a structural transition (T s = 48 K) on cooling. Most of the Fermi surface is gapped out at low temperature, leading to a very low carrier density and small Fermi surface pockets. Pressure suppresses both T N and T S and, for p > 3.5 GPa, induces a third low temperature state, which is robust up to at least 7.5 GPa.

We report dye-degradation effects of a semiconductor LiBiO3 revealed under illumination of a conventionally used white fluorescent light. Optical absorbance spectra of LiBiO3 were broadened so smoothly, with the absorption edge penetrated to around 730 nm, that the material was able to absorb a wide range of visible light. Results showed that solution of a standard dye, methylene blue, was degraded completely after 4 h illumination. Furthermore, the value of total organic carbon decreased 70% in the decolorized solution, suggesting that the molecular form of the original methylene blue was mineralized effectively to nonorganic fragments by the photoinduced oxidization effect. Moreover, the wavelength dependence of apparent photonic efficiency was evaluated using a standard Xe lamp coupled with monochromatic filters. These results were interpreted from the viewpoint of this material’s electronic structure.

A silver germanium oxide, Ag 2 GeO 3 , was developed as a novel photocatalyst for degradation of organic dyes. The chemical composition of the sample was investigated via the SEM/EDX, ICP-AES, and TG-DTA techniques. The general activity of the material was characterized by testing the photodegradations of typical organic dyes, such as Methylene Blue (one of the heteropolyaromatic dyes), Rhodamine B (one of the xanthene dyes), Fuchsin Acid (one of the sulfonic dyes), and Orange II (one of the azoic dyes). All of these dyes were degraded more than 90% within 25 min under the visible-light irradiation of Xe lamp. Besides, with a commercial white fluorescent lamp as testing light source (light intensity, 61 μW/cm 2 ), the efficient decolorizations and mineralizations of the organic dyes were achieved over this material: 79% (90%) of the organic carbon in the Methylene Blue (Rhodamine B) solution was photooxidatized to inorganic carbon forms, when these dyes were totally decolorized. The high performance of this material is due to the photophysical properties of the wide-visible-range absorption and response, and the sufficient oxidative potential of the top of the valence band.

A solid-state reaction method with urea as a nitrogen precursor was used to prepare nitrogen-doped lamellar niobic and titanic solid acids (i.e., HNb(3)O(8) and H(2)Ti(4)O(9)) with different acidities for visible-light photocatalysis. The photocatalytic activities of the nitrogen-doped solid acids were evaluated for rhodamine B (RhB) degradation and the results were compared with those obtained over the corresponding nitrogen-doped potassium salts. Techniques such as XRD, BET, SEM, X-ray photoelectron spectroscopy, and UV-visible diffuse reflectance spectroscopy were adopted to explore the nature of the materials as well as the characteristics of the doped nitrogen species. It was found that the intercalation of the urea precursor helped to stabilize the layered structures of both lamellar solid acids and enabled easier nitrogen doping. The effects of urea intercalation were more significant for the more acidic HNb(3)O(8) sample than for the less acidic H(2)Ti(4)O(9). Compared with the nitrogen-doped KNb(3)O(8) and K(2)Ti(4)O(9) samples, the nitrogen-doped HNb(3)O(8) and H(2)Ti(4)O(9) solid acids absorb more visible light and exhibit a superior activity for RhB photodegradation under visible-light irradiation. The nitrogen-doped HNb(3)O(8) sample performed the best among all the samples. The results of the current study suggest that the protonic acidity of the lamellar solid-acid sample is a key factor that influences nitrogen doping and the resultant visible-light photocatalysis.

Four Ag-based semiconductor oxides with visible-light absorption, α-AgGaO2, α-AgInO2, β-AgAlO2, and β-AgGaO2, were prepared to investigate the influences of chemical composition and the crystal structure on the electronic structures and photocatalytic properties of AgMO2 (M = Al, Ga, In). The catalytic efficiencies of these oxides were characterized by testing the photooxidation of gaseous 2-propanol to acetone under visible-light irradiation. The ranking of the activity was α-AgGaO2 > β-AgAlO2 > β-AgGaO2 > α-AgInO2. The electronic structures of these compounds were investigated in terms of density functional theory. These experimental and computational studies of these materials reveal the following: (1) regarding chemical compositions, the conduction bands constructed through hybridization of the Ag 5s5p states with Ga 4s4p states and Al 3s3p states are necessary for promotion of photocatalytic activities under visible light for α-phase and β-phase, respectively, and (2) regarding crystal structures, th...

A novel visible light sensitive photocatalyst, AgSbO3 was prepared by a conventional solid-state reaction method. This oxide belonging to a cubic-pyrochlore structure can absorb visible light with wavelength up to about 480 nm. From the band structure calculation, we found that the top of the valence band consists of the hybridized Ag 4d and O 2p orbitals and the bottom of the conduction band mainly consists of the Ag 5s and the Sb 5s orbitals. Photocatalytic activities were evaluated using O2 evolution from an aqueous silver nitrate solution and decomposition of gaseous 2-propanol under visible light irradiation. We found that AgSbO3 shows a higher O2 evolution activity than WO3 and 2-propanol can be mineralized by the AgSbO3 photocatalysis under visible light irradiation.

We report a multiple-metal oxide Ag2ZnGeO4 with cristobalite-related structure as a visible light-sensitive photocatalyst (Eg 2.29 eV) for dye degradation. The physical characteristics of the samples were examined by techniques such as XRD, UV–vis diffuse reflectance spectroscopy and SEM. The photocatalytic activity of Ag2ZnGeO4 was confirmed by Rhodamine B (RhB) and Orange II photodegradation in aqueous phase. After 360 min of visible light (λ > 420 nm) irradiation, the conversions of RhB and Orange II reached 100% and 69.2%, respectively. The electronic structure of Ag2ZnGeO4 was investigated by band structure calculation based on the density function theory (DFT). Results revealed that the hybridized Ag 4d10 and O 2p6 orbitals form the valence band top of Ag2ZnGeO4, which leads to a much narrowed band gap as compared with that of the Na2ZnGeO4 parent sample. We propose that the specific cristobalite structure of Ag2ZnGeO4 favors the mobility of photo-generated carriers, and that this contributes positively to the observed photocatalytic activity for dye degradation.

The magnetic field-induced changes in the conductivity of metals are the subject of intense interest, both for revealing new phenomena and as a valuable tool for determining their Fermi surface. Here, we report a hitherto unobserved magnetoresistive effect in ultra-clean layered metals, namely a negative longitudinal magnetoresistance that is capable of overcoming their very pronounced orbital one. This effect is correlated with the inter-layer coupling disappearing for fields applied along the so-called Yamaji angles where the inter-layer coupling vanishes. Therefore, it is intrinsically associated with the Fermi points in the field-induced quasi-one-dimensional electronic dispersion, implying that it results from the axial anomaly among these Fermi points. In its original formulation, the anomaly is predicted to violate separate number conservation laws for left- and right-handed chiral- (e.g. Weyl) fermions. Its observation in PdCoO$_2$, PtCoO$_2$ and Sr$_2$RuO$_4$ suggests that the anomaly affects the transport of clean conductors, particularly near the quantum limit., Comment: Nature Communications (in press)

We report Shubnikov-de Haas (SdH) oscillation measurements on FeSe under high pressure up to $P$ = 16.1 kbar. We find a sudden change in SdH oscillations at the onset of the pressure-induced antiferromagnetism at $P$ $\sim$ 8 kbar. We argue that this change can be attributed to a reconstruction of the Fermi surface by the antiferromagnetic order. The negative d$T_c$/d$P$ observed in a range between $P$ $\sim$ 8 and 12 kbar may be explained by the reduction in the density of states due to the reconstruction. The ratio of the transition temperature to the effective Fermi energy remains high under high pressure: $k_BT_c/E_F$ $\sim$ 0.1 even at $P$ = 16.1 kbar., 12 pages , 10 figures

A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of californium(II) is responsible for many of the unusual properties of californium including the green photoluminescence., The chemistry of the post-plutonium actinides is thought to resemble lanthanides in that bonding is primarily ionic. Here, the authors show that a californium(III) complex displays significantly different properties to those predicted for the free ion owing to a second break in actinide periodicity.

High-resolution resonant inelastic x-ray scattering (RIXS) at the oxygen K edge has been used to study the orbital excitations of Ca2RuO4 and Sr2RuO4. In combination with linear dichroism x-ray absorption spectroscopy, the ruthenium 4d-orbital occupation and excitations were probed through their hybridization with the oxygen p orbitals. These results are described within a minimal model, taking into account crystal field splitting and a spin-orbit coupling λso=200 meV. The effects of spin-orbit interaction on the electronic structure and implications for the Mott and superconducting ground states of (Ca,Sr)2RuO4 are discussed.

We performed a detailed electrical transport study at very high magnetic fields and low temperatures in high quality single crystals of Sr4Ru3O10. When the field is applied along the inter-plane direction Shubnikov-de Hass oscillations are observed showing that a metamagnetic transition leads to a quite non-trivial evolution of the geometry of the Fermi surface. It can be ascribed either that localized and itinerant bands coexist in this system, the former leading to the ferromagnetic response and the latter to itinerant metamagnetic behavior, or that itinerant metamagnetism emerges from a Stoner-like ferromagnetic ground state.

We have investigated the magnetic field and temperature dependence of the tunneling spectra of the eutectic system Sr2RuO4-Ru. Electric contacts to individual Ru lamellae embedded in Sr2RuO4 enable the tunneling spectra at the interface between ruthenate and a Ru microinclusion to be measured. A zero bias conductance peak (ZBCP) was observed in the bias voltage dependence of the differential conductance, suggesting that Andreev bound states are present at the interface. The ZBCP starts to appear at a temperature well below the superconducting transition temperature. The onset magnetic field of the ZBCP is also considerably smaller than the upper critical field when the magnetic field is parallel to the ab-plane. We propose that the difference between the onset of the ZBCP and the onset of superconductivity can be understood in terms of the existence of the single-component state predicted by Sigrist and Monien., Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jpn. vol. 74 no. 2

Hard X-ray photoemission studies are carried out to evaluate the electronic structure of iron-based superconductors BaFe2(As1−xPx)2 in a wide range of the P content 0 ≤ x ≤ 0.61. As x increases, th...

Twenty-two new lanthanide tellurite sulfates are characterized by single crystal XRD, UV/VIS/NIR and fluorescence spectroscopy, and magnetic measurements.

The crystal structure, superconducting properties, and electronic structure of a novel superconducting 122-type antimonide, BaPt$_2$Sb$_2$, have been investigated by measurements of powder X-ray diffraction patterns, electrical resistivity, ac magnetic susceptibility, specific heat as well as ab-initio calculations. This material crystallizes in a new-type of monoclinic variant of the CaBe$_2$Ge$_2$-type structure, in which Pt$_2$Sb$_2$ layers consisting of PtSb$_4$ tetrahedra and Sb$_2$Pt$_2$ layers consisting of SbPt$_4$ tetrahedra are stacked alternatively and Ba atoms are located between the layers. Measurements of electrical resistivity, ac magnetic susceptibility and specific heat revealed that BaPt$_2$Sb$_2$ is a superconducting material with a $T_{\rm c}$ of 1.8 K. The electronic heat capacity coefficient $\gamma_{\rm n}$ and Debye temperature $\theta_{\rm D}$ were 8.6(2) mJ/mol K$^2$ and 146(4) K, where the figures in parentheses represent the standard deviation. The upper critical field $\mu_{\rm 0}H_{\rm c2}(0)$ and the Ginzburg-Landau coherent length $\xi(0)$ were determined to be 0.27 T and 35 nm. Calculations showed that it has two three-dimensional Fermi surfaces (FSs) and two two-dimensional FSs, leading to anisotropic transport properties. The d-states of the Pt atoms in the Pt2Sb2 layers mainly contribute to $N(E_{\rm F})$. A comparison between experimental and calculated results indicates that BaPt$_2$Sb$_2$ is a superconducting material with moderate coupling., Comment: 24 pages, 9 figures

We report measurements of ac magnetic susceptibility ${\ensuremath{\chi}}_{\text{ac}}$ and de Haas--van Alphen (dHvA) oscillations in ${\mathrm{KFe}}_{2}$${\mathrm{As}}_{2}$ under high pressure up to 24.7 kbar. The pressure dependence of the superconducting transition temperature ${T}_{c}$ changes from negative to positive across ${P}_{c}\ensuremath{\sim}18$ kbar, as previously reported. The ratio of the upper critical field to ${T}_{c}$, i.e., ${B}_{c2}/{T}_{c}$, is enhanced above ${P}_{c}$, and the shape of the ${\ensuremath{\chi}}_{\text{ac}}$ versus field curves qualitatively changes across ${P}_{c}$. dHvA oscillations smoothly evolve across ${P}_{c}$, indicating no drastic change in the Fermi surface up to 24.7 kbar. Three dimensionality increases with pressure, while effective masses show decreasing trends. We suggest a crossover from a nodal to a full-gap $s$ wave as a possible explanation.

We report on the electronic structure of the bilayer ruthenate Ca 3 Ru 2 O 7 using high quality single-crystals grown by a floating-zone method which have the lowest residual resistivity so far achieved. The quantum oscillation, specific heat, and angle-resolved photoemission-spectroscopy (ARPES) measurements performed on these crystals establish that Ca 3 Ru 2 O 7 is a quasi two-dimensional low-carrier metal with a density-wave instability.

We have observed Shubnikov-de Haas oscillations in FeSe. The Fermi surface deviates significantly from predictions of band-structure calculations and most likely consists of one electron and one hole thin cylinder. The carrier density is in the order of 0.01 carriers/ Fe, an order-of-magnitude smaller than predicted. Effective Fermi energies as small as 3.6 meV are estimated. These findings call for elaborate theoretical investigations incorporating both electronic correlations and orbital ordering., Comment: 6 pages, 6 figures, 1 table, published in Phys. Rev. B

Hard x-ray photoemission studies of Ca${}_{3}$(Ru${}_{1\ensuremath{-}x}$Ti${}_{x}$)${}_{2}$O${}_{7}$ with $x$ $=$ 0, 0.003, and 0.005 have been carried out to clarify the origin of the extremely high sensitivity of the metal-insulator (M-I) transition to the amount of Ti substitution. All the compounds show an antiferromagnetic transition followed by a structural transition at a temperature ${T}_{\mathrm{S}}$, with decreasing temperature. For $x$ g 0, the structural transition is accompanied with a drastic M-I transition and the intensities of the screened peaks in the Ru 3$d$ core-level spectra are significantly reduced below ${T}_{\mathrm{S}}$. The spectral weight of the valence band is concurrently shifted toward the higher binding energy side by an order of 2 eV, which shows that a strong electron correlation plays an essential role for the M-I transition at ${T}_{\mathrm{S}}$ for $x$ g 0. These results provide strong evidence that Mott transition is induced by a minute amount of the Ti substitution in Ca${}_{3}$Ru${}_{2}$O${}_{7}$.

We have observed hysteresis in superconducting resistive transition curves of Ba${}_{0.07}$K${}_{0.93}$Fe${}_{2}$As${}_{2}$ (${T}_{c}\ensuremath{\sim}8$ K) below about 1 K for in-plane fields. The hysteresis is not observed as the field is tilted away from the $ab$ plane by 20${}^{\ensuremath{\circ}}$ or more. The temperature and angle dependencies of the upper critical field indicate a strong paramagnetic effect for in-plane fields. We suggest that the hysteresis can be attributed to a first-order superconducting transition due to the paramagnetic effect. Magnetic torque data are also shown.

A solid-state reaction method with urea as a nitrogen precursor was used to prepare nitrogen-doped lamellar niobic and titanic solid acids (i.e., HNb(3)O(8) and H(2)Ti(4)O(9)) with different acidities for visible-light photocatalysis. The photocatalytic activities of the nitrogen-doped solid acids were evaluated for rhodamine B (RhB) degradation and the results were compared with those obtained over the corresponding nitrogen-doped potassium salts. Techniques such as XRD, BET, SEM, X-ray photoelectron spectroscopy, and UV-visible diffuse reflectance spectroscopy were adopted to explore the nature of the materials as well as the characteristics of the doped nitrogen species. It was found that the intercalation of the urea precursor helped to stabilize the layered structures of both lamellar solid acids and enabled easier nitrogen doping. The effects of urea intercalation were more significant for the more acidic HNb(3)O(8) sample than for the less acidic H(2)Ti(4)O(9). Compared with the nitrogen-doped KNb(3)O(8) and K(2)Ti(4)O(9) samples, the nitrogen-doped HNb(3)O(8) and H(2)Ti(4)O(9) solid acids absorb more visible light and exhibit a superior activity for RhB photodegradation under visible-light irradiation. The nitrogen-doped HNb(3)O(8) sample performed the best among all the samples. The results of the current study suggest that the protonic acidity of the lamellar solid-acid sample is a key factor that influences nitrogen doping and the resultant visible-light photocatalysis.

The search for active semiconductor photocatalysts that directly split water under visible-light irradiation remains one of the most challenging tasks for solar-energy utilization. Over the past 30 years, the search for such materials has focused mainly on metal-ion substitution as in In(1-x)Ni(x)TaO(4) and (V-,Fe- or Mn-)TiO(2) (refs 7,8), non-metal-ion substitution as in TiO(2-x)N(x) and Sm(2)Ti(2)O(5)S(2) (refs 9,10) or solid-solution fabrication as in (Ga(1-x)Zn(x))(N(1-x)O(x)) and ZnS-CuInS(2)-AgInS(2) (refs 11,12). Here we report a new use of Ag(3)PO(4) semiconductor, which can harness visible light to oxidize water as well as decompose organic contaminants in aqueous solution. This suggests its potential as a photofunctional material for both water splitting and waste-water cleaning. More generally, it suggests the incorporation of p block elements and alkali or alkaline earth ions into a simple oxide of narrow bandgap as a strategy to design new photoelectrodes or photocatalysts.

We study the effects of adding electrons to the conduction bands of the itinerant metamagnet Sr3 Ru2 O7 using substitution of La3+ onto the Sr2+ site. Small changes to the chemical potential have a large effect: adding only 0.03 electrons per Ru reduces the electronic specific-heat coefficient by 30%, but makes no corresponding change to the temperature (∼8 K) at which the electronic specific-heat coefficient shows its maximum. The observations are incompatible with a simple rigid-band shift, raising the possibility that a many-body resonance plays a key role in the physics of Sr3 Ru2 O7. © 2008 The American Physical Society.

We employ a combination of chemical substitution and angle resolved photoemission spectroscopy to prove that the Fermi level in the $\ensuremath{\gamma}$ band of ${\mathrm{Sr}}_{2\ensuremath{-}y}{\mathrm{La}}_{y}{\mathrm{RuO}}_{4}$ can be made to traverse a van Hove singularity. Remarkably, the large mass renormalization has little dependence on either $\mathbf{k}$ or doping. By combining the results from photoemission with thermodynamic measurements on the same batches of crystals, we deduce a parametrization of the full many-body quasiparticle dispersion in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ which extends from the Fermi level to approximately 20 meV above it.

We report x-ray scattering studies of the $c$-axis lattice parameter in ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ as a function of temperature and magnetic field. These structural studies complement published transport and magnetization data, and therefore elucidate the spin-charge-lattice coupling near the metal-insulator transition. Strong anisotropy of the structural change for field applied along orthogonal in-plane directions is observed. Competition between a spin-polarized phase that does not couple to the lattice and an antiferromagnetic metallic phase that does gives rise to a rich behavior for $\mathbf{B}\ensuremath{\Vert}b$.

We show that the metamagnetic transition in ${\mathrm{Sr}}_{4}{\mathrm{Ru}}_{3}{\mathrm{O}}_{10}$ bifurcates into two transitions as the field is rotated away from the conducting planes. This two-step process comprises partial or total alignment of moments in ferromagnetic bands followed by an itinerant metamagnetic transition whose critical field increases with rotation. Evidence for itinerant metamagnetism is provided by the Shubnikov--de Haas effect, which shows a nontrivial evolution of the geometry of the Fermi surface and an enhancement of the quasiparticles effective mass across the transition. We conclude that the metamagnetic response of ${\mathrm{Sr}}_{4}{\mathrm{Ru}}_{3}{\mathrm{O}}_{10}$ is orbital dependent and involves both ferromagnetic and metamagnetic bands.

We report measurements of resistance and ac magnetic susceptibility on FeSe single crystals under high pressure up to 27.2 kbar. The structural phase transition is quickly suppressed with pressure, and the associated anomaly is not seen above $\sim$18 kbar. The superconducting transition temperature evolves nonmonotonically with pressure, showing a minimum at $\sim12$ kbar. We find another anomaly at 21.2 K at 11.6 kbar. This anomaly most likely corresponds to the antiferromagnetic phase transition found in $\mu$SR measurements [M. Bendele \textit{et al.}, Phys. Rev. Lett. \textbf{104}, 087003 (2010)]. The antiferromagnetic and superconducting transition temperatures both increase with pressure up to $\sim25$ kbar and then level off. The width of the superconducting transition anomalously broadens in the pressure range where the antiferromagnetism coexists., Comment: 3 figures

High-resolution angular resolved photoemission data reveal well-defined quasiparticle bands of unusually low weight, emerging in line with the metallic phase of Ca(3)Ru(2)O(7) below approximately 30 K . At the bulk structural phase transition temperature of 48 K, we find clear evidence for an electronic instability, gapping large parts of the underlying Fermi surface that appears to be nested. Metallic pockets are found to survive in the small, non-nested sections, constituting a low-temperature Fermi surface with 2 orders of magnitude smaller volume than in all other metallic ruthenates. The Fermi velocities and volumes of these pockets are in agreement with the results of complementary quantum oscillation measurements on the same crystal batches.

We report the results of a study of the Hall effect and magnetoresistance in single crystals of ${\mathrm{Sr}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$ in which ${\mathrm{Sr}}^{2+}$ has been substituted by ${\mathrm{La}}^{3+}$ $({\mathrm{Sr}}_{2\ensuremath{-}y}{\mathrm{La}}_{y}\mathrm{Ru}{\mathrm{O}}_{4})$ or ${\mathrm{Ru}}^{4+}$ by ${\mathrm{Ti}}^{4+}$ $({\mathrm{Sr}}_{2}{\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{4})$. For undoped ${\mathrm{Sr}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$, the purity is so high that the strong-field Hall coefficient can be measured for fields above $4\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The conventional weak-field Hall coefficient as a function of doping shows a sharp jump and sign change at $y\ensuremath{\sim}0.01$ that is unrelated to either a sharp change in Fermi-surface topography or a magnetic instability. The implications of these results are discussed.