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This work is supported by a KAKENHI Grants-in-Aids for Scientific Research (Grant Nos. 17H06136, 18K04715, and 21H01033), and Core-to-Core Program (No. JPJSCCA20170002) from the Japan Society for the Promotion of Science (JSPS) and by a JST-Mirai Program (Grant No. JPMJMI18A3), and by the Max Planck Society. We report the magnetocaloric effect of a bilayered perovskite ruthenate Ca3Ru2O7 that has recently been recognized as an antiferromagnetic polar metal. The magnetic entropy change obtained from temperature dependence of the DC magnetization measurements shows peaks and valleys under the magnetic field near metamagnetic transitions, and enable us to map out a thermodynamic field–temperature phase-diagram. The area surrounded by the boundaries agrees well with a novel “metamagnetic texture” with spin modulation observed recently by small angle neutron scattering measurements. We demonstrate that a thermodynamically equilibrium state is realized between the antiferromagnetic and spin-polarized states throughout the metamagnetic transition in this polar metal. Postprint

Funding: This work is supported by a KAKENHI Grants-in-Aids for Scientific Research (Grant Nos.17H06136, 18K04715, and 21H01033) from the Japan Society for the Promotion of Science (JSPS) and by a JST-Mirai Program (Grant No. JPMJMI18A3). We report the single-crystal growth of the unconventional superconductor Sr2RuO4, on which research has reached a turning point recently. In order to optimize the quality of crystals grown by the floating-zone method using an infrared image furnace, we focus on an improvement of the structure of the filament in the halogen lamps. By reducing the thickness of the total filament, the form of the molten zone was narrowed. More importantly, the molten zone was observed to be more stable during the growth process. Finally, we obtained the crystals with a length of 12 cm. Additionally, the grown crystal has high quality, displaying the 1.5 K transition temperature expected only for the purest crystals. We also discuss the availability of the newly developed halogen lamps. Publisher PDF

This work has been financially supported by the Deutsche Forschungsgemeinschaft (GR 4667/1, GRK 1621 and SFB 1143 projects C02 and C09) and the Max Planck Society. Y.M., T.M. and J.S.B. acknowledge the financial support of JSPS Kakenhi (JP15H5852, JP15K21717 and JP17H06136) and the JSPS Core-to-Core Program. N.K. acknowledges the financial support from JSPS Kakenhi (no. JP18K04715) and JST-Mirai Program (no. JPMJMI18A3). A.N. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 701647. Strontium ruthenate (Sr2RuO4) continues to present an important test of our understanding of unconventional superconductivity, because while its normal-state electronic structure is known with precision, its superconductivity remains unexplained. There is evidence that its order parameter is chiral, but reconciling this with recent observations of the spin part of the pairing requires an order parameter that is either finely tuned or implies a new form of pairing. Therefore, a definitive resolution of whether the superconductivity of Sr2RuO4 is chiral is important for the study of superconductivity. Here we report the measurement of zero-field muon spin relaxation—a probe sensitive to weak magnetism—on samples under uniaxial stresses. We observe stress-induced splitting between the onset temperatures of superconductivity and time-reversal symmetry breaking—consistent with the qualitative expectations for a chiral order parameter—and argue that this observation cannot be explained by conventional magnetism. In addition, we report the appearance of bulk magnetic order under higher uniaxial stress, above the critical pressure at which a Lifshitz transition occurs in Sr2RuO4. Postprint

We report the magnetocaloric effect of the Tsai-type 1/1 quasicrystal approximants Au64Al22R14 (R = Gd, Tb, and Dy) with the space group of Im 3 . These approximants with the electron-per-atom (e/a) ratio of 1.72 exhibit a ferromagnetic transition in bulk at the Curie temperatures of 27, 15, and 9.5 K for R = Gd, Tb, and Dy, respectively, as confirmed by both magnetic susceptibility and specific heat measurements. The magnetic entropy change (ΔSM) of the materials for a field change of 7 T are 6.3, 4.4, and 4.8 J/K mol-R for R = Gd, Tb, and Dy, respectively. Other parameters related to the magnetocaloric effect, the adiabatic temperature change (ΔTad) and the relative cooling power (RCP) are also evaluated. We also discuss the obtained magnetocaloric effect of the approximants with relation to the recently reported unique magnetic order formed on the icosahedral clusters, a building unit of the Tsai-type 1/1 quasicrystal approximants.

Nonequilibrium steady state conditions induced by a dc current can alter the physical properties of strongly correlated electron systems. In this regard, it was recently shown that dc current can trigger novel electronic states, such as current-induced diamagnetism, which cannot be realized in equilibrium conditions. However, reversible control of diamagnetism has not been achieved yet. Here, we demonstrate reversible in situ control between a Mott insulating state and a diamagnetic semimetal-like state by a dc current in the Ti-substituted bilayer ruthenate ${\mathrm{Ca}}_{3}({\mathrm{Ru}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{)}_{2}{\mathrm{O}}_{7}$ ($x=0.5%$). By performing simultaneous magnetic and resistive measurements, we map out the temperature vs current-density phase diagram in the nonequilibrium steady state of this material. The present results open up the possibility of creating novel electronic states in a variety of strongly correlated electron systems under dc current.

Magnetic properties of an Yb-based semiconductor YbCuS2 with a zigzag chain of Yb3+ ions were studied. The Curie–Weiss behavior of the magnetic susceptibility χ(T) indicates antiferromagnetic inter...

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

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...

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.

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.

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...

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.

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 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 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 X-ray scattering studies of the c-axis lattice parameter in Ca3Ru2O7 as a function of temperature and magnetic field, for B || the ground state easy (b) axis. The step-like, ∼0.1% change coincides in zero field with a spin reorientation and a metal–insulator transition, at Tm−i≈48 K, and shifts to a lower temperature upon application of magnetic field. At temperatures well below Tm−i, negligible change in the c-axis lattice parameter is observed at the metamagnetic transition to the spin-polarized phase, at Bc≈6 T, which indicates that this transition does not couple to the lattice degree of freedom.

We report the successful growth of single crystals of the perovskite ruthenate CaRuO 3 by a floating-zone method, and characterization of their physical properties by x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat. Although the system is strongly correlated, with an electronic specific heat coefficient of approximately 80 mJ/(mol K 2 Ru), the physical properties are nearly isotropic, reflecting the almost cubic crystal structure. No obvious phase transitions are observed down to 0.12 K, in contrast to observations on other metallic ruthenates with the Ruddlesden–Popper type layered perovskite structure A n +1 Ru n O 3 n +1 such as Sr 2 RuO 4 , Sr 3 Ru 2 O 7 , and Ca 3 Ru 2 O 7 .