Search

Ferroelectrics with spontaneous electric polarization play an essential role in today's device engineering, such as capacitors and memories. Their physical properties are further enriched by suppressing the long-range polar order, as is exemplified by quantum paraelectrics with giant piezoelectric and dielectric responses at low temperatures. Likewise in metals, a polar lattice distortion has been theoretically predicted to give rise to various unusual physical properties. So far, however, a "ferroelectric"-like transition in metals has seldom been controlled and hence its possible impacts on transport phenomena remain unexplored. Here we report the discovery of anomalous enhancement of thermopower near the critical region between the polar and nonpolar metallic phases in 1T'-Mo$_{1-x}$Nb$_{x}$Te$_2$ with a chemically tunable polar transition. It is unveiled from the first-principles calculations and magnetotransport measurements that charge transport with strongly energy-dependent scattering rate critically evolves towards the boundary to the nonpolar phase, resulting in large cryogenic thermopower. Such a significant influence of the structural instability on transport phenomena might arise from the fluctuating or heterogeneous polar metallic states, which would pave a novel route to improving thermoelectric efficiency., Comment: 26 pages, 4 figures

High-resolution powder x-ray diffraction and single-crystal neutron diffraction were used to investigate the crystal structure and magnetic ordering of the compound $\mathrm{P}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{V}{\mathrm{O}}_{3}$ ($0\ensuremath{\le}x\ensuremath{\le}0.3$), which undergoes an insulator-to-metal transition for $x\ensuremath{\sim}0.23$. Since the ionic radii of $\mathrm{P}{\mathrm{r}}^{3+}$ and $\mathrm{C}{\mathrm{a}}^{2+}$ are almost identical and structural disorder is minimal, $\mathrm{P}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{V}{\mathrm{O}}_{3}$ is a good model system for the influence of hole doping on the spin and orbital correlations in transition metal oxides. The end member $\mathrm{PrV}{\mathrm{O}}_{3}$ is a Mott-Hubbard insulator, which exhibits a structural phase transition at ${T}_{\mathrm{S}}=180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ from an orthorhombic to a monoclinic structure with space groups Pbnm and $P{2}_{1}/b$, respectively. This transition is associated with the onset of orbital ordering and strong Jahn-Teller distortions of the $\mathrm{V}{\mathrm{O}}_{6}$ octahedra. Antiferromagnetic $C$-type order with vanadium moments oriented in the $ab$ plane is observed below ${T}_{\mathrm{N}}=140\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Upon cooling, the vanadium moments induce a progressive magnetic polarization of the praseodymium sublattice, resulting in a ferrimagnetic structure with coexisting modes (${C}_{x}, {F}_{y}$) and (${F}_{x}, {C}_{y}$). In the insulating range of the $\mathrm{P}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{V}{\mathrm{O}}_{3}$ phase diagram, Ca doping reduces both the orbital and magnetic transition temperatures so that ${T}_{\mathrm{S}}=108\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}}=95\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $x=0.20$. The Jahn-Teller distortions and ordered vanadium moments also decrease upon doping. In a metallic sample with $x=0.30$, Jahn-Teller distortions and long-range orbital ordering are no longer observable, and the average crystal structure remains orthorhombic down to low temperature. However, broadening of some lattice Bragg reflections indicate a significant increase in lattice strain. Antiferromagnetic short-range order with a weak ordered moment of 0.14(3) ${\ensuremath{\mu}}_{\mathrm{B}}$ per vanadium atom could still be observed on the vanadium site below $T\ensuremath{\sim}60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. We discuss these observations in terms of doping-induced spin-orbital polaron formation.

Unusual enhancement of cryogenic thermopower manifests itself around the critical point of polar order in a metal., Ferroelectrics with spontaneous electric polarization play an essential role in today’s device engineering, such as capacitors and memories. Their physical properties are further enriched by suppressing the long-range polar order, as exemplified by quantum paraelectrics with giant piezoelectric and dielectric responses at low temperatures. Likewise in metals, a polar lattice distortion has been theoretically predicted to give rise to various unusual physical properties. However, to date, a “ferroelectric”-like transition in metals has seldom been controlled, and hence, its possible impacts on transport phenomena remain unexplored. We report the discovery of anomalous enhancement of thermopower near the critical region between the polar and nonpolar metallic phases in 1T′-Mo1−xNbxTe2 with a chemically tunable polar transition. It is unveiled from the first-principles calculations and magnetotransport measurements that charge transport with a strongly energy-dependent scattering rate critically evolves toward the boundary to the nonpolar phase, resulting in large cryogenic thermopower. Such a significant influence of the structural instability on transport phenomena might arise from the fluctuating or heterogeneous polar metallic states, which would pave a novel route to improving thermoelectric efficiency.

We spectroscopically investigate a series of pyrochlore iridates ${R}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ ($R$: rare-earth and Y ions) where the metal-insulator transitions are induced by systematic bandwidth control via chemical substitutions of $R$ ions. We establish the phase diagram of ${R}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, as endorsed by the variation of the optical conductivity spectra, in which the competing phases including paramagnetic insulator (PI), paramagnetic metal (PM), and antiferromagnetic insulator (AFI) show up as a function of bandwidth and temperature. For small $R$-ionic radius ($R=$ Y-Sm), i.e., strongly correlated region, pronounced peaks on the edge of the optical gap are discerned below the magnetic transition temperature ${T}_{\mathrm{N}}$, which is attributable to exciton and magnon sideband absorptions. It turns out that the estimated nearest-neighbor exchange interaction increases as $R$-ionic radius increases, whereas ${T}_{\mathrm{N}}$ monotonically decreases, indicating that the all-in all-out magnetic order arises from the interplay among several exchange interactions inherent to extended $5d$ orbitals on the frustrated lattice. For larger $R$-ionic radius ($R=$ Sm-Pr), i.e., relatively weakly correlated region, the optical conductivity spectra markedly change below 0.3 eV in the course of PM-AFI transition, implying that the magnetic order induces the insulating state. In particular, we have found distinct electrodynamics in the composition of $R=\phantom{\rule{4pt}{0ex}}{\mathrm{Nd}}_{0.5}{\mathrm{Pr}}_{0.5}$ which is located on the boundary of the quantum PM-AFI transition, pointing to the possible emergence of unconventional topological electronic phases related possibly to the correlated Weyl electrons.

Perovskite-type manganites exhibit various interesting phenomena arising from complex interplay among spin, charge, orbital, and lattice degrees of freedom. One such example is the keen competition between phases with different spin/charge/orbital orders. Keen competition between antiferromagnetic metal and orbital-ordered insulator is found in the slightly electron-doped regime near Mn4+ state which is stabilized by the high oxygen-pressure condition. Another one is the emergence of ferroelectricity either induced by the magnetic ordering or independently of the magnetic ordering. As the respective examples, perovskite-type YMnO3 and Sr1−xBaxMnO3 are discussed. In the YMnO3, the ferroelectric lattice distortion associated with the E-type spin order is observed for the first time. Displacement-type ferroelectricity with off-center magnetic ions is discovered for Sr0.5Ba0.5MnO3, which shows both large polarization value and strong coupling between ferroelectricity and magnetism.

Offline teaching based on high positioning accuracy of a robot arm is desired to take the place of manual teaching. In offline teaching, joint angles are calculated using a kinematic model of the robot arm. However, a nominal kinematic model does not consider the errors arising in manufacturing or assembly, not to mention the non-geometric errors arising in gear transmission, arm compliance, etc. Therefore, a method of precisely calibrating the parameters in a kinematic model is required. For this purpose, it is necessary to measure the three-dimensional (3-D) absolute position of the tip of a robot arm. In this paper, a laser tracking system is employed as the measurement apparatus. The geometric parameters in the robot kinematic model are calibrated by minimizing errors between the measured positions and the predicted ones based on the model. The residual errors caused by non-geometric parameters are further reduced by using neural networks, realizing high positioning accuracy of sub-millimeter order. To speed up the calibration process, a smaller number of measuring points is preferable. Optimal measuring points, which realize high positioning accuracy while remaining small in number, are selected using Genetic Algorithm (GA).

We investigate the variation of charge dynamics upon the metal–insulator transition for perovskite SrIr1−xSnxO3 by employing the optical spectroscopy. The Dirac semimetal of SrIrO3 turns into the a...

Organic ferroelectrics are multifunctional candidates as future organic electronics and optical devices. However, its observations in organic solids have been quite limited to well-known polymer ferroelectrics and only several low-molecular compounds until recently. Our non-covalent synthesis of the molecular compounds with hydrogen bonds between acid and base has realized a number of supramolecular ferroelectrics. These compounds display various mechanisms of ferroelectricity such as the molecular displacement and/or collective transfer of protons depending on the nature of hydrogen bonds. These principles succeeded in improving properties and would facilitate materials design toward future functional organics.

Measurements of the magnetic-field-dependent polarization of a one-dimensional organic quantum magnet suggest its ferroelectric behaviour is mediated by a spin–Peierls instability. Such behaviour could provide a promising new approach to the design of spin-driven ferroelectrics. In magnetically controllable ferroelectrics1,2,3, electric polarization is induced by charge redistribution or lattice distortions that occur to minimize the energy associated with both the magnetic order and interaction of spins with an applied magnetic field. Conventional approaches to designing materials that exploit such spin-mediated behaviour have focused mainly on developing the cycloidal spin order4,5, and thereby producing ferroelectric behaviour through the so-called antisymmetric Dzyaloshinskii–Moriya interaction6,7,8. However, engineering such spin structures is challenging. Here we suggest a different approach. Direct measurements of magnetic-field-dependent variations in the polarization of the one-dimensional organic quantum magnet, tetrathiafulvalene-p-bromanil, suggest a spin–Peierls instability has an important role in its response. Our results imply that one-dimensional quantum magnets, such as organic charge-transfer complexes, could be promising candidates in the development of magnetically controllable ferroelectric materials.

This study describes a device using pressure-sensitive electro-conductive knitting called PCK. PCK is electric conductive material made from fiber including PE 70% and SUS 30%. And it's resistance changes in the fibers according to the modification. So it can be used as a sensor of bending, stretching and pressure. This knitting when used as sensor, is inexpensive, highly flexible and air permeable. More importantly, a wearable device made of this material have the function as a sensor only by itself. So it is considered that this material can be applied as a sensor in various applications. In this paper, a Data-glove made of PCK and measurements of the device are presented. And a recognizing system using neural network that can recognize the form of human hand from the output of the Data-glove is also presented. This system attained the high rate of recognition of 5 patterns of hand operation.

We have investigated the lattice distortion coupled to the Co $3d$-spin-state ordering in thin films of perovskite ${\mathrm{LaCoO}}_{3}$ with various epitaxial strains by measurements of the magnetization, x-ray diffraction, and optical spectra. In the system with tensile strain about 0.5%, a lattice distortion characterized by the modulation vector $q=(1/6,1/6,1/6)$ emerges at 40 K, followed by a ferromagnetic ordering at 24 K. Alternatively, in systems with tensile strain exceeding 1%, the lattice distortion characterized by $q=(1/4,1/4,1/4)$ emerges at 120 K or higher, and subsequently the ferromagnetic or ferrimagnetic ordering occurs around 90 K. The evolution of infrared phonon spectra and resonant x-ray scattering at the Co $K$ edge suggests that the population change in the Co $3d$ spin state causes the strain-induced switching of spin-state ordering as well as of magnetic ordering in this canonical spin-state crossover system.

We investigate magnetotransport properties in a single crystal of pyrochore-type ${\mathrm{Nd}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$. The metallic conduction is observed on the antiferromagnetic domain walls of the all-in--all-out-type Ir $5d$ moment ordered insulating bulk state that can be finely controlled by an external magnetic field along [111]. On the other hand, an applied field along [001] induces the bulk phase transition from insulator to semimetal as a consequence of the field-induced modification of the Nd $4f$ and Ir $5d$ moment configurations. A theoretical calculation consistently describing the experimentally observed features suggests a variety of exotic topological states as functions of electron correlation and Ir $5d$ moment orders, which can be finely tuned by the choice of rare-earth ion and magnetic field, respectively.

We have explored metal-insulator phenomena for pyrochlore ${R}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, in which the electron correlation strength and magnetic configuration are systematically controlled by varying the average rare-earth ionic radius $(R={\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}$ and ${\mathrm{Sm}}_{y}{\mathrm{Nd}}_{1\ensuremath{-}y})$, external pressure, and magnetic field. Metal-insulator transitions in bulk are caused by increasing $x$ or tuning pressure, indicating that the effective correlation is responsible for the transition. The metallic state intervenes between the paramagnetic insulating and antiferromagnetically ordered insulating phases for $({\mathrm{Sm}}_{y}{\mathrm{Nd}}_{1\ensuremath{-}y}){}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ $(y=0.7--0.9)$, reminiscent of a first-order Mott transition. Furthermore, the metal-to-insulator crossover is observed (around $y=0.7$) for charge transport on magnetic domain walls in the insulating bulk. An application of magnetic field also drives metal-insulator transitions for $({\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}){}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, which is likely due to the modulation of Ir $5d$ band structures accompanied by a change in the spin textures. Abundant exotic states are revealed in the vicinity of metal-insulator transitions by finely tuning the physical parameters in ${R}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$.

In the course of screening for novel naturally occurring insecticides from Chinese crude drugs, the MeOH extract of the fruits of Evodia rutaecarpa Benth was found to give insecticidal activity against larvae of Drosophila melanogaster Meigen. Three alkaloids, evodiamine (1), rutaecarpine (2) and rhetsinine (3), were isolated by bioassay-guided fractionation of the extract. Insecticidal activity against larvae of D melanogaster was demonstrated; compounds 1 and 2 gave LC50 values of 0.30 and 0.28 µmol ml−1 diet respectively. Acute toxicity against adults of D melanogaster was also found; compound 2 had the most potent activity, with an LD50 value of 3.58 µg per adult. However, compound 3 had only weak activity in this study. Therefore compounds 1 and 2 were identified as insecticidal compounds from the fruits of E rutaecarpa. Compound 3 was obtained by the photoxidation of evodiamine. Investigation of the structure–activity relationship indicated the importance of the indoloquinazoline unit at the C-14 position. © 2002 Society of Chemical Industry

In the course of screening for novel naturally occurring insecticides from Chinese crude drugs, the methanolic extract of the bark of Phellodendron amurense Rupr was found to show insecticidal activity against larvae of Drosophila melanogaster Meigen. Two alkaloids, berberine (1) and palmatine (2), were isolated by bioassay-guided fractionation of the extract. Insecticidal activity against larvae of D melanogaster was demonstrated; 1 and 2 gave LC 50 values of 2.44 and 8.45 μmol ml -1 diet respectively. Acute toxicity against adult D melanogaster was also found; 1 had the more potent activity, with an LD 50 value of 19.0 μg per adult. However, 2 had weak activity in this study. Therefore 1 was identified as an insecticidal compound from the bark of P amurense Rupr. L'extrait methanolique de l'ecorce de Phellodendron amurense presente une activite insecticide contre les larves de Drosophila melanogaster Meigen. Dans cette etude, l'isolement et les activites des composes actifs sont decrits. Deux alcaloides, la berberine et la palmatine, sont isoles par un fractionnement biologique de l'extrait. La berberine est identifiee en tant que compose insecticide de l'ecorce de P. amurense.

We have investigated the dynamics of spin-state crossover (SSC) for perovskite ${\mathrm{LaCoO}}_{3}$ through optical phonons by means of infrared and inelastic x-ray spectroscopy. Upon thermally induced SSC, anomalously dispersionless Co-O bond stretching phonons coupled to the thermally excited spin state have been identified. The enhanced spin-state fluctuation irrespective of the presence of a clear charge gap suggests the emergence of complex spin-state disproportionation involving low-, intermediate-, and high-spin states due to the strong correlation among thermally activated spin states.

We studied single crystals of $\text{BaV}{}_{13}$$\text{O}{}_{18}$, in which V ions with an average valence of +2.62 ($3{d}^{2.38}$) form a quasi-fcc lattice. We found that the ground state of the stoichiometric crystal is insulating, whereas that of the off-stoichiometric crystal is metallic with a large effective mass. This metallic state can be explained by the Kondo coupling between the magnetic moment existing at the lone V ion and itinerant carriers in the V tetramers.

We have investigated the charge transport and low-energy dynamics originating from the antiferromagnetic (AF) domain wall (DW) in pyrochlore-type Nd${}_{2}$Ir${}_{2}$O${}_{7}$ with the all-in all-out type AF ground state by means of the magneto-resistance measurement and the terahertz time-domain spectroscopy. The resistivity is much lower in the multi-magnetic-domain state than in the nearly single-magnetic-domain one. Furthermore, the terahertz optical conductivity spectrum unravels a Drude-like response only in the multidomain state; the Drude-like absorption is strongly suppressed with increasing field and irreversibly disappears above 5 T. These observations suggest that the AF DW is highly conductive with a minimal damping constant of 2 meV, contrary to the fully-gapped (45 meV) AF insulating state of bulk. We discuss the nature of metallic states at AF DWs and their possible relevance to the gapless edge state inherent to the Weyl semimetal.

We found that ${\mathrm{Ba}}_{2}{\mathrm{Ti}}_{13}{\mathrm{O}}_{22}$ with ${\mathrm{Ti}}^{3+}$ ($3{d}^{1}$) ions on a triangle-based lattice exhibits a phase transition at ${T}_{c}\ensuremath{\sim}200\text{ }\text{ }\mathrm{K}$, below which the increase of electrical resistivity and decrease of magnetic susceptibility were observed. Transmission electron microscopy and optical reflectivity measurements indicate that the low-temperature phase of the present compound shares characteristics in common with a charge-density-wave state with remnant carriers, although a commensurate wave vector of the modulation and a linear temperature dependence of the magnetic susceptibility below ${T}_{c}$ suggest an exotic ordered state.

We have investigated the Co-3d spin-orbital state in a thin film of perovskite LaCoO3 to clarify the origin of strain induced spontaneous magnetization (T(C)=94 K) by means of x-ray diffraction, optical spectroscopy, and magnetization measurements. A lattice distortion with the propagation vector (1/4 -1/4 1/4) and an anomalous activation of optical phonons coupled to Co-3d orbital are observed below 126 K. Combined with the azimuthal angle analysis of superlattice reflection, we propose that the ordering of Co-3d orbital promoted by an epitaxial strain produces a unique ferrimagnetic structure.

We report on the distinct surface state of electronic orders, including spin, orbital, and spin-state degrees of freedom of Co3+ ion, in an epitaxially strained thin film of LaCoO3 grown on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrate. The surface ordered state was detected by the grazing-incidence resonant soft x-ray scattering at Co L-edge, where the probing depth is less than the topmost 4 nm of surface. Comparing with the result of bulk sensitive x-ray diffraction, we revealed that the transition temperature of the orbital order (spin order) at the surface region is about 30 K (20 K) higher (lower) than that of the bulk. A novel phenomenon of the surface order and bulk disorder of the orbital degree of freedom can be attributed to its collective and lattice-coupled nature which is strongly affected by the translational/inversion symmetry breaking at the surface.

We have spectroscopically investigated the thermally and doping-induced metal-insulator transitions for pyrochlore-type Nd2Ir2O7 as well as its Rh-doped analogs Nd2(Ir(1-x)Rh(x))(2)O(7), where the spin-orbit interaction as well as the electron correlation is effectively tuned by the doping level (x). The charge dynamics dramatically changes on an energy scale of 1 eV in the course of thermally and doping-induced metal-insulator transitions, while the insulating ground state shows a small but well-defined charge gap of 45 meV. Anomalous doping variation of the low-energy (

We have spectroscopically investigated the charge dynamics for the high-quality single crystals of perovskite $A$FeO${}_{3}$, which exhibit the helimagnetism ($A$ = Sr and Ca) and/or the charge disproportionation (CD) transition ($A$ = Ca). The metallic state at high temperatures, both for $A=$ Sr and Ca, shows highly incoherent charge dynamics, while the optical spectra for $A=$ Ca change in a wide energy upon the CD transition. These results are in accord with the picture of the phase change between the highly correlated metal and the anticorrelated CD insulator in this class of high Fe-valence perovskite.

Supramolecular ferroelectric cocrystals of phenazine (Phz) with chloranilic acid (H(2)ca), bromanilic acid (H(2)ba), and fluoranilic acid (H(2)fa) have been characterized by the interplay between their structural transformations and solid-state acid-base (proton transfer) reactions. At ambient pressure, the Phz-H(2)ca, Phz-H(2)ba, and their deuterated crystals exhibit incomplete proton displacement, which transforms the neutral molecules into semi-ionic at low temperatures below the Curie point (T(c)(IC)TT(c)(I)). For the cocrystal of the less acidic H(2)fa, the ferroelectric phase is induced only by applying hydrostatic pressure above ~0.6 GPa. According to the combined studies of temperature-dependent dielectric permittivity and synchrotron X-ray diffraction, it was proved that the ferroelectric (FE-I) phase is always accompanied at lower temperatures by successive phase transitions to the lattice modulated phases with incommensurate periodicities (IC phase, T(c)(II)TT(c)(IC)) and with commensurate (2- or 3-fold) periodicities (FE-II or FE-III phase, TT(c)(II)). Whereas the ground-state structures at ambient pressure are different from one another among the Phz-H(2)ca (FE-II form), Phz-H(2)ba (FE-III form), and Phz-H(2)fa (paraelectric form), their systematic changes under pressure depict a universal pressure-temperature phase diagram. The possible origins of structural changes are assigned to the valence instability and the frustrated Coulomb interactions that induce the charge disproportionation (coexisting neutral ionic) states with the staging spatial orders.

We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ∼70% and increases the soft-phonon energy by ∼50%, indicating the largest magnetoelectric effects yet attained.

We report a systematic investigation on the high-temperature thermoelectric response in a typical filling-control Mott transition system La${}_{1\ensuremath{-}x}$Sr${}_{x}$VO${}_{3}$. In the vicinity of the Mott transition, incoherent charge transport appears with increasing temperature and the thermopower undergoes two essential crossovers, asymptotically approaching the limit values expected from the entropy consideration, known as the Heikes formula. By comparison with the results of the dynamical mean-field theory, we show that the thermopower in the Mott critical state mainly measures the entropy per charge carrier that depends on electronic degrees of freedom available at the measurement temperature. Our findings verify that the Heikes formula is indeed applicable to the real correlated electron systems at practical temperatures ($Tg200$ K).

The structural and magnetic phase behavior of $R$VO${}_{3}$ with $R$$=$v Dy, Ho, and Er was studied by single-crystal neutron diffraction. Upon cooling, all three compounds show structural transitions from orthorhombic (space group Pbnm) to monoclinic ($p$2${}_{1}$/$b$) symmetry due to the onset of orbital order at $T$$=$ 188--200 K, followed by N\'eel transitions at $T$$=$ 110--113 K due to the onset of antiferromagnetic ($C$-type) order of the vanadium moments. Upon further cooling, additional structural phase transitions occur for DyVO${}_{3}$ and ErVO${}_{3}$ at 60 and 56 K, respectively, where the monoclinic structure changes to an orthorhombic structure with the space group Pbnm, and the magnetic order of the V sublattice changes to a $G$-type structure. These transition temperatures are reduced compared to the ones previously observed for nonmagnetic $R$${}^{3+}$ ions due to exchange interactions between the ${\mathrm{V}}^{3+}$ and ${R}^{3+}$ ions. For ErVO${}_{3}$, $R$-$R$ exchange interactions drive a transition to collinear magnetic order at $T$$=$ 2.5 K. For HoVO${}_{3}$, the onset of noncollinear, weakly ferromagnetic order of the Ho moments nearly coincides with the structural phase transition from the monoclinic to the low-temperature orthorhombic structure. This transition is characterized by an extended hysteresis between 24 and 36 K. The Dy moments in DyVO${}_{3}$ also exhibit noncollinear, weakly ferromagnetic order upon cooling below 13 K. With increasing temperature, the monoclinic structure of DyVO${}_{3}$ reappears in the temperature range between 13 and 23 K. This reentrant structural transition is associated with a rearrangement of the Dy moments. A group theoretical analysis showed that the observed magnetic states of the ${R}^{3+}$ ions are compatible with the lattice structure. The results are discussed in the light of recent data on the magnetic field dependence of the lattice structure and magnetization of DyVO${}_{3}$ and HoVO${}_{3}$.

Bilayered-structure manganites $\text{Pr}{({\text{Sr}}_{1\ensuremath{-}y}{\text{Ca}}_{y})}_{2}{\text{Mn}}_{2}{\text{O}}_{7}$ show the competing spin-charge-orbital orders; the ground state is the spin CE-type charge-orbital ordered state for $yg0.4$ and the spin-A-type ferroic ${x}^{2}\text{\ensuremath{-}}{y}^{2}$ orbital ordered state for $yl0.4$. For the two representative crystals of $y=0.9$ and $y=0$, we have investigated the optical conductivity and Raman spectra to probe the charge, spin, and lattice dynamics of the respective phases. For $y=0.9$, the charge-orbital ordered states are characterized by strongly activated Raman phonon bands corresponding to the modulated breathing and Jahn-Teller lattice distortions, as observed commonly for other charge-orbital ordered manganites. As the unique features of this bilayered manganite, however, we found that the infrared-active phonon mode can also show up in the Raman spectra in the lower-temperature charge-orbital ordered state, confirming the breaking of centrosymmetry to produce the spontaneous electric polarization. The other feature to be noted is the appearance of the two-magnon excitation band of the CE-type spin order in the Raman spectra which estimates the energy scale of spin exchange energies. For $y=0$, on the other hand, we have observed a charge gap in the optical conductivity spectrum which becomes narrowed with the evolution of the A-type (in-plane ferromagnetic) spin order but remains finite (0.15 eV) at the ground state. The persistence of the charge gap is ascribed to the vertical charge ordering or charge-density wave (CDW) that was previously verified by diffuse x-ray scattering. Such charge-order or CDW formation also activates additional infrared phonon modes at 26 and 35 meV, whose spectral intensity appears to be enhanced by resonance with the underlying electronic continuum.

Heterointerfaces of correlated electron oxides provide a good laboratory to explore novel electronic states induced by the coupling among spin, charge, and orbital degrees of freedom. For the detail understanding of the complex interface states, it is indispensable to elucidate the interface band profiles of correlated electron materials. Here we report the band profiles of $\text{Mott-insulator}/\text{Nb}:{\text{SrTiO}}_{3}$ heterojunctions revealed by optical-spectroscopic and transport measurements. Photocurrent action spectra indicate the existence of the band bending and band discontinuity similar to the rigid-band interface and we construct a band lineup of Mott insulators based on the rigid-band picture. We also estimate the width of the depletion layer in a Mott insulator by investigating thickness dependence of photocurrent amplitude.

The orbital ordering in perovskite-type vanadium oxides, RVO3 (R: rare earth), has been investigated by resonant X-ray scattering (RXS) near the V K-edge energy. The G-type orbital order, C-type orbital order and orbital disorder phases are elucidated on the basis of the azimuthal-angle and polarization dependence of the RXS signal reflecting the orbital ordering.

Almost the industrial robot tasks are performed by the teaching playback method. This method has problem that the laborious and time-consuming online manual teaching is inevitable. Thus, the offline teaching based on the high positioning accuracy is desired. However, a nominal kinematic model does not consider the geometric errors and non-geometric errors. Therefore, some method of calibrating precisely the parameters is required. The kinematic parameters are calibrated by minimizing errors between the measured positions and the predicted ones by nonlinear least square method. After that, the residual errors caused by non-geometric parameters are further reduced by using neural networks.

We have investigated the polarization $\ensuremath{\pi}$-molecular skeleton coupled dynamics for the proton-displacive organic ferroelectrics, cocrystal of phenazine with the 2,5-dihalo-3,6-dihydroxy-p-benzoquinones by measurements of the terahertz/infrared spectroscopy. In the course of the ferroelectric-to-paraelectric transition, the ferroelectric soft phonon mode originating from the intermolecular dynamical displacement is observed in the imaginary part of dielectric spectra ${ϵ}_{2}$, when the electric field of the light $(E)$ is parallel to the spontaneous polarization $(P)$. The soft phonon mode is isolated from the intramolecular vibrational mode and hence the intramolecular skeleton dynamics is almost decoupled from the polarization fluctuation. In the spectra for $E$ parallel to the hydrogen-bonded supramolecular chain, by contrast, the vibrational mode mainly originating from the oxygen atom motion within the $\ensuremath{\pi}$-molecular plane is anomalously blurred and amalgamated into the polarization relaxation mode concomitantly with the dynamical proton disorder. This indicates that the dynamical disorder of the intramolecular skeleton structure, specifically that of oxygen atom, is strongly enhanced by the proton fluctuation and is significantly coupled to the polarization fluctuation along the hydrogen-bonded supramolecular chain. The results are discussed in terms of the proton-mediated anisotropic polarization $\ensuremath{\pi}$-molecular skeleton interaction, which characterizes these emerging proton-displacive ferroelectrics.

We have investigated the optical response resulting from the proton-$\ensuremath{\pi}$-electron-molecular-skeleton coupled dynamics in an organic ferroelectric 55DMBP-Hia. Upon the ferroelectric-to-paraelectric transition, almost all of the vibrational modes below $500\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ are anomalously blurred and amalgamated into the high-frequency tail of the polarization-relaxation mode. This indicates that the constituent molecular shape is no more well defined around ${T}_{C}$ due to the dynamical disorder of the $\ensuremath{\pi}$-conjugated structure originating from proton delocalization on the intermolecular bifurcated hydrogen bond.

The wide range optical spectra on a multiferroic prototype TbMnO3 have been investigated to clarify the origin of spin excitations observed in the far-infrared region. We elucidate the full band structure, whose high energy edge (133 cm;{-1}) exactly corresponds to twice of the highest-lying magnon energy. Thus the origin of this absorption band is clearly assigned to two-magnon excitation driven by the electric field of light. There is an overlap between the two-magnon and phonon energy ranges, where the strong coupling between them is manifested by the frequency shift and transfer of oscillator strength of the phonon mode.

Charge dynamics of $({\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}{)}_{2}{\mathrm{O}}_{3}$ with $x=0--0.06$ has been investigated by measurements of charge transport and optical conductivity spectra in a wide temperature range of 2--600 K with the focus on the thermally and doping induced insulator-metal transitions (IMTs). The optical conductivity peaks for the interband transitions in the $3d$ ${t}_{2g}$ manifold are observed in both the insulating and metallic states, while their large variation (by $\ensuremath{\sim}0.4\text{ }\text{ }\mathrm{eV}$) with change of temperature and doping level scales with that of the Ti-Ti dimer bond length, indicating the weakened singlet bond in the course of IMTs. The thermally and V-doping induced IMTs are driven with the increase in carrier density by band crossing and hold doping, respectively, in contrast with the canonical IMT of correlated oxides accompanied by the whole collapse of the Mott gap.

The doping variation of charge and orbital dynamics in perovskite-type ${\text{Y}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{VO}}_{3}$ $(0\ensuremath{\le}x\ensuremath{\le}0.1)$ is investigated by measurements of the optical conductivity and Raman scattering spectra in comparison to the larger bandwidth system ${\text{La}}_{1\ensuremath{-}x}{\text{Sr}}_{x}{\text{VO}}_{3}$. We also take into consideration the magnitude of the ${\text{GdFeO}}_{3}$-type orthorhombic lattice distortion, which is large and small in ${\text{Y}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{VO}}_{3}$ and ${\text{La}}_{1\ensuremath{-}x}{\text{Sr}}_{x}{\text{VO}}_{3}$, respectively, and discuss its effect on the evolution of charge dynamics. The optical conductivity spectra show that the doped hole is well localized and forms the small polaronlike state. The hole dynamics in ${\text{Y}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{VO}}_{3}$ is nearly isotropic up to the doping level of the orbital order-disorder transition, while that in ${\text{La}}_{1\ensuremath{-}x}{\text{Sr}}_{x}{\text{VO}}_{3}$ is anisotropic in the lightly doped region due to the one-dimensional orbital exchange interaction. The possible origin of the difference in the hole dynamics is discussed in terms of the local lattice distortion, which is induced by the formation of the small polaronlike state and becomes more significant for the reduced one-electron bandwidth. In addition, the optical Mott-gap excitation in the nominally $C$-type spin and $G$-type orbital ordered phase is distinct from that for ${\text{La}}_{1\ensuremath{-}x}{\text{Sr}}_{x}{\text{VO}}_{3}$ in its intensity and spectral shape. This suggests that the orthorhombic lattice distortion enhances the modification of the spin and orbital ordering from the pure $C$ type and $G$ type, respectively. The systematic study of Raman scattering spectra has shown that the dynamic $G$-type spin and $C$-type orbital correlation subsists at low temperatures in the doping induced phase of the nominally $C$-type spin ordering and $G$-type orbital ordering.

The composition-spread epitaxial thin film of Sr1-xCaxRuO3 (0.13≤x≤0.53) was synthesized by the pulsed laser deposition technique and its x-dependent magnetic properties were probed by the magneto-optical (MO) Kerr spectroscopy. The MO spectra in the energy region of the charge-transfer excitation (O 2p to Ru 4d) are observed to change their spectral intensity critically depending on temperature (T) and x while preserving the spectral shape. The contour mapping of the MO intensity in the x–T plane clarifies the continuous ferromagnetic-to-paramagnetic phase change with increase of not only T but also x, revealing the quantum-critical point around x = 0.5.

The critical phase competition between different spin-orbital-ordered states has been investigated for the ${\mathrm{DyVO}}_{3}$ single crystal. As temperature is lowered, the compound exhibits a reentrant spin and orbital ordering (SO and OO) transition: $C\ensuremath{\rightarrow}G\ensuremath{\rightarrow}C$ type for SO and $G\ensuremath{\rightarrow}C\ensuremath{\rightarrow}G$ type for OO. It was found that a magnetic field also drives the phase transition from $C$ to $G$ for OO and concomitantly from $G$ to $C$ for SO, the latter of which is coupled with the metamagnetic transition of the Dy $4f$ moments. The mechanism of this novel magnetic-field-induced orbital switching is discussed.

Perovskite-type transition-metal oxides have a wide variety of physical properties and triggered intensive research on functional devices in the form of heteroepitaxial junctions. However, there is a missing component that is a p-type conventional band semiconductor. LaRhO3 (LRO) is one of very few promising candidates having its bandgap between filled t2g and empty eg of Rh in low-spin state, but there has been no report on the synthesis of large-size single crystals or thin films. Here, we report on the junction properties of single-crystalline thin films of LRO grown on (110) oriented Nb-doped SrTiO3 substrates. The external quantum efficiency of the photo-electron conversion exceeds 1% in the visible-light region due to the wide depletion layer and long diffusion length of minority carriers in LRO. Clear indication of p-type band semiconducting character in a perovskite oxide of LRO will pave a way to explore oxide electronics of perovskite heterostructures.

The variation of anisotropic charge dynamics in the course of a filling-control insulator-metal transition (IMT) in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{VO}}_{3}$ has been investigated by measurements of optical conductivity spectra with the focus on the role of the ${t}_{2g}$-orbital degree of freedom. The orbitally induced anisotropic feature of the Mott-gap excitation as well as of the doping-induced midinfrared excitation is suppressed with increasing $x$, and instead the isotropic and incoherent dynamics of the doped hole dominates over the low-energy excitation near and above the IMT point.