Large Enhancement of Thermoelectric Efficiency Due to a Pressure-Induced Lifshitz Transition in SnSe.

The Lifshitz transition, a change in Fermi surface topology, is likely to greatly influence exotic correlated phenomena in solids, such as high-temperature superconductivity and complex magnetism. However, since the observation of Fermi surfaces is generally difficult in the strongly correlated systems, a direct link between the Lifshitz transition and quantum phenomena has been elusive so far. Here, we report a marked impact of the pressure-induced Lifshitz transition on thermoelectric performance for SnSe, a promising thermoelectric material without a strong electron correlation. By applying pressure up to 1.6 GPa, we have observed a large enhancement of the thermoelectric power factor by more than 100% over a wide temperature range (10-300 K). Furthermore, the high carrier mobility enables the detection of quantum oscillations of resistivity, revealing the emergence of new Fermi pockets at ∼0.86 GPa. The observed thermoelectric properties linked to the multivalley band structure are quantitatively reproduced by first-principles calculations, providing novel insight into designing the SnSe-related materials for potential valleytronic as well as thermoelectric applications.

Strongly spin-orbit coupled two-dimensional electron gas emerging near the surface of polar semiconductors.

We investigate the two-dimensional highly spin-polarized electron accumulation layers commonly appearing near the surface of n-type polar semiconductors BiTeX (X=I, Br, and Cl) by angular-resolved photoemission spectroscopy. Because of the polarity and the strong spin-orbit interaction built in the bulk atomic configurations, the quantized conduction-band subbands show giant Rashba-type spin splitting. The characteristic 2D confinement effect is clearly observed also in the valence bands down to the binding energy of 4 eV. The X-dependent Rashba spin-orbit coupling is directly estimated from the observed spin-split subbands, which roughly scales with the inverse of the band-gap size in BiTeX.

Giant Rashba-type spin splitting in bulk BiTeI.

There has been increasing interest in phenomena emerging from relativistic electrons in a solid, which have a potential impact on spintronics and magnetoelectrics. One example is the Rashba effect, which lifts the electron-spin degeneracy as a consequence of spin-orbit interaction under broken inversion symmetry. A high-energy-scale Rashba spin splitting is highly desirable for enhancing the coupling between electron spins and electricity relevant for spintronic functions. Here we describe the finding of a huge spin-orbit interaction effect in a polar semiconductor composed of heavy elements, BiTeI, where the bulk carriers are ruled by large Rashba-like spin splitting. The band splitting and its spin polarization obtained by spin- and angle-resolved photoemission spectroscopy are well in accord with relativistic first-principles calculations, confirming that the spin splitting is indeed derived from bulk atomic configurations. Together with the feasibility of carrier-doping control, the giant-Rashba semiconductor BiTeI possesses excellent potential for application to various spin-dependent electronic functions.

Mechanisms of enhanced orbital dia- and paramagnetism: application to the Rashba semiconductor BiTeI.

We study the magnetic susceptibility of a layered semiconductor BiTeI with giant Rashba spin splitting both theoretically and experimentally to explore its orbital magnetism. Apart from the core contributions, a large temperature-dependent diamagnetic susceptibility is observed when the Fermi energy E(F) is near the crossing point of the Rashba spin-split conduction bands at the time-reversal symmetry point A. On the other hand, when E(F) is below this band crossing, the susceptibility turns to be paramagnetic. These features are consistent with first-principles calculations, which also predict an enhanced orbital magnetic susceptibility with both positive and negative signs as a function of E(F) due to band (anti)crossings. Based on these observations, we propose two mechanisms for the enhanced paramagnetic orbital susceptibility.

Enhanced infrared magneto-optical response of the nonmagnetic semiconductor BiTeI driven by bulk Rashba splitting.

We study the magneto-optical (MO) response of the polar semiconductor BiTeI with giant bulk Rashba spin splitting at various carrier densities. Despite being nonmagnetic, the material is found to yield a huge MO activity in the infrared region under moderate magnetic fields (up to 3 T). Our first-principles calculations show that the enhanced MO response of BiTeI comes mainly from the intraband transitions between the Rashba-split bulk conduction bands. These transitions connecting electronic states with opposite spin directions become active due to the presence of strong spin-orbit interaction and give rise to distinct features in the MO spectra with a systematic doping dependence. We predict an even more pronounced enhancement in the low-energy MO response and dc Hall effect near the crossing (Dirac) point of the conduction bands.

Spin-stretching modes in anisotropic magnets: spin-wave excitations in the multiferroic Ba2CoGe2O7.

We studied spin excitations in the magnetically ordered phase of the noncentrosymmetric Ba(2)CoGe(2)O(7) in high magnetic fields up to 33 T. In the electron spin resonance and far infrared absorption spectra we found several spin excitations beyond the two conventional magnon modes expected for such a two-sublattice antiferromagnet. We show that a multiboson spin-wave theory describes these unconventional modes, including spin-stretching modes, characterized by an oscillating magnetic dipole and quadrupole moment. The lack of inversion symmetry allows each mode to become electric dipole active. We expect that the spin-stretching modes can be generally observed in inelastic neutron scattering and light absorption experiments in a broad class of ordered S > 1/2 spin systems with strong single-ion anisotropy and/or noncentrosymmetric lattice structure.

Magnetic-field induced competition of two multiferroic orders in a triangular-lattice helimagnet MnI2.

Magnetic and dielectric properties with varying magnitude and direction of magnetic-field H have been investigated for a triangular-lattice helimagnet MnI_{2}. The in-plane electric polarization P emerges in the proper screw magnetic ground state below 3.5 K, showing the rearrangement of six possible multiferroic domains as controlled by the in-plane H. With every 60° rotation of H around the [001] axis, discontinuous 120° flop of the P vector is observed as a result of the flop of magnetic modulation vector q. With increasing the in-plane H above 3 T, however, the stable q direction changes from q‖(110[ ¯over 0]) to q‖(110), leading to a change of P-flop patterns under rotating H. At the critical field region (∼3 T), due to the phase competition and resultant enhanced q flexibility, the P vector smoothly rotates clockwise twice while the H vector rotates counterclockwise once.

Enhanced directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic Ba2CoGe2O7 oxide compound.

We propose that concurrently magnetic and ferroelectric, i.e., multiferroic, compounds endowed with electrically active magnetic excitations (electromagnons) provide a key to producing large directional dichroism for long wavelengths of light. By exploiting the control of ferroelectric polarization and magnetization in a multiferroic oxide Ba(2)CoGe(2)O(7), we demonstrate the realization of such a directional light-switch function at terahertz frequencies in resonance with the electromagnon absorption. Our results imply that this hidden potential is present in a broad variety of multiferroics.

Optical response of relativistic electrons in the polar BiTeI semiconductor.

The transitions between the spin-split bands by spin-orbit interaction are relevant to many novel phenomena such as the resonant dynamical magnetoelectric effect and the spin Hall effect. We perform optical spectroscopy measurements combined with first-principles calculations to study these transitions in the recently discovered giant bulk Rashba spin-splitting system BiTeI. Several novel features are observed in the optical spectra of the material including a sharp edge singularity due to the reduced dimensionality of the joint density of states and a systematic doping dependence of the intraband transitions between the Rashba-split branches. These confirm the bulk nature of the Rashba-type splitting in BiTeI and manifest the relativistic nature of the electron dynamics in a solid.

Ferroelectricity induced by spin-dependent metal-ligand hybridization in Ba2CoGe2O7.

We have investigated the variation of induced ferroelectric polarization under a magnetic field with various directions and magnitudes in a staggered antiferromagnet Ba2CoGe2O7. While the ferroelectric polarization cannot be explained by the well-accepted spin current model nor the exchange striction mechanism, we have shown that it is induced by the spin-dependent p-d hybridization between the transition metal (Co) and ligand (O) via the spin-orbit interaction. On the basis of the correspondence between the direction of electric polarization and the magnetic state, we have also demonstrated the electrical control of the magnetization direction.

Magnetic digital flop of ferroelectric domain with fixed spin chirality in a triangular lattice helimagnet.

The ferroelectric properties in a magnetic field (H) of varying magnitude and direction have been investigated for the triangular-lattice helimagnet CuFe(1-x)Ga(x)O(2) (x = 0.035). The in-plane H was found to induce the rearrangement of six possible multiferroic domains. Upon every 60 degrees rotation of in-plane H around the c axis, a unique 120 degrees flop of electric polarization occurs as a result of the switch of the helical magnetic q vector. The chirality of the spin helix is always conserved upon the q flop. The possible origin is discussed in light of the stable structure of the multiferroic domain wall.

Electric-field switching of a magnetic propagation vector in a helimagnet.

We report novel magnetoelectric properties of a quantum-spin helimagnet Ba2CuGe2O7 with a noncentrosymmetric (but nonpolar) crystal structure. It was found that the spin helicity of the cycloidal spin order is always fixed to the lattice, therefore the magnetic propagation vector k determines the sign of electric polarization in Ba2CuGe2O7. Consequently, not only the magnetic-field drive of the ferroelectric domain but also the electric-field switching of magnetic k vector can be achieved.

The relationship between amniotic fluid macrophage colony-stimulating factor and fetal growth.

The aim of this study was to clarify whether amniotic fluid macrophage colony-stimulating factor (M-CSF) is related to placental development and fetal growth. Maternal serum and amniotic fluid M-CSF levels were analyzed in 22 pregnant women (seven intrauterine growth retardation (IUGR) complicated and 15 normal pregnancies) at 33-40 weeks' gestation. Amniotic fluid was obtained by transabdominal amniocentesis performed under ultrasonographic guidance. The mean amniotic fluid M-CSF level of the IUGR-complicated pregnancy group (5.0 +/- 1.4 ng/ml) was significantly lower (P < 0.05) than that of the normal pregnancy group (7.4 +/- 1.6 ng/ml). All the IUGR-complicated pregnant women subsequently delivered small-for-gestational-age (SGA) infants with significantly lower placental weights than those of the normal infants. There was no significant correlation between amniotic fluid M-CSF levels and gestational age in the normal pregnancy group. The same scattergram showed the amniotic fluid M-CSF levels of the IUGR-complicated pregnancy group tended to be lower than those of the normal pregnancy group at 33-40 weeks' gestation. The results suggested that amniotic fluid M-CSF was one of the regulators of human placental development and was related to fetal growth.

Evaluation of threatened preterm delivery by transvaginal ultrasonographic measurement of cervical length.

OBJECTIVE: To establish a nomogram for the length of the uterocervical canal and to determine whether this can be used to predict preterm delivery. METHODS: Cervical length was measured by transvaginal ultrasonography in 32 women (21 primigravid, 11 multigravid) with threatened preterm delivery, and in 177 normal singleton pregnancies between 18-37 weeks' gestation. Regression analysis was used to create the nomogram. Student t test was used to compare the groups. RESULTS: A linear relationship was found between cervical length and gestational age (r = -0.4, P < .001). Comparison of cervical length on admission in the patients with threatened preterm delivery showed that 11 preterm deliveries occurred in women who had a mean cervical length of 23.2 mm (range 17-29), whereas 21 term deliveries occurred in women with a mean cervical length of 31.7 mm (range 21-42). The difference was significant (P < .001). A cervical length of less than 20 mm on admission had a positive predictive value of 100%. These patients had preterm delivery despite tocolytic therapy during hospitalization. CONCLUSION: The risk of preterm delivery is high in women whose cervical length on admission is less than 30 mm, and strict management is required for those with a cervical length of less than 20 mm.

Prednisolone plus low-dose aspirin improves the implantation rate in women with autoimmune conditions who are undergoing in vitro fertilization.

OBJECTIVE: To evaluate the effect of prednisolone plus low-dose aspirin (PSL/LDA) in women with autoimmune conditions who were enrolled in an IVF-ET program. DESIGN: A retrospective clinical study. SETTING: In vitro fertilization unit, Niigata University Hospital, Niigata, Japan. PATIENT(S): Three hundred seven women who underwent IVF-ET between January 1996 and December 1997. INTERVENTION(S): Prednisolone (10 mg/d) and aspirin (81 mg/d) were administered to the women with autoantibodies who chose to participate. MAIN OUTCOME MEASURE(S): Pregnancy and implantation rates with IVF-ET. RESULT(S): Women undergoing IVF who had positive antinuclear antibodies, with or without antiphospholipid antibodies, had significantly lower pregnancy and implantation rates than did women without autoantibodies (14.8% versus 21.7% and 6.8% versus 10.4%, respectively). The administration of PSL/LDA to women with antinuclear antibodies significantly improved the outcome of IVF-ET (40.6% pregnancy rate and 20.3% implantation rate). CONCLUSION(S): A high proportion of women who are undergoing IVF-ET have autoantibodies, which are associated with poor IVF outcomes. The administration of PSL/LDA to these women may improve their implantation rate.

Effect of troglitazone on endocrine and ovulatory performance in women with insulin resistance-related polycystic ovary syndrome.

OBJECTIVE: To investigate the effect of troglitazone, a new antidiabetic agent that improves insulin resistance, on endocrine, metabolic, and ovulatory performance in women with insulin resistance-related polycystic ovary syndrome (PCOS). DESIGN: Prospective clinical study. SETTING: Infertility outpatient clinic, Niigata University Hospital, Niigata, Japan. PATIENT(S): Thirteen women with PCOS and insulin resistance. INTERVENTION(S): Troglitazone (400 mg/d) was administered for 12 weeks. MAIN OUTCOME MEASURE(S): Insulin and other hormone (gonadotropins, androgens) levels; various parameters relating to glucose and lipid metabolism before, during, and after troglitazone administration; and ovulation rate. RESULT(S): The mean (+/-SD) fasting insulin concentration was significantly reduced, from 18.3+/-8.9 to 10.5+/-7.1 microU/mL. The LH level was reduced from 9.7+/-3.4 to 4.8+/-3.9 mIU/mL and the testosterone level was reduced from 0.9+/-0.5 to 0.5+/-0.3 ng/mL in accordance. Atherosclerotic lipid levels also were normalized. Before troglitazone administration, the ovulation rate during clomiphene citrate therapy was 34.9% per cycle (15/43). This increased significantly to 72.7% (8/11) during troglitazone coadministration. Further, an ovulation rate of 42.3% (11/26) was achieved with troglitazone alone. CONCLUSION(S): In women with PCOS and insulin resistance, the reduction of hyperinsulinemia that is produced by troglitazone improves the hyperandrogenism that characterizes PCOS, restoring ovulation.

Surgical treatment of cervical spondylotic myelopathy complicating athetoid cerebral palsy.

Operative treatment was performed in nine patients with cervical spondylotic myelopathy complicating athetoid cerebral palsy. The first two patients were treated by laminectomy, and the other seven by anterior interbody fusion. The symptoms in both the laminectomy patients improved after operation, but became worse again when cervical instability developed; they then had to have an anterior fusion in addition. In six of the seven patients who had primary anterior fusion a halo-cast (or a halo-vest) was used to keep the cervical spine immobile, and good bony fusion was obtained with satisfactory results. However, in one patient no halo apparatus was used, bony union did not occur and the radiculopathy reappeared. In cervical myelopathy complicating athetoid cerebral palsy laminectomy is contra-indicated; anterior fusion combined with a halo apparatus is, however, satisfactory.

Polycystic ovary syndrome. Insulin resistance and ovulatory responses to clomiphene citrate.

OBJECTIVE: To evaluate insulin secretion detected on oral glucose tolerance testing in relation to clomiphene citrate (CC) responses in women with polycystic ovary syndrome (PCOS). STUDY DESIGN: A total of 37 PCOS women were enrolled. Plasma baseline levels of gonadotropins, sex hormone binding globulin, androstenedione, dehydroepiandrosterone sulfate and testosterone (T) were determined. Insulin and glucose serum concentrations were analyzed in all samples after a 75-g oral glucose tolerance test. A dose of 100 mg/d of CC was given for ovulation induction. Ovulation was detected by ultrasonographic observation in conjunction with a serum progesterone level. RESULTS: During three consecutive cycles of CC administration, two or more anovulatory cycles were observed in 12 of 37 PCOS women (defined as CC nonresponders). The serum T level and the area under the curve (AUC) of insulin were significantly higher in CC nonresponders. The receiver operating characteristic curve of the AUC of insulin provided the most appropriate cutoff point for the prediction of CC resistance. CONCLUSION: We found higher androgen secretion and insulin resistance in CC nonresponders. The AUC of insulin was the most reliable method for the prediction of CC resistance associated with insulin resistance.

[University education in geriatrics: medical students' understandings of gerontology and geriatric medicine].

With the rapid aging of Japan's population, medical professionals who specialize in geriatric medicine are in unprecedented demand. To meet that demand and to improve the curriculum for teaching geriatric medicine and gerontology in Japan, we surveyed medical students' understandings of these specialties. Students at 14 schools with classes in geriatric medicine and gerontology were surveyed. A questionnaire was sent to sixth-year medical students after their classes had ended. Questionnaires were collected from 849 students (60.1%) at ten medical schools (74.1%). One quarter (24.5%) of the students were satisfied with the contents of the classes in geriatric medicine and gerontology taught in their school, whereas 39.4% were not. These specialties encompass many fields of clinical and basic medicine, and many students found the lectures difficult to understand (41.4%). Inter-school comparisons of the results showed that students' strengths and weaknesses in the various areas of geriatric medicine reflected differences in the contents of the classes among the schools. Only 35.4% of students had ever visited hospitals or other health-related facilities for the elderly. Many students (58.8%) had never lived with elderly people. Most students (63.9%) wanted visits to health-care facilities for the elderly to be included in their regular curriculum. Medical students are conscious of the medical implications of the ageing of Japan's population; 13.2% had volunteered to work with the elderly.

One-way transparency of four-coloured spin-wave excitations in multiferroic materials.

The coupling between spins and electric dipoles governs magnetoelectric phenomena in multiferroics. The dynamical magnetoelectric effect, which is an inherent attribute of the spin excitations in multiferroics, drastically changes the optical properties of these compounds compared with conventional materials where light-matter interaction is expressed only by the dielectric permittivity or magnetic permeability. Here we show via polarized terahertz spectroscopy studies on multiferroic Ca2CoSi2O7, Sr2CoSi2O7 and Ba2CoGe2O7 that such magnetoeletric spin excitations exhibit quadrochroism, that is, they have different colours for all the four combinations of the two propagation directions (forward or backward) and the two orthogonal polarizations of a light beam. We demonstrate that one-way transparency can be realized for spin-wave excitations with sufficiently strong optical magnetoelectric effect. Furthermore, the transparent and absorbing directions of light propagation can be reversed by external magnetic fields. This magnetically controlled optical-diode function of magnetoelectric multiferroics may open a new horizon in photonics.