Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid.

The quantum Hall effect in two-dimensional electron gases involves the flow of topologically protected dissipationless charge currents along the edges of a sample. Integer or fractional electrical conductance is associated with edge currents of electrons or quasiparticles with fractional charges, respectively. It has been predicted that quantum Hall phenomena can also be created by edge currents with a fundamentally different origin: the fractionalization of quantum spins. However, such quantization has not yet been observed. Here we report the observation of this type of quantization of the Hall effect in an insulating two-dimensional quantum magnet1, α-RuCl3, with a dominant Kitaev interaction (a bond-dependent Ising-type interaction) on a two-dimensional honeycomb lattice2-7. We find that the application of a magnetic field parallel to the sample destroys long-range magnetic order, leading to a field-induced quantum-spin-liquid ground state with substantial entanglement of local spins8-12. In the low-temperature regime of this state, the two-dimensional thermal Hall conductance reaches a quantum plateau as a function of the applied magnetic field and has a quantization value that is exactly half of the two-dimensional thermal Hall conductance of the integer quantum Hall effect. This half-integer quantization of the thermal Hall conductance in a bulk material is a signature of topologically protected chiral edge currents of charge-neutral Majorana fermions (particles that are their own antiparticles), which have half the degrees of freedom of conventional fermions13-16. These results demonstrate the fractionalization of spins into itinerant Majorana fermions and Z2 fluxes, which is predicted to occur in Kitaev quantum spin liquids1,3. Above a critical magnetic field, the quantization disappears and the thermal Hall conductance goes to zero rapidly, indicating a topological quantum phase transition between the states with and without chiral Majorana edge modes. Emergent Majorana fermions in a quantum magnet are expected to have a great impact on strongly correlated quantum matter, opening up the possibility of topological quantum computing at relatively high temperatures.

Unusual Thermal Hall Effect in a Kitaev Spin Liquid Candidate α-RuCl_{3}.

The Kitaev quantum spin liquid displays the fractionalization of quantum spins into Majorana fermions. The emergent Majorana edge current is predicted to manifest itself in the form of a finite thermal Hall effect, a feature commonly discussed in topological superconductors. Here we report on thermal Hall conductivity κ_{xy} measurements in α-RuCl_{3}, a candidate Kitaev magnet with the two-dimensional honeycomb lattice. In a spin-liquid (Kitaev paramagnetic) state below the temperature characterized by the Kitaev interaction J_{K}/k_{B}∼80 K, positive κ_{xy} develops gradually upon cooling, demonstrating the presence of highly unusual itinerant excitations. Although the zero-temperature property is masked by the magnetic ordering at T_{N}=7 K, the sign, magnitude, and T dependence of κ_{xy}/T at intermediate temperatures follows the predicted trend of the itinerant Majorana excitations.

Quantum-disordered state of magnetic and electric dipoles in an organic Mott system.

Strongly enhanced quantum fluctuations often lead to a rich variety of quantum-disordered states. Developing approaches to enhance quantum fluctuations may open paths to realize even more fascinating quantum states. Here, we demonstrate that a coupling of localized spins with the zero-point motion of hydrogen atoms, that is, proton fluctuations in a hydrogen-bonded organic Mott insulator provides a different class of quantum spin liquids (QSLs). We find that divergent dielectric behavior associated with the approach to hydrogen-bond order is suppressed by the quantum proton fluctuations, resulting in a quantum paraelectric (QPE) state. Furthermore, our thermal-transport measurements reveal that a QSL state with gapless spin excitations rapidly emerges upon entering the QPE state. These findings indicate that the quantum proton fluctuations give rise to a QSL-a quantum-disordered state of magnetic and electric dipoles-through the coupling between the electron and proton degrees of freedom.

Thermal Hall Effect in a Phonon-Glass Ba_{3}CuSb_{2}O_{9}.

A distinct thermal Hall signal is observed in a quantum spin liquid candidate Ba_{3}CuSb_{2}O_{9}. The transverse thermal conductivity shows a power-law temperature dependence below 50 K, where a spin gap opens. We suggest that because of the very low longitudinal thermal conductivity and the thermal Hall signals, a phonon Hall effect is induced by strong phonon scattering of orphan Cu^{2+} spins formed in the random domains of the Cu^{2+}-Sb^{5+} dumbbells in Ba_{3}CuSb_{2}O_{9}.

Interplanar coupling-dependent magnetoresistivity in high-purity layered metals.

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 interlayer coupling disappearing for fields applied along the so-called Yamaji angles where the interlayer 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 (for example, Weyl) fermions. Its observation in PdCoO2, PtCoO2 and Sr2RuO4 suggests that the anomaly affects the transport of clean conductors, in particular near the quantum limit.

Kosterlitz-Thouless-type transition in a charge ordered state of the layered organic conductor α-(BEDT-TTF)2I3.

The current-voltage characteristics in the charge order state of the two-dimensional organic conductor α-(BEDT-TTF)(2)I(3) exhibit power law behavior at low temperatures. The power law is understood in terms of the electric-field-dependent potential between electrons and holes, which are thermally excited from the charge order state. The power law exponent steeply changes from 1 to 3 in the range from 30 to 45 K with decreasing temperature, thereby suggesting the occurrence of a Kosterlitz-Thouless-type transition; many (few) unbound electron-hole pairs are thermally excited above (below) the transition. The effects of the finite size and interlayer coupling on the power law behavior are discussed.

Joint laxity, vitreoretinal degeneration, facial abnormalities, and generalized skeletal alterations: a new syndrome?

A Japanese girl with a hitherto unknown combination of malformations is reported. The cardinal features included hyperextensibility of the joints, vitreoretinal degeneration with cataracts, and facial abnormalities, comprising hypertelorism, prominent eyes, downslanting of the palpebral fissures, mid-face recession with a short nose, deformed auricles, and microretrognathia with a high arched palate. Skeletal survey revealed multiple wormian bones, hypoplastic facial bones and mandible, narrow thorax with wavy ribs, narrow ilia, and coxa valga with slight broadening of the proximal femora, findings of which were individually minor, but the assemblage of which assisted in the syndromic identification. Although skin biopsy did not contribute to the causal clarification, it was tempting to speculate that the syndromic constellation of the present disorder resulted from an underlying defect of connective tissues.

[Ultra-low-dose spiral (helical) CT of the thorax: a filtering technique].

To reduce the radiation dose from spiral (helical) CT, a custom-made aluminium filter was installed in the X-ray tube and a reduction of effective tube current was attempted. A pronounced reduction of effective tube current, namely, 6 and 3 mA, was achieved with 26 and 37 mm thick aluminium filters, respectively. Visualization of normal lung structure was accomplished with both 6 and 3 mA settings. However, images of 3 mA failed to delineate mediastinal structures because of marked beam hardening resulting from the bone structure of the thoracic inlet. Six mA was considered the lowest dose setting of spiral (helical) CT of the thorax that could be used for lung cancer screening.

Inhibition of collagen synthesis in the femur of rats orally administered stannous chloride.

The effect of stannous chloride on bone metabolism was examined in weanling male rats given oral dose of 1.0 mg Sn/kg at 12-h intervals for 28 d. Hydroxyproline content in the femoral diaphysis but not epiphysis was significantly decreased by tin administration for 14 and 28 d, while free proline contents in the femoral diaphysis and epiphysis were not changed significantly. 3H-Hydroxyproline contents in the femoral diaphysis and epiphysis labeled with 3H-proline injection were not significantly altered by tin administration. In vitro collagen synthesis in the femoral epiphysis tissue but not diaphysis was markedly reduced by tin administration between 3 and 14 d, although 3H-proline incorporations into the femoral diaphysis and epiphysis tissues were not changed significantly. On the other hand, in vitro incorporation of 3H-thymidine into the femoral epiphysis but not diaphysis was significantly decreased by tin administration between 7 and 28 d. A significant decrease of DNA content in the femoral epiphysis but not diaphysis was also observed by tin administration for 14 and 28 d. The present study suggests that tin administration causes the inhibition of collagen synthesis prior to the suppression of DNA synthesis in the femoral epiphysis of rats.

Tin decreases femoral calcium independently of calcium homeostasis in rats.

Oral administration of stannous chloride (SnCl2) (1.0 mg Sn2$/kg body weight) to rats, twice daily for 28 days, caused a significant increase in the tin (Sn) content and a corresponding decrease of the calcium (Ca) content in the femoral epiphysis, but was without effect on serum Ca, intestinal Ca absorption, and urinary and fecal Ca excretion. The results indicate that in rats Sn directly inhibits bone formation independently of Ca homeostasis.

Changes in mineral composition and its related enzyme activity in the femur of rats orally administered stannous chloride.

The effect of stannous chloride on bone metabolism was examined in weanling male rats given oral dose of 1.0 mg Sn/kg at 12-h intervals for 28 days. Tin administration produced progressive increase in tin content of the femoral diaphysis and epiphysis. Calcium content in the femoral epiphysis but not diaphysis was significantly decreased by tin administration for 28 days, while inorganic phosphorus contents in the femoral diaphysis and epiphysis were not changed significantly. Acid and alkaline phosphatase activities in the femoral diaphysis and epiphysis were markedly reduced by tin administration for 3 days, and significant decreases in the femoral epiphysis were also observed at 28 days. Meanwhile, ATPase and pyrophosphatase activities in the femoral diaphysis and epiphysis were not altered significantly by tin administration. From the present study, of mineral composition and its related enzyme activity, the decreases of acid and alkaline phosphatase activities in the femoral epiphysis were regarded as the biochemical manifestation of the toxic action of inorganic tin.

Inorganic tin in the diet affects the femur in rats.

The effects of dietary levels (10, 50, 100 and 250 ppm tin) of stannous chloride on the femur were studied for 90 days on weanling male rats. The 100 and 250 ppm tin (Sn) caused significant decreases in serum calcium (Ca) and serum inorganic phosphorus (P), Ca content in the femoral diaphysis and epiphysis, and acid phosphatase activity in the femoral epiphysis. 50 ppm Sn produced significant reduction of serum Ca concentration and Ca content in the femoral epiphysis. These significant decreases were not observed with 10 ppm Sn. These results suggest that the maximal allowable concentration of inorganic Sn contained in a diet would be less than 50 ppm Sn.

Movement of subcellular calcium in bile pool of hepatocyte in rats: effect of thyroparathyroidectomy.

The movement of subcellular calcium in the bile pool of hepatocyte was investigated after a single intraperitoneal administration of calcium chloride in rats. The administration of calcium (4.0 mg/100 g BW) produced a remarkable elevation of serum calcium and a corresponding increase in liver calcium. The calcium taken by the liver cells at 10 min after calcium administration was markedly located into the nuclei, mitochondria and microsomes, and this distribution was not accompanied by a significant elevation in the cytosol level. At 20 min after calcium administration, the calcium increase above the subcellular structure was clearly reduced. On the other hand, serum calcium was markedly increased by calcium administration in both intact and thyroparathyroidectomized rats. However, the liver calcium increase induced in intact rats by calcium administration was much more than that in thyroparathyroidectomized rats. Also, the bile calcium level was markedly elevated in thyroparathyroidectomized rats. The present results suggest that the calcium taken by the liver cells is bound to the nuclei, mitochondria and microsomes, and then transported into the biliary duct.