Signatures of a magnetic field-induced unconventional nematic liquid in the frustrated and anisotropic spin-chain cuprate LiCuSbO4

Modern theories of quantum magnetism predict exotic multipolar states in weakly interacting strongly frustrated spin-1/2 Heisenberg chains with ferromagnetic nearest neighbor (NN) inchain exchange in high magnetic fields. Experimentally these states remained elusive so far. Here we report strong indications of a magnetic field-induced nematic liquid arising above a field of ~13 T in the edge-sharing chain cuprate LiSbCuO4 ≡ LiCuSbO4. This interpretation is based on the observation of a field induced spin-gap in the measurements of the 7Li NMR spin relaxation rate T1−1 as well as a contrasting field-dependent power-law behavior of T1−1 vs. T and is further supported by static magnetization and ESR data. An underlying theoretical microscopic approach favoring a nematic scenario is based essentially on the NN XYZ exchange anisotropy within a model for frustrated spin-1/2 chains and is investigated by the DMRG technique. The employed exchange parameters are justified qualitatively by electronic structure calculations for LiCuSbO4

Different channel properties of Torpedo acetylcholine receptor monomers and dimers reconstituted in planar membranes.

It is demonstrated that the monomeric and dimeric structures of the nicotinic acetylcholine receptor of Torpedo californica electric tissue, reconstituted in planar lipid bilayers, are functionally different. The native dimer D of Mr 500,000 (heavy-form) exhibits a "single" channel conductance about twice as large as that of the monomer M of Mr 250,000 (light form). Under conditions where monomers aggregate, the conductance changes from the level of the monomer M to that of dimers M2. The dimer conductances (D and M2) seem to result from synchronous opening and closing of the two channels in the dimer, giving the impression of "single channel" activity. This channel cooperativity is apparently mediated by noncovalent interactions between the two monomers, since it requires no disulfide linkage between monomers. Both the monomers M and the dimers D and M2 show at least one substate of lower conductivity. The relative population of the two conductance levels depends on the ion type (Na+ and K+), indicating ion-specific channel states. Since the channel conductance of isolated dimers resembles those obtained from unextracted microsacs, the dimer with two synchronized channels appears to be the in vivo predominant gating unit. In the linear association of dimers, observed in the native membrane, channel synchronization may extend to more than two channels as suggested by oligomeric channel cooperativity in associations of monomers and dimers

Elemental carbon as catalytic material: Recent trends and perspectives

Elemental carbon plays a role in catalysis in several modifications which are based upon the sp2 connectivity. Supports for catalytic materials, catalysts in its own right and carbonaceous deposits can be understood in their reactivity by applying the concept of chemical anisotropy. The paper will introduce this concept and describe several case studies in which carbon of different anisotropy will be investigated. The spectrum of defined carbon materials available for such studies has increased considerably in the last years with the advent of nanocarbons characterised by the incorporation of non-six-membered carbon rings (NSMCR) into the planar graphene network causing bending of the carbon sheets. Catalytic test reactions used in this work are the selective oxidation of methanol, the decomposition of NO and the hydrogenation of CO. Metals supported in a geometrically defined way are copper and ruthenium. Methods of investigation are photoemission (UPS) and photoabsorption (XAS) spectroscopies, electron microscopy (TEM), X-ray diffraction (XRD), temperature-programmed desorption (TPD) and temperature-programmed reaction spectroscopy (TPRS)

Downscaling Effect on the Superconductivity of P₃Bi₂X₂ (X = S or Se) Nanoparticles Prepared by Microwave-Assisted Polyol Synthesis

Pd3Bi2S2 and Pd3Bi2Se2 have been successfully prepared in the form of nanoparticles with diameters of similar to 50 run by microwave-assisted modified polyol synthesis at low temperatures. The composition and morphology of the samples have been studied by means of powder X-ray diffraction as well as electron microscopy methods, including X-ray intensity mapping on the nanoscale. Superconducting properties of the as-prepared samples have been characterized by electrical resistivity measurements down to low temperatures (similar to 0.2 K). Deviations from the bulk metallic behavior originating from the sub micrometer nature of the samples were registered for both phases. A significant critical-field enhancement up to 1.4 T, i.e., 4 times higher than the value of the bulk material, has been revealed for Pd3Bi2Se2. At the same time, the critical temperature is suppressed to 0.7 K from the bulk value of similar to 1 K. A superconducting transition at 0.4 K has been observed in nanocrystalline Pd3Bi2S2. Here, a zero-temperature upper critical field of similar to 0.5 T has been estimated. Further, spark plasma-sintered Pd3Bi2S2 and Pd3Bi2Se2 samples have been investigated. Their superconducting properties are found to lie between those of the bulk and nanosized samples

Signatures of a magnetic field-induced unconventional nematic liquid in the frustrated and anisotropic spin-chain cuprate LiCuSbO₄

Modern theories of quantum magnetism predict exotic multipolar states in weakly interacting strongly frustrated spin-1/2 Heisenberg chains with ferromagnetic nearest neighbor (NN) inchain exchange in high magnetic fields. Experimentally these states remained elusive so far. Here we report strong indications of a magnetic field-induced nematic liquid arising above a field of similar to 13 T in the edge-sharing chain cuprate LiSbCuO4 = LiCuSbO4. This interpretation is based on the observation of a field induced spin-gap in the measurements of the Li-7 NMR spin relaxation rate T-1(-1) as well as a contrasting field-dependent power-law behavior of T-1(-1) vs. T and is further supported by static magnetization and ESR data. An underlying theoretical microscopic approach favoring a nematic scenario is based essentially on the NN XYZ exchange anisotropy within a model for frustrated spin-1/2 chains and is investigated by the DMRG technique. The employed exchange parameters are justified qualitatively by electronic structure calculations for LiCuSbO4