Nonpropagation of massive mode on AdS<Subscript>2</Subscript> in topologically massive gravity

Making use of Achucarro–Ortiz (AO) type of dimensional reduction, we study the topologically massive gravity with a negative cosmological constant on AdS₂ spacetimes. For a constant dilaton, this two-dimensional model also admits three AdS₂ vacuum solutions, which are related to two AdS₃ and warped AdS₃ backgrounds with an identification upon uplifting three dimensions. We carry out the perturbation analysis around these backgrounds to find what is a physically propagating field. However, it turns out that there is no propagating massive mode on AdS₂ background, in contrast to the Kaluza–Klein (KK) type of dimensional reduction. We note that two dimensionally reduced actions are different and thus, the non-equivalence of their on-shell amplitudes is obtained.     

Quasi-one-dimensional quantum spin liquid in the Cu(C<Subscript>4</Subscript>H<Subscript>4</Subscript>N<Subscript>2</Subscript>)(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> insulator

We analyze measurements of the magnetization, differential susceptibility and specific heat of quasi-onedimensional insulator Cu(C₄H₄N₂)(NO₃)₂ (CuPzN) subjected to magnetic fields. We show that the thermodynamic properties are defined by quantum spin liquid formed with spinons, with the magnetic field tuning the insulator CuPzN towards quantum critical point related to fermion condensation quantum phase transition (FCQPT) at which the spinon effective mass diverges kinematically. We show that the FCQPT concept permits to reveal and explain the scaling behavior of thermodynamic characteristics. For the first time, we construct the schematic T–H (temperature-magnetic field) phase diagram of CuPzN that contains Landau–Fermi-liquid, crossover and non-Fermi liquid parts, thus resembling that of heavy-fermion compounds.     

Shear-induced low-dimension electron transport in (LaMnO<Subscript>3</Subscript>)<Subscript>2</Subscript>/(SrMnO<Subscript>3</Subscript>)<Subscript>2</Subscript> superlattice

Effects of a mechanical shear on the electron transport properties of a (LaMnO₃)₂/(SrMnO₃)₂ superlattice are investigated using first-principle DFT calculations. While the unstrained superlattice is a 3-D conducting half metal, application of a pyramidal shear transforms it into a non-spin-polarized conductor. Depending on whether the out-of-plane component of the shear is tensile or compressive the conductivity is 1-D out-of-plane or 2-D in-plane. The shear-induced low-dimensional conductivity is also associated with the FM-AFM transition.     

Models of spin structures in Sr<Subscript>2</Subscript>RuO<Subscript>4</Subscript>

The mean-field method is used to calculate the bands, Fermi surfaces, and spin susceptibilities of a three-band model of the RuO₄ plane of Sr₂RuO₄ rutinate for states with different spin structures. In particular, the spiral state is studied with the “incommensurate” vector Q=2π(1/3, 1/3) corresponding to the nesting of bands with the population n=4. This state proves to be the lowest with respect to energy among other (paramagnetic, ferromagnetic, antiferromagnetic, and periodic) solutions. In the spiral state, in addition to the main α, β, and γ sheets of the Fermi surface, shadow Fermi boundaries along the Γ(0, 0)-M(π, 0) line (previously observed in the ARPES experiments) are revealed and explained. This may change the interpretation of the data on dispersionless peaks in photoemission, previously ascribed to surface states. The spin susceptibilities of the spiral state exhibit peaks in the dependence Im?(q, ω) at q=Q in accordance with the observed magnetic peak in neutron scattering. The hypothesis of the presence of spin structures with q=Q in the normal state of Sr₂RuO₄ and the methods of checking this hypothesis are discussed.     

State of spin glass in SmFeTi<Subscript>2</Subscript>O<Subscript>7</Subscript>

The SmFeTi₂O₇ compound has been synthesized using the solid-phase reaction method. In order to determine the magnetic state, X-ray structural, Mössbauer, calorimetric, and magnetic measurements have been performed. The state of spin glass with the freezing point T _f = 7 K has been found for SmFeTi₂O₇.     

Thermodynamic properties and structure of oxyfluorides Rb<Subscript>2</Subscript>KMoO<Subscript>3</Subscript>F<Subscript>3</Subscript> and K<Subscript>2</Subscript>NaMoO<Subscript>3</Subscript>F<Subscript>3</Subscript>

According to the results of calorimetric and structural studies, the Fm{ie1202-1}m phase in K₂NaMoO₃F₃ remains stable at least to 100 K. No ferroelectric transformation assumed earlier has been revealed in a series of Rb₂KMoO₃F₃ samples prepared using various technologies. Only a phase transition of nonferroelectric origin has been observed near 195 K, and its thermodynamic characteristics have been determined. An analysis of the stability of the cubic structure of molybdenum fluorine-oxygen elpasolites-cryolites has been performed in the framework of the hypothesis on strengths of interatomic bonds. The barocaloric effect in Rb₂KMoO₃F₃ has been estimated.     

Methane sensor based on SnO<Subscript>2</Subscript>/In<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanostructure

Two sets of samples of SnO₂/In₂O₃/TiO₂ system have been fabricated with different concentrations of component materials. In the first set TiO₂ with rutile structure was used, while in the second set it has the structure of anatase. Thin films (up to 50 nm) of obtained mixtures were deposited. Their sensitivity and selectivity with respect to methane (CH4) were studied. Nanostructure on the basis of 70%SnO₂ — 10%In₂O₃ — 20%TiO₂(anatase) exhibits sufficient sensitivity to methane.     

Photoaccumulating film systems based on TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript>:V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoheterostructures

The thin-film photocatalysts TiO₂/MoO₃ and TiO₂/MoO₃:V₂O₅ obtained by a combination of sol–gel and sintering techniques were studied using the photooxidation of probing dyes, EPR spectroscopy, X-ray diffraction analysis, and electron microscopy. It was shown that due to charge accumulation caused by UV irradiation, these photocatalysts retain their oxidative activity and ability for self-sterilization in the dark for a long time after irradiation was terminated (up to 5 h for TiO₂/MoO₃:V₂O₅).     

Methods for spin injection managing in inGaAs/GaAs/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CoPt spin light-emitting diodes

Spin injection in CoPt/Al₂O₃/(Al)GaAs spin light-emitting diodes (SLEDs) was studied. The oscillations of the degree of circular polarization upon variation of a distance between the active region of the SLED and a CoPt ferromagnetic injector were observed. The oscillations depend neither on a SLED material (GaAs or AlGaAs), nor on the type of injected spin-polarized carriers (electrons and holes) and are related to the action of a perpendicular magnetic field on the injected spin-polarized carriers that causes their precession. During the transfer to the active region through a distance of 50–100 nm from the injector, a z–component of a spin changes a phase that is detected experimentally as the change in sign of the degree of circular polarization of luminescence. Conceivably, a source of the internal magnetic field leading to spin precession is the magnetic field of the nonuniformly magnetized CoPt contact.     

Optical functions of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript> solid solutions in the range of plasmon excitation and interband transitions

The most narrow sub-Doppler frequency resonances in the linear absorption of monochromatic radiation that propagates in the normal direction through a cell containing a layer of rarefied gas medium with a thickness smaller than or on the order of the wavelength of this radiation are theoretically studied. The calculation is performed using as an example a three-dimensional gas cell shaped like a rectangular parallelepiped. It is shown that the width and amplitude of considered sub-Doppler resonances (in the vicinity of centers of rather weak quantum transitions) significantly depend on the transit relaxation of atomic particles, which is determined by their transit times through the irradiated region of the cell both in longitudinal and in transverse directions. The restrictions of the approximation of the planar one-dimensional cell that was previously used in such calculations are determined. Possible applications of linear absorption resonances in ultrathin (nanometer) gas cells as references for optical frequency standards are discussed.