Three-sublattice ordering of the SU(3) Heisenberg model of three-flavor fermions on the square and cubic lattices

Combining a semi-classical analysis with exact diagonalizations, we show that the ground state of the SU(3) Heisenberg model on the square lattice develops three-sublattice long-range order. This surprising pattern for a bipartite lattice with only nearest-neighbor interactions is shown to be the consequence of a subtle quantum order-by-disorder mechanism. By contrast, thermal fluctuations favor two-sublattice configurations via entropic selection. These results are shown to extend to the cubic lattice, and experimental implications for the Mott-insulating states of three-flavor fermionic atoms in optical lattices are discussed.Comment: 4 pages, 3 figures, minor changes, references adde

Quantum State Transfer in Spin-1 Chains

We study the transfer of quantum information through a Heisenberg spin-1 chain prepared in its ground state. We measure the efficiency of such a quantum channel {\em via} the fidelity of retrieving an arbitrarily prepared state and {\em via} the transfer of quantum entanglement. The Heisenberg spin-1 chain has a very rich quantum phase diagram. We show that the phase boundaries are reflected in sharp variations of the transfer efficiency. In the vicinity of the border between the dimer and the ferromagnetic phase (in the conjectured spin-nematic region), we find strong indications for a qualitative change of the excitation spectrum. Moreover, we identify two regions of the phase diagram which give rise to particularly high transfer efficiency; the channel might be non-classical even for chains of arbitrary length, in contrast to spin-1/2 chains.Comment: 4 pages, 4 figures, published versio

Exact models for trimerization and tetramerization in spin chains

We present exact models for an antiferromagnetic S=1 spin chain describing trimerization as well as for an antiferromagnetic S=3/2 spin chain describing tetramerization. These models can be seen as generalizations of the Majumdar-Ghosh model. For both models, we provide a local Hamiltonian and its exact three- or four-fold degenerate ground state wavefunctions, respectively. We numerically confirm the validity of both models using exact diagonalization and discuss the low lying excitations.Comment: 7 pages, 8 figure

Centipede ladder at quarter filling

We study the ground state and excitation spectrum of a quasi one-dimensional nanostructure consisting of a pole and rungs oriented in the opposite directions ("centipede ladder", CL) at quarter filling. The spin and charge excitation spectra are found in the limits of small and large longitudinal hopping $t_\|$ compared to the on-rung hopping rate $t_\perp$ and exchange coupling $I_\perp$. At small $t_\|$ the system with ferromagnetic on-rung exchange demonstrates instability against dimerization. Coherent propagation of charge transfer excitons is possible in this limit. At large $t_\|$ CL behaves like two-orbital Hubbard chain, but the gap opens in the charge excitation spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations are always gapless and their dispersion changes from quadratic magnon-like for ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic on-rung exchange in weak longitudinal hopping limit.Comment: 10 pages, 7 eps figure

Application of Nanoparticles with the Structure of the Metal Nucleus - Carbon Enclosure in Biology and Medicine

The study was carried out with the financial support of the Russian Foundation for Basic Research in the framework of the research project No. 18-33-00785

Symmetry breaking in low-dimensional SU(N) antiferromagnets

Consequences of explicit symmetry breaking in a physically motivated model of SU(N) antiferromagnet in spatial dimensions one and two are studied. It is shown that the case N=3, which can be realized in spin-1 cold atom systems, displays special properties distinctly different from those for N>=4. Qualitative form of the phase diagram depending on the model parameters is given.Comment: 10 pages, 2 figures; added references, corrected fig.2; the final version to appear in PR

Concerning Order and Disorder in the Ensemble of Cu-O Chain Fragments in Oxygen Deficient Planes of Y-Ba-Cu-O

In connection with numerous X-ray and neutron investigations of some high temperature superconductors (YBa$_2$Cu$_3$O$_{6+x}$ and related compounds) a non-trivial part of the structure factor, coming from partly disordered Cu-O-$\dots$-O-Cu chain fragments, situated within basal planes, CuO$_x$, can be a subject of theoretical interest. Closely connected to such a diffusive part of the structure factor are the correlation lengths, which are also available in neutron and X-ray diffraction studies and depend on a degree of oxygen disorder in a basal plane. The quantitative measure of such a disorder can be associated with temperature of a sample anneal, $T_q$, at which oxygen in a basal plane remains frozen-in high temperature equilibrium after a fast quench of a sample to room or lower temperature. The structure factor evolution with $x$ is vizualized in figures after the numerical calculations. The theoretical approach employed in the paper has been developed for the orthorhombic state of YBCO.Comment: Revtex, 27 pages, 14 PostScript figures upon request, ITP/GU/94/0

Physical properties of fluorides barium and calcium nanopowders produced by the pulsed electron beam evaporation method

The mesoporous nanocrystal powders BaF 2 and CaF 2 with a specific surface up to 34.8 and 88.7 sq.m/g, respectively, are produced by the pulsed electron beam evaporation method in vacuum. The influence of thermal annealing of nanoparticles on air in the range of temperature from 200 to 900°C on the size, morphology of particles and change of their magnetic and luminescent properties investigated have been investigared. The essential stoichiometric impurity (overage of metals) and significant growth in a specific surface of nanopowders (NP) BaF 2 and CaF 2 after annealing at the temperature of 200°C have been detected. It is established that the synthesized NP BaF 2 is a paramagnetic while initial material in the bulk state is diamagnetic. After annealing at 900°C appears the small ferromagnetic contribution at NP BaF 2 . Produced NP CaF 2 showed ferromagnetic behavior. In literature there is no information about the ferromagnetism of CaF 2 . Appearance of the ferromagnetic response can be explained with formation of structural and radiation defects (F-centers, etc.). The analysis of PCL and magnetization curves of samples BaF 2 and CaF 2 allows drawing conclusions about their connection. © Published under licence by IOP Publishing Ltd.The authors are grateful to Pryanichnikov S.V., a researcher of the shared equipment center “Ural” of the Institute of Metallurgy of the Ural division of RAS, for the X-ray phase analysis; to the researchers of the Institute of Electrophysics of the Ural division of RAS Demina T.M. for the texture analysis, Murzakayev A.M. and Timashenkova O.R. for the microscopic analysis, Spirina A.V. for the PCL analysis. This work has been carried out within the scope of government order No. 0389-2015-0026 and with partial support of RFBR project No. 18-08-00514. The magnetic measurements were carried out within the scope of government order under the topic MAGNIT, state registration No. AAAA-A18-118020290129-5