Spin-Orbital Liquid on a Triangular Lattice

Using Lanczos exact diagonalization of finite clusters we demonstrate that the spin-orbital $d^1$ model for triply degenerate $t_{2g}$ orbitals on a triangular lattice provides an example of a spin-orbital liquid ground state. We also show that the spin-orbital liquid involves entangled valence bond states which violate the Goodenough-Kanamori rules, and modify effective spin exchange constants.Comment: 4 pages, 2 figures, presented at Euroconference Physics of Magnetism 201

Design of the Production Technology of the Inner Square of the Casting

Bakalářská práce pojednává o návrhu technologie opracování čtyřhranného otvoru v odlitku. V úvodu jsou představeny různé možné technologie vhodné pro zhotovení čtyř-hranného otvoru. Pro vybraný díl byl zvolen optimální technologický postup opracování včetně doporučení vhodných strojů a nástrojů. Následně byl zpracován technologický postup uzpůsobený pro vybranou technologii výroby. V závěru byla provedena analýza výrobních nákladů možných technologií zhotovení čtyřhranného otvoru.Bachelor thesis is about the design proposal of the technology of processing square bore in a cast. In the introduction part different usable technologies for making the bore are introduced. For the chosen part the optimal technological process was chosen including the recommendation of suitable machines and tools. After that the technological process adapted for the used technology is depicted. In the conclusion the analysis of production costs of technologies suitable for making the square bore was conducted.346 - Katedra obrábění, montáže a strojírenské metrologiedobř

The origin of strong correlations and superconductivity in Nax_xCoO2_2

We propose a minimal model resolving a puzzle of enigmatic correlations observed in sodium-rich Na$_x$CoO$_2$ where one expects a simple, free motion of the dilute $S=1/2$ holes doped into a band insulator NaCoO$_2$. The model also predicts singlet superconductivity at experimentally observed compositions. The model is based on a key property of cobalt oxides -- the spin-state quasidegeneracy of CoO$_6$ octahedral complex -- leading to an unusual physics of, {\it e.g.}, LaCoO$_3$. We show that correlated hopping between $t_{2g}$ and $e_g$ states leads to the spin-polaron physics at $x\sim 1$, and to an extended s-wave pairing at larger doping when coherent fermionic bands are formed.Comment: 7 pages, 6 figures, extended version as published in PR

Spin polaron theory for the photoemission spectra of layered cobaltates

Recently, strong reduction of the quasiparticle peaks and pronounced incoherent structures have been observed in the photoemission spectra of layered cobaltates. Surprisingly, these many-body effects are found to increase near the band insulator regime. We explain these unexpected observations in terms of a novel spin-polaron model for CoO_2 planes which is based on a fact of the spin-state quasidegeneracy of Co^{3+} ions in oxides. Scattering of the photoholes on spin-state fluctuations suppresses their coherent motion. The observed ``peak-dip-hump'' type lineshapes are well reproduced by the theory.Comment: 4 pages, 4 figure