14,613 research outputs found
Orbital-Peierls State in NaTiSi2O6
Does the quasi one-dimensional titanium pyroxene NaTiSi2O6 exhibit the novel
{\it orbital-Peierls} state? We calculate its groundstate properties by three
methods: Monte Carlo simulations, a spin-orbital decoupling scheme and a
mapping onto a classical model. The results show univocally that for the spin
and orbital ordering to occur at the same temperature --an experimental
observation-- the crystal field needs to be small and the orbitals are active.
We also find that quantum fluctuations in the spin-orbital sector drive the
transition, explaining why canonical bandstructure methods fail to find it. The
conclusion that NaTiSi2O6 shows an orbital-Peierls transition is therefore
inevitable.Comment: 4 pages, 3 figure
The right to justification : Recensie van: Rainer Forst (2007) Das Recht auf Rechtfertigung. Elemente einer konstruktivistischer Theorie der Gerechtigkeit. Frankfurt am Main: Suhrkamp, 413 pp.
Rezension von: Rainer Forst (2007) Das Recht auf Rechtfertigung. Elemente einer konstruktivistischer Theorie der Gerechtigkeit. Frankfurt am Main: Suhrkamp, 413 pp
Spontaneous Symmetry Breaking and Decoherence in Superconductors
We show that superconductors have a thin spectrum associated with spontaneous
symmetry breaking similar to that of antiferromagnets, while still being in
full agreement with Elitzur's theorem, which forbids the spontaneous breaking
of local (gauge) symmetries. This thin spectrum in the superconductors consists
of in-gap states that are associated with the spontaneous breaking of a global
phase symmetry. In qubits based on mesoscopic superconducting devices, the
presence of the thin spectrum implies a maximum coherence time which is
proportional to the number of Cooper pairs in the device. Here we present the
detailed calculations leading up to these results and discuss the relation
between spontaneous symmetry breaking in superconductors and the Meissner
effect, the Anderson-Higgs mechanism and the Josephson effect. Whereas for the
Meissner effect a symmetry breaking of the phase of the superconductor is not
required, it is essential for the Josephson effect.Comment: 11 pages, 4 figures; corrected typo
Skewness of the wage distribution in a firm and the substitutability of labor inputs
wages;game theory;organizational structure;managerial science
Spontaneous Symmetry Breaking in Quantum Mechanics
We present a clear and mathematically simple procedure explaining spontaneous
symmetry breaking in quantum mechanical systems. The procedure is applicable to
a wide range of models and can be easily used to explain the existence of a
symmetry broken state in crystals, antiferromagnets and even superconductors.
It has the advantage that it automatically brings to the fore the main players
in spontaneous symmetry breaking: the symmetry breaking field, the
thermodynamic limit, and the global excitations of the thin spectrum.Comment: 4 pages, 0 figure
Thin Spectrum States in Superconductors
We show that finite size superconductors have a spectrum of states at
extremely low energy, i.e. inside the superconducting gap. The presence of this
{\it thin spectrum} is a generic feature and related to the fact that in a
superconductor the global phase rotation symmetry is spontaneously broken. For
a strong coupling superconductor we find the spectrum by exactly solving the
Lieb-Mattis type Hamiltonian onto which the problem maps. One of the physical
consequences of the presence of thin states is that they cause quantum
decoherence in superconducting qubits of finite extent.Comment: 4 pages, 2 figure
- …