Zur Kenntnis der Kyrine

Ohne Zusammenfassung     

Über α- und β-Isocinchonin

Ohne Zusammenfassung     

Non-local order in Mott insulators,duality and Wilson loops

It is shown that the Mott insulating and superfluid phases of bosons in an optical lattice may be distinguished by a non-local ‘parity order parameter’ which is directly accessible via single site resolution imaging. In one dimension, the lattice Bose model is dual to a classical interface roughening problem. We use known exact results from the latter to prove that the parity order parameter exhibits long range order in the Mott insulating phase, consistent with recent experiments by Endres et al. [M. Endres, M. Cheneau, T. Fukuhara, C. Weitenberg, P. Schauß, C. Gross, L. Mazza, M.C. Bañuls, L. Pollet, I. Bloch, et al., Science 334 (2011) 200]. In two spatial dimensions, the parity order parameter can be expressed in terms of an equal time Wilson loop of a non-trivial U(1)$U\left(1\right)$ gauge theory in 2+1$2+1$ dimensions which exhibits a transition between a Coulomb and a confining phase. The negative logarithm of the parity order parameter obeys a perimeter law in the Mott insulator and is enhanced by a logarithmic factor in the superfluid.     

Dynamics of a dissipative two level system

We consider the tunneling of a particle in a symmetric double well, which is coupled to its environment in a way, that classically corresponds to a damping constant γ. In the two lowest level subspace, this is described by a spin-boson model with a finite density of zero energy excitations. A relaxation kernel method is applied to calculate the low temperature, low frequency static and dynamical susceptibility. In particular we determine the average tunneling frequency, which is equivalent to the rate for the destruction of phase coherence. For weak damping this is shown to be finite in the limitT→0, whereas for large γ it vanishes with a power low inT. AtT=0 the two regimes are separated by a phase boundary, dividing regions with finite or zero effective tunnel splitting. We discuss the application of the model to the dynamics of flux states in SQUID's and also to paraelectric impurities.     

The sign of Josephson's cos θ-term

Within the tunneling Hamiltonian approximation Kramers-Kronig relations between the amplitudes j_1,2 of the sine and cosine term in the Josephson current are derived. The spectral function ωj₂(ω) determines the supercurrents dissipative response to external a.c.-voltages but has no definite sign. A generla proof is given, that nevertheless the total dissipation always remains positive.     

Clock shift in a strongly interacting two-dimensional Fermi gas

We derive universal relations for the rf spectroscopy of a two-dimensional Fermi gas consisting of two spin states interacting through an S-wave scattering length. The rf transition rate has a high-frequency tail that is proportional to the contact and displays logarithmic scaling violations, decreasing asymptotically like 1/(ω2ln2ω). Its coefficient is proportional to ln2'(a'(2D)/a(2D)), where a(2D) and a'(2D) are the two-dimensional scattering lengths associated with initial-state and final-state interactions. The clock shift is proportional to the contact and to ln(a'(2D)/a(2D)). If |ln(a'(2D)/a(2D))| > 1, the clock shift arises as a cancellation between much larger contributions proportional to ln2(a'(2D)/a(2D)) from bound-bound and bound-free rf transitions.     

Mesoscopic fluctuations of the dipole moment and the electric polarizability

We consider mesoscopic fluctuations of the dipole moment and the electric polarizability of a disordered thin film in the diffusive regime. It is shown, that the requirement of a fixed particle number is crucial for obtaining finite fluctuations at low temperatures. For systems with sufficient disorder and a long screening length a spontaneous dipole moment should be observable with an atomic force microscope.Dedicated to Prof. H. Wagner on the occasion of his 60th birthday     

Decay of the Two-Point Function in One-Dimensional O(N) Spin Models with Long-Range Interactions

Using Griffiths and Lieb–Simon type inequalities, it is shown that the two-point function of ferromagnetic spin models with N components in one dimension decays like the interaction J(n)n ^– provided that 1N4 and T>T _c.