Dynamical correlation functions of one-dimensional superconductors and Peierls and Mott insulators

I construct the spectral function of the Luther-Emery model which describes one-dimensional fermions with one gapless and one gapped degree of freedom, i.e. superconductors and Peierls and Mott insulators, by using symmetries, relations to other models, and known limits. Depending on the relative magnitudes of the charge and spin velocities, and on whether a charge or a spin gap is present, I find spectral functions differing in the number of singularities and presence or absence of anomalous dimensions of fermion operators. I find, for a Peierls system, one singularity with anomalous dimension and one finite maximum; for a superconductor two singularities with anomalous dimensions; and for a Mott insulator one or two singularities without anomalous dimension. In addition, there are strong shadow bands. I generalize the construction to arbitrary dynamical multi-particle correlation functions. The main aspects of this work are in agreement with numerical and Bethe Ansatz calculations by others. I also discuss the application to photoemission experiments on 1D Mott insulators and on the normal state of 1D Peierls systems, and propose the Luther-Emery model as the generic description of 1D charge density wave systems with important electronic correlations.Comment: Revtex, 27 pages, 5 figures, to be published in European Physical Journal

A brief introduction to Luttinger liquids

I give a brief introduction to Luttinger liquids. Luttinger liquids are paramagnetic one-dimensional metals without Landau quasi-particle excitations. The elementary excitations are collective charge and spin modes, leading to charge-spin separation. Correlation functions exhibit power-law behavior. All physical properties can be calculated, e.g. by bosonization, and depend on three parameters only: the renormalized coupling constant $K_{\rho}$, and the charge and spin velocities. I also discuss the stability of Luttinger liquids with respect to temperature, interchain coupling, lattice effects and phonons, and list important open problems.Comment: 10 pages, 2 figures, to be published in the Proceedings of the International Winterschool on Electronic Properties of Novel Materials 2000, Kirchberg, March 4-11, 200

Make Your Own Kind of Music? Komponieren mit Schüler*innen als Beitrag zu einer Pädagogik der Multiliteracies im Musikunterricht

Im vorliegenden Beitrag wird der Versuch unternommen, die von der New London Group für den Fremdsprachenunterricht vorgeschlagene Konzeption einer Pädagogik der Multiliteracies für den musikpädagogischen Diskurs fruchtbar zu machen. Dabei wird an die Vorstellung von Musik als sozialer Praxis angeknüpft, die in der wissenschaftlichen Musikpädagogik in den vergangenen zwei Jahrzehnten zunehmende Verbreitung gefunden hat. Im Zentrum steht die Fragestellung, welche Implikationen sich aus dem Konzept der Multiliteracies für produktionsdidaktische Kontexte ableiten lassen. Hierzu werden zunächst      Ergebnisse einer empirischen Studie über Response-Projekte vorgestellt, die das Spannungsfeld deutlich machen, in dem sich Komponist*innen befinden, wenn sie einerseits Schüler*innen möglichst große ästhetische Freiräume gewähren und sie andererseits an eine bestimmte kompositorische Praxis heranführen möchten. Anschließend werden die Ergebnisse in den zuvor entfalteten theoretischen Kontext eingebettet und diskutiert

SET based experiments for HTSC materials: II

The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. In this note we further discuss our original suggestion of using Single Electron Tunneling Transistor [SET] based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classed in a general sense as mesoscopic and nano characterization of cuprates and related materials. In principle such experiments can show if electron is fractionalized in cuprates as indicated by ARPES data. In contrast to flux trapping experiments SET based experiments are more direct in providing evidence about spin-charge separation. In addition a detailed picture of nano charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P: P10-0

Lattice Twisting Operators and Vertex Operators in Sine-Gordon Theory in One Dimension

In one dimension, the exponential position operators introduced in a theory of polarization are identified with the twisting operators appearing in the Lieb-Schultz-Mattis argument, and their finite-size expectation values $z_L$ measure the overlap between the unique ground state and an excited state. Insulators are characterized by $z_{\infty}\neq 0$. We identify $z_L$ with ground-state expectation values of vertex operators in the sine-Gordon model. This allows an accurate detection of quantum phase transitions in the universality classes of the Gaussian model. We apply this theory to the half-filled extended Hubbard model and obtain agreement with the level-crossing approach.Comment: 4 pages, 3 figure

Improving the flame retardance of polyisocyanurate foams by dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide-containing additives

A series of new flame retardants (FR) based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) incorporating acrylates and benzoquinone were developed previously. In this study, we examine the fire behavior of the new flame retardants in polyisocyanurate (PIR) foams. The foam characteristics, thermal decomposition, and fire behavior are investigated. The fire properties of the foams containing BPPO-based derivatives were found to depend on the chemical structure of the substituents. We also compare our results to state-of-the-art non-halogenated FR such as triphenylphosphate and chemically similar phosphinate, i.e. 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO), based derivatives to discuss the role of the phosphorus oxidation state

An Exactly Solvable Kondo Problem for Interacting One-Dimensional Fermions

The single impurity Kondo problem in the one-dimensional $\delta$-potential Fermi gas is exactly solved for two sets of special coupling constants via Bethe ansatz. It is found that ferromagnetic Kondo screening does occur in one case which confirms the Furusaki-Nagaosa conjecture while in the other case it does not, which we explain in a simple physical picture. The surface energy, the low temperature specific heat and the Pauli susceptibility induced by the impurity and thereby the Kondo temperature are derived explicitly.Comment: 8 pages, LATEX, REVTE

Non-uniform doping across the Fermi surface of NbS2_2 intercalates

Magnetic ordering of the first row transition metal intercalates of NbS$_2$ due to coupling between the conduction electrons and the intercalated ions has been explained in terms of Fermi surface nesting. We use angle-resolved photoelectron spectroscopy to investigate the Fermi surface topology and the valence band structure of the quasi-two-dimensional layer compounds Mn$_{1/3}$NbS$_2$ and Ni$_{1/3}$NbS$_2$. Charge transfer from the intercalant species to the host layer leads to non-uniform, pocket selective doping of the Fermi surface. The implication of our results on the nesting properties are discussed