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Article
Open AccessClassification and characterization of nonequilibrium Higgs modes in unconventional superconductors
Recent findings of new Higgs modes in unconventional superconductors require a classification and characterization of the modes allowed by nontrivial gap symmetry. Here we develop a theory for a tailored noneq...
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Article
Open AccessCoupling of Higgs and Leggett modes in non-equilibrium superconductors
In equilibrium systems amplitude and phase collective modes are decoupled, as they are mutually orthogonal excitations. The direct detection of these Higgs and Leggett collective modes by linear-response measu...
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Article
Hole dispersions for antiferromagnetic spin-\hbox{$\frac{1}{2}$}12 two-leg ladders by self-similar continuous unitary transformations
The hole-doped antiferromagnetic spin-\hbox{$\frac{1}{2}$}12 two-leg ladder is an important model system for the high-T c superconductors based on cupr...
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Article
Truncation errors in self-similar continuous unitary transformations
Effects of truncation in self-similar continuous unitary transformations (S-CUT) are estimated rigorously. We find a formal description via an inhomogeneous flow equation. In this way, we are able to quantify...
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Article
Thermodynamics of adiabatically loaded cold bosons in the Mott insulating phase of one-dimensional optical lattices
In this work we give a consistent picture of the thermodynamic properties of bosons in the Mott insulating phase when loaded adiabatically into one-dimensional optical lattices. We find a crucial dependence of...
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Article
Retraction Note: Evidence for spin–charge separation in quasi-one-dimensional organic conductors
Nature 418, 614–617 (2002) In this Letter, we described the anomalous behaviour of the thermal conductivity k in quasi-one-dimensional Bechgaard salts. As we have since observed a conventional temperature depe...
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Article
Spectral densities from dynamic density-matrix renormalization
Dynamic density-matrix renormalization provides valuable numerical information on dynamic correlations by computing convolutions of the corresponding spectral densities. Here we discuss and illustrate how an...
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Article
High order perturbation theory for spectral densities of multi-particle excitations: \(\mathsf{S = \frac{1}{2}}\) two-leg Heisenberg ladder
We present a high order perturbation approach to quantitatively calculate spectral densities in three distinct steps starting from the model Hamiltonian and the observables of interest. The approach is based o...
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Article
Renormalization by continuous unitary transformations: one-dimensional spinless fermions
A renormalization scheme for interacting fermionic systems is presented where the renormalization is carried out in terms of the fermionic degrees of freedom. The scheme is based on continuous unitary transfor...
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Article
Evidence for spin–charge separation in quasi-one-dimensional organic conductors
Interacting conduction electrons are usually described within Fermi-liquid theory1, which states that, in spite of strong interactions, the low-energy excitations are electron-like quasiparticles with charge and ...
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Article
Effective spin models for spin-phonon chains by flow equations
We investigate the anti-adiabatic limit of an anti-ferromagnetic S = 1/2 Heisenberg chain coupled to Einstein phonons. The flow equation method is used to decouple the spin and the phonon part of the Hamiltonian....
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Article
High temperature expansion for frustrated and unfrustrated S= \({1 \over 2}\) spin chains
A computer aided high temperature expansion of the magnetic susceptibility and the magnetic specific heat is presented and demonstrated for frustrated and unfrustrated spin chains. The results are analytic in ...
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Article
Perturbation theory by flow equations: dimerized and frustrated S = 1/2 chain
The flow equation method (Wegner, 1994) is used as continuous unitary transformation to construct perturbatively effective Hamiltonians. The method is illustrated in detail for dimerized and frustrated antifer...
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Article
Unified quantum mechanical picture for confined spinons in dimerized and frustrated spin chains
A quantum mechanical picture is presented to describe the behavior of confined spinons in a variety of S =1/2 chains. The confinement is due to dimerization and frustration and it manifests itself as a nonlinear ...
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Article
On the incommensurate phase in modulated Heisenberg chains
Using the density matrix renormalization group method (DMRG) we calculate the magnetization of frustrated S=1/2 Heisenberg chains for various modulation patterns of the nearest neighbour coupling: commensurate, i...
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Article
1/d corrections for interacting spinless fermions: One-particle properties
One-particle properties of the spinless fermion model with repulsion at half filling are calculated within an approach correct to first order in the inverse of the lattice dimensiond. Continuity of the limitd→∞ r...
