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Robustness of a perturbed topological phase.
We investigate the stability of the topological phase of the toric code model in the presence of a uniform magnetic field by means of variational and high-order series expansion approaches. We find
Low-energy effective theory of the toric code model in a parallel magnetic field
We determine analytically the phase diagram of the toric code model in a parallel magnetic field which displays three distinct regions. Our study relies on two high-order perturbative expansions in
Effective models for gapped phases of strongly correlated quantum lattice models
We present a robust scheme to derive effective models non-perturbatively for quantum lattice models when at least one degree of freedom is gapped. A combination of graph theory and the method of
Magnetization of SrCu2(BO3)2 in ultrahigh magnetic fields up to 118 T.
The magnetization process of the orthogonal-dimer antiferromagnet SrCu2(BO3)2 is investigated in high magnetic fields of up to 118 T and the main features of the high-field magnetization are shown to agree quantitatively with the Shastry-Sutherland model.
The structure of operators in effective particle-conserving models
For many-particle systems defined on lattices we investigate the global structure of effective Hamiltonians and observables obtained by means of a suitable basis transformation. We study
Disorder by disorder and flat bands in the kagome transverse field Ising model
We study the transverse field Ising model on a kagome and a triangular lattice using high-order series expansions about the high-field limit. For the triangular lattice our results confirm a
High order perturbation theory for spectral densities of multi-particle excitations: $\mathsf{S = \frac{1}{2}}$ two-leg Heisenberg ladder
Abstract.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
Mott physics in the half-filled Hubbard model on a family of vortex-full square lattices
We study the half-filled Hubbard model on a one-parameter family of vortex-full square lattices ranging from the isotropic case to weakly coupled Hubbard dimers. The ground-state phase diagram
Spectral Properties of Quasi One-dimensional Quantum Antiferromagnets . Perturbative Continuous Unitary Transformations
In this work a perturbative realization of particle conserving continuous unitary transformations is applied to study the energies and the spectral properties of quasi one-dimensional quantum
Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point
Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed matter physics. The collective excitations in the broken-symmetry phase near the quantum critical point can