W. Hanke

SO(5) theory of antiferromagnetism and superconductivity

Antiferromagnetism and superconductivity are both fundamental and common states of matter. In many strongly correlated systems, including the high Tc cuprates, the heavy fermion compounds and the organic superconductors, they occur next to each other in the phase diagram and influence each others physical properties. The SO(5) theory unifies these two basic states of matter by a symmetry principle and describes their rich phenomenology through a single low energy effective model. In this paper, we review the framework of the SO(5) theory, and its detailed comparison with numerical and experimental results.

Quasiparticle Dispersion of the 2D Hubbard Model: From an Insulator to a Metal

On the basis of Quantum-Monte-Carlo results the evolution of the spectral weight

Bismuthene on a SiC substrate: A candidate for a high-temperature quantum spin Hall material

A(\vec k, \omega)

Competing many-body instabilities and unconventional superconductivity in graphene

of the two-dimensional Hubbard model is studied from insulating to metallic behavior. As observed in recent photoemission experiments for cuprates, the electronic excitations display essentially doping-independent features: a quasiparticle-like dispersive narrow band of width of the order of the exchange interaction

Exotic d-Wave Superconducting State of Strongly Hole-Doped KxBa1-xFe2As2

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Elemental topological insulator with tunable Fermi level: strained α-Sn on InSb(001).

and a broad valence- and conduction-band background. The continuous evolution is traced back to one and the same many-body origin: the doping-dependent antiferromagnetic spin-spin correlation.

Functional renormalization group for multi-orbital Fermi surface instabilities

Making a large-gap topological insulator Although of interest to basic research, topological insulators (TIs) have not yet lived up to their technological potential. This is partly because their protected surface-edge state usually lives within a narrow energy gap, with its exotic transport properties overwhelmed by the ordinary bulk material. Reis et al. show that a judicious choice of materials can make the gap wide enough for the topological properties to be apparent at room temperature. Numerical calculations indicate that a monolayer of Bismuth grown on SiC(0001) is a two-dimensional TI with a large energy gap. The researchers fabricated such a heterostructure and characterized it using scanning tunneling spectroscopy. The size of the experimentally measured gap was consistent with the calculations. Science, this issue p. 287 Scanning tunneling spectroscopy indicates a large energy gap and conducting edge states, consistent with calculations. Quantum spin Hall materials hold the promise of revolutionary devices with dissipationless spin currents but have required cryogenic temperatures owing to small energy gaps. Here we show theoretically that a room-temperature regime with a large energy gap may be achievable within a paradigm that exploits the atomic spin-orbit coupling. The concept is based on a substrate-supported monolayer of a high–atomic number element and is experimentally realized as a bismuth honeycomb lattice on top of the insulating silicon carbide substrate SiC(0001). Using scanning tunneling spectroscopy, we detect a gap of ~0.8 electron volt and conductive edge states consistent with theory. Our combined theoretical and experimental results demonstrate a concept for a quantum spin Hall wide-gap scenario, where the chemical potential resides in the global system gap, ensuring robust edge conductance.

Variational cluster approach to spontaneous symmetry breaking: The itinerant antiferromagnet in two dimensions

The band structure of graphene exhibits van Hove singularities (VHSs) at dopings

Theory of superconductivity in a three-orbital model of Sr2RuO4

x=\ifmmode\pm\else\textpm\fi{}1/8

Spectral properties of the one-dimensional Hubbard model.

away from the Dirac point. Near the VHS, interactions effects, enhanced due to the large density of states, can give rise to various many-body phases. We study the competition between many-body instabilities in graphene using the functional renormalization group. We predict a rich phase diagram, which, depending on band structure as well as the range and scale of Coulomb interactions, contains a