Ronny Thomale

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

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.

Competing many-body instabilities and unconventional superconductivity in graphene

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

Functional renormalization group for multi-orbital Fermi surface instabilities

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

Finite-temperature phase diagram of the Heisenberg-Kitaev 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

Spin hamiltonian for which the chiral spin liquid is the exact ground state.

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Mechanism for a pairing state with time-reversal symmetry breaking in iron-based superconductors

-wave superconducting (SC) phase, or a spin-density-wave phase at the VHS. The

Chiral d-wave superconductivity in SrPtAs

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Spiral order in the honeycomb iridate Li2IrO3

state is expected to exhibit quantized charge and spin Hall response, as well as Majorana modes bound to vortices. Nearby the VHS, we find singlet

Magnetic order and paramagnetic phases in the quantumJ1-J2-J3honeycomb model

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Decomposition of fractional quantum Hall model states: Product rule symmetries and approximations

-wave and triplet