TY - JOUR A1 - Dürrnagel, Matteo A1 - Beyer, Jacob A1 - Thomale, Ronny A1 - Schwemmer, Tilman T1 - Unconventional superconductivity from weak coupling JF - The European Physical Journal B N2 - We develop a joint formalism and numerical framework for analyzing the superconducting instability of metals from a weak coupling perspective. This encompasses the Kohn–Luttinger formulation of weak coupling renormalization group for superconductivity as well as the random phase approximation imposed on the diagrammatic expansion of the two-particle Green’s function. The central quantity to resolve is the effective interaction in the Cooper channel, for which we develop an optimized numerical framework. Our code is capable of treating generic multi-orbital models in two as well as three spatial dimensions and, in particular, arbitrary avenues of spin-orbit coupling. KW - superconducting instability KW - metals KW - weak coupling KW - unconventional superconductivity Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-325153 SN - 1434-6028 VL - 95 IS - 7 ER - TY - JOUR A1 - Lee, Ching Hua A1 - Sutrisno, Amanda A1 - Hofmann, Tobias A1 - Helbig, Tobias A1 - Liu, Yuhan A1 - Ang, Yee Sin A1 - Ang, Lay Kee A1 - Zhang, Xiao A1 - Greiter, Martin A1 - Thomale, Ronny T1 - Imaging nodal knots in momentum space through topolectrical circuits JF - Nature Communications N2 - Knots are intricate structures that cannot be unambiguously distinguished with any single topological invariant. Momentum space knots, in particular, have been elusive due to their requisite finely tuned long-ranged hoppings. Even if constructed, probing their intricate linkages and topological "drumhead" surface states will be challenging due to the high precision needed. In this work, we overcome these practical and technical challenges with RLC circuits, transcending existing theoretical constructions which necessarily break reciprocity, by pairing nodal knots with their mirror image partners in a fully reciprocal setting. Our nodal knot circuits can be characterized with impedance measurements that resolve their drumhead states and image their 3D nodal structure. Doing so allows for reconstruction of the Seifert surface and hence knot topological invariants like the Alexander polynomial. We illustrate our approach with large-scale simulations of various nodal knots and an experiment which maps out the topological drumhead region of a Hopf-link. Topological phases with knotted configurations in momentum space have been challenging to realize. Here, Lee et al. provide a systematic design and measurement of a three-dimensional knotted nodal structure, and resolve its momentum space drumhead states via a topolectrical RLC-type circuit. KW - nodal knots KW - topolectrical circuits Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230407 VL - 11 ER - TY - JOUR A1 - Di Sante, Domenico A1 - Erdmenger, Johanna A1 - Greiter, Martin A1 - Matthaiakakis, Ioannis A1 - Meyer, René A1 - Fernandez, David Rodríguez A1 - Thomale, Ronny A1 - van Loon, Erik A1 - Wehling, Tim T1 - Turbulent hydrodynamics in strongly correlated Kagome metals JF - Nature Communications N2 - A current challenge in condensed matter physics is the realization of strongly correlated, viscous electron fluids. These fluids can be described by holography, that is, by mapping them onto a weakly curved gravitational theory via gauge/gravity duality. The canonical system considered for realizations has been graphene. In this work, we show that Kagome systems with electron fillings adjusted to the Dirac nodes provide a much more compelling platform for realizations of viscous electron fluids, including non-linear effects such as turbulence. In particular, we find that in Scandium Herbertsmithite, the fine-structure constant, which measures the effective Coulomb interaction, is enhanced by a factor of about 3.2 as compared to graphene. We employ holography to estimate the ratio of the shear viscosity over the entropy density in Sc-Herbertsmithite, and find it about three times smaller than in graphene. These findings put the turbulent flow regime described by holography within the reach of experiments. Viscous electron fluids are predicted in strongly correlated systems but remain challenging to realize. Here, the authors predict enhanced effective Coulomb interaction and reduced ratio of the shear viscosity over entropy density in a Kagome metal, inferring turbulent flow of viscous electron fluids. KW - coupling-constant dependence KW - shear viscosity KW - electron KW - resistance Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230380 VL - 11 ER - TY - JOUR A1 - Li, Gang A1 - Yan, Binghai A1 - Thomale, Ronny A1 - Hanke, Werner T1 - Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors JF - Scientific Reports N2 - Recent theoretical studies employing density-functional theory have predicted BaBiO\(_{3}\) (when doped with electrons) and YBiO\(_{3}\) to become a topological insulator (TI) with a large topological gap (~0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba\(_{1-X}\)K\(_{X}\)BiO\(_{3}\) and BaPb\(_{1-X}\)Bi\(_{X}\)O\(_{3}\), which are "high-Tc" bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy E\(_{F}\) a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above E\(_{F}\). Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below E\(_{F}\) for further hole doping, which manifests these systems to be candidates for both electron-and hole-doped topological insulators. KW - localized wannier functions KW - total energy calculations KW - phase transitions KW - insulator KW - BaPb\(_{1-X}\)Bi\(_{X}\)O\(_{3}\) KW - temperature KW - system KW - wave basis set KW - initio molecular dynamics KW - diffraction Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148569 VL - 5 IS - 10435 ER - TY - JOUR A1 - Elster, Lars A1 - Platt, Christian A1 - Thomale, Ronny A1 - Hanke, Werner A1 - Hankiewicz, Ewelina M. T1 - Accessing topological superconductivity via a combined STM and renormalization group analysis JF - Nature Communications N2 - The search for topological superconductors has recently become a key issue in condensed matter physics, because of their possible relevance to provide a platform for Majorana bound states, non-Abelian statistics, and quantum computing. Here we propose a new scheme which links as directly as possible the experimental search to a material-based microscopic theory for topological superconductivity. For this, the analysis of scanning tunnelling microscopy, which typically uses a phenomenological ansatz for the superconductor gap functions, is elevated to a theory, where a multi-orbital functional renormalization group analysis allows for an unbiased microscopic determination of the material-dependent pairing potentials. The combined approach is highlighted for paradigmatic hexagonal systems, such as doped graphene and water-intercalated sodium cobaltates, where lattice symmetry and electronic correlations yield a propensity for a chiral singlet topological superconductor. We demonstrate that our microscopic material-oriented procedure is necessary to uniquely resolve a topological superconductor state. KW - tunneling spectroscopy KW - Sr\(_2\)RuO\(_4\) KW - states KW - transition KW - insulators KW - surface KW - Majorana fermions KW - unconventional superconductivity KW - wave superconductors Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148181 VL - 6 IS - 8232 ER - TY - JOUR A1 - Lee, Ching Hua A1 - Papić, Zlatko A1 - Thomale, Ronny T1 - Geometric construction of quantum Hall clustering Hamiltonians JF - Physical Review X N2 - Many fractional quantum Hall wave functions are known to be unique highest-density zero modes of certain "pseudopotential" Hamiltonians. While a systematic method to construct such parent Hamiltonians has been available for the infinite plane and sphere geometries, the generalization to manifolds where relative angular momentum is not an exact quantum number, i.e., the cylinder or torus, remains an open problem. This is particularly true for non-Abelian states, such as the Read-Rezayi series (in particular, the Moore-Read and Read-Rezayi Z\(_3\) states) and more exotic nonunitary (Haldane-Rezayi and Gaffnian) or irrational (Haffnian) states, whose parent Hamiltonians involve complicated many-body interactions. Here, we develop a universal geometric approach for constructing pseudopotential Hamiltonians that is applicable to all geometries. Our method straightforwardly generalizes to the multicomponent SU(n) cases with a combination of spin or pseudospin (layer, subband, or valley) degrees of freedom. We demonstrate the utility of our approach through several examples, some of which involve non-Abelian multicomponent states whose parent Hamiltonians were previously unknown, and we verify the results by numerically computing their entanglement properties. KW - wave functions KW - Landau level KW - states KW - excitations KW - fluid Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-145233 VL - 5 IS - 4 ER - TY - JOUR A1 - Rousochatzakis, Ioannis A1 - Reuther, Johannes A1 - Thomale, Ronny A1 - Rachel, Stephan A1 - Perkins, N. B. T1 - Phase Diagram and Quantum Order by Disorder in the Kitaev K\(_1\) - K\(_2\) Honeycomb Magnet JF - Physical Review X N2 - We show that the topological Kitaev spin liquid on the honeycomb lattice is extremely fragile against the second-neighbor Kitaev coupling K\(_2\), which has recently been shown to be the dominant perturbation away from the nearest-neighbor model in iridate Na\(_2\)IrO\(_3\), and may also play a role in \(\alpha\)-RuCl\(_3\) and Li\(_2\)IrO\(_3\). This coupling naturally explains the zigzag ordering (without introducing unrealistically large longer-range Heisenberg exchange terms) and the special entanglement between real and spin space observed recently in Na\(_2\)IrO\(_3\). Moreover, the minimal K\(_1\) - K\(_2\) model that we present here holds the unique property that the classical and quantum phase diagrams and their respective order-by-disorder mechanisms are qualitatively different due to the fundamentally different symmetries of the classical and quantum counterparts. KW - model KW - anyons KW - lattice KW - confinement-deconfinement transition Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-137235 VL - 5 IS - 041035 ER -