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Project Leader: Titus Neupert

Main Contributors: Martina Soldini, Andrea Kouta Dagnino, Midori Pittini

The recently introduced topological quantum chemistry (TQC) framework has provided a description of universal topological properties of all possible band insulators in all space groups based on crystalline unitary symmetries and time reversal. While this formalism filled the gap between the mathematical classification and the practical diagnosis of topological materials, an obvious limitation is that it only applies to weakly interacting systems, which can be described within band theory. It is an open question to which extent this formalism can be generalized to correlated systems that can exhibit symmetry-protected topological phases which are not adiabatically connected to any band insulator. Within a SNF consolidator grant, our group…

Key Publications:

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*Interacting topological quantum chemistry of Mott atomic limits*", Phys. Rev. B**107**, 245145 (2023)

Project Leaders: Titus Neupert, Mark H. Fischer

Main Contributors: Glenn Wagner, Bernhard E Lüscher, Sofie Castro Holbæk

Crystals realizing a kagome lattice exhibit a host of phenomena related to their lattice geometry, topological electron behaviour and the competition between different possible ground states. A particularly interesting family are the compounds of AVS (KV3Sb5, CsV3Sb5 and RbV3Sb5), with a kagome net of vanadium atoms. These materials feature an unconventional cdw below approx 100K and superconductivity at low temperature. In our group, we study these phases both on theoretical grounds, as well as in close collaboration with experimental colleagues.

Key Publications:

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*Switchable chiral transport in charge-ordered kagome metal CsV*", Nature_{3}Sb_{5}**611**, 461 (2022) - "
*Correlated order at at the tipping point in the kagome metal CsV*", Nature Physics_{3}Sb_{5}**20**, 579 (2024) *"Chiral kagome superconductivity modulations with residual Fermi arcs"*, Nature**632**, 775 (2024)

Project Leaders: Mark H. Fischer, Titus Neupert

Main Contributors: Glenn Wagner, Sofie Castro HolbækBernhard E Lüscher, Martina Soldini

Superconductivity takes a particular role among correlated phases of quantum matter in that quantum physics is dramatically manifested in a macroscopic ‘classical’ observable, the (vanishing) resistivity. The Department of Physics at the University of Zurich has a strong tradition in the study of superconductors: the Nobel laureate Prof. Karl Alex Müller, who discovered high-temperature superconductivity in the Cuprates, was an emeritus and Prof. Andreas Schilling holds the world record for the highest transition temperature under ambient pressure. In our theoretical research, we are primarily interested in the interplay of superconducting order with topological features of materials, crystalline symmetries and strong spin-orbit coupling.

Key Publications:

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*Superconductivity and Local Inversion-Symmetry Breaking*", Annual Review of Condensed Matter Physics**14**, 153 (2023) - "
*Atomic limit and inversion-symmetry indicators for topological superconductors*", Phys. Rev. Research**2**, 013064 (2020)

Project Leader: Titus Neupert

Main Contributors: Martina Soldini, Glenn Wagner

Artificial Lattices, not naturally occurring but created in the lab, can exhibit novel and intriguing phenomena. A particularly prominent example of recent years that our group studies is twisted bilayer graphene, which, for the right ‘magic’ angles, shows both correlated insulating behavior and superconductivity. Novel physics can emerge when placing atoms on a material in a periodic fashion using an STM tip. Depositing magnetic atoms on the surface of a (conventional) superconductor, for example, can lead to the emergence of topological bands formed by the resulting Shiba bound states.

Key Publications:

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*Two-dimensional Shiba lattices as a possible platform for crystalline topological superconductivity***",**Nature Physics**19**, 1848 (2023)