Riccardo Vocaturo

Leibniz Institute for Solid State and Materials Research

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Jeroen van den Brink

TU Dresden

Jorge I. Facio

Consejo Nacional de Investigaciones Científicas y Técnicas

Klaus Koepernik

Leibniz Institute for Solid State and Materials Research

Oleg Janson

Leibniz Institute for Solid State and Materials Research

Saicharan Aswartham

Leibniz Institute for Solid State and Materials Research

Grigory Shipunov

Leibniz Institute for Solid State and Materials Research

Ion Cosma Fulga

Leibniz Institute for Solid State and Materials Research

Carsten Timm

TU Dresden

B. Büchner

Leibniz Institute for Solid State and Materials Research

Yanina Fasano

Leibniz Institute for Solid State and Materials Research

Cooperative Institutions

Leibniz Institute for Solid State and Materials Research

TU Dresden

Complexity and Topology in Quantum Matter

Helmholtz-Zentrum Berlin für Materialien und Energie

Bariloche Atomic Centre

Consejo Nacional de Investigaciones Científicas y Técnicas

G.V. Kurdyumov Institute for Metal Physics

Lanzhou University

Balseiro Institute

Centre National de la Recherche Scientifique

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Fermi Arcs Dominating the Electronic Surface Properties of Trigonal PtBi₂

Advanced Physics Research (2024)

Sven Hoffmann Sebastian Schimmel Riccardo Vocaturo Joaquín Puig Grigory Shipunov

Materials combining topologically non-trivial behavior and superconductivity offer a potential route for quantum computation. However, the set of available materials intrinsically realizing these properties are scarce. Recently, surface superconductivity has been reported in PtBi$_2$ in its trigonal phase and an inherent Weyl semimetal phase has been predicted. Here, based on scanning tunneling microscopy experiments, we reveal the signature of topological Fermi arcs in the normal state patterns of the quasiparticle interference. We show that the scattering between Fermi arcs dominates the interference spectra, providing conclusive evidence for the relevance of Weyl fermiology for the surface electronic properties of trigonal PtBi$_2$.

Trigonal crystal system

10.1002/apxr.202400150

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Electronic structure of the surface-superconducting Weyl semimetal PtBi2

Physical review. B./Physical review. B (2024)

Riccardo Vocaturo Klaus Koepernik Jorge I. Facio Carsten Timm Ion Cosma Fulga

Trigonal ${\mathrm{PtBi}}_{2}$ is a layered semimetal without inversion symmetry, featuring 12 Weyl points in the vicinity of the Fermi energy. Its topological Fermi arcs were recently shown to superconduct at low temperatures where bulk superconductivity is absent. Here, we perform first-principles calculations to investigate in detail the bulk and surface electronic structure of ${\mathrm{PtBi}}_{2}$, and obtain the spin texture as well as the momentum-dependent localization of the arcs. Motivated by the experimentally observed recovery of inversion symmetry under pressure or upon doping, we interpolate between the two structures and determine the energy and momentum dependence of the Weyl nodes. For deeper insights into the surface superconductivity of ${\mathrm{PtBi}}_{2}$, we construct a symmetry-adapted effective four-band model that accurately reproduces the Weyl points of ${\mathrm{PtBi}}_{2}$. We supplement this model with an analysis of the symmetry-allowed pairings between the Fermi arcs, which naturally mix spin-singlet and spin-triplet channels. Moreover, the presence of surface-only superconductivity facilitates an intrinsic superconductor-semimetal-superconductor Josephson junction, with the semimetallic phase sandwiched between the two superconducting surfaces. For a phase difference of $\ensuremath{\pi}$, zero-energy Andreev bound states develop between the two terminations.

Weyl semimetal

10.1103/physrevb.110.054504

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Prediction of ambient-pressure superconductivity in ternary hydride PdCuHx

Journal of Applied Physics (2022)

Riccardo Vocaturo Cesare Tresca G. Ghiringhelli G. Profeta

We present an ab initio study of the ternary hydride PdCuHx, a parent compound of the superconducting PdH, at different hydrogen content (x=1,2). We investigate its structural, electronic, dynamical, and superconducting properties, demonstrating that, at low hydrogen content, the system is not a superconductor above 1 K; however, the highly hydrogenated structure is a strongly coupled superconductor. We give a solid rationale for the unusual increase of the superconducting critical temperature in hydrogenated palladium when alloyed with noble metals (Cu, Ag, and Au), as observed in Stritzker’s experiments in 1972 [B. Stritzker, Z. Phys. 268, 261–264 (1974)] but never investigated with modern experimental and theoretical techniques. We highlight the important role played by H-derived phonon modes at intermediate frequencies, dynamically stabilized by anharmonic effects, as they strongly couple with states at the Fermi level. We hope that the present results will stimulate additional experimental investigations of structural, electronic, and superconducting properties of hydrogenated palladium–noble metal alloys. Indeed, if confirmed, these compounds could be considered a novel class of superconducting hydrides, showing different coupling mechanisms, which can be exploited to engineer new ambient-pressure superconductors.

Ambient pressure

10.1063/5.0076728

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Evidence of superconducting Fermi arcs

Nature (2024)

Andrii Kuibarov Olexandr Suvorov Riccardo Vocaturo Alexander Fedorov Rui Lou

Abstract An essential ingredient for the production of Majorana fermions for use in quantum computing is topological superconductivity 1,2 . As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity 3 , making systems fragile and difficult to realize 4–7 . Due to their intrinsic topology 8 , Weyl semimetals are also potential candidates 1,2 , but have always been connected with bulk superconductivity, leaving the possibility of intrinsic superconductivity of their topological surface states, the Fermi arcs, practically without attention, even from the theory side. Here, by means of angle-resolved photoemission spectroscopy and ab initio calculations, we identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material trigonal PtBi 2 (ref. 9 ). We show these states become superconducting at temperatures around 10 K. Remarkably, the corresponding coherence peaks appear as the strongest and sharpest excitations ever detected by photoemission from solids. Our findings indicate that superconductivity in PtBi 2 can occur exclusively at the surface, rendering it a possible platform to host Majorana modes in intrinsically topological superconductor–normal metal–superconductor Josephson junctions.

Surface States

10.1038/s41586-023-06977-7

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Electronic structure of the surface superconducting Weyl semimetal PtBi$_2$

arXiv (Cornell University) (2024)

Riccardo Vocaturo Klaus Koepernik Jorge I. Facio Carsten Timm Ion Cosma Fulga

Trigonal PtBi$_2$ is a layered semimetal without inversion symmetry, featuring 12 Weyl points in the vicinity of the Fermi energy. Its topological Fermi arcs were recently shown to superconduct at low temperatures where bulk superconductivity is absent. Here, we perform first-principles calculations to investigate in detail the bulk and surface electronic structure of PtBi$_2$, and obtain the spin texture as well as the momentum-dependent localization of the arcs. Motivated by the experimentally observed recovery of inversion symmetry under pressure or upon doping, we interpolate between the two structures and determine the energy and momentum dependence of the Weyl nodes. For deeper insights into the surface superconductivity of PtBi$_2$, we construct a symmetry-adapted effective four-band model that accurately reproduces the Weyl points of PtBi$_2$. We supplement this model with an analysis of the symmetry-allowed pairings between the Fermi arcs, which naturally mix spin-singlet and spin-triplet channels. Moreover, the presence of surface-only superconductivity facilitates an intrinsic superconductor-semimetal-superconductor Josephson junction, with the semimetallic phase sandwiched between the two superconducting surfaces. For a phase difference of $\pi$, zero-energy Andreev bound states develop between the two terminations.

Weyl semimetal

10.1103/physrevb.110.054504

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Citations (1)