Surface superconductivity in the topological Weyl semimetal t-PtBi.

Topological superconductivity is a promising concept for generating fault-tolerant qubits. Early experimental studies looked at hybrid systems and doped intrinsic topological or superconducting materials at very low temperatures. However, higher critical temperatures are indispensable for technological exploitation.

Evidence of superconducting Fermi arcs.

An essential ingredient for the production of Majorana fermions for use in quantum computing is topological superconductivity. As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity, making systems fragile and difficult to realize. Due to their intrinsic topology, Weyl semimetals are also potential candidates, 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.

Origin of the Magnetic Exciton in the van der Waals Antiferromagnet NiPS_{3}.

An ultrasharp photoluminescence line intimately related to antiferromagnetic order has been found in NiPS_{3}, a correlated van der Waals material, opening prospects for magneto-optical coupling schemes and spintronic applications. Here we unambiguously clarify the singlet origin of this excitation, confirming its roots in the spin structure. Based on a comprehensive investigation of the electronic structure using angle-resolved photoemission and q-dependent electron energy loss spectroscopy as experimental tools we develop, in a first step, an adequate theoretical understanding using density functional theory (DFT).

Berezinskii-Kosterlitz-Thouless Transition in the Type-I Weyl Semimetal PtBi.

Symmetry breaking in topological matter has become in recent years a key concept in condensed matter physics to unveil novel electronic states. In this work, we predict that broken inversion symmetry and strong spin-orbit coupling in trigonal PtBi lead to a type-I Weyl semimetal band structure. Transport measurements show an unusually robust low dimensional superconductivity in thin exfoliated flakes up to 126 nm in thickness (with ∼ 275-400 mK), which constitutes the first report and study of unambiguous superconductivity in a type-I Weyl semimetal.

Fermi surface tomography.

Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (k) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of k -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic.