Abstract
Topological semimetals can support one-dimensional Fermi lines or zero-dimensional Weyl points in momentum space, where the valence and conduction bands touch. While the degeneracy points in Weyl semimetals are robust against any perturbation that preserves translational symmetry, nodal lines require protection by additional crystalline symmetries such as mirror reflection. Here we report, based on a systematic theoretical study and a detailed experimental characterization, the existence of topological nodal-line states in the non-centrosymmetric compound PbTaSe2 with strong spin-orbit coupling. Remarkably, the spin-orbit nodal lines in PbTaSe2 are not only protected by the reflection symmetry but also characterized by an integer topological invariant. Our detailed angle-resolved photoemission measurements, first-principles simulations and theoretical topological analysis illustrate the physical mechanism underlying the formation of the topological nodal-line states and associated surface states for the first time, thus paving the way towards exploring the exotic properties of the topological nodal-line fermions in condensed matter systems.
Highlights
Topological semimetals can support one-dimensional Fermi lines or zero-dimensional Weyl points in momentum space, where the valence and conduction bands touch
Our angleresolved photoemission (ARPES) measurements together with density functional theory (DFT) calculations show that the conduction band originated from Pb-6p orbitals and the valence band from Ta-5d orbitals cross each other, forming three nodalline states close to the Fermi energy
The samples were of high structural quality, which was confirmed by our X-ray diffraction and scanning tunnelling microscopy (STM) measurements
Summary
Topological semimetals can support one-dimensional Fermi lines or zero-dimensional Weyl points in momentum space, where the valence and conduction bands touch. Line-like touchings of a conduction and valence band need extra symmetries besides translation, such as mirror reflection, to be topologically protected. This protection involves a finite fraction of Brillouin zone. In this work we performed systematic theoretical study and experimental characterization of the electronic structure of a spin-orbit metal PbTaSe2, indicating the existence of topological nodal-line phase in this compound for the first time. Our detailed theoretical modelling and calculation, aided by a systematic experimental characterization, establish the existence of topological nodal-line fermions in the superconducting compound PbTaSe2, opening the door for exploring the exotic properties of nodal-line states in condensed matter
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