Topological Lifshitz transition in Weyl semimetal NbP decorated with heavy elements

TL;DR

This study investigates how depositing heavy elements like Pb and Nb on NbP semimetal surfaces induces topological Lifshitz transitions, revealing the robustness of bulk topology despite surface modifications.

Contribution

It demonstrates that even a monolayer of heavy elements can induce topological Lifshitz transitions in NbP, highlighting the surface-bulk interplay in topological semimetals.

Findings

Pb causes significant Fermi surface shifts and topological transitions.

Nb has a weaker impact on the electronic structure than Pb.

Surface decoration can induce topological Lifshitz transitions without destroying bulk topology.

Abstract

Studies of the Fermi surface modification after in-situ covering NbP semimetal with heavy elements Pb and Nb ultrathin layers were performed by means of angle-resolved photoemission spectroscopy (ARPES). First, the electronic structure was investigated for pristine single crystals with two possible terminations (P and Nb) of the (0 0 1) surface. The nature of the electronic states of these two cleaving planes is different: P-terminated surface shows spoon and bow tie shaped fingerprints, whereas these shapes are not present in Nb-terminated surfaces. ARPES studies show that even 1 monolayer (ML) of Pb causes topological quantum Lifshitz transition (TQLT) in P- and Nb-terminated surfaces. Deposited Pb 5d electrons have wide extended atomic orbitals which leads to strong hybridization with Pb-terminated surface and a corresponding shift in the Fermi energy. Nb has less capability to perturb the system than Pb because Nb has weaker spin-orbit coupling than Pb. Nb-terminated surface subjected to surface decoration with approximately 1.3 ML of Nb shows no dramatic modification in the Fermi surface. In the case of Nb decorated P-terminated surface, deposition of approximately 1 ML modifies the electronic structure of NbP and it is on the verge of TQLT. Despite the strong spin-orbit and strong hybridization of the heavy elements on the surface, it is possible to observe the TQLT of the surface states thanks to the robustness of the bulk topology.