Potential Lifshitz transition at optimal substitution in nematic pnictide Ba1- xSr x Ni2As2

Dushyant M Narayan; Peipei Hao; Rafał Kurleto; Bryan S Berggren; A Garrison Linn; Christopher Eckberg; Prathum Saraf; John Collini; Peter Zavalij; Makoto Hashimoto; Donghui Lu; Rafael M Fernandes; Johnpierre Paglione; Daniel S Dessau

doi:10.1126/sciadv.adi4966

Potential Lifshitz transition at optimal substitution in nematic pnictide Ba_{1- x}Sr _x Ni₂As₂

Sci Adv. 2023 Oct 20;9(42):eadi4966. doi: 10.1126/sciadv.adi4966. Epub 2023 Oct 18.

Authors

Affiliations

¹ Center for Experiments on Quantum Materials, Department of Physics, University of Colorado, Boulder, CO 80309, USA.
² Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA.
³ Department of Chemistry, University of Maryland, College Park, MD 20742, USA.
⁴ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
⁵ School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA.
⁶ Canadian Institute for Advanced Research, Toronto, ON M5G-1Z8, Canada.

Abstract

BaNi₂As₂ is a structural analog of the pnictide superconductor BaFe₂As₂, which, like the iron-based superconductors, hosts a variety of ordered phases including charge density waves (CDWs), electronic nematicity, and superconductivity. Upon isovalent Sr substitution on the Ba site, the charge and nematic orders are suppressed, followed by a sixfold enhancement of the superconducting transition temperature (T_c). To understand the mechanisms responsible for enhancement of T_c, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements of the Ba_1-xSr_xNi₂As₂ series, which agree well with our density functional theory (DFT) calculations throughout the substitution range. Analysis of our ARPES-validated DFT results indicates a Lifshitz transition and reasonably nested electron and hole Fermi pockets near optimal substitution where T_c is maximum. These nested pockets host Ni d_xz/d_yz orbital compositions, which we associate with the enhancement of nematic fluctuations, revealing unexpected connections to the iron-pnictide superconductors. This gives credence to a scenario in which nematic fluctuations drive an enhanced T_c.