Superconductivity and a van Hove singularity confined to the surface of a topological semimetal

Md Shafayat Hossain; Rajibul Islam; Zi-Jia Cheng; Zahir Muhammad; Qi Zhang; Zurab Guguchia; Jonas A Krieger; Brian Casas; Yu-Xiao Jiang; Maksim Litskevich; Xian P Yang; Byunghoon Kim; Tyler A Cochran; Ilias E Perakis; Thomas Hicken; Hubertus Luetkens; Fei Xue; Mehdi Kargarian; Weisheng Zhao; Luis Balicas; M Zahid Hasan

doi:10.1038/s41467-025-58024-w

Superconductivity and a van Hove singularity confined to the surface of a topological semimetal

Nat Commun. 2025 Apr 29;16(1):3998. doi: 10.1038/s41467-025-58024-w.

Authors

Md Shafayat Hossain^#¹, Rajibul Islam^#², Zi-Jia Cheng^#³, Zahir Muhammad^#^{4

5}, Qi Zhang³, Zurab Guguchia⁶, Jonas A Krieger⁶, Brian Casas⁷, Yu-Xiao Jiang³, Maksim Litskevich³, Xian P Yang³, Byunghoon Kim³, Tyler A Cochran³, Ilias E Perakis², Thomas Hicken⁶, Hubertus Luetkens⁶, Fei Xue², Mehdi Kargarian⁸, Weisheng Zhao⁴, Luis Balicas^{6

9}, M Zahid Hasan¹⁰

Affiliations

¹ Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey, USA. mdsh@princeton.edu.
² Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama, USA.
³ Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey, USA.
⁴ National Key Laboratory of Spintronics, Hangzhou International Innovation Institute, Beihang University, Hangzhou, P.R. China.
⁵ Hefei Innovation Research Institute, School of Microelectronics, Beihang University, Hefei, P.R. China.
⁶ PSI Center for Neutron and Muon Sciences CNM, Villigen PSI, Switzerland.
⁷ National High Magnetic Field Laboratory, Tallahassee, Florida, USA.
⁸ Department of Physics, Sharif University of Technology, Tehran, Iran.
⁹ Physics Department, Florida State University, Tallahassee, FL, USA.
¹⁰ Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey, USA. mzhasan@princeton.edu.

^# Contributed equally.

Abstract

The interplay between topology and superconductivity generated great interest in condensed matter physics. Here, we unveil an unconventional two-dimensional superconducting state in the Dirac nodal line semimetal ZrAs₂ which is exclusively confined to the top and bottom surfaces within the crystal's ab plane. As a remarkable consequence, we present the first clear evidence of a Berezinskii-Kosterlitz-Thouless (BKT) transition occurring solely on a material's surface-specifically, ZrAs₂-unlike the inconsistent reports on PtBi₂, CaAgP, and CaAg₁₋ₓPdₓP. Furthermore, we find that these same surfaces also host a two-dimensional van Hove singularity near the Fermi energy. This leads to enhanced electronic correlations that contribute to the stabilization of superconductivity at the surface of ZrAs₂. The`surface-confined nature of the van Hove singularity and associated superconductivity, realized for the first time, allows exploring the interplay between low-dimensional quantum topology and superconductivity in a bulk material without resorting to the superconducting proximity effect.