Fermiology and type-I superconductivity in the chiral superconductor NbGe2 with Kramers-Weyl fermions

Eve Emmanouilidou, Sougata Mardanya, Jie Xing, P. V.Sreenivasa Reddy, Amit Agarwal, Tay Rong Chang, Ni Ni

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Abstract

In this paper we present a systematic study of the de Haas-van Alphen (dHvA) oscillations, magnetotransport, and superconductivity in the Kramers-Weyl semimetal candidate NbGe2. We show that NbGe2 is a type-I chiral superconductor with a Tc of 2.06 K, a full gap, a type-II to type-I crossover around 1.5 K, and an enhanced critical field from filamentary superconductivity suggested by resistivity measurements. The study of the dHvA oscillations reveals three distinct frequency branches β and the spin-split α/α′, with cyclotron effective masses of 1.21(5)me, 0.21(1)me, and 0.24(1)me, respectively. The magnetoresistance of NbGe2 exceeds 1000% at 2.4 K and 9 T and exhibits quasilinear behavior at low temperatures. The comparison between experimental results and first-principles calculations shows excellent agreement between the two and suggests that α and α′ correspond to the hole Fermi pockets centered around the Weyl M point, while β is associated with the hole pocket near the trivial H point in the Brillouin zone. Furthermore, we show that a Van Hove singularity arising from the contributions of the M and H points at the Fermi level, together with the calculated electron-phonon coupling, is strong enough to account for the observed superconductivity. Last, our calculation of the conductivity tensor within the relaxation time approximation suggests that the observed linear magnetoresistance most likely arises from the presence of open Fermi surfaces.

Original languageEnglish
Article number235144
JournalPhysical Review B
Volume102
Issue number23
DOIs
StatePublished - Dec 21 2020
Externally publishedYes

Funding

Work at UCLA was supported by the NSF DMREF program under NSF DMREF Project No. DMREF-1629457. T.-R.C. was supported by the Young Scholar Fellowship Program from the Ministry of Science and Technology (MOST) in Taiwan, under a MOST grant for the Columbus Program, Grant No. MOST108-2636-M-006-002; National Cheng Kung University, Taiwan; and the National Center for Theoretical Sciences, Taiwan. This work was supported partially by the MOST, Taiwan, under Grant No. MOST107-2627-E-006-001. This research was supported, in part, by the Higher Education Sprout Project, Ministry of Education to the Headquarters of University Advancement at National Cheng Kung University (NCKU). The work at IIT Kanpur benefited from the high-performance facilities of the computer center of IIT Kanpur.

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