Observation of a Pronounced Hebel-Slichter Peak in the Spin-Lattice Relaxation Rate and Implications for Gap and Pairing Symmetry in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>LaNiGa</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math>

P. Sherpa; R. Hingorani; A. Menon; I. Vinograd; C. Chaffey; A. P. Dioguardi; R. Yamamoto; M. Hirata; F. Ronning; J. R. Badger; P. Klavins; R. R. P. Singh; V. Taufour; N. J. Curro

doi:10.1103/tsnb-1mxc

Observation of a Pronounced Hebel-Slichter Peak in the Spin-Lattice Relaxation Rate and Implications for Gap and Pairing Symmetry in ${LaNiGa}_{2}$

P. Sherpa ¹, R. Hingorani ¹, A. Menon ¹, I. Vinograd ², C. Chaffey ¹, A. P. Dioguardi ³, R. Yamamoto ^3,*, M. Hirata ³, F. Ronning ³ et al.

J. R. Badger⁴, P. Klavins ¹, R. R. P. Singh ¹, V. Taufour ¹, and N. J. Curro ¹

¹Department of Physics and Astronomy, University of California, Davis, California 95616, USA
²Laboratoire National des Champs Magnétiques Intenses, CNRS - Université Grenoble Alpes - Université Paul Sabatier - Institut National des Sciences Appliquées - European Magnetic Field Laboratory, 38042 Grenoble, France
³Materials Physics and Applications - Quantum, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁴Department of Chemistry, University of California, Davis, California 95616, USA

^*Present address: Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA.

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Phys. Rev. Lett. 136, 186001 – Published 6 May, 2026

DOI: https://doi.org/10.1103/tsnb-1mxc

Abstract

We report a pronounced Hebel-Slichter coherence peak in the zero field nuclear quadrupolar resonance (NQR) spin-lattice relaxation rate of the topological crystalline superconductor ${LaNiGa}_{2}$ in the superconducting state. Previously, a two-band internally antisymmetric nonunitary triplet pairing state was proposed for this system, with equal spin pairing and two distinct gaps associated with different spins. A detailed examination of the temperature dependence of the NQR data shows that the data best fit an internally antisymmetric triplet pairing model if the two gaps are equal and the model is unitary. Even a tiny nonunitarity with two unequal gaps causes the coherence peak to diminish rapidly and deviate from the data. On the other hand, the data are well fit by a two-band singlet Bardeen-Cooper-Schrieffer (BCS)-like pairing with two distinct gaps consistent with previous measurements. This raises doubts on the identification of nonunitary triplet pairing with time-reversal symmetry breaking in this material.

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Observation of a Pronounced Hebel-Slichter Peak in the Spin-Lattice Relaxation Rate and Implications for Gap and Pairing Symmetry in ${LaNiGa}_{2}$

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Observation of a Pronounced Hebel-Slichter Peak in the Spin-Lattice Relaxation Rate and Implications for Gap and Pairing Symmetry in LaNiGa2

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Observation of a Pronounced Hebel-Slichter Peak in the Spin-Lattice Relaxation Rate and Implications for Gap and Pairing Symmetry in ${LaNiGa}_{2}$