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Two-gap superconductivity in LaNiGa\(_2\) with nonunitary triplet pairing and even parity gap symmetry

Weng, Z.F., Zhang, J.L., Smidman, M., Shang, T., Quintanilla, J., Annett, J.F., Nicklas, M., Pang, G.M., Jiao, L., Jiang, W.B., and others. (2016) Two-gap superconductivity in LaNiGa\(_2\) with nonunitary triplet pairing and even parity gap symmetry. Physical Review Letters, 117 (2). ISSN 0031-9007. E-ISSN 1079-7114. (doi:10.1103/PhysRevLett.117.027001)

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Abstract

The nature of the pairing states of superconducting LaNiC\(_2\) and LaNiGa\(_2\) has to date remained a puzzling question. Broken time reversal symmetry has been observed in both compounds and a group theoretical analysis implies a non-unitary triplet pairing state. However all the allowed non-unitary triplet states have nodal gap functions but most thermodynamic and NMR measurements indicate fully gapped superconductivity in LaNiC\(_2\). Here we probe the gap symmetry of LaNiGa\(_2\) by measuring the London penetration depth, specific heat and upper critical field. These measurements demonstrate two-gap nodeless superconductivity in LaNiGa\(_2\), suggesting that this is a common feature of both compounds. These results allow us to propose a novel triplet superconducting state, where the pairing occurs between electrons of the same spin, but on different orbitals. In this case the superconducting wavefunction has a triplet spin component but isotropic even parity gap symmetry, yet the overall wavefunction remains antisymmetric under particle exchange. This model leads to a nodeless two-gap superconducting state which breaks time reversal symmetry, and therefore accounts well for the seemingly contradictory experimental results.

Item Type: Article
DOI/Identification number: 10.1103/PhysRevLett.117.027001
Uncontrolled keywords: Physics of Quantum Materials, LaNiGa2, superconductivity, centrosymmetric, broken time-reversal symmetry, gap, BCS theory, LaNiC2
Subjects: Q Science > QC Physics > QC173.45 Condensed Matter
Q Science > QC Physics > QC176 Solid state physics
Divisions: Faculties > Sciences > School of Physical Sciences > Functional Materials Group
Depositing User: Jorge Quintanilla
Date Deposited: 15 Jun 2016 10:33 UTC
Last Modified: 24 Jan 2020 16:24 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/55951 (The current URI for this page, for reference purposes)
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