Superconducting Energy Gap Structure of Quasi-1D Spin-Triplet Candidate Li<sub>0.9</sub>Mo<sub>6</sub>O<sub>17</sub>
ORAL
Abstract
Li0.9Mo6O17 (LMO), a quasi-one-dimensional purple bronze, is a leading candidate for the realisation of a Tomonaga-Luttinger liquid (TLL) and exhibits an emergent symmetry at low temperature [1,2]. Superconductivity emerges from this non-Fermi liquid normal state at Tc ≈ 2.3 K, with the upper critical field along the conductive b-axis (Hc2 ≈ 15 T) exceeding the Pauli paramagnetic limit, indicative of unconventional spin-triplet pairing [3]. Possible signatures of re-entrant superconductivity at 45 T further suggests exotic behaviour in the superconducting phase [4]. Despite these intriguing observations, the superconducting gap structure and pairing mechanism in LMO have remained unexplored.
We report the first investigation of the superconducting energy gap structure of LMO, using tunnel-diode oscillator-based magnetic penetration depth measurements down to 70 mK, alongside specific heat measurements down to 300 mK. These complementary techniques, probing the low-energy excitations in the superconducting state, reveal a fully gapped Fermi surface with the penetration depth data suggesting a gap minimum of Δ ≈ 0.1 meV. However, the large specific heat anomaly observed suggests a strong coupling scenario and a larger gap maximum. These findings suggest a complex, anisotropic superconducting order parameter. We discuss the implications of these results in the context of potential pairing symmetries and models that could explain the unconventional superconductivity in LMO.
[1] N. Wakeham et al., Nat Commun. 2, 396 (2011)
[2] P. Chudzinski et al., Science 382, 792 (2023)
[3] J.-F. Mercure et al., Phys. Rev. Lett. 108, 187003 (2012)
[4] X. Xu et al., Phys. Rev. Lett. 102, 206602 (2009)
We report the first investigation of the superconducting energy gap structure of LMO, using tunnel-diode oscillator-based magnetic penetration depth measurements down to 70 mK, alongside specific heat measurements down to 300 mK. These complementary techniques, probing the low-energy excitations in the superconducting state, reveal a fully gapped Fermi surface with the penetration depth data suggesting a gap minimum of Δ ≈ 0.1 meV. However, the large specific heat anomaly observed suggests a strong coupling scenario and a larger gap maximum. These findings suggest a complex, anisotropic superconducting order parameter. We discuss the implications of these results in the context of potential pairing symmetries and models that could explain the unconventional superconductivity in LMO.
[1] N. Wakeham et al., Nat Commun. 2, 396 (2011)
[2] P. Chudzinski et al., Science 382, 792 (2023)
[3] J.-F. Mercure et al., Phys. Rev. Lett. 108, 187003 (2012)
[4] X. Xu et al., Phys. Rev. Lett. 102, 206602 (2009)
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Presenters
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Morgan J Grant
University of Bristol
Authors
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Morgan J Grant
University of Bristol