| CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES |
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Superconductivity with a Violation of Pauli Limit and Evidences for Multigap in $\eta$-Carbide Type Ti$_4$Ir$_2$O |
| Bin-Bin Ruan1,2*, Meng-Hu Zhou1,2, Qing-Song Yang2,3, Ya-Dong Gu2,3, Ming-Wei Ma2, Gen-Fu Chen2,3, and Zhi-An Ren2,3* |
1Songshan Lake Materials Laboratory, Dongguan 523808, China
2Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China
3School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
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| Cite this article: |
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Bin-Bin Ruan, Meng-Hu Zhou, Qing-Song Yang et al 2022 Chin. Phys. Lett. 39 027401 |
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Abstract We report the synthesis, crystal structure, and superconductivity of Ti$_4$Ir$_2$O. The title compound crystallizes in an $\eta$-carbide type structure of the space group $Fd\bar{3}m$ (No. 227), with lattice parameters $a=b=c=11.6194(1)$ Å. The superconducting temperature $T_{\rm c}$ is found to be 5.1–5.7 K. Most surprisingly, Ti$_4$Ir$_2$O hosts an upper critical field of 16.45 T, which is far beyond the Pauli paramagnetic limit. Strong coupled superconductivity with evidences for multigap is revealed by the measurements of heat capacity and upper critical field. First-principles calculations suggest that the density of states near the Fermi level originates from the hybridization of Ti-3$d$ and Ir-5$d$ orbitals, and the effect of spin-orbit coupling on the Fermi surfaces is prominent. Large values of the Wilson ratio ($R_{\rm W} \sim 3.9$), the Kadowaki–Woods ratio [$A/\gamma^2 \sim 9.0 \times 10^{-6}$ $µ\Omega\cdot$cm/(mJ$\cdot$mol$^{-1}\cdot$K$^{-1}$)$^2$], and the Sommerfeld coefficient ($\gamma = 33.74$ mJ$\cdot$mol$^{-1}\cdot$K$^{-2}$) all suggest strong electron correlations (similar to heavy fermion systems) in Ti$_4$Ir$_2$O. The violation of Pauli limit is possibly due to a combination of strong-coupled superconductivity and large spin-orbit scattering. With these intriguing behaviors, Ti$_4$Ir$_2$O serves as a candidate for unconventional superconductor.
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Received: 14 December 2021
Editors' Suggestion
Published: 29 January 2022
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| PACS: |
74.25.-q
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(Properties of superconductors)
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71.27.+a
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(Strongly correlated electron systems; heavy fermions)
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74.25.Op
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(Mixed states, critical fields, and surface sheaths)
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74.25.Bt
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(Thermodynamic properties)
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