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Structure, composition, and high-field superconductivity in metal-rich η-carbide-type compounds

Manuele Balestra1, KeYuan Ma2, Harald O. Jeschke3, and Fabian O. von Rohr1,*

  • *Contact author: fabian.vonrohr@unige.ch
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Phys. Rev. Materials 10, 050301 – Published 28 May, 2026

DOI: https://doi.org/10.1103/yg12-fm19

Abstract

η-Carbide-type compounds have recently emerged as a diverse class of materials in the study of superconductivity. These phases contribute to a growing family of metal-rich quantum materials that exhibit unusual superconducting properties emerging from complex metallic bonding. Several members of the η-carbide-type phases have been found to be bulk superconductors, such as Nb4Rh2C1−δ, Ta4Rh2C1−δ, Ti4Ir2O1−δ, and Ti4Co2O1−δ–with transition temperatures up to Tc≈ 10 K and upper critical fields as high as μ0Hc2(0)≈ 30 T. Whereas the transition temperatures may fall within the range typical for intermetallic superconductors, the pronounced violation of the weak-coupling Pauli limit in many of these crystallographically high-symmetry materials is noteworthy. Here, we review recent progress on superconducting η-carbide-type phases, emphasizing how crystal symmetry, synthetic challenges, transition-metal composition, and electronic structure govern their superconducting properties. Furthermore, we outline open questions and future directions, including the possible discovery of additional η-carbide-type materials.

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Phys. Rev. Materials 10, 050301– Published 28 May, 2026
  • Received 28 January 2026
  • Accepted 26 March 2026
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