NaAlSi: Self-doped semimetallic superconductor with free electrons and covalent holes

Journal Article · 14 June 2010 · Physical Review. B, Condensed Matter and Materials Physics

DOI: https://doi.org/10.1103/PhysRevB.81.245114 · OSTI ID:1329349

Rhee, H. B. ^[1]; Banerjee, S. ^[2]; Ylvisaker, E. R. ^[2]; Pickett, W. E. ^[2]

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1. Univ. of California, Davis, CA (United States); UC Davis
2. Univ. of California, Davis, CA (United States)

In a layered ternary sp conductor NaAlSi, possessing the iron-pnictide “111” crystal structure, it superconducts at 7 K. Using density-functional methods, we show that this compound is an intrinsic (self-doped) low-carrier-density semimetal with a number of unusual features. Covalent Al-Si valence bands provide the holes, and free-electronlike Al 3s bands, which propagate in the channel between the neighboring Si layers, dip just below the Fermi level to create the electron carriers. The Fermi level (and therefore the superconducting carriers) lies in a narrow and sharp peak within a pseudogap in the density of states. The small peak arises from valence bands which are nearly of pure Si, quasi-two-dimensional, flat, and coupled to Al conduction bands. Isostructural NaAlGe, which is not superconducting above 1.6 K, has almost exactly the same band structure except for one missing piece of small Fermi surface. At certain deformation potentials induced by Si and Na displacements along the c axis are calculated and discussed. Finally, it seems likely that the mechanism of pairing is related to that of several other lightly doped two-dimensional nonmagnetic semiconductors (TiNCl, ZrNCl, HfNCl), which is not well understood but apparently not of phonon origin.

• Research Organization: Univ. of California, Davis, CA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: FG52-09NA29464
• OSTI ID: 1329349
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 24 Vol. 81; ISSN 1098-0121; ISSN PRBMDO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English