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

Abstract

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.

Authors:
 [1];  [1];  [1];  [1]
  1. Univ. of California, Davis, CA (United States)
Publication Date:
Research Org.:
Univ. of California, Davis, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1329349
Grant/Contract Number:  
FG52-09NA29464
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 81; Journal Issue: 24; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Rhee, H. B., Banerjee, S., Ylvisaker, E. R., and Pickett, W. E. NaAlSi: Self-doped semimetallic superconductor with free electrons and covalent holes. United States: N. p., 2010. Web. doi:10.1103/PhysRevB.81.245114.
Rhee, H. B., Banerjee, S., Ylvisaker, E. R., & Pickett, W. E. NaAlSi: Self-doped semimetallic superconductor with free electrons and covalent holes. United States. doi:10.1103/PhysRevB.81.245114.
Rhee, H. B., Banerjee, S., Ylvisaker, E. R., and Pickett, W. E. Tue . "NaAlSi: Self-doped semimetallic superconductor with free electrons and covalent holes". United States. doi:10.1103/PhysRevB.81.245114. https://www.osti.gov/servlets/purl/1329349.
@article{osti_1329349,
title = {NaAlSi: Self-doped semimetallic superconductor with free electrons and covalent holes},
author = {Rhee, H. B. and Banerjee, S. and Ylvisaker, E. R. and Pickett, W. E.},
abstractNote = {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.},
doi = {10.1103/PhysRevB.81.245114},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 24,
volume = 81,
place = {United States},
year = {2010},
month = {6}
}

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Works referenced in this record:

Accurate and simple analytic representation of the electron-gas correlation energy
journal, June 1992