Electronic fine structure in the nickel carbide superconductor Th2NiC2

Y. Quan; W. E. Pickett

doi:10.1103/PhysRevB.88.014501

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Electronic fine structure in the nickel carbide superconductor Th2NiC2

Y. Quan, W. E. Pickett

DOI 10.1103/PhysRevB.88.014501 · Physical Review B

T1

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Bibliographic access preserves source history; it does not approve extracted materials or validate reported claims. Review warnings on each occurrence separately.

Abstract

The recently reported nickel carbide superconductor body centered tetragonal I4/mmm Th2NiC2 with Tc=8.5 K increasing to 11.2 K upon alloying Th with Sc is found to have very fine structure in its electronic spectrum, according to density functional based first-principles calculations. The filled Ni 3d band complex is hybridized with C 2p and Th character to and through the Fermi level (EF), and a sharply structured density of states arises only when spin-orbit coupling is included, which splits a zone-center degeneracy, leaving a very flat band edge lying at the Fermi level. The flat part of the band corresponds to an effective mass mz*→∞ with large and negative mx*=my*. Although the region over which the effective mass characterization applies is less than 1% of the zone volume, it supplies on the order of half the states at (or just above) the Fermi level. The observed increase of Tc by hole doping is accounted for if the reference as-synthesized sample is minutely hole doped, which decreases the Fermi level density of states and will provide some stabilization. In this scenario, electron doping will increase the Fermi level density of states and the superconducting critical temperature. Vibrational properties are presented, and enough coupling to the C-Ni-C stretch mode at 70 meV is obtained to imply that superconductivity is electron-phonon mediated.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Th2NiC2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8.5	Pressure not reported	unknown
Th2-xScxNiC2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	11.2	Pressure not reported	unknown
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	40	Pressure not reported	unknown
YPd2B2C Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	23	Pressure not reported	unknown
MgCNi3 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8	Pressure not reported	unknown
ZrNi2Ca Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	3	Pressure not reported	unknown
LaNiBN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	4	Pressure not reported	unknown
La3Ni2B2N3 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	12	Pressure not reported	unknown
Th3Ni5C5 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5	Pressure not reported	unknown
ThNi4C Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	5.5	Pressure not reported	unknown
LaNiC2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	2.7	Pressure not reported	unknown