Abstract
The possible role of electronic structure on observed phonon anomalies in high-temperature superconducting transition-metal carbides is studied by means of accurate ab initio calculations of the conduction electron response function. From augmented-plane-wave determinations of the electronic band structure, density of states, and Fermi surface of NbC and TaC, the wave-vector-dependent generalized susceptibility, χ(q→), is calculated in the constant-matrix-element approximation. For both NbC and TaC, χ(q→) has strong maxima at precisely those q→ values at which soft modes were observed by Smith and Gläser. Maxima in χ(q→) are predicted for other directions. The locus of these q→max values can be represented by a warped cube of dimension ∼1.2(2πa) in momentum space-in striking agreement with the soft-mode surface proposed phenomenologically by Weber. In sharp contrast, the χ(q→) calculated for both ZrC and HfC-for which no phonon anomalies have been observed-fall off in all symmetry directions away from the zone center. In agreement with Phillips, we thus interpret the phonon anomalies in the transition-metal carbides as due to an "overscreening" effect resulting from an anomalous increase of the response function of the conduction electrons.
| Original language | English |
|---|---|
| Pages (from-to) | 5205-5217 |
| Number of pages | 13 |
| Journal | Physical Review B |
| Volume | 14 |
| Issue number | 12 |
| DOIs | |
| Publication status | Published - 1976 |
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ASJC Scopus subject areas
- Condensed Matter Physics
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Role of electronic structure on observed phonon anomalies of transition-metal carbides. / Gupta, Michèle; Freeman, Arthur J.
In: Physical Review B, Vol. 14, No. 12, 1976, p. 5205-5217.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Role of electronic structure on observed phonon anomalies of transition-metal carbides
AU - Gupta, Michèle
AU - Freeman, Arthur J
PY - 1976
Y1 - 1976
N2 - The possible role of electronic structure on observed phonon anomalies in high-temperature superconducting transition-metal carbides is studied by means of accurate ab initio calculations of the conduction electron response function. From augmented-plane-wave determinations of the electronic band structure, density of states, and Fermi surface of NbC and TaC, the wave-vector-dependent generalized susceptibility, χ(q→), is calculated in the constant-matrix-element approximation. For both NbC and TaC, χ(q→) has strong maxima at precisely those q→ values at which soft modes were observed by Smith and Gläser. Maxima in χ(q→) are predicted for other directions. The locus of these q→max values can be represented by a warped cube of dimension ∼1.2(2πa) in momentum space-in striking agreement with the soft-mode surface proposed phenomenologically by Weber. In sharp contrast, the χ(q→) calculated for both ZrC and HfC-for which no phonon anomalies have been observed-fall off in all symmetry directions away from the zone center. In agreement with Phillips, we thus interpret the phonon anomalies in the transition-metal carbides as due to an "overscreening" effect resulting from an anomalous increase of the response function of the conduction electrons.
AB - The possible role of electronic structure on observed phonon anomalies in high-temperature superconducting transition-metal carbides is studied by means of accurate ab initio calculations of the conduction electron response function. From augmented-plane-wave determinations of the electronic band structure, density of states, and Fermi surface of NbC and TaC, the wave-vector-dependent generalized susceptibility, χ(q→), is calculated in the constant-matrix-element approximation. For both NbC and TaC, χ(q→) has strong maxima at precisely those q→ values at which soft modes were observed by Smith and Gläser. Maxima in χ(q→) are predicted for other directions. The locus of these q→max values can be represented by a warped cube of dimension ∼1.2(2πa) in momentum space-in striking agreement with the soft-mode surface proposed phenomenologically by Weber. In sharp contrast, the χ(q→) calculated for both ZrC and HfC-for which no phonon anomalies have been observed-fall off in all symmetry directions away from the zone center. In agreement with Phillips, we thus interpret the phonon anomalies in the transition-metal carbides as due to an "overscreening" effect resulting from an anomalous increase of the response function of the conduction electrons.
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U2 - 10.1103/PhysRevB.14.5205
DO - 10.1103/PhysRevB.14.5205
M3 - Article
VL - 14
SP - 5205
EP - 5217
JO - Physical Review B-Condensed Matter
JF - Physical Review B-Condensed Matter
SN - 1098-0121
IS - 12
ER -