Electronic structure and electron-phonon interaction in the ternary silicides<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>M</mml:mi><mml:mi mathvariant="normal">AlSi</mml:mi></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo>(</mml:mo><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">Ca</mml:mi><mml:mo>,</mml:mo></mml:math>Sr, and Ba)

Huang, G. Q.; Chen, L. F.; Liu, M.; Xing, D. Y.

doi:10.1103/physrevb.69.064509

Cited by 58 publications

(50 citation statements)

References 18 publications

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“…g and Debye temperature in CaAlSi is 4.5 mJ/mol/K 2 , 225 K, respectively [9]. On the other hand, in BaAlSi, g is 7.0 mJ/mol/K 2 , and Debye temperature is 217 K. The larger g in BaAlSi is consistent with the band-structure calculation even after considering the renormalization by electron-phonon coupling [10,13]. The lower Debye temperature in BaAlSi is reasonable, since Ca is lighter than Ba.…”

Section: Article In Presssupporting

confidence: 76%

Comparison of physical properties in BaAlSi and CaAlSi

Sugawara

Sato

Souma

et al. 2006

Science and Technology of Advanced Materials

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CaAlSi, with the AlB 2 -type structure, is a superconductor with relatively high T c of 7.7 K and the related compounds, SrAlSi and BaAlSi have the same crystal structure. Despite the fact that the density of states in SrAlSi and BaAlSi is higher than that of CaAlSi, T c of SrAlSi is 4.2 K and BaAlSi does not show superconductivity down to 2 K. We synthesize polycrystalline and single crystalline BaAlSi and compare their physical properties with those in CaAlSi. The transport and the specific heat measurements show the higher density of states in BaAlSi, consistent with the band structure calculations. We interpret that the absence of superconductivity in BaAlSi is due to the much weaker electron-phonon coupling constant compared with that in CaAlSi, because of the absence of the soft-phonon mode. In the course of the study, we find a superconductor with a composition close to Ba 2 Al 4 Si 3 .

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Section: Article In Presssupporting

confidence: 76%

Comparison of physical properties in BaAlSi and CaAlSi

Sugawara

Sato

Souma

et al. 2006

Science and Technology of Advanced Materials

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“…CaAlSi). Concerning the superconducting mechanism, Mazin et al 8 have suggested that the available experimental data could be reconciled with a traditional e-ph scenario, assuming the existence of a soft phonon mode (∼ 30-40 cm −1 ); recently Huang et al 9,10 have calculated the phonon spectrum and electron-phonon coupling of CaAlSi, revealing the existence of a very soft (and, at some wavevector, even unstable) B 1g branch, which plays an important role in its superconducting properties; they also claim that this mode, which gets softer under pressure, can be invoked to explain the positive pressure effect on T c .…”

Section: The Discoverymentioning

confidence: 99%

“…3 Superconductivity has been detected in the whole composition range; the critical temperature T c (x) strongly depends on composition, showing a sharp peak at x = 1 (where T c = 7.8 K), and dropping off rapidly as the Al/Si ratio departs from unity. 3 Several experiments 4,5,6 and ab initio calculations 7,8,9,10 have concentrated on the x = 1 case (i.e. CaAlSi).…”

Section: The Discoverymentioning

confidence: 99%

Electrons and phonons in the ternary alloyCaAl2−xSixas a function of composition

2005

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We report a detailed first-principles study of the structural, electronic and vibrational properties of the superconducting C32 phase of the ternary alloy CaAl2−xSix, both in the experimental range 0.6 ≤ x ≤ 1.2, for which the alloy has been synthesised, and in the theoretical limits of high aluminium and high silicon concentration. Our results indicate that, in the experimental range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this range. Such a breakdown, in the (theoretical) limit of high aluminium concentration, is connected to the appearance of vibrational instabilities, and results in important differences between CaAl2 and MgB2. Unlike MgB2, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related C32 intermetallic compounds.

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“…13,14 The interplay of these two ingredients gives rise to intriguing effects both on the normal and the superconducting properties. The presence of an ultrasoft phonon mode at ∼7 meV was initially evidenced by first-principles calculations 11,12,15,16,17 and recently confirmed by neutron-scattering experiments. 17 The ultrasoft phonon modes are believed to induce strong eph coupling and to lead to an enhanced specific heat anomaly at T c as well as to a positive pressure dependence of T c in CaAlSi.…”

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confidence: 99%

Pressure effects on the superconducting transition innH-CaAlSi

et al. 2008

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We present a combined experimental and theoretical study of the effects of pressure on Tc of the hexagonal layered superconductors nH -CaAlSi (n = 1, 5, 6), where nH labels the different stacking variants that were recently discovered. Experimentally, the pressure dependence of Tc has been investigated by measuring the magnetic susceptibility of single crystals up to 10 kbar. In contrast to previous results on polycrystalline samples, single crystals with different stacking sequences display different pressure dependences of Tc. 1H-CaAlSi shows a decrease of Tc with pressure, whereas 5H and 6H-CaAlSi exhibit an increase of Tc with pressure. Ab-initio calculations for 1H, 5H and 6H -CaAlSi reveal that an ultrasoft phonon branch associated to out-of-plane vibrations of the Al-Si layers softens with pressure, leading to a structural instability at high pressures. For 1H-CaAlSi the softening is not sufficient to cause an increase of Tc, which is consistent with the present experiments, but adverse to previous reports. For 5H and 6H the softening provides the mechanism to understand the observed increase of Tc with pressure. Calculations for hypothetical 2H and 3H stacking variants reveal qualitative and quantitative differences.

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Electronic structure and electron-phonon interaction in the ternary silicidesMAlSi(M=Ca,Sr, and Ba)

Cited by 58 publications

References 18 publications

Comparison of physical properties in BaAlSi and CaAlSi

Comparison of physical properties in BaAlSi and CaAlSi

Electrons and phonons in the ternary alloyCaAl2−xSixas a function of composition

Pressure effects on the superconducting transition innH-CaAlSi

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