Structure and superconductivity in the ternary silicide CaAlSi |
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Authors: | Ma Rong Huang Gui-qin and Liu Mei |
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Institution: | (1) Department of Physics, Southeast University, Nanjing, 210096, China;(2) Department of Physics, Nanjing Normal University, Nanjing, 210097, China |
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Abstract: | Using the linear response-linearized Muffin-tin orbital (LR-LMTO) method, we study the electronic band structure, phonon spectra,
electron-phonon coupling and superconductivity for c-axis ferromagnetic-like (F-like) and antiferromagnetic-like (AF-like) structures in ternary silicide CaAlSi. The following
conclusions are drawn from our calculations. If Al and Si atoms are assumed to arrange along the c axis in an F-like long-range
ordering (-Al-Al-Al-and-Si-Si-Si-), one could obtain the ultrasoft B1g phonon mode and thus very strong electron-phonon coupling in CaAlSi. However, the appearance of imaginary frequency phonon
modes indicates the instability of such a structure. For Al and Si atoms arranging along the c axis in an AF-like long-range ordering (-Al-Si-Al-), the calculated electron-phonon coupling constant is equal to 0.8 and
the logarithmically averaged frequency is 146.8 K. This calculated result can correctly yield the superconducting transition
temperature of CaAlSi by the standard BCS theory in the moderate electron-phonon coupling strength. We propose that an AF-like
superlattice model for Al (or Si) atoms along the c direction may mediate the inconsistency estimated from theory and experiment,
and explain the anomalous superconductivity in CaAlSi.
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Keywords: | superconductivity band structure |
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