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Strong-coupling superconductivity due to soft boson modes in MgB_2, cuprates, borocarbides and some heavy fermions

D. Lampakis·A. Tatsi·E. Liarokapis·G. Varelogiannis·P. M. Oppeneer·M. Pissas·T. Nishizaki
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Abstract

We report micro-Raman measurements that reveal a low-energy soft mode at 16-19 meV in MgB_2 which becomes sharper in the superconducting state. With a boson spectrum based on this mode we reproduce, within Eliashberg theory, the T_c, the T-shape of the NMR relaxation rate as well as unusual dip-hump features in available tunneling data. We compare MgB_2 to cuprates, borocarbides and UPd_2Al_3, where we identify soft bosonic modes at energies which scale with their T_c suggesting that all these materials are very strong coupling superconductors to soft bosonic modes, that are possibly precursors of quantum instabilities.

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D. Lampakis, A. Tatsi, E. Liarokapis, G. Varelogiannis, P. M. Oppeneer, M. Pissas, T. Nishizaki. 2001-05-22. Strong-coupling superconductivity due to soft boson modes in MgB_2, cuprates, borocarbides and some heavy fermions. https://arxiv.org/abs/cond-mat/0105447

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