Negative isotope effect of a BCS-like gap; an inelastic light scattering study

In-Sang Yang; M. V. Klein; S. Bud'ko; P. C. Canfield

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Negative isotope effect of a BCS-like gap; an inelastic light scattering study

In-Sang Yang·M. V. Klein·S. Bud'ko·P. C. Canfield

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Abstract

In a prior study of the boron isotope effect on the transition temperature ($T_c$) of $R$Ni$_2$B$_2$C ($R$ = Y, Lu) system, a positive isotope effect was observed, e.g., $T_{c}(^{10}B)> T_{c}(^{11}B)$. BCS theory predicts that the superconducting gap at zero temperature ($Δ_0$) is proportional to $T_c$. Therefore, the gap should also show a positive boron isotope effect. On the contrary, in an inelastic light scattering study, we report a negative boron isotope effect on the energy $Ω$ of the gap-like feature in B$_{2g}$ symmetry, e.g., $Ω(^{10}B)< Ω(^{11}B)$. The origin of the effect is discussed in terms of selective probing of a non-conventional electron-phonon interaction on part of the Fermi surface, probably near the X point in the Brillouin zone.

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In-Sang Yang, M. V. Klein, S. Bud'ko, P. C. Canfield. 2002-02-08. Negative isotope effect of a BCS-like gap; an inelastic light scattering study. https://arxiv.org/abs/cond-mat/0202134

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