The Dominant Role of Critical Valence Fluctuations on High $T_{\mathrm{c}}$ Superconductivity in Heavy Fermions

Abstract

Despite almost 40 years of research, the origin of heavy-fermion superconductivity is still strongly debated. Especially, the pressure-induced enhancement of superconductivity in CeCu${}_2$Si${}_2$ away from the magnetic breakdown is not sufficiently taken into consideration. As recently reported in CeCu${}_2$Si${}_2$ and several related compounds, optimal superconductivity occurs at the pressure of a valence crossover, which arises from a virtual critical end point at negative temperature $T_{\mathrm{cr}}$. In this context, we did a meticulous analysis of a vast set of top-quality high-pressure electrical resistivity data of several Ce-based heavy fermion compounds. The key novelty is the salient correlation between the superconducting transition temperature $T_{\mathrm{c}}$ and the valence instability parameter $T_{\mathrm{cr}}$, which is in line with theory of enhanced valence fluctuations. Moreover, it is found that, in the pressure region of superconductivity, electrical resistivity is governed by the valence crossover, which most often manifests in scaling behavior. We develop the new idea that the optimum superconducting $T_{\mathrm{c}}$ of a given sample is mainly controlled by the compound's $T_{\mathrm{cr}}$ and limited by non-magnetic disorder. In this regard, the present study provides compelling evidence for the crucial role of critical valence fluctuations in the formation of Cooper pairs in Ce-based heavy fermion superconductors besides the contribution of spin fluctuations near magnetic quantum critical points, and corroborates a plausible superconducting mechanism in strongly correlated electron systems in general.

Supplementary Material follows after the bibliography

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Cited by in corpus (7)

• Non-symmorphic symmetry and field-driven odd-parity pairing in CeRh${}_2$As${}_2$
• Emergent Charge Fluctuations at the Kondo Breakdown of Heavy Fermions
• Tuning the parity of superconductivity in CeRh2As2 via pressure
• Sr${}_2$RuO${}_4$, like doped cuprates and barium bismuthate, is a negative charge-transfer gap even parity superconductor with $\frac{3}{4}$-filled oxygen band
• Novel attractive pairing interaction in strongly correlated superconductors
• Magnetism trends in doped Ce-Cu intermetallics in the vicinity of quantum criticality: realistic Kondo lattice models based on dynamical mean-field theory
• Navigating the trends in the proximity to magnetic quantum critical point and superconductivity for Ce-based heavy-fermion compounds