Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCu${}_2$Si${}_2$ versus YbRh${}_2$Si${}_2$

Abstract

In this paper the low-temperature properties of two isostructural canonical heavy-fermion compounds are contrasted with regards to the interplay between antiferromagnetic (AF) quantum criticality and superconductivity. For CeCu${}_2$Si${}_2$, fully-gapped d-wave superconductivity forms in the vicinity of an itinerant three-dimensional heavy-fermion spin-density-wave (SDW) quantum critical point (QCP). Inelastic neutron scattering results highlight that both quantum critical SDW fluctuations as well as Mott-type fluctuations of local magnetic moments contribute to the formation of Cooper pairs in CeCu${}_2$Si${}_2$. In YbRh${}_2$Si${}_2$, superconductivity appears to be suppressed at $T\gtrsim 10$ mK by AF order ($T_N$ = 70 mK). Ultra-low temperature measurements reveal a hybrid order between nuclear and 4f-electronic spins, which is dominated by the Yb-derived nuclear spins, to develop at $T_A$ slightly above 2 mK. The hybrid order turns out to strongly compete with the primary 4f-electronic order and to push the material towards its QCP. Apparently, this paves the way for heavy-fermion superconductivity to form at $T_c$ = 2 mK. Like the pressure - induced QCP in CeRhIn${}_5$, the magnetic field - induced one in YbRh${}_2$Si${}_2$ is of the local Kondo-destroying variety which corresponds to a Mott-type transition at zero temperature. Therefore, these materials form the link between the large family of about fifty low-$T$ unconventional heavy - fermion superconductors and other families of unconventional superconductors with higher $T_c$s, notably the doped Mott insulators of the cuprates, organic charge-transfer salts and some of the Fe-based superconductors. Our study suggests that heavy-fermion superconductivity near an AF QCP is a robust phenomenon.

arXiv comment30 pages, 7 Figures, Accepted for publication in Philosophical Magazine

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Cited by in corpus (13)

• Quantum phases driven by strong correlations
• Anisotropic c-f hybridization in the ferromagnetic quantum critical metal CeRh${}_6$Ge${}_4$
• Two scenarios for superconductivity in CeRh${}_2$As${}_2$
• Superconductivity in disordered locally noncentrosymmetric materials: an application to CeRh${}_2$As${}_2$
• Revealing the Heavy Quasiparticles in the Heavy-Fermion Superconductor CeCu2Si2
• Unconventional fully-gapped superconductivity in the heavy-fermion metal CeCu${}_2$Si${}_2$
• Multiorbital singlet pairing and $d+d$ superconductivity
• Iron-based superconductors: teenage, complex, challenging
• Multiple superconducting phases in heavy-fermion metals
• Pairing symmetry of an intermediate valence superconductor CeIr3 investigated using muSR measurements
• Electro-nuclear transition into a spatially modulated magnetic state in YbRh${}_2$Si${}_2$
• Spin-singlet and spin-triplet pairing correlations in antiferromagnetically coupled Kondo systems
• Theory of $(s+id)$ pairing in mixed-valent correlated metals