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 CeCuSi, 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 CeCuSi. In YbRhSi, superconductivity appears to be suppressed at mK by AF order ( = 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 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 = 2 mK. Like the pressure - induced QCP in CeRhIn, the magnetic field - induced one in YbRhSi 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- unconventional heavy - fermion superconductors and other families of unconventional superconductors with higher 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.
Keywords
Cite
@article{arxiv.1808.02277,
title = {Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCu$_2$Si$_2$ versus YbRh$_2$Si$_2$},
author = {M. Smidman and O. Stockert and J. Arndt and G. M. Pang and L. Jiao and H. Q. Yuan and H. A. Vieyra and S. Kitagawa and K. Ishida and K. Fujiwara and T. C. Kobayashi and E. Schuberth and M. Tippmann and L. Steinke and S. Lausberg and A. Steppke and M. Brando and H. Pfau and U. Stockert and P. Sun and S. Friedemann and S. Wirth and C. Krellner and S. Kirchner and E. M. Nica and R. Yu and Q. Si and F. Steglich},
journal= {arXiv preprint arXiv:1808.02277},
year = {2018}
}
Comments
30 pages, 7 Figures, Accepted for publication in Philosophical Magazine