Gernot Scheerer

Jeudi 6 Juillet 2017 à 14h00
Amphi Holweck, Esc C
1ème etage

Pressure induced Heavy Fermion Superconductivity in CeAu2Si2and CeAg2Si2
-Leading Role or Valence Fluctuations-

Two years ago, we discovered pressure-induced heavy fermion superconductivity in CeAu2Si2 [1] and very recently in CeAg2Si2. The case of CeAu2Si2 (T_SC^max = 2.5 K) is a real novelty [1,2] : superconductivity emerges, not on the verge, but deep inside the magnetic phase. The case of CeAg2Si2 (T_SC^max = 1.5 K) seems to be more classical, i.e., the superconducting dome emerges at the collapse of magnetic order.
We present the p-T phase diagram of both systems and compare them to their parent compounds CeCu2(Si/Ge)2. We have observed quantum critical behavior in the ground-state properties. A resistivity-scaling behavior is related to a pressure-induced valence crossover (COV) with a critical endpoint at p_cr and at slightly negative temperature Tcr (cf. [2,3]). With p_cr situated at or just above the pressure of the Tc-maximum, the COV is intimately linked to superconductivity. Actually the crossover-induced scaling behavior of resistivity is found systematically in all Ce-based systems, which have been studied by our group (also CeRhIn5, CeIrIn5, CeCu2Ge2, CePd2Si2, CeCu6, and CeCu5Au).
Therefore, we propose that critical valence fluctuations are the pairing glue for HF-SC in theses systems.

References

[1] Z. Ren et al., Phys Rev. X 4, 031055 (2014).
[2] G. Seyfarth et al., Phys. Rev. B 85, 205105 (2012).
[2] Z. Ren et al., Phys. Rev. B 91, 094515 (2015)

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