Effect of disorder on the pressure-induced superconducting state ofCeAu2Si2

Abstract

CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor which shows very unusual interplay between superconductivity and magnetism under pressure. Here we compare the results of high-pressure measurements on single crystalline CeAu2Si2 samples with different levels of disorder. It is found that while the magnetic properties are essentially sample independent, superconductivity is rapidly suppressed when the residual resistivity of the sample increases. We show that the depression of bulk Tc can be well understood in terms of pair breaking by nonmagnetic disorder, which strongly suggests an unconventional pairing state in pressurized CeAu2Si2. Furthermore, increasing the level of disorder leads to the emergence of another phase transition at T * within the magnetic phase, which might be in competition with superconductivity.

Ubiquity of unconventional phenomena associated with critical valence fluctuations in heavy fermion metals

“…Although the existence of the two peaks in ρ(T ) and the mergence of them under pressure can be shown theoretically as an effect of smearing crystalline-electric-field (CEF) splitting by the increase of the c-f hybridization under pressure in general [47], it is non-trivial that the mergence occurs at around P = P v . This behavior was also observed in CeCu 2 Ge 2 [22], CeAu 2 Si 2 [48], and CeAl 2 [49], suggesting a generic property associated with the sharp valence crossover of Ce ion as argued below [24].…”

The dominant role of critical valence fluctuations on high Tc superconductivity in heavy fermions

“…Evidently, a simple fit to χ(T ) yields T cr . The empirical law (T − T cr ) −1 is confirmed by data from several samples of CeCu 2 Si 2 [8], CeAu 2 Si 2 [18,26,27], and CeRhIn 5 [17], which are by the way the compounds with highest T c and least negative T cr . Note that the plot of χ(T ) is limited to a temperature (15 K), which corresponds to a small fraction of the first crystal-field-splitting energy.…”

“…After identifying T cr , one can apply the scaling treatment developed in Ref. [8] for CeCu 2 Si 2 within the framework of universal scaling theory of critical phenomena and subsequently applied on data from CeAu 2 Si 2 [18,26,27] and CeRhIn 5 [17]. To this end, a generalized distance h/θ from the CEP is calculated, where h = (p − p VCO )/p VCO and θ = (T − T cr )/|T cr |.…”

High-Pressure Study of the Ground- and Superconducting-State Properties of CeAu2Si2

“…The SC dome of this sample has only half the width of that of a low-ρ 0 sample and SC is absent for V > 163Å 3 , which corresponds to the observed p c in CeCu 2 (Si/Ge) 2 . Moreover, the maximum T bulk c of the three systems displays the same reduction versus ρ 0 , indicating pair breaking by nonmagnetic disorder [2]. Such an effect appears to be even stronger for V > 163Å 3 , which suggests that SC is not yet observed in CeCu 2 Ge 2 for p < 10 GPa or in partially Gesubstituted CeCu 2 Si 2 [25,46] because of the too short mean free path l ∝ ρ −1 0 in the investigated samples.…”

“…Furthermore, the strong pair-breaking effect of non-magnetic impurities attests unconventional SC [2]. CeAu 2 Si 2 has a tetragonal ThCr 2 Si 2 -type structure with the space group I4/mmm (D 17 4h ) [3,4] and orders antiferromagnetically below T N = 9.6 K [5,6].…”