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TT: Tiefe Temperaturen
TT 4: Schwere Fermionen, Kondo-Systeme
TT 4.7: Vortrag
Montag, 24. März 2003, 16:15–16:30, HSZ03
Evidence for two different superconducting states in CeCu2(Si/Ge)2 under pressure — •H. Q. Yuan, M. Deppe, G. Sparn, C. Geibel, F. M. Grosche, and F. Steglich — MPI-CPFS, Nöthnitzer Str. 40, 01187, Dresden.
There is a growing number of heavy fermion compounds showing pressure induced superconductivity near a magnetic quantum critical point (QCP). Among these systems, CeCu2Si2 presented a very peculiar pressure dependence of Tc: Tc≃0.7 K being almost pressure independent at low pressures (p<2 GPa), but increasing steeply at p≃3 GPa up to Tc≃2.3 K. The origin of this strange increase is controversial. We present here a pressure study on single crystals of CeCu2(Si1−xGex)2 (0<x≤0.25). The superconducting region, which is continuous and broad in pure CeCu2Si2, splits in Ge-doped single crystals into two distinct regimes: one at low pressures and one at high pressures, suggesting different superconducting coupling mechanisms under pressure in the two regimes. For the low pressure regime (e.g. p<3 GPa for x=0.1), superconductivity occurs around the antiferromagnetic QCP, consistent with the model of magnetically mediated superconductivity. For the high pressure regime, we propose that it may originate from valence fluctuation, suggested in the theory presented by Miyake et al [1]. Non Fermi liquid behavior (ρ=ρ0+ATn: 1<n<1.5) exists over a broad pressure range.
[1] J. Onishi et al, J. Phys. Soc. Jpn. 69, 3955 (2000); K. Miyake et al, J. Phys. Soc. Jpn. 71, 1007 (2002).