Superconductivity and pressure-induced electronic topological changes in

Abstract

Refined measurements are reported on the pressure dependence of the superconducting transition temperature in the heavy-fermion (HF) superconductor CeCu 2 Si 2 . Two characteristic pressures, p 1 ≈ 3 GPa and p 2 ≈ 7.6 GPa, delimit three ranges of the superconducting state. The present study confirms the unique behaviour of CeCu 2 Si 2 in the series of HF superconductors. This particular behaviour is interpreted as resulting from two contributions: a smooth one due to the pressure-increased Kondo temperature and sharper additional features reflecting topological changes in the renormalized heavy bands.

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

“…1, but may exhibit a jump close to 8 GPa. 41 As a general feature, the bulk (not shown, but similar to reports in Refs. 4 and 7).…”

“…T onset c (p) has already reached the level of the maximum T c at ∼2.5 GPa, but without a cusplike feature as in previous reports. 7,41 This rather quick increase of T onset c (p) may point to the fact that the VF pairing mechanism needs to be considered already at low p (at least in some form), as already inferred from the very weak decrease of T c (p) above p c . 42 Around p V , the maximum T onset c and T ρ=0 c coincide.…”

“…42 Around p V , the maximum T onset c and T ρ=0 c coincide. Above p V , in several samples 3,41,43 the superconducting region extends to high p; that is, the decrease of T onset c (p > p V ) is less steep than shown in Fig. 1, but may exhibit a jump close to 8 GPa.…”

“…In this context, it may be worthwhile to notice that the T c 's from Ref. 41 phenomena observed in the Ce-115 series, 44 or more directly to the presence of critical VF. Indeed, one could imagine a nonhomogeneous nucleation and spread of superconducting domains within the sample or on the surface, depending on the local distribution of T cr and the closeness to p V .…”

Spin and valence-fluctuation mediated superconductivity in pressurised Fe and CeCu2(Si/Ge)2

“…As a function of pressure, T c onset exhibits strange kinks similar to those reported in Ref. [42] drop above 2.3 K have been previously reported, but T ðR¼0Þ c never exceeded 1.8 K. This effect was never seen at low pressure. Contrary to the bulk T c , the highest value of T c onset is much more sensitive to the enhanced residual resistivity r 0 ; indicating a subtle pair breaking effect.…”