Magnetism and superconductivity in heavy fermion compounds at high pressure

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

“…4. All major characteristics are in line with previous reports, 2,7,8 the parameters ρ 0 , A, and n, obtained from simple fits to ρ(T 4.2 K,H = 0) = ρ 0 + A * T n . In particular, from the inset of Fig.…”

“…5(b)]. As mentioned earlier, such a trend had already been inferred from resistivity and a kind of "plateau" in A(p ∼ 4 GPa), 2,7,8 which has now grown into a clear maximum in the present high-quality single crystal [ Fig. 5(b)].…”

“…Instead, in CeCu 2 Si 2 the superconducting region extends far beyond the magnetic quantum critical point (located at p c ≈ 0 GPa) and exhibits an enhanced transition temperature (T c ), culminating at ∼2.4 K around 4 GPa. 2,[6][7][8] The most elaborate scenario 9,10 invokes critical charge or valence fluctuations (VF) associated with an underlying valence transition (VT), that is, delocalization of the Ce 4f electron when tuning p across the critical region (p V ). In elementary Ce (see inset of Fig.…”

“…Preceding experiments point toward distinct natures of the two superconducting (sc) phases 7,9 (related to p c and p V , respectively) and have unveiled close to p V features peculiar to the concept of critical VF, such as a T -linear resistivity and an increased residual resistivity ρ 0 . 2,8 Despite such compelling indications for the presence of critical VF in proximity to a CEP, additional signatures of the putative VT are still highly desirable in order to consolidate the decisive role of the 4f electron delocalization in the properties of CeCu 2 Si 2 and accordingly in other Ce-based compounds.…”

Strain enhancement of superconductivity in CePd2Si2under pressure

“…The exponent in ρ(T ) = ρ 0 + AT n in all cases reaches remarkably low values with n ≃ 1.2−1.3, a value generally attributed to a non 3D spin-fluctuation spectrum. However, let us recall that in other compounds such as CeCu 2 Ge 2 , a minimum of n close to 1 was found only for P > P c , in a pressure domain where k B T K reaches the CF splitting energy [19]. As this happens for P ≃ P c in CePd 2 Si 2 , one may wonder if the low exponent observed is not a consequence of this change of regime.…”