Flux crystal growth of CeCu₂Si₂: Revealing the effect of composition

Abstract

The low-temperature properties of CeCu 2 Si 2 are extremely sensitive to deviations from stoichiometry and defects, leading to a strong dependence of the observed properties on sample preparation conditions. In the past few years we have developed a flux method which allows the growth of large single crystals with controlled physical properties. Here, we demonstrate that the Ce content in the starting melt, one of the most important parameters in our growth process, mainly influences the Cu/Si ratio in the single crystals but not their Ce content. A higher Cu/ Si ratio yields a smaller c/a ratio, while the unit cell volume remains roughly constant. We observe a clear correlation between the Cu/Si ratio and the physical properties, showing that electronic effects are more important than volume effects.

Superconducting gap and vortex lattice of the heavy-fermion compoundCeCu2Si2

“…It is interesting to compare our observations to the case of CeCoIn 5 , where experiments suggest a d-wave symmetry of the order parameter [22,23]. The spectra we have observed at base temperature [see Fig.…”

“…The features observed in the tunneling spectra at low energy support a multigap scenario. The shape of the gap detected in tunneling spectroscopy as well as the distortion of the vortex lattice indicate similarities with superconductivity in CeCoIn 5 .…”

“…Figure 2(a) shows for comparison tunneling spectra taken at T = 200 mK (<T c ) at zero magnetic field and at a field of μ 0 H = 2 T parallel to c, close to the upper critical field H c2 [5]. As can be seen from the spectrum measured at 2 T, the gap has almost closed completely.…”

“…CeCu 2 Si 2 crystallizes in the ThCr 2 Si 2 I 4/mmm bodycentered tetragonal structure with lattice parameters a = 4.1031(2)Å and c = 9.9266(5)Å [5] [see Fig. 1(a)].…”

“…The physics near the quantum critical point sensitively depends on the balance between screening of the local magnetic moments and interactions between them [3]. In CeCu 2 Si 2 , slight changes in the exact composition (specifically the Cu-to-Si ratio) result in superconducting crystals (S type), magnetically ordered samples (A type), or samples which exhibit competing phases (A/S type) [4,5]. Superconductivity occurs close to a spindensity-wave-type quantum critical point and is expected to be unconventional in nature.…”