Response of the heavy-fermion superconductor CeCoIn₅to pressure: roles of dimensionality and proximity to a quantum-critical point

Abstract

Abstract. We report measurements of the pressure-dependent superconducting transition temperature Tc and electrical resistivity of the heavy-fermion compound CeCoIn 5 . Pressure moves CeCoIn 5 away from its proximity to a quantum-critical point at atmospheric pressure. Experimental results are qualitatively consistent with theoretical predictions for strong-coupled, d-wave superconductivity in an anisotropic 3D superconductor. Although heavy-fermion superconductivity has been known for over two decades, a microscopic theory of this broken-symmetry state has remained elusive. Experiments have established, however, that the unconventional superconductivity in heavyfermion compounds most likely is mediated by magnetic fluctuations, which also are responsible for enhancing the effective mass of itinerant quasiparticles by two to three orders of magnitude. [1,2,3] In spite of 20 years of searching, there has been, until very recently, only one example of a Ce-based heavy-fermion compound, CeCu 2 Si 2 , that is superconducting at atmospheric pressure. [4] In contrast, several examples of Cebased heavy-fermion antiferromagnets have been found in which superconductivity appears as their Néel temperature is tuned toward T = 0 with the application of pressure. [5,6,7,8] This recent series of discoveries re-enforces the belief not only that a magnetic interaction is responsible for superconductivity in these materials but also that heavy-fermion superconductivity may be favored at a particular 'soft-spot' in phase space, i.e., near a quantum-critical point

Quantum critical scaling and superconductivity in heavy electron materials

“…Since f 0 (p L ) is a material sensitive parameter, we see that the ratio of T c to T * will in general vary from one [13,14]. It shows the coherence temperature, T * (> 30Tc), at which itinerant heavy electrons emerge to form a Kondo liquid, and the delocalization line, TL, that marks the boundary between fully itinerant and partially localized heavy electron quasiparticles.…”

“…Since partial localization (f < 1) competes with superconductivity, the two-fluid model predicts that the maximum in the superconducting transition temperature, T max c , will be found at the pressure p L , at which the delocalization line, T L , intersects T c ; experiments on CeCoIn 5 and CeRhIn 5 [13,14] show that this is the case for these materials for which p L =1.4 GPa and 2.4 GPa, respectively. For pressures less than p L , partial quasiparticle localization reduces the number of heavy electrons able to become superconducting and so suppresses T c , while for pressures greater than p L , it is physically appealing to assume that the attractive interaction between heavy electron quasiparticles becomes increasingly less effective [15].…”

Emergence of superconductivity in heavy-electron materials

“…2A as input and determine λ max to be 1.23 for CeCoIn 5 and 0.62 for CeRhIn 5 from experiments at p L , Eq. 4 provides a remarkably good quantitative explanation of the dome-like structure observed as the pressure is varied in CeCoIn 5 and CeRhIn 5 (18,19). We note that both κ(p) and T c (p) are peaked at p L , the pressure at which the delocalization line, T L , intersects with T c .…”

“…In finding a way to characterize heavy-electron quantum critical superconductivity it is helpful to begin by recalling the principal features of its remarkably similar emergence in two of the best-studied materials, CeCoIn 5 and CeRhIn 5 (18)(19)(20)(21)(22)(23). As may be seen in Fig.…”

Crossover from Landau Fermi liquid to non-Fermi liquid behavior: Indications from Hall measurements on CeCoIn5

“…2). This ''peak feature'' is likely related with the AFM spin fluctuations (SF), based on the following observations: (i) p dependence: Applying pressure to CeCoIn 5 drives the system towards a heavy Landau Fermi liquid (LFL) state [6] by gradually suppressing the AFM SF [7]. This is likely related to the increase of T c with p for small p, leading to maximum T c at p * $ 1.3 GPa.…”