Evidence for charge delocalization crossover in the quantum critical superconductor CeRhIn5.

The nature of charge degrees-of-freedom distinguishes scenarios for interpreting the character of a second order magnetic transition at zero temperature, that is, a magnetic quantum critical point (QCP). Heavy-fermion systems are prototypes of this paradigm, and in those, the relevant question is where, relative to a magnetic QCP, does the Kondo effect delocalize their f-electron degrees-of-freedom. Herein, we use pressure-dependent Hall measurements to identify a finite-temperature scale Eloc that signals a crossover from f-localized to f-delocalized character. As a function of pressure, Eloc(P) extrapolates smoothly to zero temperature at the antiferromagnetic QCP of CeRhIn5 where its Fermi surface reconstructs, hallmarks of Kondo-breakdown criticality that generates critical magnetic and charge fluctuations. In 4.4% Sn-doped CeRhIn5, however, Eloc(P) extrapolates into its magnetically ordered phase and is decoupled from the pressure-induced magnetic QCP, which implies a spin-density-wave (SDW) type of criticality that produces only critical fluctuations of the SDW order parameter. Our results demonstrate the importance of experimentally determining Eloc to characterize quantum criticality and the associated consequences for understanding the pairing mechanism of superconductivity that reaches a maximum Tc in both materials at their respective magnetic QCP.

Study on superconducting properties of CeIrIn5thin films grown via pulsed laser deposition.

We report the growth of CeIrIn5thin films with different crystal orientations on a MgF2(001) substrate using pulsed laser deposition technique. X-ray diffraction analysis showed that the thin films were either mainlya-axis-oriented (TF1) or a combination ofa- andc-axis-oriented (TF2). The characteristic features of heavy-fermion superconductors, i.e. Kondo coherence and superconductivity, were clearly observed, where the superconducting transition temperature (Tc) and Kondo coherence temperature (Tcoh) are 0.58 K and 41 K for TF1 and 0.52 K and 37 K for TF2, respectively. The temperature dependencies of the upper critical field (Hc2) of both thin films and the CeIrIn5single crystal revealed a scaling behavior, indicating that the nature of unconventional superconductivity has not been changed in the thin film. The successful synthesis of CeIrIn5thin films is expected to open a new avenue for novel quantum phases that may have been difficult to explore in the bulk crystalline samples.