Hybridization-Controlled Pseudogap State in the Quantum Critical Superconductor CeCoIn5

TL;DR

This study investigates the pseudogap state in CeCoIn$_5$, revealing it is driven by Kondo hybridization rather than superconducting pairing, with pressure tuning its properties and highlighting a novel pseudogap mechanism.

Contribution

It demonstrates that the pseudogap in CeCoIn$_5$ is controlled by hybridization effects, distinct from the superconducting gap, providing new insights into pseudogap phenomena in quantum critical superconductors.

Findings

Pseudogap energy increases with pressure, following hybridization trends.

Superconducting gap exhibits a dome-shaped dependence on pressure.

Pseudogap is less involved in Cooper pair formation, driven by Kondo hybridization.

Abstract

The origin of the partial suppression of the electronic density states in the enigmatic pseudogap behavior, which is at the core of understanding high-$T_c$ superconductivity, has been hotly contested as either a hallmark of preformed Cooper pairs or an incipient order of competing interactions nearby. Here, we report the quasi-particle scattering spectroscopy of the quantum critical superconductor CeCoIn$_5$, where a pseudogap with energy $\Delta_g$ was manifested as a dip in the differential conductance ($dI/dV$) below the characteristic temperature of $T_g$. When subjected to external pressure, $T_g$ and $\Delta_g$ gradually increase, following the trend of increase in quantum entangled hybridization between Ce 4$f$ moment and conduction electrons. On the other hand, the superconducting (SC) energy gap and its phase transition temperature shows a maximum, revealing a dome shape under pressure. The disparate dependence on pressure between the two quantum states shows that the pseudogap is less likely involved in the formation of SC Cooper pairs, but rather is controlled by Kondo hybridization, indicating that a novel type of pseudogap is realized in CeCoIn$_5$.