Observation of Kondo condensation in a degenerately doped silicon metal

Abstract

When a magnetic moment is embedded in a metal, it captures nearby itinerant electrons to form a so-called Kondo cloud. When magnetic impurities are sufficiently dense that their individual clouds overlap with each other they are expected to form a correlated electronic ground state. This is known as Kondo condensation and can be considered a magnetic version of Bardeen–Cooper–Schrieffer pair formation. Here, we examine this phenomenon by performing electrical transport and high-precision tunnelling density-of-states spectroscopy measurements in a highly P-doped crystalline silicon metal in which disorder-induced localized magnetic moments exist. We detect the Kondo effect in the resistivity of the Si metal at temperatures below 2 K and an unusual pseudogap in the density of states with gap edge peaks below 100 mK. The pseudogap and peaks are tuned by applying an external magnetic field and transformed into a metallic Altshuler–Aronov gap associated with a paramagnetic disordered Fermi liquid phase. We interpret these observations as evidence of Kondo condensation followed by a transition to a disordered Fermi liquid.

Many‐body Effects on Electronic Transport in Molecular Junctions: A Quantum Perspective

“…The discovery of Kondo condensation [22] in silicon metals with high levels of impurity constitutes a significant advancement in elucidating the intricate principles governing electronelectron interactions, disorder, and spin correlations in solid materials. In metals, introducing a magnetic moment captures nearby free electrons, forming a 'Kondo cloud' that may span several micrometers.…”

“…The recent study by Im et al [22] (Figure 4) delineates the evolution of magnetic impurity interactions within metallic matrices, ranging from isolated Kondo singlets -where individual impurities are surrounded by localized electron clouds -to a collective phase marked by the merging of overlapping Kondo clouds, fostering a correlated electron ground state. This progression advances toward a Kondo lattice, characterized by regular interactions between conduction electrons and an assortment of impurities, culminating in the emergence of a random singlet state.…”

“…Im and co-workers [22] explored this phenomenon by conducting electrical transport and high-precision tunneling density-of-states (DOS) spectroscopy measurements in highly Pdoped crystalline silicon metal, where disorder-induced localized magnetic moments are present. They observed the Kondo effect in the resistivity of the Si metal below 2 K and identified an exotic pseudogap in the DOS, with gap edge peaks occurring at a Fermi energy below 100 mK.…”