Asia Pacific Physics Week 2023 (APPW2023)

Monday, Nov. 6, 2023

2:00 PM - 2:40 PM  Plenary Talk  Hyunsik Im (Dongguk University)

Kondo cloud condensation in P-doped silicon metal

Hyunsik Im

Department of Physics and Semiconductor Science, Dongguk University, Seoul, South Korea

Semiconductors are materials that possess the unique ability to extensively control their electronic nature by adding impurities, and this makes them valuable in applications and studying fundamental physics. Especially, how the interaction between magnetic impurity and electrons affects the electronic phase transition of solids has remained a challenging issue over many years.

A Kondo cloud is a bound state of fermions in which the combination produces a composite boson with zero net spin (similar to Cooper pairs and excitons). Analogous to the condensation of Cooper pairs and excitons, overlapping Kondo clouds in a metal with reasonably dense magnetic impurities are expected to form a coherent ground state. Here, I present bulk properties and tunneling DOS spectroscopy measurements in a crystalline silicon metal where localized magnetic moments exist. We detect the Kondo effect in the resistivity of the Si metal and an exotic BCS-like pseudogap in the DOS near the Fermi energy. The BCS-like DOS structure is tuned by applying an external magnetic field and transformed into a paramagnetic Coulomb gap. This phenomenon is interpreted as the formation of a correlated ground state of overlapping Kondo clouds (Kondo cloud condensate). I also discuss the interplay between the Kondo condensate and BCS-superconductor in the DOS spectrum of a Si:P-SiO2-Al tunnel junction where some interesting features are observed (i.e., Andreev reflection and particle-hole asymmetry like behavior). Our experimental findings demonstrate the observation of entangled electron-electron pair condensation and will be useful for understanding complex Kondo systems.