Mesoscopic and Condensed Matter Physics

Biography

Biography: Yasutami Takada

Abstract

Hydrogen in metals has attracted attention for a long time from both basic scientific and technological points of view. Its electronic state has been investigated in terms of a proton embedded in the electron gas mostly by the local density approximation (LDA) to the density functional theory (DFT). At high electronic densities, it is well described by a bare proton H+ screened by metallic electrons (charge resonance), while at low densities two electrons are localized at the proton site to form a closed-shell negative ion H- protected from surrounding metallic electrons by the Pauli exclusion principle. However, no details are known about the transition from H+ to H- in the intermediate-density region. In my talk, I shall explain its complete picture, in particular, a sharp transition from H+ screening charge resonance to Kondo-like spin-singlet resonance, the emergence of which is confirmed by the presence of an anomalous Friedel oscillation characteristic to the Kondo singlet state through diffusion Monte Carlo (DMC) calculations with total electron number up to 170. This picture enriches the paradigm for metallic screening to a point charge with the addition of a possibility of spin resonance with a very long screening length, depending on the metallic density and the magnitude of charge. Besides, this work reveals that hydrogen is most stably embedded in the form of this spin-singlet resonance state, which may be important information for hydrogen storage in metals.