Finite bias evolution of bosonic insulating phase and zero bias conductance in boron-doped diamond: A charge-Kondo effect

Nano-Scale Transport Physics Laboratory, School of Physics and DST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand - Private Bag 3, WITS, 2050 Johannesburg, South Africa

^(a) somnath.bhattacharyya@wits.ac.za

Received: 7 August 2018
Accepted: 26 November 2018

Abstract

We report novel transport features in heavily boron-doped nanocrystalline diamond films, in particular an anomalous resistance peak near to the superconducting transition temperature and a strong zero bias conductance peak in the differential current-voltage spectra. The shape of the resistance-temperature curves near the critical temperature is seen to be strongly influenced by both magnetic field and bias current. As the bias current is lowered, the resistance peak becomes more pronounced, whereas when the magnetic field is varied the peak shifts towards lower temperatures. The resistance upturn shows a quadratic temperature dependence as expected for a Kondo transition. We find that a number of transport features such as resistance peak height, zero bias conduction peak height and width scale according to a power law dependence. We interpret these features as a result of a charge-Kondo effect where hole dopants act as degenerate Kondo impurities by opening additional pseudo-spin scattering channels.