Talk: Quantum confinement and coherence in nanodiamond

Talk by Assistant professor Gufei Zhang

University of Southern Denmark

Abstract:

Quantum Confinement and Coherence in Nanodiamond

Gufei Zhang 

NanoSYD, Mads Clausen Institute and DIAS Danish Institute for Advanced Study, University of Southern Denmark, Alsion 2, DK-6400 Sonderborg, Denmark

Superconductivity, or infinite conductivity, appears as a result of formation of quantum condensate of Cooper pairs making possible a dissipationless flow of charged bosons. At first sight, superconductivity should be provided by well established conducting state, but in reality the best conductors (Ag, Au) do not superconductor at all, while, instead, superconductivity gains a lot from
being situated in the vicinity of the insulator-metal transition induced by doping, e.g., doped copper oxides and iron pnictides [1]. Another interesting puzzle, related to the origin of superconductivity,
is whether the insulating state results from the direct localization of Cooper pairs or a two-step process where the destruction of Cooper pairs is followed by the localization of single quasiparticles [2].

Lab-grown boron-doped diamond, increasingly being recognized as a piece of jewelry for science and technology, provides a powerful platform for answering these questions [3-8]. To demonstrate
the quantum confinement and coherence of charge carriers in nanogranular diamond, I will brief on our electrical transport and direct local measurements on this material. The talk will be focused on a series of intriguing bosonic anomalies such as the bosonic insulating state [4-6,8]. These anomalies are interpreted in the framework of the quantum confinement and coherence of single quasiparticles and Cooper pairs in the presence of granular disorder. Our data unveil the percolative nature of the electrical transport in nanodiamond, and reveal the essential role of grain boundaries in determining the electronic properties of this material.

[1] G. Zhang et al. Global and local superconductivity in boron-doped granular diamond. Adv. Mater. 26, 2034 (2014).

[2] B. Sacépé et al. Localization of preformed Cooper pairs in disordered superconductors. Nature Phys. 7, 239 (2011).

[3] G. Zhang et al. Role of grain size in superconducting boron-doped nanocrystalline diamond thin films grown by CVD. Phys. Rev. B 84, 214517 (2011).

[4] G. Zhang et al. Metal–bosonic insulator–superconductor transition in boron-doped granular diamond. Phys. Rev. Lett. 110, 077001 (2013).

[5] G. Zhang et al. Bosonic anomalies in boron-doped polycrystalline diamond. Phys. Rev. Appl. 6, 064011 (2016).

[6] G. Zhang et al. Bosonic confinement and coherence in disordered nanodiamond arrays. ACS Nano 11, 11746 (2017).

[7] G. Zhang et al. Superconducting ferromagnetic nanodiamond. ACS Nano 11, 5358 (2017).

[8] G. Zhang et al. Superconductor-insulator transition driven by pressure-tuned intergrain coupling in nanodiamond films. Phys. Rev. Mater. 3, 034801 (2019).

Tidspunkt

ons 08 maj 19
14:00

Hvor

DTU Fysik
Bygning 344
Room 125