Nanoseminar in Physics

ONLINE EVENT BY ZOOM - REGISTER HERE to attend

Speaker: Prof. Catalin D. Spataru, Sandia National Labs, Livermore CA, USA

Abstract: During the first part of the talk I will discuss our recent efforts to shed light on some still not fully understood aspects of the electronic and transport properties of graphene: i) Motivated by recent transport experiments, we have studied from first principles the lifetime of low-energy quasiparticles in bilayer graphene by taking take into account the scattering rate arising from electron–electron interactions. We find good agreement with experiments in the undoped case and show that an additional decay channel -mediated by acoustic plasmons- opens up in the doped case. ii) We have also studied the impact of Coulomb dynamical effects on the superconducting properties of doped graphene. Extending Eliashberg’s approach to incorporate superconducting plasmonic pairing effects, we find that plasmonic contributions tend to support superconductivity but overestimate pairing contributions.

The second part of the talk will focus on artificially-tailored semiconducting quantum materials such as meta-graphene. First, we demonstrate quantitative agreement between the Hall conductivity predicted using an efficient framework rooted in numerical K-theory and experimental observations of meta-graphene created in a semiconductor heterostructure. Then, we show numerical results of the Hall conductivity as function of the potential strength associated with the nanopatterning of the semiconducting surface, demonstrating how Hofstadter's butterfly forms from an unpatterned system. Finally, I will discuss the topological properties of interface states realizable in meta-graphene at domain wall edges.

Biography: 

Education and Training :University of California at Berkeley Berkeley, California Physics Ph.D., 2004

Research and Professional Experience

2008-present Member of Technical Staff, Materials Physics Department, Sandia National Labs

Supporting a variety of programs in energy research, device physics and materials reliability.

2005-2008 Postdoctoral Researcher, Center for Electron Transport in Molecular Nanostructures, Columbia University Studying electron correlation effects in electronic transport through nanojunctions.

2004-2005 Postdoctoral Researcher, Lawrence Berkeley National Laboratory Studying electron excitations in nanomaterials.

1998-2004 Graduate Student, Department of Physics, University of California at Berkeley

Studying electron excitations in solids and novel materials (group of Steven Louie).

INTRODUCTORY TALK: Disorder and Delocalization in Magic Angle Twisted Bilayer Graphene by Pedro Alcázar, Doctoral Student at Theoretical and Computational Nanoscience group, ICN2

Abstract: Twisted multilayers of graphene have been the subject of intense research in recent years. Of particular interest is twisted bilayer graphene, which when rotated to a “magic angle” (~1.05º) has been discovered to present exotic many-body states of matter such as superconducting and Mott insulating phases. These states are connected with the formation of a flat band with vanishing kinetic energy and strong electronic localization, which emerges as a result of the Moiré potential (superperiodicity) and triggers a dominant contribution of the Coulomb interaction.

While the role of the superperiodicity is now well known for these systems, relatively little is known about the effect of disorder and its impact on localization. In our study we make use of numerical simulations to study the electronic transport of states in magic angle twisted bilayer graphene and show how the inclusion of electrostatic disorder can lead to delocalization in the flat bands. This suggests that even weak disorder can have a strong impact on the forces driving electronic interactions in twisted multilayer systems.

Hosted by Dr Aron Cummings, Theoretical and Computational Nanoscience Senior Researcher