June 10, 2021

GRAPHENE SEMINAR: Engineering Deformed Graphene Membranes: From Confined Charges and Valley Filters to Moire Structures and Tambourines

NANCY SANDLER

Department of Physics and Astronomy, and Nanoscale and Quantum Phenomena Institute @Ohio University, USA

 

ABSTRACT:

As an atomically thin membrane, graphene is a highly flexible material, a property that provides the opportunity to use strain engineering to control its electronic properties. Wrinkled or rippled graphene, either suspended or on a substrate, reveals inhomogeneous charge distributions originated by underlying strain fields. Scanning tunneling microscopy (STM) measurements on deformed samples demonstrated electron confinement with peculiar charge distributions that break sublattice symmetry.

The phenomena that differentiate carbon atoms in each unit cell results in local valley currents with application in the field of valleytronics, i.e., the manipulation of the valley degree of freedom for electronic purposes. Because valley filtering properties in these structures are highly dependent on the type of deformation considered, we identified the relevant factors determining the optimal operation and detection of valley currents. We showed that extended deformations such as folds, in addition, to confine charges, also serve as electronic waveguides, a phenomenon confirmed by transport measurements. However, designing proper geometries is not enough to isolate valley states fully embedded in the continuum that makes graphene a semimetal.

We proposed that an external magnetic field makes it possible to separate these states from the continuum and provides the flexibility of positioning them at different locations in the sample, as observed in experiments.

More exciting is the possibility of developing band structure engineering protocols by designing substrates able to induce specific strain patterns. Results from our recent studies on supported and suspended samples exemplify these effects. For samples supported on regular arrays of deformations, we observe features characteristic of moirè structures in images of electronic charge distributions. These systems exhibit narrow bands at low energies reminiscent of those observed in twisted bilayer structures, suggesting the possibility for the emergence of novel correlated physics in single graphene membranes. Suspended samples driven by periodic time-dependent deformations exhibit gaps in the band structure at energies determined by the frequency of the drive and amplitudes set by strain parameters.

BIO:
Professor Nancy Sandler is a faculty in the Department of Physics and Astronomy and a member of the Nanoscale and Quantum Phenomena Institute (NQPI) at Ohio University (OU) in Athens, Ohio USA. Her research focuses on the equilibrium and non-equilibrium electronic properties of novel low-dimensional materials and the effects of strong correlations.

A native of Argentina, she obtained her Lic. en Ciencias Fisicas degree from the Universidad Nacional de Buenos Aires. She continued her studies at the University of Urbana-Champaign in Illinois, USA, where she received her Ph.D. in theoretical physics (1998) under the supervision of Prof. E. Fradkin. After holding postdoctoral positions at ENS and Orsay (France) and Brandeis and BU (USA), she joined the Ohio University faculty in 2005. She was a visiting professor at the Dahlem Center for Complex Quantum Systems at Freie Universitat, Berlin, Germany (2012-13), and is currently a visiting faculty in the Department of Physics at the Technical University of Denmark (DTU) and the Niels Bohr Institute (NBI) at the University of Copenhagen, Denmark.

Her other interests involve outreach and education activities that include serving as a board member in the Margaret Boyd Scholar Program, a leadership program for women undergraduates, and the physics science director in the NSF-funded NOYCE teacher fellowship program at OU.

 

Thursday, June 10, 2021, 12:00. Online               

Hosted by Prof Dr Valerio Pruneri (ICFO)

 

ZOOM LINK TO JOIN IN

This seminar is open to all interested. Please, register to get the Zoom link to join in.

 

This activity is co-funded by the European Regional Development Funds (ERDF) allocated to the Programa operatiu FEDER de Catalunya 2014-2020, with the support of the Secretaria d’Universitats i Recerca of the Departament d’Empresa i Coneixement of the Generalitat de Catalunya for emerging technology clusters devoted to the valorization and transfer of research results (GraphCAT 001-P-001702).