Project

Theoretical modeling of quasiparticle interference in graphene Moire superlattices

Publisher

Supervisor

Location

Greater Copenhagen area

When an electron -- or quasiparticle -- in a material scatter off an external impurity potential, interference between the scattered waves generates characteristic patterns in local density of states (LDOS) in real-space which resemble Friedel oscillations. By analyzing the real-space modulation of the LDOS in Fourier space (see picture), useful information about the band structure and dominant scattering processes (which are often detrimental for the electrical and optical material properties) can be obtained.

Experimentally, measurements of the real-space modulation of the LDOS are performed on surfaces via Scanning Tunneling Spectroscopy (STS). For a two-dimensional (2D) material like, e.g., graphene, the surface is basically the bulk of the material, and in this case, STS allows to probe the quasiparticle properties important for device applications etc (see, e.g., Ref. [1]).

The newest generation of graphene devices are build as socalled van der Waals (vdW) heterostructures where graphene is sandwiched between other types of 2D materials, such as, e.g., hexagonal Boron Nitride (h-BN). In such structures, the small mismatch in the lattice constant between graphene and h-BN leads to the formation of Moiré superlattices (see picture) which give rise to new and unexpected changes in the electronic structure of graphene.

The purpose of this project is to develop a suitable model for such Moiré superlattices within a tight-binding scheme and study their impact on STS spectra for graphene in both real and Fourier space.  The calculation of the STS spectra proceeds via the Green's function of the system [2], which must take into account the details of the Moiré lattice. In addition, the combined effect of Moiré lattice and  atomic-scale defects [2] as well as other exciting 2D materials (silicene, phosphorene, ...) may be investigated.

Altogether, the project will familiarize the student with advanced electronic-structure and quantum-transport theory as well as their practical implementations, and it will provide a solid platform for further courses (e.g., 33206) and projects in this direction.


References:

[1] Energy-Dependent Chirality Effects in Quasifree-Standing Graphene, Phys. Rev. Lett. 118, 116401 (2017).

[2] Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides, Phys. Rev. B 96, 241411(R) (2017) [attached for download].



Requirements

Condensed matter physics

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Contact

Company / Organization

DTU Fysik

Name

Kristen Kaasbjerg

Position

Seniorforsker

Mail

kkaa@dtu.dk

Supervisor info

MSc in Physics and Nanotechnology

Supervisor

Kristen Kaasbjerg

Co-supervisors

Antti-Pekka Jauho

ECTS credits

15 - 30

Type

BSc project, MSc thesis, Special course

Must be completed

10303

Technical University of Denmark

For almost two centuries DTU, Technical University of Denmark, has been dedicated to fulfilling the vision of H.C. Ørsted – the father of electromagnetism – who founded the university in 1829 to develop and create value using the natural sciences and the technical sciences to benefit society.


Today, DTU is ranked as one of the foremost technical universities in Europe, continues to set new records in the number of publications, and persistently increases and develops our partnerships with industry, and assignments accomplished by DTU’s public sector consultancy.

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Denmark



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CVR-nr. 30 06 09 46

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