Novel two-dimensional structures
RESEARCH PROGRAMME
P2: Quantum materials at the nanoscale
PhD PROJECT DESCRIPTION
The discovery of graphene opened a new paradigm in material science. Recently, twisted bilayer graphene (TBG), a system where two atom-thick layers are superimposed and rotated by an arbitrary twist angle has emerged as a very interesting metamaterial. Interestingly, the effect of twisting two periodic systems with respect to each other results in the formation of superlattices, also known as moiré patterns. When the graphene layers are rotated at the so-called magic angle, the moiré pattern induces very narrow bands and TBG hosts high correlated states such as superconductivity.
Nowadays, twisted and untwisted multilayer graphene systems are being heavily studied. Furthermore, other materials, such as transition metal dichalcogenides and hexagonal boron nitride also present interesting phenomena when two of their layers are twisted.
Importantly, in order to bring these exotic properties of TBG and related materials to novel technological devices, further theoretical studies must be carried out. For example, superconductivity has been studied only for a few twist angles in both bilayer and multilayer systems, other correlated effects are found only for certain twist angles, chemical doping or with a substrate. In addition, the bands and their topological properties appear to have an angle dependence. Therefore, it is of key importance that the fundamental understanding of this phenomena are established.
The main areas of work developed during the PhD program would be in the following:
- Novel electronic and structural properties of twisted bilayer graphene and related systems. Extensions to other two-dimensional materials: hexagonal Boron Nitride, transition metal dichalcogenides, etc.
- Stacks of 2D layers with different properties. Combinations of superconducting and magnetic layers. Proximity effects. Role of spin-orbit coupling. Emergence of new features.
- Interplay between geometric structure and electronic properties. Role of natural and induced deformations.
- Local modulations of the properties of 2D materials. Application to the design of nanoscale devices.
The PhD candidate will have several options within IMDEA Nanociencia (Prof. Rodolfo Miranda) and external ICFO (Prof. Frank Koppens) and NIST (Prof. David Gundlach).
Possible secondment destinations will be: DIPC, University of Manchester (Prof. Niels Walet) and MIT (Prof. Liang Fu).
APPLICANT’S REQUIREMENTS
A typical background would be in condensed matter and statistical physics, with experience in modelling of materials and computational methods. High knowledge of written and spoken English is desired. The candidate is expected to have proficient programming capabilities (Mathematica, Python). The candidate should also have teamwork capacities.
RESEARCH GROUP DESCRIPTION
The main goal of the research within the group is the development of models which describe the properties of novel two dimensional materials. The best-known case is graphene, which permits the fabrication of films of widths comparable to the radius of a single atom. After the synthesis of graphene, many other two-dimensional materials have been fabricated, with a broad range of properties. Finally, layers of different materials can be combined, leading to “metamaterials” with pre-designed features.
The models developed in the group emphasize those properties which are unique to these materials, and they include geometrical and structural features, electronic and superconducting properties and magnetic phases. We also consider devices based on these materials, highlighting those with functionalities which cannot be achieved in devices fabricated using other materials. A wide variety of techniques are applied, from numerical calculations to
RESEARCH SUPERVISOR
Prof. Francisco Guinea
paco.guinea@imdea.org
Research Group website: https://www.imdeananociencia.org/graphene/group-home