As of January 2012, I am involved in postdoctoral research in the Physics department at Trinity College Dublin in the fields of theoretical and computational condensed matter physics. From 2007 to 2011, I completed my Ph.D. on the topic Impurities and magnetic interactions in graphene: a theoretical study under the supervision of Dr. Mauro Ferreira and funded by the Irish Research Council for Science, Engineering and Technology (IRCSET) under the EMBARK initiative.

From September 2012, I will be working at the Centre for Nanostructured Graphene at the Technical University of Denmark.

 

A complete list of peer-reviewed publications and preprints with citation information can be found on my Google Scholar profile

 

Impurities and magnetic interactions in graphene: a theoretical study

Graphene is a two-dimensional carbon material that until its recent discovery was assumed not to exist in the free state. Graphene-related materials have been in the scientific limelight since then due to several key discoveries regarding their production and properties. There are numerous technological applications envisaged for them. Besides the huge potential for applicability, one key feature that makes graphene particularly popular is the simplicity with which many of its physical properties can be described, primarily due to the simple dispersion relation for its electrons. In this thesis a number of different topics relating to graphene systems, and in particular those doped with impurities, are investigated using a combination of analytical and numerical methods. We consider both graphene sheets and quasi-one-dimensional strips of graphene that are called `nanoribbons'.

 

 

The electronic properties of materials can be engineered by doping, but in the case of graphene nanoribbons the introduction of two symmetry-breaking edges introduces an additional dependence on the location of an impurity across the width of the ribbon. This dependence has been noted previously in electronic transport calculations, but in this work we extend the discussion to the binding energy of the impurity and also to the magnetic moment that is formed if the impurity is magnetic. The results of simple model calculations are found to match those of more sophisticated ab initio calculations.

 

 

Magnetically-doped graphene systems are potential candidates for application in future spintronic devices. A key step is to understand the pairwise interactions that occur between magnetic impurities embedded in graphene that are mediated by the graphene conduction electrons. In this thesis we examine interactions between such impurities using a Green function formalism. By developing an analytical expression for the Green function in graphene, we are able to explore the distance dependence of these interactions in a mathematically transparent fashion. We also demonstrate that ab initio calculations may yield spurious results if the effects of this interaction are neglected. The quick decay with separation of the interaction in graphene, reported by many authors, is often seen as a major obstacle for the spintronic application of these systems. However, in this work we report that a significant augmentation of the interaction is possible when the impurity moments are set to precess. An experimental setup to probe this dynamic form of the magnetic interaction in graphene is also suggested.

 

Research Interests

• Disorder in Graphene Systems: How are the properties of graphene-based structures, such as nanoribbons and nanotubes affected by the introduction of impurity atoms?
• Magnetic Moments in Graphene Systems: How do magnetic objects embedded in graphene-based structures interact, and how does this interaction change when disorder or precessing moments are considered?
• Quantum Hall Effect in Graphene: How does the quantum Hall response of a graphene system vary when impurities or invasive electrodes are considered?

 

Publications

06.   Strain-induced modulation of magnetic interactions in graphene
        S. R. Power, P. D. Gorman, J. M. Duffy and M. S. Ferreira
        arXiv: arXiv:1207.3015

05.   Dynamic RKKY interaction in graphene
        S. R. Power, F. S. M. Guimaraes, A. T. Costa, R. B. Muniz and M. S. Ferreira
        Phys. Rev. B 85, 195411 (2012)
        DOI: 10.1103/PhysRevB.85.195411         arXiv: arXiv:1112.0205

04.   Magnetization profile for impurities in graphene nanoribbons
        S. R. Power, V. M. de Menezes, S. B. Fagan, and M. S. Ferreira
        Phys. Rev. B 84, 195431 (2011)
        DOI: 10.1103/PhysRevB.84.195431         arXiv: arXiv:1108.6199

03.   Electronic structure of graphene beyond the linear dispersion regime
        S. R. Power and M. S. Ferreira
        Phys. Rev. B 83, 155432 (2011)
        DOI: 10.1103/PhysRevB.83.155432         arXiv: arXiv:1010.0908

02.   Emergence of local magnetic moments in doped graphene-related materials
        P. Venezuela, R. B. Muniz, A. T. Costa, D. M. Edwards, S. R. Power, and M. S. Ferreira
        Phys. Rev. B 80, 241413 (2009)
        DOI: 10.1103/PhysRevB.80.241413

01.   Model of impurity segregation in graphene nanoribbons
        S. R. Power, V. M. de Menezes, S. B. Fagan, and M. S. Ferreira
        Phys. Rev. B 80, 235424 (2009)
        DOI: 10.1103/PhysRevB.80.235424