Sankar Das Sarma talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of
Article: Dielectric function, screening, and
plasmons in two-dimensional graphene
Authors: Hwang, EH;Das
Journal: PHYS REV B, 75 (20): art. no.-205418 MAY
Addresses: Univ Maryland, Dept Phys, Condensed Matter
Theory Ctr, College Pk, MD 20742 USA.
Univ Maryland, Dept Phys, Condensed Matter Theory Ctr,
College Pk, MD 20742 USA.
> View the corresponding Research Front Map for
Why do you think your paper is highly
This paper is highly cited because it solves the outstanding quantum
mechanical problem of theoretically and quantitatively understanding the
dielectric screening properties of graphene. Graphene has two-dimensional
electrons and holes. These electrons and holes respond to an external
electric field by screening the external field, i.e., modifying or changing
the external field in a complex manner.
It is extremely important to know how this screening behavior manifests
itself in the actual two-dimensional graphene system since all graphene
properties will, in the end, depend on how these two-dimensional carriers
respond to external perturbations. Our work solves this important problem.
screening paper which we are
discussing right now will
continue to be cited in the
literature for a while since
the prospective use of
graphene in microelectronics
remains an active area of
research all around the
Since this screening behavior manifests itself in many graphene properties,
other researchers need to use our theoretical results in their work,
leading to a high rate of citations for this paper.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
It describes a new theoretical discovery, i.e., the screening properties of
graphene were simply unknown before our work, and became quite well-known
Would you summarize the significance of your paper
in layman's terms?
I touch upon this issue in my response to the first question. But let me
elaborate. An important reason for the high level of interest in
two-dimensional (2D) graphene is the possibility of its eventual use in
micro- or nano-electronic applications such as transistors or other
Our work in this paper and the closely related work, (EH Hwang, S Adam, and
S Das Sarma, "Carrier Transport in Two-Dimensional Graphene Layers,"
Phys. Rev. Lett. 98: 186806, 2007), establish theoretically
how the movement of electrons carrying electrical current in 2D graphene
will be affected by unintentional charged impurities and defects invariably
present in the graphene environment—these impurities cause electrical
circuits to have finite resistivity. Since the response of the electrons in
2D graphene to the impurities and defects must include the effect of
screening, i.e., how the graphene electrons themselves respond to external
electric fields, our paper on screening takes on a special significance.
In summary, our paper is significant (and highly cited) because it enables
researchers to estimate the electrical resistance of a graphene-based
electronic device. Our work has been fully verified by subsequent
experiments carried out all around the world, and therefore, future
graphene-based electronic devices will use our theory in figuring out the
How did you become involved in this research and
were there any particular problems encountered along the way?
I became involved in this work because the United States Office of Naval
Research (USONR) approached me, asking if I would be interested in looking
into the prospects for 2D graphene-based electronic applications. Since I
have extensive experience and background in theoretical research on
semiconductor-based 2D transistors (e.g., Si MOSFETs and GaAs HEMTs and
HIGFETs), it was quite natural for me and my long-term collaborator Dr.
Euyheon Hwang (who did his Ph.D. under my supervision 10 years ago and has
continued a very fruitful research collaboration with me for the last 15
years) to become involved in this graphene research.
The surprising thing is that we had very great difficulties publishing this
highly cited paper. It took eight months for the paper to be
published—submission in October of 2006 and publication in May of
2007—and in fact, the first journal (which shall remain un-named)
that we submitted our paper to decided not to publish it! This is perhaps
not as strange as it sounds. First, the field of 2D graphene is highly
competitive, and second, original theoretical discoveries are often not
appreciated when they are put forward for the first time.
Where do you see your research leading in the
I continue to remain very active in the 2D graphene field, and have several
other highly cited publications. I believe that our screening paper which
we are discussing right now will continue to be cited in the literature for
a while since the prospective use of graphene in microelectronics remains
an active area of research all around the world. I believe that our
screening work will remain an important theoretical ingredient in graphene
research for the reasons I've discussed above.
Do you foresee any social or political implications
for your research?
Our work is mathematical and theoretical physics research. It can at best
have some technological implications, and I believe that it does. Physics
research typically does not have any direct social or political
Sankar Das Sarma
Distinguished University Professor
Director of the Condensed Matter Theory Center
Department of Physics
University of Maryland
College Park, MD, USA
Related: View the corresponding Research Front Map for Physics
Keywords: dielectric screening, graphene properties,
electrons in two-dimensional graphene, micro- or nano-electronic
applications, graphene-based electronic device, graphene environment, 2D
graphene-based electronic applications, semiconductor-based 2D