2,969 research outputs found
Singular-phase nanooptics: towards label-free single molecule detection
Non-trivial topology of phase is crucial for many important physics phenomena
such as, for example, the Aharonov-Bohm effect 1 and the Berry phase 2. Light
phase allows one to create "twisted" photons 3, 4 , vortex knots 5,
dislocations 6 which has led to an emerging field of singular optics relying on
abrupt phase changes 7. Here we demonstrate the feasibility of singular
visible-light nanooptics which exploits the benefits of both plasmonic field
enhancement and non-trivial topology of light phase. We show that properly
designed plasmonic nanomaterials exhibit topologically protected singular phase
behaviour which can be employed to radically improve sensitivity of detectors
based on plasmon resonances. By using reversible hydrogenation of graphene 8
and a streptavidin-biotin test 9, we demonstrate areal mass sensitivity at a
level of femto-grams per mm2 and detection of individual biomolecules,
respectively. Our proof-of-concept results offer a way towards simple and
scalable single-molecular label-free biosensing technologies.Comment: 19 pages, 4 figure
Electrostatically confined Quantum Rings in bilayer Graphene
We propose a new system where electron and hole states are electrostatically
confined into a quantum ring in bilayer graphene. These structures can be
created by tuning the gap of the graphene bilayer using nanostructured gates or
by position-dependent doping. The energy levels have a magnetic field ()
dependence that is strikingly distinct from that of usual semiconductor quantum
rings. In particular, the eigenvalues are not invariant under a
transformation and, for a fixed total angular momentum index , their field
dependence is not parabolic, but displays two minima separated by a saddle
point. The spectra also display several anti-crossings, which arise due to the
overlap of gate-confined and magnetically-confined states.Comment: 5 pages, 6 figures, to appear in Nano Letter
Proximity-induced superconductivity in graphene
We propose a way of making graphene superconductive by putting on it small
superconductive islands which cover a tiny fraction of graphene area. We show
that the critical temperature, T_c, can reach several Kelvins at the
experimentally accessible range of parameters. At low temperatures, T<<T_c, and
zero magnetic field, the density of states is characterized by a small gap
E_g<T_c resulting from the collective proximity effect. Transverse magnetic
field H_g(T) E_g is expected to destroy the spectral gap driving graphene layer
to a kind of a superconductive glass state. Melting of the glass state into a
metal occurs at a higher field H_{g2}(T).Comment: 4 pages, 3 figure
Two Dimensional Electron and Hole Gases at the Surface of Graphite
We report high-quality two-dimensional (2D) electron and hole gases induced
at the surface of graphite by the electric field effect. The 2D carriers reside
within a few near-surface atomic layers and exhibit mobilities up to 15,000 and
60,000 cm2/Vs at room and liquid-helium temperatures, respectively. The
mobilities imply ballistic transport at micron scale. Pronounced Shubnikov-de
Haas oscillations reveal the existence of two types of carries in both 2D
electron and hole gases.Comment: related to cond-mat/0410631 where preliminary data for this
experimental system were reporte
Graphene field-effect-transistors with high on/off current ratio and large transport band gap at room temperature
Graphene is considered to be a promising candidate for future
nano-electronics due to its exceptional electronic properties. Unfortunately,
the graphene field-effect-transistors (FETs) cannot be turned off effectively
due to the absence of a bandgap, leading to an on/off current ratio typically
around 5 in top-gated graphene FETs. On the other hand, theoretical
investigations and optical measurements suggest that a bandgap up to a few
hundred meV can be created by the perpendicular E-field in bi-layer graphenes.
Although previous carrier transport measurements in bi-layer graphene
transistors did indicate a gate-induced insulating state at temperature below 1
Kelvin, the electrical (or transport) bandgap was estimated to be a few meV,
and the room temperature on/off current ratio in bi-layer graphene FETs remains
similar to those in single-layer graphene FETs. Here, for the first time, we
report an on/off current ratio of around 100 and 2000 at room temperature and
20 K, respectively in our dual-gate bi-layer graphene FETs. We also measured an
electrical bandgap of >130 and 80 meV at average electric displacements of 2.2
and 1.3 V/nm, respectively. This demonstration reveals the great potential of
bi-layer graphene in applications such as digital electronics,
pseudospintronics, terahertz technology, and infrared nanophotonics.Comment: 3 Figure
Planar Heterostructure Graphene -- Narrow-Gap Semiconductor -- Graphene
We investigate a planar heterostructure composed of two graphene films
separated by a narrow-gap semiconductor ribbon. We show that there is no the
Klein paradox when the Dirac points of the Brillouin zone of graphene are in a
band gap of a narrow-gap semiconductor. There is the energy range depending on
an angle of incidence, in which the above-barrier damped solution exists.
Therefore, this heterostructure is a "filter" transmitting particles in a
certain range of angles of incidence upon a potential barrier. We discuss the
possibility of an application of this heterostructure as a "switch".Comment: 9 pages, 2 figure
Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman Intensity
A simple, non-invasive method using Raman spectroscopy for the estimation of
the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is
presented, enabling simultaneous determination of thickness, grain size and
disorder using the spectra. The attenuation of the substrate Raman signal due
to the graphene overlayer is found to be dependent on the graphene film
thickness deduced from X-ray photoelectron spectroscopy and transmission
electron microscopy of the surfaces. We explain this dependence using an
absorbing overlayer model. This method can be used for mapping graphene
thickness over a region and is capable of estimating thickness of multilayer
graphene films beyond that possible by XPS and Auger electron spectroscopy
(AES).Comment: 14 pages, 9 figure
Coexistence of electron and hole transport in graphene
When sweeping the carrier concentration in monolayer graphene through the
charge neutrality point, the experimentally measured Hall resistivity shows a
smooth zero crossing. Using a two- component model of coexisting electrons and
holes around the charge neutrality point, we unambiguously show that both types
of carriers are simultaneously present. For high magnetic fields up to 30 T the
electron and hole concentrations at the charge neutrality point increase with
the degeneracy of the zero-energy Landau level which implies a quantum Hall
metal state at \nu=0 made up by both electrons and holes.Comment: 5 pages, 6 figure
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