36 research outputs found
Direct observation of valley-hybridization and universal symmetry of graphene with mesoscopic conductance fluctuations
In graphene, the valleys represent spin-like quantities and can act as a
physical resource in valley-based electronics to novel quantum computation
schemes. Here we demonstrate a direct route to tune and read the valley quantum
states of disordered graphene by measuring the mesoscopic conductance
fluctuations. We show that the conductance fluctuations in graphene at low
temperatures are reduced by a factor of four when valley triplet states are
gapped in the presence of short range potential scatterers at high carrier
densities. We also show that this implies a gate tunable universal symmetry
class which outlines a fundamental feature arising from graphene's unique
crystal structure.Comment: 5 pages, 5 figure
Resistance noise in electrically biased bilayer graphene
We demonstrate that the low-frequency resistance fluctuations, or noise, in
bilayer graphene is strongly connected to its band structure, and displays a
minimum when the gap between the conduction and valence band is zero. Using
double-gated bilayer graphene devices we have tuned the zero gap and charge
neutrality points independently, which offers a versatile mechanism to
investigate the low-energy band structure, charge localization and screening
properties of bilayer graphene.Comment: 5 pages, 4 figure
An experimental set up to probe the quantum transport through single atomic/molecular junction at room temperature
Understanding the transport characteristics at the atomic limit is the
prerequisite for futuristic nano-electronic applications. Among various
experimental procedures, mechanically controllable break junction (MCBJ) is one
of the well adopted experimental technique to study and control the atomic or
molecular scale devices. Here, we present the details of the development of a
piezo controlled table top MCBJ set up, working at ambient condition, along
with necessary data acquisition technique and analysis of the data. We
performed conductance experiment on a macroscopic gold wire, which exhibits
quantized conductance plateau upon pulling the wire with the piezo. Conductance
peak up to (, being the electronic charge and
being the plank's constant) could be resolved at room temperature. A
well-known test bed molecule, bipyridine, was introduced between
the gold electrodes and conductance histogram exhibits two distinctive
conductance peaks, confirming the formation of single molecular junction, in
line with the previous reports. This demonstrate that our custom-designed MCBJ
set up is capable of measuring quantum transport of a single molecular junction
at ambient condition.Comment: 15 pages, 8 figure
Influence of etching processes on electronic transport in mesoscopic InAs/GaSb quantum well devices
We report the electronic characterization of mesoscopic Hall bar devices
fabricated from coupled InAs/GaSb quantum wells sandwiched between AlSb
barriers, an emerging candidate for two-dimensional topological insulators. The
electronic width of the etched structures was determined from the low field
magneto-resistance peak, a characteristic signature of partially diffusive
boundary scattering in the ballistic limit. In case of dry-etching the
electronic width was found to decrease with electron density. In contrast, for
wet etched devices it stayed constant with density. Moreover, the boundary
scattering was found to be more specular for wet-etched devices, which may be
relevant for studying topological edge states.Comment: 5 pages, 2 figure
Detection of nontrivial topology driven by charge density wave in a semi-Dirac metal
The presence of electron correlations in a system with topological order can
lead to exotic ground states. Considering single crystals of LaAgSb2 which has
a square net crystal structure, one finds multiple charge density wave
transitions (CDW) as the temperature is lowered. We find large planar Hall
(PHE) signals in the CDW phase, which are still finite in the high temperature
phase though they change sign. Optimising the structure within first-principles
calculations, one finds an unusual chiral metallic phase. This is because as
the temperature is lowered, the electrons on the Ag atoms get more localized,
leading to stronger repulsions between electrons associated with atoms on
different layers. This leads to successive layers sliding with respect to each
other, thereby stabilising a chiral structure in which inversion symmetry is
also broken. The large Berry curvature associated with the low temperature
structure explains the low temperature PHE. At high temperature the PHE arises
from the changes induced in the tilted Dirac cone in a magnetic field. Our work
represents a route towards detecting and understanding the mechanism in a
correlation driven topological transition through electron transport
measurements, complemented by ab-initio electronic structure calculations.Comment: 11 pages, 4 figures, Includes supplementary information, Accepted in
Advanced Functional Material
Valley polarization and photocurrent generation in transition metal dichalcogenide alloy MoSSe
Monolayer transition metal dichalcogenides (TMDCs) constitute the core group
of materials in the emerging semiconductor technology of valleytronics. While
the coupled spin-valley physics of pristine TMDC materials and their
heterstructures has been extensively investigated, less attention was given to
TMDC alloys, which could be useful in optoelectronic applications due to the
tunability of their band gaps. We report here our experimental investigations
of the spin-valley physics of the monolayer and bilayer TMDC alloy,
MoSSe, in terms of valley polarization and the generation as
well as electrical control of a photocurrent utilising the circular
photogalvanic effect. Piezoelectric force microscopy provides evidence for an
internal electric field perpendicular to the alloy layer, thus breaking the
out-of-plane mirror symmetry. The experimental observation is supported by
first principles calculations based on the density functional theory. A
comparison of the photocurrent device, based on the alloy material, is made
with similar devices involving other TMDC materials