69 research outputs found
Effect of ambient on the resistance fluctuations of graphene
In this letter we present the results of systematic experimental
investigations of the effect of different chemical environments on the low
frequency resistance fluctuations of single layer graphene field effect
transistors (SLG-FET). The shape of the power spectral density of noise was
found to be determined by the energetics of the adsorption-desorption of
molecules from the graphene surface making it the dominant source of noise in
these devices. We also demonstrate a method of quantitatively determining the
adsorption energies of chemicals on graphene surface based on noise
measurements. We find that the magnitude of noise is extremely sensitive to the
nature and amount of the chemical species present. We propose that a chemical
sensor based on the measurement of low frequency resistance fluctuations of
single layer graphene field effect transistor devices will have extremely high
sensitivity, very high specificity, high fidelity and fast response times
Low frequency random telegraphic noise (RTN) and 1/f noise in the rare-earth manganite PrCaMnO near the charge-ordering transition
We have studied low frequency resistance fluctuations (noise) in a single
crystal of the rare earth perovskite manganite PrCaMnO
which shows a charge ordering transition at a temperature ~ 245K. The
noise measurements were made using an ac bias with and without a dc bias
current imposed on it. We find that the spectral power contains two
components - one broad band 1/f part that exists for all frequency and
temperature ranges and a single frequency Lorentzian of frequency which
is strongly temperature dependent. The Lorentzian in which appears due
to Random telegraphic noise (RTN) as seen in the time series of the
fluctuation, is seen in a very narrow temperature window around where
it makes the dominating contribution to the fluctuation. When the applied dc
bias is increased beyond a certain threshold current density , the
electrical conduction becomes non-linear and one sees appearance of a
significant Lorentzian contribution in the spectral power due to RTN. We
explain the appearance of the RTN as due to coexisting Charge ordered (CO) and
reverse orbitally ordered (ROO) phases which are in dynamical equilibrium over
a mesoscopic length scale () and the kinetics being controlled by
an activation barrier T>>T_{CO}T_{CO}$ is
approached from above and the probability distribution function (PDF) deviates
strongly from a Gaussian. We explain this behavior as due to approach of charge
localization with correlated fluctuators which make the PDF non-Gaussian.Comment: 23 pages, 14 figure
1/f noise in nanowires
We have measured the low-frequency resistance fluctuations (1 mHz<f<10 Hz) in
Ag nanowires of diameter 15 nm<d<200 nm at room temperatures. The power
spectral density (PSD) of the fluctuations has a 1/f^{\alpha} character as seen
in metallic films and wires of larger dimension. Additionally, the PSD has a
significant low-frequency component and the value of \alpha increases from the
usual 1 to ~3/2 as the diameter d is reduced. The value of the normalized
fluctuation \frac{}{R^2} also increases as the diameter d is
reduced. We observe that there are new features in the 1/f noise as the size of
the wire is reduced and they become more prominent as the diameter of the wires
approaches 15nm. It is important to investigate the origin of the new behavior
as 1/f noise may become a limiting factor in the use of metal wires of
nanometer dimensions as interconnects.Comment: 9 pages, 6 figures, published in Nanotechnolog
Probing the interplay between surface and bulk states in the topological Kondo insulator SmB through conductance fluctuation spectroscopy
We present results of resistance fluctuation spectroscopy on single crystals
of the predicted Kondo topological insulator material SmB. Our measurements
show that at low temperatures, transport in this system takes place only
through surface states. The measured noise in this temperature range arises due
to Universal Conductance Fluctuations whose statistics was found to be
consistent with theoretical predictions for that of two-dimensional systems in
the Symplectic symmetry class. At higher temperatures, we find signatures of
glassy dynamics and establish that the measured noise is caused by mobility
fluctuations in the bulk. We find that, unlike the topological insulators of
the dichalcogenide family, the noise in surface and bulk conduction channels in
SmB are completely uncorrelated. Our measurements establish that at
sufficiently low temperatures, the bulk has no discernible contribution to
electrical transport in SmB making it an ideal platform for probing the
physics of topological surface states.Comment: 9 pages, 11 figure
Observation of large low-frequency resistance fluctuations in metallic nanowires: implications on its stability
We have measured the low frequency (1mHz≤f≤10 Hz) resistance fluctuations in metallic nanowires (diameter 15 nm to 200 nm) in the temperature range 77 K to 400 K. The nanowires were grown electrochemically in polycarbonate membranes and the measurements were carried out in arrays of nanowires by retaining them in the membrane. A large fluctuation in excess of conventional 1/f noise which peaks beyond a certain temperature was found. The fluctuations with a significant low frequency component (⋍1/f3/2) arise when the diameter of the wire ⋍15 nm and vanish rapidly as the diameter is increased. We argue that Rayleigh-Plateau instability is the likely cause of this excess noise
Effect of multiband transport on charge carrier density fluctuations at the LaAlO/SrTiO interface
Multiband transport in superconductors is interesting both from an academic
as well as an application point of view. It has been postulated that interband
scattering can significantly affect the carrier dynamics in these materials. In
this article we present a detailed study of the electrical transport properties
of the high-mobility two-dimensional electron gas residing at the interface of
LaAlO/SrTiO, a prototypical multi-band superconductor. We show, through
careful measurements of the gate dependence of the magnetoresistance and
resistance fluctuations at ultra-low temperatures, that transport in the
superconducting regime of this system has contributions from two bands which
host carriers of very different characters. We identify a gate-voltage tunable
Lifshitz transition in the system and show that the resistance fluctuations
have strikingly different features on either side of it. At low carrier
densities, resistance noise is dominated by number-density fluctuations arising
from trapping-detrapping of charge carriers from defects in the underlying
SrTiO substrate, characteristic of a single-band semiconductor. Above the
Lifshitz transition, the noise presumably originates from inter-band
scattering. Our work highlights the importance of inter-band scattering
processes in determining the transport properties of low-dimensional systems
and projects resistance fluctuation spectroscopy as a viable technique for
probing the charge carrier dynamics across a Lifshitz transition.Comment: 6 pages, 5 figure
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