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

Probing long-range correlations in the Berezinskii-Kosterlitz-Thouless fluctuation regime of ultra-thin NbN superconducting films using transport noise measurements

We probe the presence of long-range correlations in phase fluctuations by analyzing the higher-order spectrum of resistance fluctuations in ultra-thin NbN superconducting films. The non-Gaussian component of resistance fluctuations is found to be sensitive to film thickness close to the transition, which allows us to distinguish between mean field and Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transitions. The extent of non-Gaussianity was found to be bounded by the BKT and mean field transition temperatures and depend strongly on the roughness and structural inhomogeneity of the superconducting films. Our experiment outlines a novel fluctuation-based kinetic probe in detecting the nature of superconductivity in disordered low-dimensional materials.Comment: submitted to PR

Robust local and non-local transport in the Topological Kondo Insulator SmB6_{6} in the presence of high magnetic field

SmB$_6$ has been predicted to be a Kondo Topological Insulator with topologically protected conducting surface states. We have studied quantitatively the electrical transport through surface states in high quality single crystals of SmB$_6$. We observe a large non-local surface signal at temperatures lower than the bulk Kondo gap scale. Measurements and finite element simulations allow us to distinguish unambiguously between the contributions from different transport channels. In contrast to general expectations, the electrical transport properties of the surface channels was found to be insensitive to high magnetic fields. Local and non-local magnetoresistance measurements allowed us to identify definite signatures of helical spin states and strong inter-band scattering at the surface.Comment: 7 pages, 8 figures, 1 tabl

Universality of Anderson Localization Transitions in the Integer and Fractional Quantum Hall Regime

Understanding the interplay between electronic interactions and disorder-induced localization has been a longstanding quest in the physics of quantum materials. One of the most convincing demonstrations of the scaling theory of localization for noninteracting electrons has come from plateau transitions in the integer quantum Hall effect with short-range disorder, wherein the localization length diverges as the critical filling factor is approached with a measured scaling exponent close to the theoretical estimates. In this work, we extend this physics to the fractional quantum Hall effect, a paradigmatic phenomenon arising from a confluence of interaction, disorder, and topology. We employ high-mobility trilayer graphene devices where the transport is dominated by short-range impurity scattering, and the extent of Landau level mixing can be varied by a perpendicular electric field. Our principal finding is that the plateau-to-plateau transitions from N+1/3 to N+2/5 and from N+2/5 to N+3/7 fractional states are governed by a universal scaling exponent, which is identical to that for the integer plateau transitions and is independent of the perpendicular electric field. These observations and the values of the critical filling factors are consistent with a description in terms of Anderson localization-delocalization transitions of weakly interacting electron-flux bound states called composite Fermions. This points to a universal effective physics underlying fractional and integer plateau-to-plateau transitions independent of the quasiparticle statistics of the phases and unaffected by weak Landau level mixing. Besides clarifying the conditions for the realization of the scaling regime for composite fermions, the work opens the possibility of exploring a wide variety of plateau transitions realized in graphene, including the fractional anomalous Hall phases and non-abelian FQH states

A gate-tunable graphene Josephson parametric amplifier

With a large portfolio of elemental quantum components, superconducting quantum circuits have contributed to dramatic advances in microwave quantum optics. Of these elements, quantum-limited parametric amplifiers have proven to be essential for low noise readout of quantum systems whose energy range is intrinsically low (tens of $\mu$eV ). They are also used to generate non classical states of light that can be a resource for quantum enhanced detection. Superconducting parametric amplifiers, like quantum bits, typically utilize a Josephson junction as a source of magnetically tunable and dissipation-free nonlinearity. In recent years, efforts have been made to introduce semiconductor weak links as electrically tunable nonlinear elements, with demonstrations of microwave resonators and quantum bits using semiconductor nanowires, a two dimensional electron gas, carbon nanotubes and graphene. However, given the challenge of balancing nonlinearity, dissipation, participation, and energy scale, parametric amplifiers have not yet been implemented with a semiconductor weak link. Here we demonstrate a parametric amplifier leveraging a graphene Josephson junction and show that its working frequency is widely tunable with a gate voltage. We report gain exceeding 20 dB and noise performance close to the standard quantum limit. Our results complete the toolset for electrically tunable superconducting quantum circuits and offer new opportunities for the development of quantum technologies such as quantum computing, quantum sensing and fundamental science

Supporting children through family change A review of services

Full report by Joanna Hawthorne, ISBN 1842630733SIGLEAvailable from British Library Document Supply Centre- DSC:3927. 734141(323) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Graphene as a sensor

Graphene has emerged as one of the strongest candidates for post-silicon technologies. One of the most important applications of graphene in the foreseeable future is sensing of particles of gas molecules, biomolecules or different chemicals or sensing of radiation of particles like alpha, gamma or cosmic particles. Several unique properties of graphene such as its extremely small thickness, very low mass, large surface to volume ratio, very high absorption coefficient, high mobility of charge carriers, high mechanical strength and high Young's modulus make it exceptionally suitable for making sensors. In this article we review the state-of-the-art in the application of graphene as a material and radiation detector, focusing on the current experimental status, challenges and the excitement ahead