8 research outputs found
Graphene-based Josephson junction single photon detector
We propose to use graphene-based Josephson junctions (gJjs) to detect single
photons in a wide electromagnetic spectrum from visible to radio frequencies.
Our approach takes advantage of the exceptionally low electronic heat capacity
of monolayer graphene and its constricted thermal conductance to its phonon
degrees of freedom. Such a system could provide high sensitivity photon
detection required for research areas including quantum information processing
and radio-astronomy. As an example, we present our device concepts for gJj
single photon detectors in both the microwave and infrared regimes. The dark
count rate and intrinsic quantum efficiency are computed based on parameters
from a measured gJj, demonstrating feasibility within existing technologies.Comment: 11 pages, 6 figures, and 1 table in the main tex
Development of high frequency and wide bandwidth Johnson noise thermometry
We develop a high frequency, wide bandwidth radiometer operating at room temperature, which augments the traditional technique of Johnson noise thermometry for nanoscale thermal transport studies. Employing low noise amplifiers and an analog multiplier operating at 2 GHz, auto- and cross-correlated Johnson noise measurements are performed in the temperature range of 3 to 300 K, achieving a sensitivity of 5.5 mK (110 ppm) in 1 s of integration time. This setup allows us to measure the thermal conductance of a boron nitride encapsulated monolayer graphene device over a wide temperature range. Our data show a high power law (T similar to 4) deviation from the Wiedemann-Franz law above T similar to 100 K. (C) 2015 AIP Publishing LLCclose
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Observation of the Dirac fluid and the breakdown of the Wiedemann-Franz law in graphene
Interactions between particles in quantum many-body systems can lead to collective behavior described by hydrodynamics. One such system is the electron-hole plasma in graphene near the charge neutrality point which can form a strongly coupled Dirac fluid. This charge neutral plasma of quasi-relativistic fermions is expected to exhibit a substantial enhancement of the thermal conductivity, due to decoupling of charge and heat currents within hydrodynamics. Employing high sensitivity Johnson noise thermometry, we report the breakdown of the Wiedemann-Franz law in graphene, with a thermal conductivity an order of magnitude larger than the value predicted by Fermi liquid theory. This result is a signature of the Dirac fluid, and constitutes direct evidence of collective motion in a quantum electronic fluid.Physic
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Transport in inhomogeneous quantum critical fluids and in the Dirac fluid in graphene
We develop a general hydrodynamic framework for computing direct current thermal and electric transport in a strongly interacting finite temperature quantum system near a Lorentz-invariant quantum critical point. Our framework is non-perturbative in the strength of long wavelength fluctuations in the background charge density of the electronic fluid, and requires the rate of electron-electron scattering to be faster than the rate of electron-impurity scattering. We use this formalism to compute transport coefficients in the Dirac fluid in clean samples of graphene near the charge neutrality point, and find results insensitive to long range Coulomb interactions. Numerical results are compared to recent experimental data on thermal and electrical conductivity in the Dirac fluid in graphene and substantially improved quantitative agreement over existing hydrodynamic theories is found. We comment on the interplay between the Dirac fluid and acoustic and optical phonons, and qualitatively explain experimentally observed effects. Our work paves the way for quantitative contact between experimentally realized condensed matter systems and the wide body of high energy inspired theories on transport in interacting many-body quantum systems.Physic
Guided Modes of Anisotropic van der Waals Materials Investigated by near-Field Scanning Optical Microscopy
Guided
modes in nanometer thick anisotropic van der Waals materials
are experimentally investigated and their refractive indices in visible
wavelengths are extracted. Our method involves near-field scanning
optical microscopy of waveguide (transverse electric) and surface
plasmon polariton (transverse magnetic) modes in h-BN/SiO<sub>2</sub>/Si and Ag/h-BN stacks, respectively. We determine the dispersion
of these modes and use this relationship to extract anisotropic refractive
indices of h-BN flakes. In the wavelength interval 550–700
nm, the in-plane and out-of-plane refractive indices are in the range
1.98–2.12 and 1.45–2.12, respectively. Our approach
of using near-field scanning optical microscopy allows for the direct
study of the interaction between light and two-dimensional van der
Waals materials and heterostructures