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Quantum capacitance
About: Quantum capacitance is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 24165 citations.
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TL;DR: In this article, the authors demonstrate that quantum capacitance of graphene-based electrodes can be improved by the N-doping, vacancy defects, and adsorbed transition-metal atoms.
Abstract: With first-principles density functional theory calculations, we demonstrate that quantum capacitance of graphene-based electrodes can be improved by the N-doping, vacancy defects, and adsorbed transition-metal atoms. The enhancement of the quantum capacitance can be contributed to the formation of localized states near Dirac point and/or shift of Fermi level induced by the defects and doping. In addition, the quantum capacitance is found to increase monotonically following the increase of defect concentrations. It is also found that the localized states near Fermi level results in the spin-polarization effect.
138 citations
TL;DR: In this article, a Cooper-pair transistor (CPT) was fabricated with parameters such that for appropriate voltage biases, it behaves essentially like a single SCB and was detected by measuring the in phase and quadrature rf signal reflected from a resonant circuit in which the CPT was embedded.
Abstract: We have fabricated a Cooper-pair transistor (CPT) with parameters such that for appropriate voltage biases, it behaves essentially like a single Cooper-pair box (SCB). The effective capacitance of a SCB can be defined as the derivative of the induced charge with respect to gate voltage and has two parts, the geometric capacitance, C-geom, and the quantum capacitance C-Q. The latter is due to the level anticrossing caused by the Josephson coupling and is dual to the Josephson inductance. It depends parametrically on the gate voltage and its magnitude may be substantially larger than C-geom. We have detected C-Q in our CPT, by measuring the in phase and quadrature rf signal reflected from a resonant circuit in which the CPT is embedded. C-Q can be used as the basis of a charge qubit readout by placing a Cooper-pair box in such a resonant circuit.
133 citations
TL;DR: In this article, analytical expressions for the intraband conductivity tensor of graphene that includes spatial dispersion for arbitrarily wave-vector values and the presence of a nonzero Fermi energy are presented.
Abstract: Analytical expressions are presented for the intraband conductivity tensor of graphene that includes spatial dispersion for arbitrarily wave-vector values and the presence of a nonzero Fermi energy. The conductivity tensor elements are derived from the semiclassical Boltzmann transport equation under both the relaxation-time approximation and the Bhatnagar-Gross-Krook model (which allows for an extra degree of freedom to enforce number conservation). The derived expressions are based on linear electron dispersion near the Dirac points, and extend previous results that assumed small wave-vector values; these are shown to be inadequate for the very slow waves expected on graphene nanoribbons. The new expressions are also compared to results obtained by numericalintegrationoverthefirstBrillouinzoneusingtheexact(tight-binding)electrondispersionrelation.Very good agreement is found between the new analytical expressions and the exact numerical results. Furthermore, a comparison with the longitudinal random-phase conductivity is also made. It is shown analytically that these new expressions lead to the correct value of the quantum capacitance of a graphene sheet and that ignoring spatial dispersion leads to serious errors in the propagation properties of fundamental modes on graphene nanoribbons.
132 citations
TL;DR: In this article, the quantum capacitance and total capacitance of single-layer graphene electrodes as a function of the number of graphene layers were studied. And the authors found that quantum capacitances play a dominant role in the performance of single layer graphene both in aqueous and ionic-liquid electrolytes.
Abstract: Quantum capacitance has been recently measured for electric double layers (EDL) at electrolyte/graphene interfaces. However, the importance of quantum capacitance in realistic carbon electrodes is not clear. Toward understanding that from a theoretical perspective, here we studied the quantum capacitance and total capacitance of graphene electrodes as a function of the number of graphene layers. The quantum capacitance was obtained from electronic density functional theory based on fixed band approximation with an implicit solvation model, while the EDL capacitances were from classical density functional theory. We found that quantum capacitance plays a dominant role in total capacitance of the single-layer graphene both in aqueous and ionic-liquid electrolytes but the contribution decreases as the number of graphene layers increases. The total integral capacitance roughly levels off and is dominated by the EDL capacitance beyond about four graphene layers. Because many porous carbons have nanopores with ...
131 citations
TL;DR: This work strongly couple multilayer graphene resonators to superconducting cavities in order to achieve a displacement sensitivity of 1.3 fm Hz−1/2 and holds promise for studying the quantum capacitance of graphene, its magnetization, and the electron and nuclear spins of molecules adsorbed on its surface.
Abstract: Mechanical resonators based on low-dimensional materials are promising for force and mass sensing experiments. The force sensitivity in these ultra-light resonators is often limited by the imprecision in the measurement of the vibrations, the fluctuations of the mechanical resonant frequency and the heating induced by the measurement. Here, we strongly couple multilayer graphene resonators to superconducting cavities in order to achieve a displacement sensitivity of 1.3 fm Hz(-1/2). This coupling also allows us to damp the resonator to an average phonon occupation of 7.2. Our best force sensitivity, 390 zN Hz(-1/2) with a bandwidth of 200 Hz, is achieved by balancing measurement imprecision, optomechanical damping, and measurement-induced heating. Our results hold promise for studying the quantum capacitance of graphene, its magnetization, and the electron and nuclear spins of molecules adsorbed on its surface.
128 citations