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[en] For surface plasmons on graphene in an arbitrary dielectric environment, combinations of the plasmon energy and frequency (adiabatic invariants) that are conserved during slow time-variations of the graphene free carrier density are obtained. The invariants allow one to find the plasmon energy changes directly from the frequency shift without solving a dynamic equation. The invariants have a different form in the cases of increasing and decreasing carrier density. In both cases, however, they predict that plasmon frequency shifting is accompanied by a decrease of the plasmon energy. (paper)
[en] A phenomenological investigation of the dc Josephson current in superconductor endash (S-) normal-metal endash (N) [semiconductor endash (Sm-)] superconductor junctions is carried out as a function of the carrier concentration in the barrier. The occurrence of a nonmonotonic dependence of the Josephson current on the carrier concentration is predicted within some limits. This study suggests that in S-N- (Sm-) S structures there is an optimum carrier concentration range which gives the maximum value of the Josephson current IC and the junction parameter ICRN. copyright 1997 The American Physical Society
[en] We study charge transport in a monolayer MoS2 nanoflake over a wide range of carrier density, temperature and electric bias. We find that the transport is best described by a percolating picture in which the disorder breaks translational invariance, breaking the system up into a series of puddles, rather than previous pictures in which the disorder is treated as homogeneous and uniform. Our work provides insight to a unified picture of charge transport in monolayer MoS2 nanoflakes and contributes to the development of next-generation MoS2-based devices. (paper)
[en] High precision electron probe microanalysis (EPMA) has been used to measure the correlation of oxygen deficiency with carrier concentration in thin films of amorphous indium oxide. This has shown that there are ten times as many oxygen vacancies as would be expected from the carrier concentration measurements, giving a doping efficiency of 0.1. It is therefore clear that the doping mechanism is more complex than the usual picture of every oxygen vacancy producing two free electrons
[en] Under the auspices of this funding, we have developed a program to synthesize and characterize highly monodispersed magnetic nanoparticles. We have been particularly interested in the origin of the exchange bias effect, which occurs in compound nanoparticles with a ferromagnetic core and an antiferromagnetic shell, and have mostly focused on Co/CoO core-shell nanoparticles. The exchange bias effect involves exchange coupling between the core moment and the antiferromagnetic shell which stabilizes the core moment, which would otherwise be quickly reorienting in ferromagnetic particles of this size.
[en] Two-photon absorption (TPA) testing is employed to analyze the laser-induced latchup sensitive-volume (SV) of a specially designed test structure. This method takes into account the existence of an onset region in which the probability of triggering latchup transitions from zero to one as the laser pulse energy increases. This variability is attributed to pulse-to-pulse variability, uncertainty in measurement of the pulse energy, and variation in local carrier density and temperature. For each spatial position, the latchup probability associated with a given energy is calculated from multiple pulses. The latchup probability data are well-described by a Weibull distribution. The results show that the area between p-n-p-n cell structures is more sensitive than the p+ and n+ source areas, and locations far from the well contacts are more sensitive than those near the contact region. The transition from low probability of latchup to high probability is more abrupt near the source contacts than it is for the surrounding areas.
[en] A theory of the spectral linewidth for a multi-mode laser is presented and used to explain experiment results. It turned out that linewidth is much greater than predicted by Schawlow-Townes theory. Henry attributed this enhancement to variation of real part of refractive index with carrier density. Spontaneous emissions cause changes to imaginary part of refractive index, which is coupled to changes in a real counterpart. This approach is expanded to cover multi-mode lasers and interactions between modes. (paper)
[en] Optical gain spectra are computed for quantum dots under high excitation conditions, where there is a non-negligible two-dimensional carrier density surrounding the dots. Using a screened Hartree-Fock theory to describe the influence of the Coulomb interaction, we find different self-energy shifts for the dot and quantum-well transitions. Furthermore, in contrast to the result for quantum-well and bulk systems, the peak gain at the quantum-dot transition computed including Coulomb effects is reduced from its free carrier value
[en] We calculate the contribution of unscreened and screened scalar (DP) and vector potential(VP) electron-acoustic phonon coupling to resistivity in disordered graphene through Keldysh Green’s function method within the diffusive limit, k F l ≫ 1. We obtain analytical results in the asymptotic limits of clean and strong impurities for both DP and VP coupling, which is in observed to be in good agreement with the resistivity behavior in these limits. We find that the complete numerical results approach the analytical result in the extreme limits, but give different temperature dependencies in between these limits. The graphene resistivity has been investigated as functions of temperature, mean free path and carrier density. We also evaluated the screened behavior in the Thomas-Fermi and Random phase approximation dielectric function and obtained the temperature power exponents. We find that in the absence of screening when the electronic disorder (T < T dr), the two coupling mechanisms are affected differently and the relaxation rate associated with the VP coupling is suppressed by disorder as compared to the DP coupling, and the DP coupling is enhanced by disorder. (paper)