As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies--for example, displays, fluorescence tagging, solid-state lighting and lasers. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron-hole pairs (the electron-hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron-hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.

A method for calculating the free energy of an inhomogeneous superconductor is presented. This method is based on the quasiclassical limit ͑or Andreev approximation͒ of the Bogoliubov-de Gennes ͑or wave function͒ formulation of the theory of weakly coupled superconductors. The method is applicable to any pure bulk superconductor described by a pair potential with arbitrary spatial dependence, in the presence of supercurrents and external magnetic field. We find that both the local density of states and the free energy density of an inhomogeneous superconductor can be expressed in terms of the diagonal resolvent of the corresponding Andreev Hamiltonian, which obeys the so-called Gelfand-Dikii equation. Also, the connection between the well known Eilenberger equation for the quasiclassical Green's function and the less known Gelfand-Dikii equation for the diagonal resolvent of the Andreev Hamiltonian is established. These results are used to construct a general algorithm for calculating the ͑gauge invariant͒ gradient expansion of the free energy density of an inhomogeneous superconductor at arbitrary temperatures.

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We calculate the rate of non-radiative, Förster-type energy transfer (ET) from an excited epitaxial quantum well (QW) to a proximal monolayer of semiconductor nanocrystal quantum dots (QDs).Different electron-hole configurations in the QW are considered as a function of temperature and excited electron-hole density. A comparison of the theoretically determined ET rate and QW radiative recombination rate shows that, depending on the specific conditions, the ET rate is comparable to or even greater than the radiative recombination rate. Such efficient Förster ET is promising for the implementation of ET-pumped, nanocrystal QD-based light emitting devices.

We measure the spin lattice relaxation of the In(1) nuclei in the CeMIn5 materials, extract quantitative information about the low energy spin dynamics of the lattice of Ce moments in both CeRhIn5 and CeCoIn5, and identify a crossover in the normal state. Above a temperature T * the Ce lattice exhibits "Kondo gas" behavior characterized by local fluctuations of independently screened moments; below T * both systems exhibit a "Kondo liquid" regime in which interactions between the local moments contribute to the spin dynamics. Both the antiferromagnetic and superconducting ground states in these systems emerge from the "Kondo liquid" regime. Our analysis provides strong evidence for quantum criticality in CeCoIn5. 75.25.+z ,71.27.+a The CeMIn 5 heavy fermion materials possess a rich phase diagram revealing a fascinating interplay between the antiferromagnetic behavior of incompletely screened Ce local moments, an unconventional normal state, and superconducting behavior of the heavy electrons that is reminiscent of that found in the cuprates [1,2]. The nonFermi liquid behavior of the itinerant heavy electrons and the possible d-wave symmetry of their superconducting state has led to the proposal that the superconducting pairing mechanism arises from their coupling to spin fluctuations [1,3,4,5,6]. In this Letter, we consider the information about the coupled system of Ce local moments and itinerant heavy electrons that can be derived from Nuclear Magnetic Resonance (NMR) experiments on the spin lattice relaxation rate (T −1 1 ) of the In(1) nuclei located in the plane of the Ce moments. We show that the In(1) nuclei are strongly coupled to their four nearest neighbor Ce spins by an anisotropic hyperfine interaction, and that the resulting anomalous behavior of T 1 T provides important information on the low frequency dynamics of the lattice of Ce spins, and the quasiparticles to which they couple. Because the coupling is anisotropic, it does not vanish for antiferromagnetically correlated Ce moments, so that T −1 1 provides valuable information on the dynamics of their magnetic ordering, as well as on the influence of Kondo screening of the moments on their relaxation rate, and departures from Kondo behavior at low temperatures [7,8]. We present our results for both the antiferromagnet CeRhIn 5 and the superconductor CeCoIn 5 .Previous reports of T is dominated by local fluctuations of the Ce moments. Below T * the qindependent local moment contribution to T −1 1 becomes temperature independent, and and a second q and T dependent component emerges. We identify this emergent component with the heavy electrons, that is the itinerant component of the Ce 4f electrons arising from their coupling to one another and to the conduction electrons. This extra contribution to the relaxation agrees quantitatively with inelastsic neutron scattering (INS) results in CeRhIn 5 , and suggests that the antiferromagnetic correlations in CeCoIn 5 are primarily 2D, and that in the absence of superconductivity one would have a quant...