Building large solar power plants requires significant long-term investment so understanding impacts from climate change will aid financial planning, technology selection, and energy output projections. In this article we examine how projected changes in temperature and insolation over the 21st century will affect photovoltaic (PV) and concentrated solar power (CSP) output. Projected climate data was obtained from the coupled ocean-atmosphere climate models HadGEM1 and HadCM3 under the IPCC SRES A1B scenario which describes a future world of rapid economic growth with a balanced use of renewable and fossil fuel power generation. Our calculations indicate that under this scenario PV output from 2010 to 2080 is likely to increase by a few percent in Europe and China, see little change in Algeria and Australia, and decrease by a few percent in western USA and Saudi Arabia. CSP output is likely to increase by more than 10% in Europe, increase by several percent in China and a few percent in Algeria and Australia, and decrease by a few percent in western USA and Saudi Arabia. The results are robust to uncertainty in projected temperature change. A qualitative analysis of uncertainty in projected insolation change suggests strongest confidence in the results for Europe and least confidence in the results for western USA. Changes in PV and CSP output are further studied by calculating fractional contributions from changes in temperature and insolation. For PV there is considerable variation in contribution depending on location. For CSP the contribution from changes in insolation is always dominant.

We present data from an induced gallium arsenide (GaAs) quantum wire that exhibits an additional conductance plateau at 0.5(2e2/h), where e is the charge of an electron and h is Planck's constant, in zero magnetic field. The plateau was most pronounced when the potential landscape was tuned to be symmetric by using low-temperature scanning-probe techniques. Source-drain energy spectroscopy and temperature response support the hypothesis that the origin of the plateau is the spontaneous spin-polarization of the transport electrons: a ferromagnetic phase. Such devices may have applications in the field of spintronics to either generate or detect a spin-polarized current without the complications associated with external magnetic fields or magnetic materials.

We present scanning-probe images and magnetic-field plots which reveal fractal conductance fluctuations in a quantum billiard. The quantum billiard is drawn and tuned using erasable electrostatic lithography, where the scanning probe draws patterns of surface charge in the same environment used for measurements. A periodicity in magnetic field, which is observed in both the images and plots, suggests the presence of classical orbits. Subsequent high-pass filtered highresolution images resemble the predicted probability density of scarred wave functions, which describe the classical orbits. , are observed in disordered systems due to multiple-path interference as electrons scatter from random impurities [1]. A quantum billiard is a large quantum dot where electron trajectories are ballistic, meaning scattering occurs predominantly at the billiard boundary. If the electron phase coherence length is longer than the billiard dimensions, then conductance fluctuations can also be observed in quantum billiards where electrons scatter off the billiard boundary instead of impurities [2][3][4][5]. A soft-walled quantum billiard is a classically mixed system, with regions of regular and chaotic behavior, characterized by the presence of fractal magnetoconductance fluctuations [4,6,7]. The system is chaotic in the sense that a small change, in the magnetic field for example, strongly modifies conductance on an arbitrarily fine scale. Quantum billiards often exhibit Aharonov-Bohm like [1] periodic conductance fluctuations, which are understood to be the signature of stable closed-loop orbits with well defined areas whose quantum states are preferentially excited due to collimation from the leads [2]. The amplitude of the associated wave functions, which are known as scarred wave functions, are concentrated along the underlying classical trajectories and are found through simulation to also exist periodically in magnetic field [8][9][10]. In this letter we provide a further link between experiment and simulation by presenting high resolution scanning probe images of fractal conductance fluctuations which reveal structure remarkably similar to that seen in theoretical images of scarred wave functions [8]. Figure 1 illustrates the billiard construction. A 2D electron system (2DES) with electron mobility 6 10 5 × cm 2 V -1 s -1 and density 11 10 1 . 3 × cm -2 forms at a GaAs/AlGaAs heterojunction 97 nm beneath the surface. The billiard is defined from the 2DES using erasable electrostatic lithography (EEL) where a conductive scanning probe draws spots of negative charge on the GaAs surface to locally deplete 2DES electrons [11]. Uniquely, EEL uses the same low-temperature high-vacuum environment as used for measurement, so device geometry can be modified during the experiment. A row of EEL spots, separated by 100 nm, creates a linear barrier in the 2DES which defines the quantum billiard walls. The lithographic dimension of the billiard is 2 by 3.5 m, but EEL line width and lateral depletion decrease the 2DES billiard dimension ...

No abstract

Quantum electronic components--such as quantum antidots and one-dimensional channels--are usually defined from doped GaAs/AlGaAs heterostructures using electron-beam lithography or local oxidation by conductive atomic force microscopy. In both cases, lithography and measurement are performed in very different environments, so fabrication and test cycles can take several weeks. Here we describe a different lithographic technique, which we call erasable electrostatic lithography (EEL), where patterns of charge are drawn on the device surface with a negatively biased scanning probe in the same low-temperature high-vacuum environment used for measurement. The charge patterns locally deplete electrons from a subsurface two-dimensional electron system (2DES) to define working quantum components. Charge patterns are erased locally with the scanning probe biased positive or globally by illuminating the device with red light. We demonstrate and investigate EEL by drawing and erasing quantum antidots, then develop the technique to draw and tune high-quality one-dimensional channels. The quantum components are imaged using scanned gate microscopy. A technique similar to EEL has been reported previously, where tip-induced charging of the surface or donor layer was used to locally perturb a 2DES before charge accumulation imaging.