Undoped diamond, a remarkable bulk electrical insulator, exhibits a high surface conductivity in air when the surface is hydrogen-terminated. Although theoretical models have claimed that a two-dimensional hole gas is established as a result of surfa
ce energy band bending, no definitive experimental demonstration has been reported so far. Here, we prove the two-dimensional character of the surface conductivity by low temperature characterization of diamond in-plane gated field-effect transistors that enable the lateral confinement of the transistors drain-source channel to nanometer dimensions. In these devices, we observe Coulomb blockade effects of multiple quantum islands varying in size with the gate voltage. The charging energy and thus the size of these zero-dimensional islands exhibits a gate voltage dependence which is the direct result of the two-dimensional character of the conductive channel formed at hydrogen-terminated diamond surfaces.
We present weak lensing data from the HST/STAGES survey to study the three-dimensional spatial distribution of matter and galaxies in the Abell 901/902 supercluster complex. Our method improves over the existing 3D lensing mapping techniques by calib
rating and removing redshift bias and accounting for the effects of the radial elongation of 3D structures. We also include the first detailed noise analysis of a 3D lensing map, showing that even with deep HST quality data, only the most massive structures, for example M200>~10^15 Msun/h at z~0.8, can be resolved in 3D with any reasonable redshift accuracy (Delta z~0.15). We compare the lensing map to the stellar mass distribution and find luminous counterparts for all mass peaks detected with a peak significance >3sigma. We see structures in and behind the z=0.165 foreground supercluster, finding structure directly behind the A901b cluster at z~0.6 and also behind the SW group at z~0.7. This 3D structure viewed in projection has no significant impact on recent mass estimates of A901b or the SW group components SWa and SWb.
This paper studies the relative spatial distribution of red-sequence and blue-cloud galaxies, and their relation to the dark matter distribution in the COMBO-17 survey as function of scale down to z~1. We measure the 2nd-order auto- and cross-correla
tion functions of galaxy clustering and express the relative biasing by using aperture statistics. Also estimated is the relation between the galaxies and the dark matter distribution exploiting galaxy-galaxy lensing (GGL). All observables are further interpreted in terms of a halo model. To fully explain the galaxy clustering cross-correlation function with a halo model, we need to introduce a new parameter,R, that describes the statistical relation between numbers of red and blue galaxies within the same halo. We find that red and blue galaxies are clearly differently clustered, a significant evolution of the relative clustering with redshift was not found. There is evidence for a scale-dependence of relative biasing. The relative clustering, the GGL and, with some tension, the galaxy numbers can be explained consistently within a halo model. For the cross-correlation function one requires a HOD variance that becomes Poisson even for relatively small occupancy numbers. For our sample, this rules out with high confidence a Poisson satellite scenario as found in semi-analytical models. Red galaxies have to be concentrated towards the halo centre, either by a central red galaxy or by a concentration parameter above that for dark matter.The value of R depends on the presence or absence of central galaxies: If no central galaxies or only red central galaxies are allowed, R is consistent with zero, whereas a positive correlation $R=+0.5pm0.2$ is needed if both blue and red galaxies can have central galaxies.[ABRIDGED]
The weak gravitational lensing effect, small coherent distortions of galaxy images by means of a gravitational tidal field, can be used to study the relation between the matter and galaxy distribution. In this context, weak lensing has so far only be
en used for considering a second-order correlation function that relates the matter density and galaxy number density as a function of separation. We implement two new, third-order correlation functions that have recently been suggested in the literature, and apply them to the Red-Sequence Cluster Survey. We demonstrate that it is possible, even with already existing data, to make significant measurements of third-order lensing correlations. We develop an optimised computer code for the correlation functions. To test its reliability a set of tests are performed. The correlation functions are transformed to aperture statistics, which allow easy tests for remaining systematics in the data. In order to further verify the robustness of our measurement, the signal is shown to vanish when randomising the source ellipticities. Finally, the lensing signal is compared to crude predictions based on the halo-model. On angular scales between roughly 1 arcmin and 11 arcmin a significant third-order correlation between two lens positions and one source ellipticity is found. We discuss this correlation function as a novel tool to study the average matter environment of pairs of galaxies. Correlating two source ellipticities and one lens position yields a less significant but nevertheless detectable signal on a scale of 4 arcmin. Both signals lie roughly within the range expected by theory which supports their cosmological origin.[ABRIDGED]
