Electronic transport through a quantum dot network

The conductance through a finite quantum dot network is studied as a function of inter-dot coupling. As the coupling is reduced, the system undergoes a transition from the antidot regime to the tight binding limit, where Coulomb resonances with on average increasing charging energies are observed. Percolation models are used to describe the conduction in the open and closed regime and contributions from different blockaded regions can be identified. A strong negative average magnetoresistance in the Coulomb blockade regime is in good quantitative agreement with theoretical predictions for magnetotunneling between individual quantum dots.Comment: 5 pages, 5 figure

Simulating cosmic rays in clusters of galaxies - I. Effects on the Sunyaev-Zel'dovich effect and the X-ray emission

We performed high-resolution simulations of a sample of 14 galaxy clusters that span a mass range from 5 x 10^13 M_solar/h to 2 x 10^15 M_solar/h to study the effects of cosmic rays (CRs) on thermal cluster observables such as X-ray emission and the Sunyaev-Zel'dovich effect. We analyse the CR effects on the intra-cluster medium while simultaneously taking into account the cluster's dynamical state as well as the mass of the cluster. The modelling of the cosmic ray physics includes adiabatic CR transport processes, injection by supernovae and cosmological structure formation shocks, as well as CR thermalization by Coulomb interaction and catastrophic losses by hadronic interactions. While the relative pressure contained in CRs within the virial radius is of the order of 2 per cent in our non-radiative simulations, their contribution rises to 32 per cent in our simulations with dissipative gas physics including radiative cooling, star formation, and supernova feedback. Interestingly, in the radiative simulations the relative CR pressure reaches high values of the order of equipartition with the thermal gas in each cluster galaxy due to the fast thermal cooling of gas which diminishes the thermal pressure support relative to that in CRs. This also leads to a lower effective adiabatic index of the composite gas that increases the compressibility of the intra-cluster medium. This effect slightly increases the central density, thermal pressure and the gas fraction. While the X-ray luminosity in low mass cool core clusters is boosted by up to 40 per cent, the integrated Sunyaev-Zel'dovich effect appears to be remarkably robust and the total flux decrement only slightly reduced by typically 2 per cent. The resolved Sunyaev-Zel'dovich maps, however, show a larger variation with an increased central flux decrement. [abridged]Comment: 25 pages, 15 figures, accepted by MNRAS, full resolution version available at http://www.cita.utoronto.ca/~pfrommer/Publications/CRs_clusters.pd

Transport in a three-terminal graphene quantum dot in the multi-level regime

We investigate transport in a three-terminal graphene quantum dot. All nine elements of the conductance matrix have been independently measured. In the Coulomb blockade regime accurate measurements of individual conductance resonances reveal slightly different resonance energies depending on which pair of leads is used for probing. Rapid changes in the tunneling coupling between the leads and the dot due to localized states in the constrictions has been excluded by tuning the difference in resonance energies using in-plane gates which couple preferentially to individual constrictions. The interpretation of the different resonance energies is then based on the presence of a number of levels in the dot with an energy spacing of the order of the measurement temperature. In this multi-level transport regime the three-terminal device offers the opportunity to sense if the individual levels couple with different strengths to the different leads. This in turn gives qualitative insight into the spatial profile of the corresponding quantum dot wave functions.Comment: 12 pages, 6 figure