The discovery of graphene raises the prospect of a new class of nanoelectronic devices based on t... more The discovery of graphene raises the prospect of a new class of nanoelectronic devices based on the extraordinary physical properties of this one-atom-thick layer of carbon. Unlike two-dimensional electron layers in semiconductors, where the charge carriers become immobile at low densities, the carrier mobility in graphene can remain high, even when their density vanishes at the Dirac point. However, when the graphene sample is supported on an insulating substrate, potential fluctuations induce charge puddles that obscure the Dirac point physics. Here we show that the fluctuations are significantly reduced in suspended graphene samples and we report low- temperature mobility approaching 200,000 cm2/V^2/s^2 for carrier densities below 5 x 10^9 cm^2. Such values cannot be attained in semiconductors or non-suspended graphene. Moreover, unlike graphene samples supported by a substrate, the conductivity of suspended graphene at the Dirac point is strongly dependent on temperature and approaches ballistic values at liquid helium temperatures. At higher temperatures, above 100 K, we observe the onset of thermally induced long- range scattering.
Searches for “natural” supersymmetry (SUSY) scenarios are presented in which only neutralinos, ch... more Searches for “natural” supersymmetry (SUSY) scenarios are presented in which only neutralinos, charginos, and potentially also the top-quark superpartner (stop) are assumed to be accessible, and which result in multi-boson final states. These efforts rely on a novel and versatile method where by the narrow H → γγ resonance is used to identify events with a Higgs boson candidate, and to determine backgrounds. This provides a sufficiently clean search environment to largely overcome the small H → γγ branching fraction. First, a search is performed for stop pair production resulting in 2b2H. Events with two photons forming a Higgs boson candidate and at least two b-jets are selected and missing transverse energy is examined. Then, the diphoton components of a comprehensive search for electroweak production of neutralinos and charginos are presented, which may decay to Higgs and Z, bosons and undetected lightest SUSY particles (LSPs). This latter search is then reinterpreted in terms of chargino-neutralino pair production, leading to HW± states with MET. The searches are performed using 19.5 fb−1 of proton-proton collisions at √s = 8 TeV, recorded in the Compact Muon Solenoid (CMS) detector. No compelling evidence for new physics is found and 95% confidence limits are set.
The discovery of graphene raises the prospect of a new class of nanoelectronic devices based on t... more The discovery of graphene raises the prospect of a new class of nanoelectronic devices based on the extraordinary physical properties of this one-atom-thick layer of carbon. Unlike two-dimensional electron layers in semiconductors, where the charge carriers become immobile at low densities, the carrier mobility in graphene can remain high, even when their density vanishes at the Dirac point. However, when the graphene sample is supported on an insulating substrate, potential fluctuations induce charge puddles that obscure the Dirac point physics. Here we show that the fluctuations are significantly reduced in suspended graphene samples and we report low- temperature mobility approaching 200,000 cm2/V^2/s^2 for carrier densities below 5 x 10^9 cm^2. Such values cannot be attained in semiconductors or non-suspended graphene. Moreover, unlike graphene samples supported by a substrate, the conductivity of suspended graphene at the Dirac point is strongly dependent on temperature and approaches ballistic values at liquid helium temperatures. At higher temperatures, above 100 K, we observe the onset of thermally induced long- range scattering.
Searches for “natural” supersymmetry (SUSY) scenarios are presented in which only neutralinos, ch... more Searches for “natural” supersymmetry (SUSY) scenarios are presented in which only neutralinos, charginos, and potentially also the top-quark superpartner (stop) are assumed to be accessible, and which result in multi-boson final states. These efforts rely on a novel and versatile method where by the narrow H → γγ resonance is used to identify events with a Higgs boson candidate, and to determine backgrounds. This provides a sufficiently clean search environment to largely overcome the small H → γγ branching fraction. First, a search is performed for stop pair production resulting in 2b2H. Events with two photons forming a Higgs boson candidate and at least two b-jets are selected and missing transverse energy is examined. Then, the diphoton components of a comprehensive search for electroweak production of neutralinos and charginos are presented, which may decay to Higgs and Z, bosons and undetected lightest SUSY particles (LSPs). This latter search is then reinterpreted in terms of chargino-neutralino pair production, leading to HW± states with MET. The searches are performed using 19.5 fb−1 of proton-proton collisions at √s = 8 TeV, recorded in the Compact Muon Solenoid (CMS) detector. No compelling evidence for new physics is found and 95% confidence limits are set.
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Papers by Anthony Barker