Coulomb blockade microscopy of spin density oscillations and fractional charge in quantum spin Hall dots

We evaluate the spin density oscillations arising in quantum spin Hall quantum dots created via two localized magnetic barriers. The combined presence of magnetic barriers and spin-momentum locking, the hallmark of topological insulators, leads to peculiar phenomena: a half-integer charge is trapped in the dot for antiparallel magnetization of the barriers, and oscillations appear in the in-plane spin density, which are enhanced in the presence of electron interactions. Furthermore, we show that the number of these oscillations is determined by the number of particles inside the dot, so that the presence or the absence of the fractional charge can be deduced from the in-plane spin density. We show that when the dot is coupled with a magnetized tip, the spatial shift induced in the chemical potential allows to probe these peculiar features.Comment: 6 pages, 6 figure

Dimensional reduction in networks of non- Markovian spiking neurons: Equivalence of synaptic filtering and heterogeneous propagation delays

Understanding the collective behavior of the intricate web of neurons composing a brain is one of the most challenging and complex tasks of modern neuroscience. Part of this complexity resides in the distributed nature of the interactions between the network components: for instance, the neurons transmit their messages (through spikes) with delays, which are due to different axonal lengths (i.e., communication distances) and/or noninstantaneous synaptic transmission. In developing effective network models, both of these aspects have to be taken into account. In addition, a satisfactory description level must be chosen as a compromise between simplicity and faithfulness in reproducing the system behavior. Here we propose a method to derive an effective theoretical description - validated through network simulations at microscopic level - of the neuron population dynamics in many different working conditions and parameter settings, valid for any synaptic time scale. In doing this we assume relatively small instantaneous fluctuations of the input synaptic current. As a by-product of this theoretical derivation, we prove analytically that a network with non-instantaneous synaptic transmission with fixed spike delivery delay is equivalent to a network characterized by a suited distribution of spike delays and instantaneous synaptic transmission, the latter being easier to treat

Search for heavy lepton partners of neutrinos in proton-proton collisions in the context of the type III seesaw mechanism

This is the Pre-print version of the Article. The official publishe version can be accessed from the link below - Copyright @ 2012 ElsevierA search is presented in proton–proton collisions at sqrt(s) = 7TeV for fermionic triplet states expected in type III seesaw models. The search is performed using final states with three isolated charged leptons and an imbalance in transverse momentum. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 4.9 fb−1. No excess of events is observed above the background predicted by the standard model, and the results are interpreted in terms of limits on production cross sections and masses of the heavy partners of the neutrinos in type III seesaw models. Depending on the considered scenarios, lower limits are obtained on the mass of the heavy partner of the neutrino that range from 180 to 210 GeV. These are the first limits on the production of type III seesaw fermionic triplet states reported by an experiment at the LHC.This study is spported by the BMWF and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MEYS (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); ThEP, IPST and NECTEC (Thailand); TUBITAK and TAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie programme and the European Research Council (European Union); the Leventis Foundation; the A. P. Sloan Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation a la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS) of Czech Republic; the Council of Science and Industrial Research, India; the Compagnia di San Paolo (Torino); and the HOMING PLUS programme of Foundation for Polish Science, cofinanced from European Union, Regional Development Fund

A Low-Complexity Circuit Model of Hysteresis

A circuit architecture modelling rate-independenthysteretic phenomena is presented and discussed. The core ofthe circuit is a ladder structure with longitudinal nonlinearresistors and transverse linear capacitors. In a separate loop, alinear combination of input and capacitor voltages provides thedriving voltage for a resistor with monotonic, piecewise-lineardriving-point characteristic. The resistor current represents theoutput variable. The circuit parameters can be found fromexperimental data through a standard quadratic programmingoptimization procedure. The model fitting features are tested byusing two experimental data sets. One is theB(H)function of amagnetic material; the other is the deformation of a piezoelectricactuator as a function of the applied voltage. In this last case,an accurate comparison with the predictions of the well-knownPreisach model evidences that the circuit model achieves the sameaccuracy with a much smaller number of parameters. All thecircuit simulations are performed by using PSPICE

Accurate and efficient PSD computation in mixed-signal circuits: a time domain approach

The aim of this brief is twofold. On one side, the time-domain technique presented by Vasudevan to obtain the average and instantaneous power-spectral density of electrical variables in analog circuits characterized by (non)stationary noise sources is rigorously extended to the wide class of analog mixed-signal circuits modeled as hybrid dynamical systems. On the other side, an efficient numerical implementation is proposed to overcome the computational effort required by the original approach. The reliability of the method is first tested through the analog ring oscillator analyzed by Vasudevan. A fractional delta\u2013sigma phase-locked loop with dithering is then simulated and the obtained results are partially validated through experimental measurements

Transient dynamics of an adiabatic NEMS

This paper is focused on the transient dynamics of an adiabatic nano-electromechanical system (NEMS), consisting of a nano-mechanical oscillator coupled to a quantum dot. By numerically solving the nonlinear stochastic differential equation governing the oscillator, the time evolution of the oscillator position, of the dot occupation number and of the current are studied. Different parameter settings are studied where the system exhibits bi-stable, tri-stable or mono-stable behavior on a finite-time horizon. It is shown that, after a typically long transient, the system under investigation exhibits no hysteretic behavior and that a unique steady state is reached, independently of the initial conditions. The transient dynamics is marked out by one or two well separated characteristic times, depending on the considered case (i.e., mono- or multi-stable). These times are evaluated for a dot on-resonance or off-resonance. It turns out that the characteristic time scales are long in comparison to the period of the uncoupled oscillator, particularly at low bias, suggesting that the predicted transient dynamics may be observed in state-of-the-art experimental setups

Efficient Transient Noise Analysis of Non-Periodic Mixed Analog/Digital Circuits

This paper proposes a numerical method for accurate time-domain noise simulation of mixed analog/digital electrical circuits that in principle do not admit a periodic steady-state working condition, such as fractional $DeltaSigma$ PLL. By means of a tool known as saltation matrix, which allows dealing with non-smooth vector fields, a variational approach is adopted. The power spectral density of a noisy electrical variable is computed by applying the Thomson's MTM to the numerical solution of the stochastic variational model of the circuit. This allows to resort to a single transient simulation run, thus avoiding cpu time consuming Monte-Carlo-like approaches. The effectiveness of the proposed method is shown by comparing simulation results related to a commercial fractional $DeltaSigma$ PLL with experimental data