Electron Mobility and Magneto Transport Study of Ultra-Thin Channel Double-Gate Si MOSFETs

We report on detailed room temperature and low temperature transport properties of double-gate Si MOSFETs with the Si well thickness in the range 7-17 nm. The devices were fabricated on silicon-on-insulator wafers utilizing wafer bonding, which enabled us to use heavily doped metallic back gate. We observe mobility enhancement effects at symmetric gate bias at room temperature, which is the finger print of the volume inversion/accumulation effect. An asymmetry in the mobility is detected at 300 K and at 1.6 K between the top and back interfaces of the Si well, which is interpreted to arise from different surface roughnesses of the interfaces. Low temperature peak mobilities of the reported devices scale monotonically with Si well thickness and the maximum low temperature mobility was 1.9 m2/Vs, which was measured from a 16.5 nm thick device. In the magneto transport data we observe single and two sub-band Landau level filling factor behavior depending on the well thickness and gate biasing

Determination of m_s and |V_us| from hadronic tau decays

The mass of the strange quark is determined from SU(3)-breaking effects in the tau hadronic width. Compared to previous analyses, the contributions from scalar and pseudoscalar spectral functions, which suffer from large perturbative corrections, are replaced by phenomenological parametrisations. This leads to a sizeable reduction of the uncertainties in the strange mass from tau decays. Nevertheless, the resulting m_s value is still rather sensitive to the moment of the invariant mass distribution which is used for the determination, as well as the size of the quark-mixing matrix element |V_us|. Imposing the unitarity fit for the CKM matrix, we obtain m_s(2 GeV)=117+-17 MeV, whereas for the present Particle Data Group average for |V_us|, we find m_s(2 GeV)=103+-17 MeV. On the other hand, using an average of m_s from other sources as an input, we are able to calculate the quark-mixing matrix element |V_us|, and we demonstrate that if the present measurement of the hadronic decay of the tau into strange particles is improved by a factor of two, the determination of |V_us| is more precise than the current world average.Comment: 25 pages, 1 eps figur

MS-EMC vs. NEGF: A comparative study accounting for transport quantum corrections

As electronic devices approach the nanometer scale, quantum transport theories have been recognized as the best option to reproduce their performance. Other possible trend, mainly focused on reducing the computational effort, is the inclusion of quantum effects in semi-classical simulators. This work presents a comparison between a NEGF simulator and a MS-EMC tool including S/D tunneling both applied on a DGSOI transistor

Experimental analysis of variability in WS2_2-based devices for hardware security

This work investigates the variability of tungsten disulfide (WS$_2$)-based devices by experimental characterization in view of possible application in the field of hardware security. To this aim, a preliminary analysis was performed by measurements across voltages and temperatures on a set of seven Si/SiO$_2$/WS$_2$ back-gated devices, also considering the effect of different stabilization conditions on their conductivity. Obtained results show appreciable variability in the conductivity, while also revealing similar dependence on bias and temperature across tested devices. Overall, our analysis demonstrates that WS$_2$-based devices can be potentially exploited to ensure adequate randomness and robustness against environmental variations and then used as building blocks for hardware security primitives

More Benefits of Semileptonic Rare B Decays at Low Recoil: CP Violation

We present a systematic analysis of the angular distribution of Bbar -> Kbar^\ast (-> Kbar pi) l^+ l^- decays with l = e, mu in the low recoil region (i.e. at high dilepton invariant masses of the order of the mass of the b-quark) to account model-independently for CP violation beyond the Standard Model, working to next-to-leading order QCD. From the employed heavy quark effective theory framework we identify the key CP observables with reduced hadronic uncertainties. Since some of the CP asymmetries are CP-odd they can be measured without B-flavour tagging. This is particularly beneficial for Bbar_s,B_s -> phi(-> K^+ K^-) l^+ l^- decays, which are not self-tagging, and we work out the corresponding time-integrated CP asymmetries. Presently available experimental constraints allow the proposed CP asymmetries to be sizeable, up to values of the order ~ 0.2, while the corresponding Standard Model values receive a strong parametric suppression at the level of O(10^-4). Furthermore, we work out the allowed ranges of the short-distance (Wilson) coefficients C_9,C_10 in the presence of CP violation beyond the Standard Model but no further Dirac structures. We find the Bbar_s -> mu^+ mu^- branching ratio to be below 9*10^-9 (at 95% CL). Possibilities to check the performance of the theoretical low recoil framework are pointed out.Comment: 18 pages, 3 fig.; 1 reference and comment on higher order effects added; EOS link fixed. Minor adjustments to Eqs 4.1-4.3 to match the (lower) q^2-cut as given in paper. Main results and conclusions unchanged; v3+v4: treatment of exp. uncert. in likelihood-function in EOS fixed and constraints from scan on C9,C10 updated (Fig 2,3 and Eqs 3.2,3.3). Main results and conclusions absolutely unchange

Constraints on charged Higgs bosons from D(s)+- -> mu+- nu and D(s)+- -> tau+- nu

The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been used to measure the D(s)+- meson decay constant f_D(s). Recent measurements at CLEO-c and the B factories suggest a branching ratio for both decays somewhat higher than the Standard Model prediction using f_D(s) from unquenched lattice calculations. The charged Higgs boson (H+-) in the Two Higgs Doublet Model (Type II) would also mediate these decays, but any sizeable contribution from H+- can only suppress the branching ratios and consequently is now slightly disfavoured. It is shown that constraints on the parameters tan(beta) and m_H+- from such decays can be competitive with and complementary to analogous constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+- -> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) < 250 MeV.Comment: 18 pages, 4 figure

Heavy-meson physics and flavour violation with a single generation

We study flavour-violating processes which involve heavy B- and D-mesons and are mediated by Kaluza-Klein modes of gauge bosons in a previously suggested model where three generations of the Standard Model fermions originate from a single generation in six dimensions. We find the bound on the size R of the extra spatial dimensions 1/R>3.3 TeV, which arises from the three-body decay B_s to K mu e. Due to the still too low statistics this bound is much less stringent than the constraint arising from K to mu e, 1/R>64 TeV, which was found in a previous work (Frere et al., JHEP, 2003). Nevertheless, we argue that a clear signature of the model would be an observation of K to mu e and B_s to K mu e decays without observations of other flavour and lepton number changing processes at the same precision level.Comment: 15 page

Flavour constraints on scenarios with two or three heavy squark generations

We re-assess constraints from flavour-changing neutral currents in the kaon system on supersymmetric scenarios with a light gluino, two heavy generations of squarks and a lighter third generation. We compute for the first time limits in scenarios with three heavy squark families, taking into account QCD corrections at the next-to-leading order. We compare our limits with those in the case of two heavy families. We use the mass insertion approximation and consider contributions from gluino exchange to constrain the mixing between the first and second squark generation. While it is not possible to perform a general analysis, we assess the relevance of each kind of flavour- and CP-violating parameters. We also provide ready to use magic numbers for the computation of the Wilson coefficients at 2 GeV for these scenarios.Comment: 23 pages, 14 figures; v3: matches published version (contains improvements in the presentation and clarifications

The decay Bs -> mu+ mu-: updated SUSY constraints and prospects

We perform a study of the impact of the recently released limits on BR(Bs -> mu+ mu-) by LHCb and CMS on several SUSY models. We show that the obtained constraints can be superior to those which are derived from direct searches for SUSY particles in some scenarios, and the use of a double ratio of purely leptonic decays involving Bs -> mu+ mu- can further strengthen such constraints. We also discuss the experimental sensitivity and prospects for observation of Bs -> mu+ mu- during the sqrt(s)=7 TeV run of the LHC, and its potential implications.Comment: 30 pages, 21 figures. v2: Improved discussion of constraints from B -> tau nu, references adde