Waveguide-integrated van der Waals heterostructure photodetector at telecom band with high speed and high responsivity

Intensive efforts have been devoted to exploit novel optoelectronic devices based on two-dimensional (2D) transition-metal dichalcogenides (TMDCs) owing to their strong light-matter interaction and distinctive material properties. In particular, photodetectors featuring both high-speed and high-responsivity performance are of great interest for a vast number of applications such as high-data-rate interconnects operated at standardized telecom wavelengths. Yet, the intrinsically small carrier mobilities of TMDCs become a bottleneck for high-speed application use. Here, we present high-performance vertical van der Waals heterostructure-based photodetectors integrated on a silicon photonics platform. Our vertical MoTe2/graphene heterostructure design minimizes the carrier transit path length in TMDCs and enables a record-high measured bandwidth of at least 24GHz under a moderate bias voltage of -3 volts. Applying a higher bias or employing thinner MoTe2 flakes boosts the bandwidth even to 50GHz. Simultaneously, our device reaches a high external responsivity of 0.2A/W for incident light at 1300nm, benefiting from the integrated waveguide design. Our studies shed light on performance trade-offs and present design guidelines for fast and efficient devices. The combination of 2D heterostructures and integrated guided-wave nano photonics defines an attractive platform to realize high-performance optoelectronic devices, such as photodetectors, light-emitting devices and electro-optic modulators

Phenomenology of the Neutrino-Mass-Giving Higgs Triplet and the Low-Energy Seesaw Violation of Lepton Number

Small realistic Majorana neutrino masses can be generated via a Higgs triplet $(\xi^{++}, \xi^+, \xi^0)$ without having energy scales larger than $M_*={\cal O}(1)$ TeV in the theory. The large effective mass scale $\Lambda$ in the well-known seesaw neutrino-mass operator $\Lambda^{-1} (LL\Phi\Phi)$ is naturally obtained with $\Lambda\sim M_*^2/\mu,$ where $\mu$ is a {\it small} scale of lepton-number violation. In theories with large extra dimensions, the smallness of $\mu$ is naturally obtained by the mechanism of ``shining'' if the number of extra dimensions $n\ge 3.$ We study here the Higgs phenomenology of this model, where the spontaneous violation of lepton number is treated as an external source from extra dimensions. The observable decays $\xi^{++} \to l_i^+l_j^+$ will determine directly the magnitudes of the $\{ij\}$ elements of the neutrino mass matrix. The decays $\xi^+ \to W^+ J^0$ and $\xi^0 \to Z J^0$, where $J^0$ is the massless Goldstone boson (Majoron), are also possible, but of special importance is the decay $\xi^0 \to J^0 J^0$ which provides stringent constraints on the allowed parameter space of this model. Based on the current neutrino data, we also predict observable rates of $\mu-e$ conversion in nuclei.Comment: Minor changes in the text, results unchange

Yukawa Textures From Heterotic Stability Walls

A holomorphic vector bundle on a Calabi-Yau threefold, X, with h^{1,1}(X)>1 can have regions of its Kahler cone where it is slope-stable, that is, where the four-dimensional theory is N=1 supersymmetric, bounded by "walls of stability". On these walls the bundle becomes poly-stable, decomposing into a direct sum, and the low energy gauge group is enhanced by at least one anomalous U(1) gauge factor. In this paper, we show that these additional symmetries can strongly constrain the superpotential in the stable region, leading to non-trivial textures of Yukawa interactions and restrictions on allowed masses for vector-like pairs of matter multiplets. The Yukawa textures exhibit a hierarchy; large couplings arise on the stability wall and some suppressed interactions "grow back" off the wall, where the extended U(1) symmetries are spontaneously broken. A number of explicit examples are presented involving both one and two stability walls, with different decompositions of the bundle structure group. A three family standard-like model with no vector-like pairs is given as an example of a class of SU(4) bundles that has a naturally heavy third quark/lepton family. Finally, we present the complete set of Yukawa textures that can arise for any holomorphic bundle with one stability wall where the structure group breaks into two factors.Comment: 53 pages, 4 figures and 13 table

Naturally Small Seesaw Neutrino Mass with No New Physics Beyond the TeV Scale

If there is no new physics beyond the TeV energy scale, such as in a theory of large extra dimensions, the smallness of the seesaw neutrino mass, i.e. $m_\nu = m_D^2/m_N$, cannot be explained by a very large $m_N$. In contrast to previous attempts to find an alternative mechanism for a small $m_\nu$, I show how a solution may be obtained in a simple extension of the Standard Model, without using any ingredient supplied by the large extra dimensions. It is also experimentally testable at future accelerators.Comment: 9 pages, in final form for PR

Neutrinos Confronting Large Extra Dimensions

We study neutrino physics in a model with one large extra dimension. We assume the existence of two four-dimensional branes in the five-dimensional space-time, one for the ordinary particles and the other one for mirror particles, and we investigate neutrino masses and mixings in this scheme. Comparison of experimental neutrino data with the predictions of the model leads to various restrictions on the parameters of the model. For instance, the size of the extra dimension, R, turns out to be bounded from below. Cosmological considerations seem to favor a large R. The usual mixing schemes proposed as solutions to the solar and atmospheric neutrino anomalies are compatible with our model.Comment: 19 pages, LATEX, 4 figure

Connecting bimaximal neutrino mixing to a light sterile neutrino

It is shown that if small neutrino masses owe their origin to the conventional seesaw mechanism and the MNS mixing matrix is in the exact bimaximal form, then there exist symmetries in the theory that allow one of the righthanded neutrinos to become naturally massless, making it a candidate for the sterile neutrino discussed in the literature. Departures from the exact bimaximal limit leads to tiny mass for the sterile neutrino as well as its mixing to the active neutrinos. This provides a minimal theoretical framework where a simultaneous explanation of the solar, atmospheric and LSND observations within the so-called 3+1 scenario may be possible.Comment: new references added; paper accepted for publication in Phys. Rev. D.(rapid communications); note adde

Influence of heart rate, blood pressure, and beta-blocker dose on outcome and the differences in outcome between carvedilol and metoprolol tartrate in patients with chronic heart failure: results from the COMET trial.

AIMS: We studied the influence of heart rate (HR), systolic blood pressure (SBP), and beta-blocker dose on outcome in the 2599 out of 3029 patients in Carvedilol Or Metoprolol European Trial (COMET) who were alive and on study drug at 4 months after randomization (time of first visit on maintenance therapy). METHODS AND RESULTS: By multivariable analysis, baseline HR, baseline SBP, and their change after 4 months were not independently related to subsequent outcome. In a multivariable analysis including clinical variables, HR above and SBP below the median value achieved at 4 months predicted subsequent increased mortality [relative risk (RR) for HR>68 b.p.m. 1.333; 95% confidence intervals (CI) 1.152-1.542; P120 mmHg 0.78; 95% CI 0.671-0.907; P<0.0013]. Achieving target beta-blocker dose was associated with a better outcome (RR 0.779; 95% CI 0.662-0.916; P<0.0025). The superiority of carvedilol as compared to metoprolol tartrate was maintained in a multivariable model (RR 0.767; 95% CI 0.663-0.887; P=0.0004) and there was no interaction with HR, SBP, or beta-blocker dose. CONCLUSION: Beta-blocker dose, HR, and SBP achieved during beta-blocker therapy have independent prognostic value in heart failure. None of these factors influenced the beneficial effects of carvedilol when compared with metoprolol tartrate at the pre-defined target doses used in COMET

Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons

One of the most remarkable results of quantum mechanics is the fact that many-body quantum systems may exhibit phase transitions even at zero temperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty principle, and not thermal fluctuations, drive the system from one phase to another. Typically, the relative strength of two competing terms in the system's Hamiltonian is changed across a finite critical value. A well-known example is the Mott-Hubbard quantum phase transition from a superfluid to an insulating phase, which has been observed for weakly interacting bosonic atomic gases. However, for strongly interacting quantum systems confined to lower-dimensional geometry a novel type of quantum phase transition may be induced for which an arbitrarily weak perturbation to the Hamiltonian is sufficient to drive the transition. Here, for a one-dimensional (1D) quantum gas of bosonic caesium atoms with tunable interactions, we observe the commensurate-incommensurate quantum phase transition from a superfluid Luttinger liquid to a Mott-insulator. For sufficiently strong interactions, the transition is induced by adding an arbitrarily weak optical lattice commensurate with the atomic granularity, which leads to immediate pinning of the atoms. We map out the phase diagram and find that our measurements in the strongly interacting regime agree well with a quantum field description based on the exactly solvable sine-Gordon model. We trace the phase boundary all the way to the weakly interacting regime where we find good agreement with the predictions of the 1D Bose-Hubbard model. Our results open up the experimental study of quantum phase transitions, criticality, and transport phenomena beyond Hubbard-type models in the context of ultracold gases

Contribution of DNA repair and cell cycle checkpoint arrest to the maintenance of genomic stability

DNA damage response mechanisms encompass pathways of DNA repair, cell cycle checkpoint arrest and apoptosis. Together, these mechanisms function to maintain genomic stability in the face of exogenous and endogenous DNA damage. ATM is activated in response to double strand breaks and initiates cell cycle checkpoint arrest. Recent studies in human fibroblasts have shown that ATM also regulates a mechanism of end-processing that is required for a component of double strand break repair. Human fibroblasts rarely undergo apoptosis after ionising radiation and, therefore, apoptosis is not considered in our review. The dual function of ATM raises the question as to how the two processes, DNA repair and checkpoint arrest, interplay to maintain genomic stability. In this review, we consider the impact of ATM's repair and checkpoint functions to the maintenance of genomic stability following irradiation in G2. We discuss evidence that ATM's repair function plays little role in the maintenance of genomic stability following exposure to ionising radiation. ATM's checkpoint function has a bigger impact on genomic stability but strikingly the two damage response pathways co-operate in a more than additive manner. In contrast, ATM's repair function is important for survival post irradiation

Neutrino anomalies and large extra dimensions

Theories with large extra dimensions can generate small neutrino masses when the standard model neutrinos are coupled to singlet fermions propagating in higher dimensions. The couplings can also generate mass splittings and mixings among the flavour neutrinos in the brane. We systematically study the minimal scenario involving only one singlet bulk fermion coupling weakly to the flavour neutrinos. We explore the neutrino mass structures in the brane that can potentially account for the atmospheric, solar and LSND anomalies simultaneously in a natural way. We demonstrate that in the absence of a priori mixings among the SM neutrinos, it is not possible to reconcile all these anomalies. The presence of some structure in the mass matrix of the SM neutrinos can solve this problem. This is exemplified by the Zee model, which when embedded in extra dimensions in a minimal way can account for all the neutrino anomalies.Comment: 23 Revtex pages with 2 eps figure