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Scalability assessment of Group-IV mono-chalcogenide based tunnel FET
No full textSelection of appropriate channel material is the key to design high performance tunnel field effect transistor (TFET), which promises to outperform the conventional metal oxide semiconductor field effect transistor (MOSFET) in ultra-low energy switching applications. Recently discovered atomically thin GeSe, a group IV mono-chalcogenide, can be a potential candidate owing to its direct electronic band gap and low carrier effective mass. In this work we employ ballistic quantum transport model to assess the intrinsic performance limit of monolayer GeSe-TFET. We first study the electronic band structure by regular and hybrid density functional theory and develop two band k center dot p hamiltonian for the material. We find that the complex band wraps itself within the conduction band and valence band edges and thus signifies efficient band to band tunneling mechanism. We then use the k center dot p hamiltonian to calculate self-consistent solution of the transport equations within the non-equilibrium Green's function formalism and the Poisson's equation based electrostatic potential. Keeping the OFF-current fixed at 10 pA/mu m we investigate different static and dynamic performance metrics (ON current, energy and delay) under three different constant-field scaling rules: 40, 30 and 20 nm/V. Our study shows that monolayer GeSe-TFET is scalable till 8 nm while preserving ON/OFF current ratio higher than 10(4)
Topological magnons in a kagome-lattice spin system with &ITXXZ&IT and Dzyaloshinskii-Moriya interactions
No full textWe study the phases of a spin system on the kagome lattice with nearest-neighbor XXZ interactions with anisotropy ratio Delta and Dzyaloshinskii-Moriya interactions with strength D. In the classical limit where the spin S at each site is very large, we find a rich phase diagram of the ground state as a function of Delta and D. There are five distinct phases which correspond to different ground-state spin configurations in the classical limit. We use spin-wave theory to find the bulk energy bands of the magnons in some of these phases. We also study a strip of the system which has infinite length and finite width; we find states which are localized near one of the edges of the strip with energies which lie in the gaps of the bulk states. In the ferromagnetic phase in which all the spins point along the +(z)over-cap or -(z)over-cap direction, the bulk bands are separated from each other by finite energy gaps. This makes it possible to calculate the Berry curvature at all momenta, and hence the Chern numbers for every band; the number of edge states is related to the Chern numbers. Interestingly, we find that there are four different regions in this phase where the Chern numbers are different. Hence there are four distinct topological phases even though the ground-state spin configuration is identical in all these phases. We calculate the thermal Hall conductivity of the magnons as a function of the temperature in the above ferromagnetic phase; we find that this can distinguish between the various topological phases. These results are valid for all values of S. In the other phases, there are no gaps between the different bands; hence the edge states are not topologically protected
Vortex depinning as a nonequilibrium phase transition phenomenon: Scaling of current-voltage curves near the low and the high critical-current states in 2H-NbS2 single crystals
No full textThe vortex depinning phenomenon in single crystals of 2H-NbS2 superconductors is used as a prototype for investigating properties of the nonequilibrium (NEQ) depinning phase transition. The 2H-NbS2 is a unique system as it exhibits two distinct depinning thresholds, viz., a lower critical current I-c(l) and a higher one I-c(h). While I-c(l) is related to depinning of a conventional, static (pinned) vortex state, the state with I-c(h) is achieved via a negative differential resistance (NDR) transition where the velocity abruptly drops. Using a generalized finite-temperature scaling ansatz, we study the scaling of current (I)-voltage (V) curves measured across I-c(l) and I-c(h). Our analysis shows that for I > I-c(l), the moving vortex state exhibits Arrhenius-like thermally activated flow behavior. This feature persists up to a current value where an inflexion in the IV curves is encountered. While past measurements have often reported similar inflexion, our analysis shows that the inflexion is a signature of a NEQ phase transformation from a thermally activated moving vortex phase to a free flowing phase. Beyond this inflection in IV, a large vortex velocity flow regime is encountered in the 2H-NbS2 system, wherein the Bardeen-Stephen flux flow limit is crossed. In this regime the NDR transition is encountered, leading to the high I-c(h) state. The IV curves above I-c(h) we show do not obey the generalized finite-temperature scaling ansatz (as obeyed near I-c(l)). Instead, they scale according to the Fisher's scaling form Fisher, Phys. Rev. B 31, 1396 (1985)] where we show thermal fluctuations do not affect the vortex flow, unlike that found for depinning near I-c(l)
Disentangled Cooperative Orderings in Artificial Rare-Earth Nickelates
No full textCoupled transitions between distinct ordered phases are important aspects behind the rich phase complexity of correlated oxides that hinder our understanding of the underlying phenomena. For this reason, fundamental control over complex transitions has become a leading motivation of the designer approach to materials. We have devised a series of new superlattices by combining a Mott insulator and a correlated metal to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings in RENiO3. Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism. This designer approach emphasizes the potential of heterointerfaces for selective control of simultaneous transitions in complex materials with entwined broken symmetries
SIRT2 deacetylase represses NFAT transcription factor to maintain cardiac homeostasis
No full textHeart failure is an aging-associated disease that is the leading cause of death worldwide. Sirtuin family members have been largely studied in the context of aging and aging-associated diseases. Sirtuin 2 (SIRT2) is a cytoplasmic protein in the family of sirtuins that are NAD(+)-dependent class III histone deacetylases. In this work, we studied the role of SIRT2 in regulating nuclear factor of activated T-cells (NFAT) transcription factor and the development of cardiac hypertrophy. Confocal microscopy analysis indicated that SIRT2 is localized in the cytoplasm of cardiomyocytes and SIRT2 levels are reduced during pathological hypertrophy of the heart. SIRT2-deficient mice develop spontaneous pathological cardiac hypertrophy, remodeling, fibrosis, and dysfunction in an age-dependent manner. Moreover, young SIRT2-deficient mice develop exacerbated agonist-induced hypertrophy. In contrast, SIRT2 overexpression attenuated agonist-induced cardiac hypertrophy in cardiomyocytes in a cell-autonomous manner. Mechanistically, SIRT2 binds to and deacetylates NFATc2 transcription factor. SIRT2 deficiency stabilizes NFATc2 and enhances nuclear localization of NFATc2, resulting in increased transcription activity. Our results suggest that inhibition of NFAT rescues the cardiac dysfunction in SIRT2-deficient mice. Thus, our study establishes SIRT2 as a novel endogenous negative regulator of NFAT transcription factor
Intermolecular Hydrogen Bonding Controlled Intersystem Crossing Rates of Benzophenone
No full textSolvation plays a critical role in various physicochemical and biological processes. Here, the rate of intersystem crossing (ISC) of benzophenone from its S-1(n pi*) state to its triplet manifold of states is shown to be modified by hydrogen-bonding interactions with protic solvent molecules. We selectively photoexcite benzophenone with its carbonyl group either solvent coordinated or uncoordinated by tuning the excitation wavelength to the band center (lambda = 340 nm) or the long-wavelength edge (lambda = 380 nm) of its pi* <- n absorption band. A combination of ultrafast absorption and Raman spectroscopy shows that the hydrogen-bonding interaction increases the time constant for ISC from <200 fs to 1.7 +/- 0.2 ps for benzophenone in CH3OH. The spectroscopic evidence suggests that the preferred pathway for ISC is from the S-1(n pi) to the T-2(pi pi*) state, with the rate of internal conversion from T-2(pi pi*) to T-1(n pi*) controlled by solvent quenching of excess vibrational energy
A topological nullstellensatz for tensor-triangulated categories
No full textLet Spec(T) be the spectrum of a tensor- triangulated category (T, circle times , 1). We show that there is a homeomorphism between the spectral space of radical thick tensor ideals in (T, circle times , 1) and the collection of open subsets of Spec(T) in inverse topology. In fact, we prove a more general result in terms of supports on (T, circle times , 1) and work by combining methods from commutative algebra, topology and tensor triangular geometry. (C) 2018 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved
Distinct Phase Formation of BiREWO6 (RE = La-Yb) Nanoparticles by a One Step Hydrothermal Synthesis and Their Photocatalytic Applications
No full textUnder identical hydrothermal condition, remarkably, Aurivillius BiREWO6 nanoparticles crystallize in an orthorhombic phase for RE = Ce and La, while the RE = Nd-Yb materials crystallize in the monoclinic phase. This kind of distinct phase formation in this series is not observed in solid state synthesis, where for all RE substitution, only the monoclinic phase is formed. Moreover, formation of the orthorhombic phase for BiLaWO6 and BiCeWO6 has been observed for the first time. Calcination of as-synthesized BiLaWO6 and BiCeWO6 nanomaterials results in the monoclinic phase and this indicates that the formation of the orthorhombic phase is favored only under mild reaction conditions. This could be attributed to the crucial role of the ionic radii of RP3+ and Be3+ ions in solution. Rietveld refinement confirms the BiCeWO6 and BiGdWO6 are isostrutural to the low temperature (LT) orthorhombic phase and mondinic high temperature (HT) phase of Bi2WO6, respectively. Additionally phase dependent distinct morphology and photocatalytic activity is observed. As a representative example, it is observed that needle/plate-shaped monoclinic BiGdWO6 nanoparticles show superior visible light driven photocatalytic activity for the Congo-red dye degradation over the spherically agglomerated orthorhombic BiCeWO6 nanomaterial
Marginal cost pricing for system optimal traffic assignment with recourse under supply-side uncertainty
No full textTransportation networks are often subject to fluctuations in supply-side parameters such as capacity and free-flow travel time due to factors such as incidents, poor weather, and bottlenecks. In such scenarios, assuming that network arcs exist in a finite number of states with different delay functions with different probabilities, a marginal cost pricing scheme that leads to a socially optimal outcome is proposed. The suggested framework makes the behavioral assumption that travelers do not just choose paths but follow routing policies that respond to en route information. Specifically, it is assumed that travelers are fully-rational and that they compute the optimal online shortest path assuming full reset. However, such policies may involve cycling, which is unrealistic in practice. Hence, a network transformation that helps restrict cycles up to a certain length is devised and the problem is reformulated as a convex optimization problem with symmetric delay functions. The results of numerical tests on the Sioux Falls test network are presented using the Frank-Wolfe algorithm. (C) 2018 Elsevier Ltd. All rights reserved
Chemically stabilized epitaxial wurtzite-BN thin film
No full textWe report on the chemically stabilized epitaxial w-BN thin film grown on c-plane sapphire by pulsed laser deposition under slow kinetic condition. Traces of no other allotropes such as cubic (c) or hexagonal (h) BN phases are present. Sapphire substrate plays a significant role in stabilizing the metastable w-BN from h-BN target under unusual PLD growth condition involving low temperature and pressure and is explained based on density functional theory calculation. The hardness and the elastic modulus of the w-BN film are 37 & 339 GPa, respectively measured by indentation along <0001> direction. The results are extremely promising in advancing the microelectronic and mechanical tooling industry. (C) 2018 Elsevier Ltd. All rights reserved