Enhanced tunneling across nanometer-scale metal-semiconductor interfaces

We have measured electrical transport across epitaxial, nanometer-sized metal-semiconductor interfaces by contacting CoSi2-islands grown on Si(111) with an STM-tip. The conductance per unit area was found to increase with decreasing diode area. Indeed, the zero-bias conductance was found to be about 10^4 times larger than expected from downscaling a conventional diode. These observations are explained by a model, which predicts a narrower barrier for small diodes and therefore a greatly increased contribution of tunneling to the electrical transport.Comment: 3 pages, 2 EPS-figures; accepted for publication in Appl. Phys. Let

Scaling of nano-Schottky-diodes

A generally applicable model is presented to describe the potential barrier shape in ultra small Schottky diodes. It is shown that for diodes smaller than a characteristic length $l_c$ (associated with the semiconductor doping level) the conventional description no longer holds. For such small diodes the Schottky barrier thickness decreases with decreasing diode size. As a consequence, the resistance of the diode is strongly reduced, due to enhanced tunneling. Without the necessity of assuming a reduced (non-bulk) Schottky barrier height, this effect provides an explanation for several experimental observations of enhanced conduction in small Schottky diodes.Comment: 4 pages, 4 figures, accepted for publication in Appl. Phys. Lett., some minor additions and correction

Anomalous Hall effect as a probe of the chiral order in spin glasses

Anomalous Hall effect arising from the noncoplanar spin configuration (chirality) is discussed as a probe of the chiral order in spin glasses. It is shown that the Hall coefficient yields direct information about the linear and nonlinear chiral susceptibilities of the spin sector, which has been hard to obtain experimentally from the standard magnetic measurements. Based on the chirality scenario of spin-glass transition, predictions are given on the behavior of the Hall resistivity of canonical spin glasses.Comment: Order estimate of the effect given, one reference added. To appear in Phys. Rev. Letter

A Conclusive Test of Abelian Dominance Hypothesis for Topological Charge in the QCD Vacuum

We study the topological feature in the QCD vacuum based on the hypothesis of abelian dominance. The topological charge $Q_{\rm SU(2)}$ can be explicitly represented in terms of the monopole current in the abelian dominated system. To appreciate its justification, we directly measure the corresponding topological charge $Q_{\rm Mono}$, which is reconstructed only from the monopole current and the abelian component of gauge fields, by using the Monte Carlo simulation on SU(2) lattice. We find that there exists a one-to-one correspondence between $Q_{\rm SU(2)}$ and $Q_{\rm Mono}$ in the maximally abelian gauge. Furthermore, $Q_{\rm Mono}$ is classified by approximately discrete values.Comment: LATTICE98(confine), 3 pages, Latex, 3 figures include

Exotic Meson Decay Widths using Lattice QCD

A decay width calculation for a hybrid exotic meson h, with JPC=1-+, is presented for the channel h->pi+a1. This quenched lattice QCD simulation employs Luescher's finite box method. Operators coupling to the h and pi+a1 states are used at various levels of smearing and fuzzing, and at four quark masses. Eigenvalues of the corresponding correlation matrices yield energy spectra that determine scattering phase shifts for a discrete set of relative pi+a1 momenta. Although the phase shift data is sparse, fits to a Breit-Wigner model are attempted, resulting in a decay width of about 60 MeV when averaged over two lattice sizes.Comment: 9 pages, 8 figures, RevTex4, minor change to Fig.

Global Climate Action 2022: How have international initiatives delivered, and what more is possible

Contains fulltext : 285265.pdf (Publisher’s version ) (Open Access)This report is the latest stocktake of international cooper- ative climate action. International cooperative initiatives (ICIs) have been a major feature of international climate governance ever since the UNFCCC started recording them in 2013. These partnerships engage a wide range of non- state and subnational actors, including businesses, inves- tors, civil society, national governments, and international organizations. We identified 601 ICIs launched since 2013 with more than 70,000 instances1 of participation by cities and regions, businesses, and by domestic and international NGOs. The total number of ICIs covered in this study has more than doubled compared to previous analyses as a result of examining outcomes from all major climate summits and campaigns since 2014. The growth of active initiatives (85% of all ICIs launched since 2013) has flat- tened since 2019. This is partly explained by the expiration of many initiatives that were launched prior or around the UN Climate Conference in Paris in 2015. The outbreak of the COVID 19 pandemic may also explain lower growth of new initiatives, especially in 2020. Overall productivity of initiatives is trending downwards. Through assessing the extent whether initiatives’ outputs (e.g., infrastructure, research, new installations) are consist- ent with their functions (e.g., training, norm-/standard set- ting, technical on-the-ground implementation), we observed a higher share of low or non-performing initiatives in both mitigation and adaptation since 2019. Overall productivity of initiatives is also trending downwards. ICIs have been launched without further implementation and operation- alization of commitments. This gap between commitments and implementation risks to undermine the credibility of ICIs and the campaigns and summits that convene them. The downwards trend in productivity may be explained by ICIs initially picking ‘low-hanging fruit’ and subsequently having to take more difficult measures. Moreover, the COVID-19 pandemic has likely affected the performance of ICIs. During the pandemic, ICIs’ production of outputs that are location-specific (such as in-person trainings, and new infrastructure or installations) decreased at a faster rate than those that are not location specific (such as websites, online platforms, and research publications). Conversely, we observe a rapid growth of webcasted events, which may reflect a replacement of physical activities by virtual ones. Our analysis suggests a strong and growing underrep- resentation of the Global South. Although ICIs have great potential to contribute to sustainable development in devel- oping countries, studies have consistently shown a strong underrepresentation of the Global South. Implementation disproportionately takes place in the Global North. In line with previous assessments our analysis shows the under- representation of funders, leaders, and participants of ICIs based in non-OECD countries. Moreover, since 2015 the share of outputs produced in the Global North has steadily grown. Some imbalances are to be expected as they appro- priately and reflect differentiated responsibilities and the need for a strong focus on climate mitigation. Nonetheless, the benefits of ICIs, particularly adaptation and resilience building, should also accrue to developing countries. Summit and campaign organizers should steer towards higher performance by setting requirements for ICIs, particularly among initiatives that are launched at cli- mate conferences, summits and by COP presidencies. For instance, before featuring ICIs at climate conferences, organizers should require ICIs to provide evidence that they are making progress against targets and/or have capacities and resources to deliver on pledges. Possible measures identified in the literature include the appointment of dedi- cated staff and/or a secretariat, regular reporting, credible budgets, and openness for new partners to join an initiative, while facilitating interfaces between non-state, subnational actors, policymakers and funders. The report assessed the potential contributions of 12 international sector initiatives launched around and during COP26 (hereinafter, ‘Glasgow initiatives’) on future green- house gas (GHG) emission reductions. We found that the theoretical coverage of these Glasgow initiatives is large: they cover sectors that could potentially lead to 11 GtCO2e lower emissions in 2030 compared to the aggregate of NDCs, addressing a considerable part of the ‘ambition gap’ between the NDC scenario and the benchmark 1.5°C scenario (Figure ES-1). However, not all governments have signed up and impact of signatories is quite small because many already have the action included in their NDC: There- fore, a full implementation of the initiatives’ 1.5°C-aligned goals by the current signatories would only lead to about 5 GtCO2e of emission reductions additional to the NDC scenario (Figure ES- 1). Ambition can be raised in two ways based on these results: First, the biggest potential lies in additional governments signing up to initiatives that have not yet done so (6 GtCO2e). The theory of change of the initiatives is to put non-signatories on the spot, but membership since the Glasgow COP has changed only marginally. Second, govern- ments that have signed up have not yet fully taken these actions into account in their NDCs and therefore could increase the ambition in their NDCs (5 GtCO2e). Future COPs could generate momentum in sectors not covered by the Glasgow initiatives. Although the Glasgow initiatives’ emission reduction potential is substantial, there are still sectors in which momentum for rapid transition toward decarbonisation is needed, including the buildings sector and heavy industry sectors other than steel, such as chemicals and cement. These sectors have not been well covered by ICIs, especially by those that involve large emitting countries and established international institutions. The presidencies of the next few COPs as well as the UN Climate Change High-Level Champions may take the leader- ship to generate momentum to accelerate decarbonisation in these sectors. We also compared these Glasgow initiatives to those pre- viously launched at major international conferences, which have shown mixed performance results , in terms of, for example, financing and reporting requirements. The lim- ited literature indicates that there continues to be a lack of enforcement mechanisms in some Glasgow initiatives. However, there are also noticeable improvements in other Glasgow initiatives , such as annual progress assessment mandated to international organisations and, more impor- tantly, securing finance for implementation. Continued political drive from national governments can help realize the Glasgow initiatives’ potential. The political drive as shown by the UK Presidency has been crucial for establishing the Glasgow initiatives with their launch. Continued political drive is required for the poten- tial impact of the initiatives to materialise and expand. Upcoming COP Presidencies and UN Climate Change High- Level Champions may represent this political drive and generate more leadership, particularly among large emitting countries, in order to maintain momentum and credibility after COP27 and to drive towards more signatories and implementation of global climate action.28 p

On the Formation of Copper Linear Atomic Suspended Chains

We report high resolution transmission electron microscopy and classical molecular dynamics simulation results of mechanically stretching copper nanowires conducting to linear atomic suspended chains (LACs) formation. In contrast with some previous experimental and theoretical work in literature that stated that the formation of LACs for copper should not exist our results showed the existence of LAC for the [111], [110], and [100] crystallographic directions, being thus the sequence of most probable occurence.Comment: 4 pages, 3 figure

Static and dynamic properties of the interface between a polymer brush and a melt of identical chains

Molecular dynamics simulations of a short-chain polymer melt between two brush-covered surfaces under shear have been performed. The end-grafted polymers which constitute the brush have the same chemical properties as the free chains in the melt and provide a soft deformable substrate. Polymer chains are described by a coarse-grained bead-spring model with Lennard-Jones interactions between the beads and a FENE potential between nearest neighbors along the backbone of the chains. The grafting density of the brush layer offers a way of controlling the behavior of the surface without altering the molecular interactions. We perform equilibrium and non-equilibrium Molecular Dynamics simulations at constant temperature and volume using the Dissipative Particle Dynamics thermostat. The equilibrium density profiles and the behavior under shear are studied as well as the interdigitation of the melt into the brush, the orientation on different length scales (bond vectors, radius of gyration, and end-to-end vector) of free and grafted chains, and velocity profiles. The viscosity and slippage at the interface are calculated as functions of grafting density and shear velocity.Comment: 12 pages, submitted to J Chem Phy

First Principles Calculation of Anomalous Hall Conductivity in Ferromagnetic bcc Fe

We perform a first principles calculation of the anomalous Hall effect in ferromagnetic bcc Fe. Our theory identifies an intrinsic contribution to the anomalous Hall conductivity and relates it to the k-space Berry phase of occupied Bloch states. The theory is able to account for both dc and magneto-optical Hall conductivities with no adjustable parameters.Comment: 4 pages, 6 figures, author list correcte