Atomic-Scale Interface Engineering of Majorana Edge Modes in a 2D Magnet-Superconductor Hybrid System

Topological superconductors are predicted to harbor exotic boundary states - Majorana zero-energy modes - whose non-Abelian braiding statistics present a new paradigm for the realization of topological quantum computing. Using low-temperature scanning tunneling spectroscopy (STS), we here report on the direct real-space visualization of chiral Majorana edge states in a monolayer topological superconductor, a prototypical magnet-superconductor hybrid system comprised of nano-scale Fe islands of monoatomic height on a Re(0001)-O(2$\times$1) surface. In particular, we demonstrate that interface engineering by an atomically thin oxide layer is crucial for driving the hybrid system into a topologically non-trivial state as confirmed by theoretical calculations of the topological invariant, the Chern number.Comment: 26 pages, 9 figure

A Human Development Framework for CO2 Reductions

Although developing countries are called to participate in CO2 emission reduction efforts to avoid dangerous climate change, the implications of proposed reduction schemes in human development standards of developing countries remain a matter of debate. We show the existence of a positive and time-dependent correlation between the Human Development Index (HDI) and per capita CO2 emissions from fossil fuel combustion. Employing this empirical relation, extrapolating the HDI, and using three population scenarios, the cumulative CO2 emissions necessary for developing countries to achieve particular HDI thresholds are assessed following a Development As Usual approach (DAU). If current demographic and development trends are maintained, we estimate that by 2050 around 85% of the world's population will live in countries with high HDI (above 0.8). In particular, 300Gt of cumulative CO2 emissions between 2000 and 2050 are estimated to be necessary for the development of 104 developing countries in the year 2000. This value represents between 20% to 30% of previously calculated CO2 budgets limiting global warming to 2{\deg}C. These constraints and results are incorporated into a CO2 reduction framework involving four domains of climate action for individual countries. The framework reserves a fair emission path for developing countries to proceed with their development by indexing country-dependent reduction rates proportional to the HDI in order to preserve the 2{\deg}C target after a particular development threshold is reached. Under this approach, global cumulative emissions by 2050 are estimated to range from 850 up to 1100Gt of CO2. These values are within the uncertainty range of emissions to limit global temperatures to 2{\deg}C.Comment: 14 pages, 7 figures, 1 tabl

The Use of Goal Programming for Resource Assessment, With an Application to Forest Energy Developments in Eastern Ontario

This research was primarily concerned with the identification, development and application of methods for the purpose of providing information to assist resource management decisions. The type of information sought was defined by four questions, which essentially relate to the ability to achieve specified development goals and the identification of conflicts amongst goals. Analysis directed at resolving these questions was referred to as resource assessment. The first major component of the research involved the search for appropriate methods by which to undertake resource assessment analysis. The ability to account for multiple, and possibly conflicting goals, which may be expressed in disparate metrics, was an explicit concern in evaluating the various methods. Multiobjective goal programming was identified as one method well-suitable to resource assessment analysis. Application of a goal programming model in an assessment of proposed forest energy developments in Eastern Ontario constituted the second major component of the research. This provided an applied context within which to further evaluate the suitability of goal programming for resource assessment. Application of the method was also expected to provided useful insights into the implications for the Eastern region of forest energy developments. Results suggest that energy plantation developments could make a substantial contribution to the Eastern region of Ontario, through the development of under-utilized land resources, the generation of regional income, the provision of jobs, and the production of energy for local markets and perhaps beyond. The analysis clearly indicates, however, that conflicts exist amongst the specified development goals. Resource allocations which imply favourable results in terms of one development goal may mean relatively poor achievement levels with respect to some of the other goals. This suggests that considerable caution must be exercised in selecting development strategies with respect to a forest energy system. The research makes an important contribution in a methodological sense, by demonstrating that scientific procedures can be employed to systematically and rigorously address questions of fundamental importance in resource assessment. In particular, this research has shown that it is possible to assess captions in resource use with respect to several, potentially incompatible goals. By providing useful information relating to the possible socio-economic and environmental consequences of forest energy developments in Eastern Ontario, the research also makes an important contribution in all applied sense.Doctor of Philosophy (PhD

Surface X-ray Diffraction Studies of Electrode/Vacuum and Electrode/Electrolyte Interfaces

This thesis presents in situ Surface X-ray Diffraction (SXRD) studies of surfaces and interfaces, in both Ultra High Vacuum (UHV) and an electrochemical environment. Primarily Crystal Truncation Rod (CTR) measurements are utilised to determine a model for the atomic structure at the interface. A SXRD characterisation of the clean Ag(110) and Ag(111) surfaces in UHV were determined as a reference for the rest of the work in this thesis. Following this the growth conditions and structures of a silicene layer on Ag(111) were investigated, by Low Energy Electron Diffraction (LEED) and preliminary SXRD study of the interface structure is presented. A comprehensive study of the Ag(hkl)/alkaline interface is presented. X-ray Voltammetry (XRV) measurements have been performed to determine the potential dependence of the system. CTR measurements have been used to determine the structure at both the electrode and electrolyte sides of the interface. The results reveal large structural changes on the electrolyte side of the interface, with the response of relaxation of the surface layers in the metal. The presence of specifically adsorbed OH on the surface stabilises cations in a compact double layer through non-covalent interactions. The studies were extended to determine the effects of saturating the electrolyte gases, CO and O2 on the double layer structure. The results indicate that double layer structure is subtly perturbed, and hints at a change in the nature of bonding at the interface. Time resolved SXRD measurements are utilised to determine the dynamics of the restructuring of the electrolyte layering at the Ag(111)/Alkaline interface. In order to gain a comprehensive picture of the structural dynamics, two other systems are studied; the Au(111) reconstruction to determine the timescale of the (1 x 1) ↔ (p ×√3) reconstruction, and the underpotential deposition of Ag on Au(111). The results indicate that the mass transport of ions through electrolyte is on a timescale comparable to the charge transfer, whereas the ordering of ions and surface metal atoms occurs on much longer timescales