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In a multi-valley electronic band structure, lifting of the valley degeneracy is associated with rotational symmetry breaking in the electronic fluid, and may emerge through spontaneous symmetry breaking order, or through a large response to a small external perturbation such as strain. In this work we use scanning tunneling microscopy to investigate an unexpected rotational symmetry breaking in Landau levels formed in the unusual floating surface band of ZrSiS. We visualize a ubiquitous splitting of Landau levels into valley-polarized sub-levels. We demonstrate methods to measure valley-selective Landau level spectroscopy, to infer unknown Landau level indices, and to precisely measure each valley's Berry phase in a way that is agnostic to the band structure and topology of the system. These techniques allow us to obtain each valley's dispersion curve and infer a rigid valley-dependent contribution to the band energies. Ruling out spontaneous symmetry breaking by establishing the sample-dependence of this valley splitting, we explain the effect in terms of residual strain. A quantitative estimate indicates that uniaxial strain can be measured to a precision of $ \lt 0.025 \% $. The extreme valley-polarization of the Landau levels results from as little as $ \sim 0.1 \% $ strain, and this suggests avenues for manipulation using deliberate strain engineering., Comment: 13 pages, 9 figures (plus 13 pages, 9 figures)

Magnetic skyrmions were thought to be stabilised only in inversion-symmetry breaking structures, but skyrmion lattices were recently discovered in inversion symmetric Gd-based compounds, spurring questions of the stabilisationmechanism. A natural consequence of a recent theoretical proposal, a coupling between itinerant electrons and localised magnetic moments, is that the skyrmions are amenable to detection using even non-magnetic probes such as spectroscopic-imaging scanning tunnellingmicroscopy (SI-STM). Here SI-STM observations of GdRu$_2$Si$_2$ reveal patterns in the local density of states that indeed vary with the underlying magnetic structures. These patterns are qualitatively reproduced by model calculations which assume exchange coupling between itinerant electrons and localised moments. These findings provide a clue to understand the skyrmion formation mechanism in GdRu$_2$Si$_2$., Comment: 21+7 pages, 4+11 figures, to appear in Nature Communications

Assessing regulatory compliance of personal financial advice is currently a complex manual process. In Australia, only 5%- 15% of advice documents are audited annually and 75% of these are found to be non-compliant(ASI 2018b). This paper describes a pilot with an Australian government regulation agency where Artificial Intelligence (AI) models based on techniques such natural language processing (NLP), machine learning and deep learning were developed to methodically characterise the regulatory risk status of personal financial advice documents. The solution provides traffic light rating of advice documents for various risk factors enabling comprehensive coverage of documents in the review and allowing rapid identification of documents that are at high risk of non-compliance with government regulations. This pilot serves as a case study of public-private partnership in developing AI systems for government and public sector., Comment: Presented at AAAI FSS-19: Artificial Intelligence in Government and Public Sector, Arlington, Virginia, USA

Scanning tunneling microscopy visualizations of quasiparticle interference (QPI) enable powerful insights into the k-space properties of superconducting, topological, Rashba and other exotic electronic phases, but their reliance on impurities acting as scattering centers is rarely scrutinized. Here we investigate QPI at the vacuum-cleaved (001) surface of the Dirac semimetal ZrSiS. We find that interference patterns around impurities located on the Zr and S lattice sites appear very different, and can be ascribed to selective scattering of different sub-sets of the predominantly Zr 4d-derived band structure, namely the m = 0 and m = +/-1 components. We show that the selectivity of scattering channels requires an explanation beyond the different bands' orbital characteristics and their respective charge density distributions over Zr and S lattices sites. Importantly, this result shows that the usual assumption of generic scattering centers allowing observations of quasiparticle interference to shed light indiscriminately and isotropically upon the \textit{q}-space of scattering events does not hold, and that the scope and interpretation of QPI observations can therefore be be strongly contingent on the material defect chemistry. This finding promises to spur new investigations into the quasiparticle scattering process itself, to inform future interpretations of quasiparticle interference observations, and ultimately to aid the understanding and engineering of quantum electronic transport properties., Comment: This version is as accepted for PRB

The Dirac semimetal phase found in Cd$_{3}$As$_{2}$ is protected by a $C_{4}$ rotational symmetry derived from a corkscrew arrangement of systematic Cd vacancies in its complicated crystal structure. It is therefore surprising that no microscopic observation, direct or indirect, of these systematic vacancies has so far been described. To this end, we revisit the cleaved (112) surface of Cd$_{3}$As$_{2}$ using a combined approach of scanning tunneling microscopy and \textit{ab initio} calculations. We determine the exact position of the (112) plane at which Cd$_{3}$As$_{2}$ naturally cleaves, and describe in detail a structural periodicity found at the reconstructed surface, consistent with that expected to arise from the systematic Cd vacancies. This reconciles the current state of microscopic surface observations with those of crystallographic and theoretical models, and demonstrates that this vacancy superstructure, central to the preservation of the Dirac semimetal phase, survives the cleavage process and retains order at the surface., Comment: Supplemental Material included. 16 pages, 7 figures

In large-scale emergencies social media has become a key source of information for public awareness, government authorities and relief agencies. However, the sheer volume of data and the low signal-to- noise ratio limit the effectiveness and the efficiency of using social media as an intelligence resource. We describe Australian Crisis Tracker (ACT), a tool designed for agencies responding to large- scale emergency events, to facilitate the understanding of critical information in Twitter. ACT was piloted by the Australian Red Cross (ARC) during the 2013-2014 Australian bushfires season. Video is available at: https://www.youtube.com/watch?v=Y-1rtNFqQbE