Exploring 4D Quantum Hall Physics with a 2D Topological Charge Pump

The discovery of topological states of matter has profoundly augmented our understanding of phase transitions in physical systems. Instead of local order parameters, topological phases are described by global topological invariants and are therefore robust against perturbations. A prominent example thereof is the two-dimensional integer quantum Hall effect. It is characterized by the first Chern number which manifests in the quantized Hall response induced by an external electric field. Generalizing the quantum Hall effect to four-dimensional systems leads to the appearance of a novel non-linear Hall response that is quantized as well, but described by a 4D topological invariant - the second Chern number. Here, we report on the first observation of a bulk response with intrinsic 4D topology and the measurement of the associated second Chern number. By implementing a 2D topological charge pump with ultracold bosonic atoms in an angled optical superlattice, we realize a dynamical version of the 4D integer quantum Hall effect. Using a small atom cloud as a local probe, we fully characterize the non-linear response of the system by in-situ imaging and site-resolved band mapping. Our findings pave the way to experimentally probe higher-dimensional quantum Hall systems, where new topological phases with exotic excitations are predicted

Nanomechanical and microstructural characterization of a zirconia-toughened alumina composite after aging

This study's objective was to mechanically characterize and validate the synthesis method of a polycrystalline composite comprised of 80% alumina reinforced with 20% translucent zirconia (zirconia-toughened alumina, ZTA) and compare to an experimental translucent zirconia. Experimental ZTA (ZTA ZPEX 80/20) and translucent Y-TZP (ZPEX) green-state disc-shaped specimens were obtained via uniaxial/isostatic ceramic powder pressing technique. The discs were sintered using a predefined protocol after both sides of the discs were polished. The specimens were subjected to nanoindentation testing to acquire their elastic modulus (E) and hardness (H) before and after a simulated low temperature degradation (LTD) challenge. Subsequently, the fabricated discs had their 3D surface topographical (Sa/Sq) parameters assessed via interferometry before and after exposure to a simulated LTD aging protocol. The specimens were evaluated using X-ray diffraction (XRD) to assess the tetragonal-monoclinic phase transformation and via scanning electron microscopy (SEM) to evaluate the homogeneity of the surfaces and distribution of the grains. The apparent density was measured using Archimedes' principle. All of the data were statistically evaluated through repeated measures ANOVA following post-hoc comparisons using the Tukey test (p 0.05). A significant decrease in the E values after the aging protocol was observed for both groups (p < 0.01). While ZTA ZPEX 80/ 20 did not show statistically significant differences in the hardness values after the aging protocol (p = 0.36), ZPEX demonstrated a significant decrease in the H values (p = 0.03). For ZTA ZPEX 80/20, simulated LTD aging did not affect the tested properties, except for the E values. Although artificial aging did not affect the surface roughness of ZPEX, the E and H values significantly decreased after aging45788408846CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP304589/2017-9; 434487/2018-0não tem2012/19078-7; EMU 2016/18818-8; 2016/17793-1; 2017/19362-0; 2018/03072-