Material Physics Center

Polymorphism in polyarenes significantly impacts their applications, yet remains underexplored in curved species like corannulene. To this end, we utilised fast scanning calorimetry and X-ray diffraction to explore its stability regimes. Unlike its flat counterpart perylene, corannulene exhibits a glass transition at Tg=323 K when cooled from the melt at rates exceeding -500 K s-1. Upon heating, three thermal events at ca. 380, 430, and 500 K reveal hitherto unknown polymorphs. Diffraction data link these transitions to well-defined and thermally activated rotations within the crystal, inducing a sharp density decrease matching Tg. These changes are accompanied by abnormal atomic displacement parameters. Unlike flat polyarenes of a similar molecular size, the diffraction data also provide strong evidence that this solid ought to be regarded as two distinctly different materials below and above Tg. Altogether, our findings bring to the fore the unanticipated complexity underpinning the structure and thermodynamic response of solid corannulene, the simplest geodesic polyarene.

This conceptual understanding article is part of a series where we explore the recognition and conversion between representations of the electric field concept; in this article, we present the vector field plot’s case. We conducted a study with higher education introductory and upper-division Physics students in a large private Mexican university, intending to learn how students recognize the electric field’s main characteristics in the vector field plot independently and as a source or target representation in conversion processes. We used the theory of registers of semiotic representations and a phenomenographic approach as a framework to analyze data. We explored students’ recognition and conversion abilities through interpretation and construction tasks. We found that the main difficulties of interpreting and constructing the vector field plot are related to the representation’s surface features, often delimited by physical considerations. In the interpretation tasks, this was observed as the interpretation of the physical symmetry, while in construction tasks, it was evident by the confinement of vectors and other associated difficulties. In conversion processes, we observed that there might be an interaction between the source and the target representation, which may result in difficulties in interpreting the vector field plot. We recommend that higher education introductory and upper-division electricity and magnetism instructors and physics education researchers be aware of the difficulties that some interpretation and construction tasks may present to students learning the electric field concept.

The thermal transitions of amorphous poly­(l-lactide)(PLLA)were investigated by combining standard calorimetry (DSC), fast scanningcalorimetry (FSC), and infrared spectroscopy. By following the enthalpicevolution, the glass transition temperature (Tg) change, and the chains’ conformational behavior ofPLLA during sub-Tg and supra-Tg annealing isotherms, a transition was identified inthe supercooled liquid (SCL) phasethe so-called SCL transformationoccurringbefore crystallization. SCL transformation kinetics was assessed andintroduced into the relaxation map of amorphous PLLA, revealing ahierarchical pathway. The SCL transformation allows the unstable PLLA-quenchedliquid to relax toward a metastable SCL with a lower free energy.This occurs through conformational rearrangement of a small fractionof gg conformers into the more stable gt form. Ultimately, SCL kinetics was compared to PLLA liquid dynamics,providing a suggestive scenario where the SCL transformation is mediatedby both α-relaxation and non-α relaxation mechanismstheSlow Arrhenius Process (SAP).

The superconducting proximity effect induces pairing correlations in metallic systems via Andreev scattering. This effect is particularly intriguing in graphene as it enables two-dimensional superconductivity that is tunable through doping. Understanding how superconducting correlations propagate within the metal is crucial to unveiling the key factors behind this tunability. Here, we employ scanning tunneling microscopy to investigate the energy and length scales of the proximity effect induced by Pb islands on graphene. Using tip-induced manipulation, we assemble S/N/S junctions with tunable N-region spacing and explore the evolution of the proximitized state in the confined normal region. We find that different doping levels can lead to either localized or collective superconducting states. By combining our experimental results with quasiclassical theory, we demonstrate that interface conductance plays a key role in determining the strength and coherence length of pairing correlations and interisland coupling. Our findings provide new insights into the design of novel superconducting states and the control of their properties.

Dirac Fermions onthe surface of the topological insulator arespin-momentum locked and topologically protected, making them interestingfor spintronics and quantum computing applications. When in proximityto magnetism and superconductivity, these electronic states couldresult in quantum anomalous Hall effect and Majorana Fermions, respectively.An even more dramatic enrichment of the topological insulators’physics is expected for moiré superlattices, where, analogouslyto the twisted graphene layers, electronic correlations could be stronglyenhanced, a task previously notoriously difficult to achieve in topologicalmatter. Until now, the experimental confirmation of such moiréproperties has remained elusive. Here, we grow the two-dimensionalvan der Waals magnetic insulators FeX2 (where X = Cl orBr) on top of the topological insulator Bi2Se3 and establish a moiré superlattice formation at the interface.By means of scanning tunneling microscopy and angle-resolved photoemissionspectroscopy, we investigate the electronic properties of the formedmoiré superlattice and demonstrate its tunability via the filmchoice. We reveal replicated Dirac cones and focus on their intersections,which, in the case of FeBr2/Bi2Se3, occur below the Fermi level. We identify the signatures of smallgaps at the intersections around the M̅i points that we attribute to the moiré interaction.These findings point to the specific type of magnetic moirépotential that breaks the time-reversal symmetry at these points butnot at the Γ̅ point. Our observations provide an intriguingscenario of correlated topological phases induced by moirésuperlattice that may result in topological superconductivity, highChern number phases, and exotic noncollinear magnetic textures.

Clathrin assembly lymphoid myeloid leukaemia protein (CALM) is involved in the formation of clathrin-mediated endocytic coats by virtue of binding many proteins involved in the process, including clathrin itself and AP2 cargo adaptor complex. CALM is able to specifically recognize the inner leaflet of the plasma membrane by binding the membrane's phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). Here, a quantitative biophysical approach -combining neutron/X-ray scattering, solid-state NMR, atomic force microscopy, and quartz crystal microbalance with dissipationmonitoring-, was exploited to investigate CALM interaction with PtdIns(4,5)P2-presenting model membranes. The presented experimental data reveal CALM's folded domain partially embeds (12% volume occupancy) within the membrane, directly coordinating a cluster of 4 to 5 PtdIns(4,5)P2 molecules via phosphate interactions. The N-terminal amphipathic helix inserts ~8 Å into the headgroup region, reducing local membrane stiffness by 36% (from 22 to 14 MPa) while increasing viscoelastic dissipation. These results establish a plausible threefold curvature-generation mechanism: PtdIns(4,5)P2 clustering, helix insertion-induced lipid compaction and global mechanical softening-collectively lowering the energy barrier for membrane deformation.