36 research outputs found
Emergent D6 symmetry in fully relaxed magic-angle twisted bilayer graphene
We present a tight-binding calculation of a twisted bilayer graphene at magic angle \u3b8 3c1.08, allowing for full, in- and out-of-plane, relaxation of the atomic positions. The resulting band structure displays, as usual, four narrow minibands around the neutrality point, well separated from all other bands after the lattice relaxation. A thorough analysis of the miniband Bloch functions reveals an emergent D6 symmetry, despite the lack of any manifest point-group symmetry in the relaxed lattice. The Bloch functions at the \u393 point are degenerate in pairs, reflecting the so-called valley degeneracy. Moreover, each of them is invariant under C3z, i.e., transforming like a one-dimensional, in-plane symmetric irreducible representation of an "emergent" D6 group. Out of plane, the lower doublet is even under C2x, while the upper doublet is odd, which implies that at least eight Wannier orbitals, two s-like and two pz-like ones for each of the supercell sublattices AB and BA, are necessary but probably not sufficient to describe the four minibands. This unexpected one-electron complexity is likely to play an important role in the still unexplained metal-insulator-superconductor phenomenology of this system
Pressure--enhanced fractional Chern insulators in moir\'e transition metal dichalcogenides along a magic line
We show that pressure applied to twisted WSe can enhance the many-body
gap and region of stability of a fractional Chern insulator at filling . Our results are based on exact diagonalization of a continuum model,
whose pressure-dependence is obtained through {\it ab initio} methods. We
interpret our results in terms of a {\it magic line} in the pressure-{\it
vs}-twist angle phase diagram: along the magic line, the bandwidth of the
topmost moir\'e valence band is minimized while simultaneously its quantum
geometry nearly resembles that of an ideal Chern band. We expect our results to
generalize to other twisted transition metal dichalcogenide homobilayers.Comment: 11 pages, 9 figure
Macroscopic coherence as an emergent property in molecular nanotubes
Nanotubular molecular self-aggregates are characterized by a high degree of symmetry and they are fundamental systems for light-harvesting and energy transport. While coherent effects are thought to be at the basis of their high efficiency, the relationship between structure, coherence and functionality is still an open problem. We analyse natural nanotubes present in Green Sulphur Bacteria. We show that they have the ability to support macroscopic coherent states, i.e. delocalized excitonic states coherently spread over many molecules, even at room temperature. Specifically, assuming a canonical thermal state we find, in natural structures, a large thermal coherence length, of the order of 1000 molecules. By comparing natural structures with other mathematical models, we show that this macroscopic coherence cannot be explained either by the magnitude of the nearest-neighbour coupling between the molecules, which would induce a thermal coherence length of the order of 10 molecules, nor by the presence of long-range interactions between the molecules. Indeed we prove that the existence of macroscopic coherent states is an emergent property of such structures due to the interplay between geometry and cooperativity (superradiance and super-transfer). In order to prove that, we give evidence that the lowest part of the spectrum of natural systems is determined by a cooperatively enhanced coupling (super-transfer) between the eigenstates of modular sub-units of the whole structure. Due to this enhanced coupling strength, the density of states is lowered close to the ground state, thus boosting the thermal coherence length. As a striking consequence of the lower density of states, an energy gap between the excitonic ground state and the first excited state emerges. Such energy gap increases with the length of the nanotube (instead of decreasing as one would expect), up to a critical system size which is close to the length of the natural complexes considered
Domain-dependent surface adhesion in twisted few-layer graphene: Platform for moir\'e-assisted chemistry
Twisted van der Waals multilayers are widely regarded as a rich platform to
access novel electronic phases, thanks to the multiple degrees of freedom such
as layer thickness and twist angle that allow control of their electronic and
chemical properties. Here, we propose that the stacking domains that form
naturally due to the relative twist between successive layers act as an
additional "knob" for controlling the behavior of these systems, and report the
emergence and engineering of stacking domain-dependent surface chemistry in
twisted few-layer graphene. Using mid-infrared near-field optical microscopy
and atomic force microscopy, we observe a selective adhesion of metallic
nanoparticles and liquid water at the domains with rhombohedral stacking
configurations of minimally twisted double bi- and tri-layer graphene.
Furthermore, we demonstrate that the manipulation of nanoparticles located at
certain stacking domains can locally reconfigure the moir\'e superlattice in
their vicinity at the {\mu}m-scale. In addition, we report first-principles
simulations of the energetics of adhesion of metal atoms and water molecules on
the stacking domains in an attempt to elucidate the origin of the observed
selective adhesion. Our findings establish a new approach to controlling
moir\'e-assisted chemistry and nanoengineering.Comment: 11 pages, 3 figure
Proton block of the CLC-5 Cl−/H+ exchanger
CLC-5 is a H+/Cl− exchanger that is expressed primarily in endosomes but can traffic to the plasma membrane in overexpression systems. Mutations altering the expression or function of CLC-5 lead to Dent’s disease. Currents mediated by this transporter show extreme outward rectification and are inhibited by acidic extracellular pH. The mechanistic origins of both phenomena are currently not well understood. It has been proposed that rectification arises from the voltage dependence of a H+ transport step, and that inhibition of CLC-5 currents by low extracellular pH is a result of a reduction in the driving force for exchange caused by a pH gradient. We show here that the pH dependence of CLC-5 currents arises from H+ binding to a single site located halfway through the transmembrane electric field and driving the transport cycle in a less permissive direction, rather than a reduction in the driving force. We propose that protons bind to the extracellular gating glutamate E211 in CLC-5. It has been shown that CLC-5 becomes severely uncoupled when SCN− is the main charge carrier: H+ transport is drastically reduced while the rate of anion movement is increased. We found that in these conditions, rectification and pH dependence are unaltered. This implies that H+ translocation is not the main cause of rectification. We propose a simple transport cycle model that qualitatively accounts for these findings
Functional impairment of systemic scleroderma patients with digital ulcerations: Results from the DUO registry
Roadmap on printable electronic materials for next-generation sensors
The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g., via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g., printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world