Spin-polarized gapless surface states in topological insulators form chiral Dirac cones. When such materials are reduced to thin films, the Dirac states on the two faces of the film can overlap and ...couple by quantum tunneling, resulting in a thickness-dependent insulating gap at the Dirac point. Calculations for a freestanding Sb film with a thickness of four atomic bilayers yield a gap of 36 meV, yet angle-resolved photoemission measurements of a film grown on Si(111) reveal no gap formation. The surprisingly robust Dirac cone is explained by calculations in terms of interfacial interaction.
We show that bismuth nanostructures form three-dimensional patterns governed by two-dimensional electronic effects. Scanning tunneling microscopy reveals that both the vertical and the lateral ...dimensions of the structures strongly favor certain values and that the preferred widths are substantially different for each preferred height. First-principles calculations demonstrate that this vertical–lateral correlation is governed by the Fermi surface topology and that this is itself sensitively dependent on the dimensions of the structure.
Topological materials have unusual surface spin properties including a net surface spin current protected by the bulk symmetry properties. When such materials are reduced to thin films, their gapless ...spin-polarized surface states must connect, by analytic continuation, to bulk-derived quantum-well states, which are spin-unpolarized in centrosymmetric systems. The nature of this passage in a model system, Sb films, is investigated. Angle-resolved photoemission shows a smooth transition, while calculations elucidate the correlated evolution of the spin and charge distributions in real space.
•The surface states of a tensile-strained α-Sn consist of two Dirac cones.•The upper Dirac cone vanishes in the absence of either strain or SOC.•The surface states in the lower part of sp gap survive ...regardless of strain and SOC.•Without SOC, the surface states are spin unpolarized.
α-Sn is on the boundary of a couple of distinct topological phases. It will transform into a topological insulator under a suitable strain. However, a clear picture of its topological surface states (TSSs) is still lacking. Here we perform first-principles calculations on the electronic structure of α-Sn(111) surface to identify its TSSs and reveal their properties. The results show that the presence of valence band reorganizes the TSSs in the inverted sp gap into two Dirac cones. The lower one is in the valence band continuum; the upper one resides in the gap between the valence and conduction bands. We also demonstrate the transformation of the surface states by switching on or off of strain and/or spin-orbit coupling. Without spin-orbit coupling, only the TSSs associated with the lower Dirac cone survive, and they are spin unpolarized. The results are useful for understanding and engineering the topological properties of α-Sn.
A van der Waals bonded moiré bilayer formed by sequential growth of TiSe2 and TiTe2 monolayers exhibits emergent electronic structure as evidenced by angle-resolved photoemission band mapping. The ...two monolayers adopt the same lattice orientation but incommensurate lattice constants. Despite the lack of translational symmetry, sharp dispersive bands are observed. The dispersion relations appear distinct from those for the component monolayers alone. Theoretical calculations illustrate the formation of composite bands by coherent electronic coupling despite the weak interlayer bonding, which leads to band renormalization and energy shifts.
Researchers have indicated that the collaborative problem‐solving space afforded by the collaborative systems significantly impact the problem‐solving process. However, recent investigations into ...collaborative simulations, which allow a group of students to jointly manipulate a problem in a shared problem space, have yielded divergent results regarding their effects on collaborative learning. Hence, this study analysed how students solved a physics problem using individual‐based and collaborative simulations to understand their effects on science learning. Multiple data sources including group discourse, problem‐solving activities, learning test scores, and questionnaire feedback were analysed. Lag sequential analysis on the data found that students using the two simulations collaborated with peers to solve the problem in significantly different patterns. The students using the collaborative simulations demonstrated active engagement in the collaborative activity; however, they did not transform discussions into workable problem‐solving activities. The students using the individual‐based simulation showed a lower level of collaboration engagement, starting with individual exploration of the problem with the simulation, followed by group reflection. The two groups also showed significant differences in their learning test scores. The findings and pedagogical suggestions are discussed in the hope of addressing critical activity design issues in using computer simulations for facilitating collaborative learning.
Lay Description
What is currently known about the subject matter?
Students tend to solve problems with simulations individually rather than collaboratively.
The free‐riding effect impedes student engagement in the collaborative process.
Collaborative simulations offer new affordances to better facilitate CPS processes.
What their paper adds to this?
Collaborative simulations strengthen interdependence and engagement in collaboration.
However, students did not show a significant enhancement in the learning tests.
They had difficulties transforming discussions into workable problem‐solving actions.
What the implications of study findings for practitioners?
Collaborative simulations can be applied to enhance collaborative engagement.
CPS activities should carefully leverage individual and collaborative learning.
Prompts that help students to closely relate their discussion to the simulation are needed.
Background and purpose
No study has established a prediction dementia model in the Asian populations. This study aimed to develop a prediction model for dementia in Chinese type 2 diabetes patients.
...Methods
The retrospective cohort study included 27 540 Chinese type 2 diabetes patients (aged 50–94 years) enrolled in the Taiwan National Diabetes Care Management Program. Participants were randomly allocated into derivation and validation sets at a 2:1 ratio. Cox proportional hazards regression models were used to identify risk factors for dementia in the derivation set. Steps proposed by the Framingham Heart Study were used to establish a prediction model with a scoring system.
Results
The average follow‐up was 8.09 years, with a total of 853 incident dementia cases in the derivation set. The dementia risk score summed up the individual scores (from 0 to 20). The areas under the curve of 3‐, 5‐ and 10‐year dementia risks were 0.82, 0.79 and 0.76 in the derivation set and 0.84, 0.80 and 0.75 in the validation set, respectively.
Conclusions
The proposed score system is the first dementia risk prediction model for Chinese type 2 diabetes patients in Taiwan.
Platinum ditelluride (PtTe2), a type-II Dirac semimetal, remains semimetallic in ultrathin films down to just two triatomic layers (TLs) with a negative gap of −0.36 eV. Further reduction of the ...film thickness to a single TL induces a Lifshitz electronic transition to a semiconductor with a large positive gap of +0.79 eV. This transition is evidenced by experimental band structure mapping of films prepared by layer-resolved molecular beam epitaxy, and by comparing the data to first-principles calculations using a hybrid functional. The results demonstrate a novel electronic transition at the two-dimensional limit through film thickness control.
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