Light-Induced Nonthermal Phase Transition to the Topological Crystalline Insulator State in SnSe

Femtosecond pulses have been used to reveal hidden broken symmetry states and induce transitions to metastable states. However, these states are mostly transient and disappear after laser removal. Photoinduced phase transitions toward crystalline metastable states with a change of topological order are rare and difficult to predict and realize experimentally. Here, by using constrained density functional perturbation theory and accounting for light-induced quantum anharmonicity, we show that ultrafast lasers can permanently transform the topologically trivial orthorhombic structure of SnSe into the topological crystalline insulating rocksalt phase via a first-order nonthermal phase transition. We describe the reaction path and evaluate the critical fluence and possible decay channels after photoexcitation. Our simulations of the photoexcited structural and vibrational properties are in excellent agreement with recent pump–probe data in the intermediate fluence regime below the transition with an error on the curvature of the quantum free energy of the photoexcited state that is smaller than 2%

Misfit Layer Compounds as Ultratunable Field Effect Transistors: From Charge Transfer Control to Emergent Superconductivity

Misfit layer compounds are heterostructures composed of rocksalt units stacked with few-layer transition metal dichalcogenides. They host Ising superconductivity, charge density waves, and good thermoelectricity. The design of misfits’ emergent properties is, however, hindered by the lack of a global understanding of the electronic transfer among the constituents. Here, by performing first-principles calculations, we unveil the mechanism controlling the charge transfer and demonstrate that rocksalt units are always donor and dichalcogenides acceptors. We show that misfits behave as a periodic arrangement of ultratunable field effect transistors where a charging as large as ≈6 × 1014 e– cm–2 can be reached and controlled efficiently by the La–Pb alloying in the rocksalt. Finally, we identify a strategy to design emergent superconductivity and demonstrate its applicability in (LaSe)1.27(SnSe2)2. Our work paves the way to the design synthesis of misfit compounds with tailored physical properties

Annual synthetic indexes.

Boxplot (2.5%, 25%, 75% and 97.5% quantile and median) of predicted onset (lower orange bars in panel a) and offset (higher orange bars in panel a), defined as the week of the year when the 5% and the 95% of the cumulative captures are reached respectively; week of the year associated with peak (highest) capture (red bars in panel b); total annual captures, i.e. the sum of the 20 weekly captures (green bars in panel c); peak capture, i.e. maximum number of trapped adults in a single capture session (purple bars in panel d). Blue boxplots represent the distributions of the observed site-specific values. Distributions of the observed peak capture were obtained by computing the maximum of 3-point moving average of weekly captures.</p

Model fit.

Average number of weekly captured Cx. pipiens during the twenty-week survey period observed in Piedmont region from 2000 to 2011 (blue points) and predicted by model simulation based on the estimated posterior distribution of free parameters (median in red, pink region defines 2.5–97.5% quantile predictions).</p

Model parameters.

Model parameters.</p

Effect of temperature variations on <i>Cx</i>. <i>pipiens</i>.

<p>Boxplots (2.5%, 25%, 75% and 97.5% quantile and median) of predicted annual synthetic indexes associated with different temperature inputs (x-axis, from -2.5°C to +2.5°C with respect to actual records). Panel (a) shows the effect on the duration of the breeding season, defined as the difference between the week of the year when the 95% and the 5% of the cumulative captures are reached; panels (b) and (c) show respectively the effect on the timing and the value of the peak capture; panel (d) shows the effect on the total annual captures.</p

The Role of Climatic and Density Dependent Factors in Shaping Mosquito Population Dynamics: The Case of <i>Culex pipiens</i> in Northwestern Italy

<div><p><i>Culex pipiens</i> mosquito is a species widely spread across Europe and represents a competent vector for many arboviruses such as West Nile virus (WNV), which has been recently circulating in many European countries, causing hundreds of human cases. In order to identify the main determinants of the high heterogeneity in <i>Cx</i>. <i>pipiens</i> abundance observed in Piedmont region (Northwestern Italy) among different seasons, we developed a density-dependent stochastic model that takes explicitly into account the role played by temperature, which affects both developmental and mortality rates of different life stages. The model was calibrated with a Markov chain Monte Carlo approach exploring the likelihood of recorded capture data gathered in the study area from 2000 to 2011; in this way, we disentangled the role played by different seasonal eco-climatic factors in shaping the vector abundance. Illustrative simulations have been performed to forecast likely changes if temperature or density–dependent inputs would change. Our analysis suggests that inter-seasonal differences in the mosquito dynamics are largely driven by different temporal patterns of temperature and seasonal-specific larval carrying capacities. Specifically, high temperatures during early spring hasten the onset of the breeding season and increase population abundance in that period, while, high temperatures during the summer can decrease population size by increasing adult mortality. Higher densities of adult mosquitoes are associated with higher larval carrying capacities, which are positively correlated with spring precipitations. Finally, an increase in larval carrying capacity is expected to proportionally increase adult mosquito abundance.</p></div

Estimated parameters.

<p>Boxplot (2.5%, 25%, 75% and 97.5% quantile and median) of posterior distributions of parameters <i>A</i>_<i>0</i> (panel a) and <i>K</i> (panel b) estimated in different years. Histograms of relative frequencies for posterior distributions of parameters α (panel c) and β (panel d).</p

Effects of density-dependent factor variations on <i>Cx</i>. <i>pipiens</i>.

<p>Boxplots (2.5%, 25%, 75% and 97.5% quantile and median) of predicted annual synthetic indexes associated with different values of <i>K</i> (x-axis, from -50% to +50% with respect to fitted values). Panel (a) shows the effect on the duration of the breeding season; panels (b) and (c) show respectively the effect on the timing and the value of the peak capture; panel (d) shows the effect on the total annual captures.</p

Sensitivity analysis on effectiveness of control interventions.

Violin plots for the distributions of the average percentage of avoided DENV symptomatic cases by (a) radius of the treated area, (b) average delay between symptom onset and intervention and (c) proportion of mosquitoes killed by ULV spraying. The distributions are computed from 100 averages over 1,000 clusters randomly sampled from the 20,000 simulated clusters. Squares represent the average values.</p