Electronic viscosity in a quantum well: A test for the local density approximation

In the local density approximation (LDA) for electronic time-dependent current-density functional theory (TDCDFT) many-body effects are described in terms of the visco-elastic constants of the homogeneous three-dimensional electron gas. In this paper we critically examine the applicability of the three-dimensional LDA to the calculation of the viscous damping of 1-dimensional collective oscillations of angular frequency $\omega$ in a quasi 2-dimensional quantum well. We calculate the effective viscosity $\zeta(\omega)$ from perturbation theory in the screened Coulomb interaction and compare it with the commonly used three-dimensional LDA viscosity $Y(\omega)$. Significant differences are found. At low frequency $Y(\omega)$ is dominated by a shear term, which is absent in $\zeta(\omega)$. At high frequency $\zeta(\omega)$ and $Y(\omega)$ exhibit different power law behaviors ($\omega^{-3}$ and $\omega^{-5/2}$ respectively), reflecting different spectral densities of electron-hole excitations in two and three dimensions. These findings demonstrate the need for better approximations for the exchange-correlation stress tensor in specific systems where the use of the three-dimensional functionals may lead to unphysical results.Comment: 10 pages, 7 figures, RevTex

Large Biaxial Compressive Strain Tuning of Neutral and Charged Excitons in Single-Layer Transition Metal Dichalcogenides

The absorption and emission of light in single-layer transition metal dichalcogenides are governed by the formation of excitonic quasiparticles. Strain provides a powerful technique to tune the optoelectronic properties of two-dimensional materials and thus to adjust their exciton energies. The effects of large compressive strain in the optical spectrum of two-dimensional (2D) semiconductors remain rather unexplored compared to those of tensile strain, mainly due to experimental constraints. Here, we induced large, uniform, biaxial compressive strain (∼1.2%) by cooling, down to 10 K, single-layer WS2, MoS2, WSe2, and MoSe2 deposited on polycarbonate substrates. We observed a significant strain-induced modulation of neutral exciton energies, with blue shifts up to 160 meV, larger than in any previous experiments. Our results indicate a remarkably efficient transfer of compressive strain, demonstrated by gauge factor values exceeding previous results and approaching theoretical expectations. At low temperatures, we investigated the effect of compressive strain on the resonances associated with the formation of charged excitons. In WS2, a notable reduction of gauge factors for charged compared to neutral excitons suggests an increase in their binding energy, which likely results from the effects of strain added to the influence of the polymeric substrate.The authors acknowledge funding from the Generalitat Valenciana through grants IDIFEDER/2020/005 and IDIFEDER/2021/016 and support from the Plan Gen-T of Excellence for M.R.C (CideGenT2018004) and from the Spanish MCINN through grants PLASTOP PID2020-119124RB-I00, TED2021-131641B-C43, PID2020-115566RB-I00, TED2021-132267B-I00, and PID2020-112811GB-I00. This work was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 755655, ERC-StG 2017 project 2D-TOPSENSE). The authors also acknowledge funding from the EU FLAG-ERA project To2Dox (JTC-2019-009) and the Comunidad de Madrid through the CAIRO-CM project (Y2020/NMT-6661). H.L. acknowledges support from China Scholarship Council (CSC) under grant no. 201907040070. D.G.-M. thanks the Maria Zambrano Program at the University of Alicante founded by the European Union-Next Generation EU. R.D’A. acknowledges support from the Grant No. IT1453- 22 “Grupos Consolidados UPV/EHU del Gobierno Vasco”

Acute Delta Hepatitis in Italy spanning three decades (1991–2019): Evidence for the effectiveness of the hepatitis B vaccination campaign

Updated incidence data of acute Delta virus hepatitis (HDV) are lacking worldwide. Our aim was to evaluate incidence of and risk factors for acute HDV in Italy after the introduction of the compulsory vaccination against hepatitis B virus (HBV) in 1991. Data were obtained from the National Surveillance System of acute viral hepatitis (SEIEVA). Independent predictors of HDV were assessed by logistic-regression analysis. The incidence of acute HDV per 1-million population declined from 3.2 cases in 1987 to 0.04 in 2019, parallel to that of acute HBV per 100,000 from 10.0 to 0.39 cases during the same period. The median age of cases increased from 27 years in the decade 1991-1999 to 44 years in the decade 2010-2019 (p < .001). Over the same period, the male/female ratio decreased from 3.8 to 2.1, the proportion of coinfections increased from 55% to 75% (p = .003) and that of HBsAg positive acute hepatitis tested for by IgM anti-HDV linearly decreased from 50.1% to 34.1% (p < .001). People born abroad accounted for 24.6% of cases in 2004-2010 and 32.1% in 2011-2019. In the period 2010-2019, risky sexual behaviour (O.R. 4.2; 95%CI: 1.4-12.8) was the sole independent predictor of acute HDV; conversely intravenous drug use was no longer associated (O.R. 1.25; 95%CI: 0.15-10.22) with this. In conclusion, HBV vaccination was an effective measure to control acute HDV. Intravenous drug use is no longer an efficient mode of HDV spread. Testing for IgM-anti HDV is a grey area requiring alert. Acute HDV in foreigners should be monitored in the years to come

Beyond the State of the Art: Novel Approaches for Thermal and Electrical Transport in Nanoscale Devices

Almost any interaction between two physical entities can be described through the transfer of either charge, spin, momentum, or energy. Therefore, any theory able to describe these transport phenomena can shed light on a variety of physical, chemical, and biological effects, enriching our understanding of complex, yet fundamental, natural processes, e.g., catalysis or photosynthesis. In this review, we will discuss the standard workhorses for transport in nanoscale devices, namely Boltzmann's equation and Landauer's approach. We will emphasize their strengths, but also analyze their limits, proposing theories and models useful to go beyond the state of the art in the investigation of transport in nanoscale devices.This research was funded by the Spanish Ministerio de Economia y Competitividad (MINECO) grant number FIS2016-79464-P (SElecT-DFT) and MINECOG17/A01 (TOWTherm), by the Basque Government (Eusko Jaurlaritza) through the Grupos Consolidados (IT578-13 and IT1249-19). R. B. acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 793318. The APC was funded by Dresden University of Technology (TU Dresden)

Strain tuning MoO3 vibrational and electronic properties

Abstract This work investigates the vibrational and electrical properties of molybdenum trioxide (α-MoO3) upon tensile strain applied along different crystal directions. Using a three-point bending setup in combination with Raman spectroscopy, we report measurements of a blueshift of the Raman modes when uniaxial tensile strain is applied along the a- and c-axis to this material. Furthermore, the electrical measurements reveal an increase in resistance with strain applied along both in-plane directions. The findings from the uniaxial strain and Raman spectroscopy measurements are further confirmed by ab-initio calculations. This study provides valuable insights into the mechanical and vibrational properties of α-MoO3 and its potential use in several applications. This study contributes to the growing body of knowledge on the properties of α-MoO3 and lays the foundation for further exploration of its potential applications. Given MoO3 holding the natural hyperbolic phonon polaritons, attracting significant research interest, this study has the potential to arouse the curiosity of the scientific community