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We use the 1-bond→2-phonon percolation doublet of zincblende alloys as a 'mesoscope' for an unusual insight into their phonon behavior under pressure. We focus on (Zn,Be)Se and show by Raman scattering that the original Be-Se doublet at ambient pressure, of the stretching-bending type, turns into a pure-bending singlet at the approach of the high-pressure ZnSe-like rocksalt phase, an unnatural one for the Be-Se bonds. The 'freezing' of the Be-Se stretching mode is discussed within the scope of the percolation model (mesoscopic scale), with ab initio calculations in support (microscopic scale).

The generic 1-bond → 2-mode “percolation-type” Raman signal inherent to the short bond of common A1−xBxC semiconductor mixed crystals with zincblende (cubic) structure is exploited as a sensitive “mesoscope” to explore how various ZnSe-based systems engage their pressure-induced structural transition (to rock-salt) at the sub-macroscopic scale—with a focus on Zn1−xCdxSe. The Raman doublet, that distinguishes between the AC- and BC-like environments of the short bond, is reactive to pressure: either it closes (Zn1−xBexSe, ZnSe1−xSx) or it opens (Zn1−xCdxSe), depending on the hardening rates of the two environments under pressure. A partition of II–VI and III–V mixed crystals is accordingly outlined. Of special interest is the “closure” case, in which the system resonantly stabilizes ante transition at its “exceptional point” corresponding to a virtual decoupling, by overdamping, of the two oscillators forming the Raman doublet. At this limit, the chain-connected bonds of the short species (taken as the minor one) freeze along the chain into a rigid backbone. This reveals a capacity behind alloying to reduce the thermal conductivity as well as the thermalization rate of photo-generated electrons.

We report Raman signatures of electronic topological transition (ETT) at 3. Electronic mail-asood@physics.iisc.ernet.in

Raman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1−xBexTe under pressure. The dependence of the Be–Te (distinct) and Zn–Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x ~ (0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a «phonon exceptional point» is reached at the resonance. Only the out-of-chain vibrations «survive» the resonance, the in-chain ones are «killed». This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

Memristive devices are among the most emerging electronic elements to realize artificial synapses for neuromorphic computing (NC) applications and have potential to replace the traditional von-Neumann computing architecture in recent times. In this work, pulsed laser deposition-manufactured Ag/TiO2/Pt memristor devices exhibiting digital and analog switching behavior are considered for NC. The TiO2 memristor shows excellent performance of digital resistive switching with a memory window of order ∼103. Furthermore, the analog resistive switching offers multiple conductance levels supporting the development of the bioinspired synapse. A possible mechanism for digital and analog switching behavior in our device is proposed. Remarkably, essential synaptic functions such as pair-pulse facilitation, long-term potentiation (LTP), and long-term depression (LTD) are successfully realized based on the change in conductance through analog memory characteristics. Based on the LTP-LTD, a neural network simulation for the pattern recognition task using the MNIST data set is investigated, which shows a high recognition accuracy of 95.98%. Furthermore, more complex synaptic behavior such as spike-time-dependent plasticity and Pavlovian classical conditioning is successfully emulated for associative learning of the biological brain. This work enriches the TiO2-based resistive random-access memory, which provides information about the simultaneous existence of digital and analog behavior, thereby facilitating the further implementation of memristors in low-power NC.

Vanadium disulfide−black phosphorus (VS 2 −BP) hybrids were synthesized by a one-pot hydrothermal-assisted method to achieve enhanced electrochemical activity for supercapacitor applications. The concentration of BP was optimized to prevent the restacking nature of VS 2 and to enrich the active edges for electrolytic ion intercalation. The charge storage kinetics of the best-performing VS 2 −BP as an active electrode has demonstrated the dominance of the pseudocapacitive nature of the material. Furthermore, by sandwiching with a PVA/K 2 SO 4 gel electrolyte, an all-solid-state (ASS) vanadium disulfide−black phosphorus-50 mg (VS 2 −BP-50) symmetric device was developed on highly conductive carbon paper. The ASS VS 2 −BP-50 symmetric device displays the highest specific areal capacitance of 203.25 mF/cm 2 and exhibits the maximum areal energy density of 28.22 μW h cm −2 at an areal power density of 596.09 mW cm −2 , outperforming the previous literature. To understand the origin of the high quantum capacitance, we used density functional theory (DFT) and found that the charge accumulation region between VS 2 and BP monolayers and the charge transfer are the origin of the improved density of states in the VS 2 −BP hybrid. Moreover, exceptional mobility of K + ions and a higher diffusion rate were observed using the DFT method.