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We investigate novel transport properties of chiral continuous-time quantum walks (CTQWs) on graphs. By employing a gauge transformation, we demonstrate that CTQWs on chiral chains are equivalent to those on non-chiral chains, but with additional momenta from initial wave packets. This explains the novel transport phenomenon numerically studied in (Khalique et al 2021 New J. Phys. 23 083005). Building on this, we delve deeper into the analysis of chiral CTQWs on the Y-junction graph, introducing phases to account for the chirality. The phase plays a key role in controlling both asymmetric transport and directed complete transport among the chains in the Y-junction graph. We systematically analyze these features through a comprehensive examination of the chiral CTQW on a Y-junction graph. Our analysis shows that the CTQW on Y-junction graph can be modeled as a combination of three wave functions, each of which evolves independently on three effective open chains. By constructing a lattice scattering theory, we calculate the phase shift of a wave packet after it interacts with the potential-shifted boundary. Our results demonstrate that the interplay of these phase shifts leads to the observed enhancement and suppression of quantum transport. The explicit condition for directed complete transport or 100 % efficiency is analytically derived. Our theory has applications in building quantum versions of binary tree search algorithms.

The transport properties of iron under Earth’s inner core conditions are essential input for the geophysical modelling but are poorly constrained experimentally. Here we show that the thermal and electrical conductivity of iron at those conditions remains high even if the electron-electron-scattering (EES) is properly taken into account. This result is obtained by ab initio simulations taking into account consistently both thermal disorder and electronic correlations. Thermal disorder suppresses the non-Fermi-liquid behavior of the body-centered cubic iron phase, hence, reducing the EES; the total calculated thermal conductivity of this phase is 220 Wm −1  K −1 with the EES reduction not exceeding 20%. The EES and electron-lattice scattering are intertwined resulting in breaking of the Matthiessen’s rule with increasing EES. In the hexagonal close-packed iron the EES is also not increased by thermal disorder and remains weak. Our main finding thus holds for the both likely iron phases in the inner core. The heat and electrical conductivity of Earth’s core matter represent key input quantities for geophysical models of the Earth’s core evolution and geodynamo. Here, the authors show how the scattering due to interactions between electrons has a relatively weak impact on the electrical and thermal conductivities of iron at core conditions.

In this paper, we present an empirical model for the bulk electron mobility in Si as a function of doping and temperature, down to the cryogenic range. With regard to lattice scattering, we have proposed an empirical model for the lattice dilation energy as a function of doping, using the data extracted from experimental results of bulk electron mobility at higher temperatures and low doping levels. We have also developed a new model for the ionized impurity scattering time using a novel approach of combining the scattering cross-section and the carrier velocity into a single variable. Finally, the Matthiessen’s rule was applied in order to obtain the net mobility. The results showed an excellent match with the experimental data reported in the literature over a wide range of temperature (20–400 K). Also, when compared to the results of some other classic models, with respect to the same set of experimental data, our results showed a much superior match, particularly in the cryogenic range. Finally, this model can be integrated easily to any of the empirical surface carrier mobility models for MOSFETs.

Entropy engineering has been demonstrated to be an effective strategy to regulate the thermoelectric properties of materials. In this work, we report a series of single-phase cubic (La0.25Sr0.25Ba0.25Ca0.25)CoO3 (LSBC), (La0.25Nd0.25Sr0.25Ba0.25)CoO3 (LNSB), and (La0.2Nd0.2Sr0.2Ba0.2Ca0.2)CoO3 (LNSBC) ceramics based on high-entropy design in the Re site of perovskite RECoO3. Electron microscopy results indicate that the three samples have high crystallinity and exhibit a clear pore structure with rich lattice defects. Electrical transport measurements show that LNSB and LNSBC show metallic conductive behaviors with the lowest resistivity of only 2.25 mΩ cm at 973 K, while LSBC exhibits a semiconductor–metal transition at around 650 K due to the lower average chemical valences in the RE site. Meanwhile, the low average chemical valences also cause the increasing proportion of Co4+ due to the requirement of charge neutrality of the samples, which inhibits their Seebeck coefficients. However, compared with the reported Co-based perovskite oxides, their thermal conductivities are greatly reduced owing to high-entropy enhanced lattice scattering. LSBC in particular obtains the lowest thermal conductivity of 1.25 W·m−1·K−1 at 937 K, while LNSB and LNSBC characterized by high carrier thermal conductivity exhibit a thermal conductivity of 1.52 W·m−1·K−1 at the same temperature. These findings reveal that high-entropy design in the RE site of perovskite RECoO3 ceramics enables the effective reduction of thermal conductivity and the maintenance of the excellent electrical properties simultaneously, which provides a novel route for the development of high-performance thermoelectric materials.

This work demonstrates the systematic investigation of the effects of high temperature on key performance parameters including speed, sensitivity, stability, and repeatability of a 3C-SiC/Si ultraviolet (UV) photodetector (PD) at various operating temperatures ranging from 50°C to 200°C. The device with very low dark current (∼ 0.08 pA) exhibited high sensitivity of 4466 and fast rise and decay times of 0.34 s and 0.30 s at 50°C to exposure of 254 nm UV light at a bias voltage of 20 V. Additionally, the device showed very good performance at a low operating voltage of 0.5 V and high temperature of 200°C, with a rise time of 2.68 s and decay time of 1.44 s, while maintaining good stability and repeatability. The slight decrease in performance (sensitivity from 4466 to 932) at 200°C was attributed to the increase in lattice scattering at elevated temperatures, leading to a decrease in carrier mobility. Moreover, the device was fabricated using a very cost-effective process flow. Consequently, this study can contribute to the development of low-power, fast, highly sensitive, and cost-effective 3C-SiC UVPDs for use in high-temperature photonic applications.

A Correction to this paper has been published: https://doi.org/10.1038/s41586-020-03142-2.

Quantum well states of Ag films grown on stepped Au(111) surfaces are shown to undergo lateral scattering, in analogy with surface states of vicinal Ag(111). Applying angle resolved photoemission spectroscopy we observe quantum well bands with zone-folding and gap openings driven by surface/interface step lattice scattering. Experiments performed on a curved Au(111) substrate allow us to determine a subtle terrace-size effect, i.e., a fine step-density-dependent upward shift of quantum well bands. This energy shift is explained as mainly due to the periodically stepped crystal potential offset at the interface side of the film. Finally, the surface state of the stepped Ag film is analyzed with both photoemission and scanning tunneling microscopy. We observe that the stepped film interface also affects the surface state energy, which exhibits a larger terrace-size effect compared to surface states of bulk vicinal Ag(111) crystals.

We studied the temperature dependence (77–300 K) of the electron concentration and mobility using the Hall method under ultrasound (the acoustic Hall method) to determine the mechanisms by which ultrasound influences the electrical activity of near-dislocation clusters in n-type low-ohmic Cd1−xZnxTe single crystals (NCl ≈ 1024 m−3; x = 0; 0.04) with different dislocation density (0.4–5.1) × 1010 m−2. Changes in electrophysical parameters were found to occur as a function of temperature and ultrasound intensity. To evaluate the relative contribution of different charge carrier scattering mechanisms (lattice scattering, ionized impurity scattering, neutral impurity scattering, and dislocation scattering) and their change under ultrasound, a differential evolution method was used. This method made it possible to analyze experimental mobility μH(T) by its nonlinear approximation with characteristic temperature dependence for each mechanism. An increase in neutral impurity scattering and a decrease in ionized impurity and dislocation scattering components were observed under ultrasound. The character and the amount of these acoustically induced changes correlate with particular sample dislocation characteristics. It was concluded that the observed effects are related to the acoustically induced transformation of the point-defect structure, mainly in the near dislocation crystal regions.

Black phosphorus (BP) shows great potential in electronic and optoelectronic applications; however, maintaining the stable performance of BP devices over temperature is still challenging. Here, a novel BP field-effect transistor (FET) fabricated on the atomic layer deposited AlN/SiO /Si substrate is demonstrated. Electrical measurement results show that BP FETs on the AlN substrate possess superior electrical performance compared with those fabricated on the conventional SiO /Si substrate. It exhibits a large on-off current ratio of 5 × 10 , a low subthreshold swing of <0.26 V/dec, and a high normalized field-effect carrier mobility of 1071 cm V s in the temperature range from 77 to 400 K. However, these stable electrical performances are not found in the BP FETs on SiO /Si substrate when the temperature increases up to 400 K; instead, the electrical performance of BP FETs on the SiO /Si substrate degrades drastically. Furthermore, to gain a physical understanding on the stable performance of BP FETs on the AlN substrate, low-frequency noise analysis was performed, and it revealed that the AlN film plays a significant role in suppressing the lattice scattering and charge trapping effects at high temperatures.

One-dimensional nanocomposite containing multiwall carbon nanotubes (MWCNTs) and thin bismuth tellurite (Bi2Te3) nanotubes have been synthesized using ball-milling process. The primary focus of this work is to study the morphological, molecular bonding, and structure of the novel nanocomposite and to explore the underlying mechanism to synthesize a novel nanocomposite for thermoelectric applications. The experimental results from the high-resolution TEM revealed that MWCNTs are uniformly coated on the surface of the Bi2Te3 nanotubes consisting of a bundle of two. Furthermore, it indicated that minimal strain is present at the interface between MWCNTs and Bi2Te3 nanotubes which can add additional lattice scattering, and hence, the lattice contribution to the thermal conductivity can be further reduced due to phonon-blocking phenomena. Analytical analysis results further indicated that the MWCNTs incorporated in the nanocomposites showed less disorder and successfully formation of the nanocomposites. We believe that our approach provides the advantages of simplicity, efficient and opens a new way to prepare a novel 1D thermoelectric nanocomposite which can further improve the thermophysical properties for future energy-harvesting applications and thermoelectric devices.