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<jats:p>Two novel nonlinear mode coupling processes for reversed shear Alfvén eigenmode (RSAE) nonlinear saturation are proposed and investigated. In the first process, the RSAE nonlinearly couples to a co-propagating toroidal Alfvén eigenmode (TAE) with the same toroidal and poloidal mode numbers, and generates a geodesic acoustic mode. In the second process, the RSAE couples to a counter-propagating TAE and generates an ion acoustic wave quasi-mode. The condition for the two processes to occur is favored during current ramp. Both the processes contribute to effectively saturate the Alfvénic instabilities, as well as nonlinearly transfer of energy from energetic fusion alpha particles to fuel ions in burning plasmas.</jats:p>

<jats:p>Interaction between shear Alfvén wave (SAW) and energetic particles (EPs) is one of major concerns in magnetically confined plasmas since it may lead to excitation of toroidal symmetry breaking collective instabilities, thus enhances loss of EPs and degrades plasma confinement. In the last few years, Alfvénic zoology has been constructed on HL-2A tokamak and series of EPs driven instabilities, such as toroidal Alfvén eigenmodes (TAEs), revered shear Alfvén eigenmodes (RSAEs), beta induced Alfvén eigenmodes (BAEs), Alfvénic ion temperature gradient (AITG) modes and fishbone modes, have been observed and investigated. Those Alfvénic fluctuations show frequency chirping behaviors through nonlinear wave-particle route, and contribute to generation of axisymmetric modes by nonlinear wave-wave resonance in the presence of strong tearing modes. It is proved that the plasma confinement is affected by Alfvénic activities from multiple aspects. The RSAEs resonate with thermal ions, and this results in an energy diffusive transport process while the nonlinear mode coupling between core-localized TAEs and tearing modes trigger avalanche electron heat transport events. Effective measures have been taken to control SAW fluctuations and the fishbone activities are suppressed by electron cyclotron resonance heating. Those experimental results will not only contribute to better understandings of energetic particles physics, but also provide technology bases for active control of Alfvénic modes on International Thermonuclear Experimental Reactor (ITER) and Chinese Fusion Engineering Testing Reactor (CFETR).</jats:p>

<jats:p>Due to their unique structure properties, most of the electrides that possess extra electrons locating in interstitial regions as anions are insulators. Metallic and superconducting electrides are very rare under ambient conditions. We systematically search possible compounds in Ca–S systems stabilized under various pressures up to 200 GPa, and investigate their crystal structures and properties using first-principles calculations. We predict a series of novel stoichiometries in Ca–S systems as potential superconductors, including <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic> Ca<jats:sub>3</jats:sub>S, <jats:italic>P</jats:italic>4mbm Ca<jats:sub>3</jats:sub>S, Pnma Ca<jats:sub>2</jats:sub>S, <jats:italic>Cmcm</jats:italic> Ca<jats:sub>2</jats:sub>S, <jats:italic>Fddd</jats:italic> CaS<jats:sub>2</jats:sub>, <jats:italic>Immm</jats:italic> CaS<jats:sub>3</jats:sub> and <jats:italic>C</jats:italic>2/<jats:italic>c</jats:italic> CaS<jats:sub>4</jats:sub>. The <jats:italic>P</jats:italic>4<jats:italic>mbm</jats:italic> Ca<jats:sub>3</jats:sub>S phase exhibits a maximum <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> value of ∼20 K. It is interesting to notice that the <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic> Ca<jats:sub>3</jats:sub>S and <jats:italic>Pnma</jats:italic> Ca<jats:sub>2</jats:sub>S stabilized at 60 and 50 GPa behave as superconducting electrides with critical temperatures <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> of 7.04 K and 0.26 K, respectively. More importantly, our results demonstrate that <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic> Ca<jats:sub>3</jats:sub>S and <jats:italic>Pnma</jats:italic> Ca<jats:sub>2</jats:sub>S are dynamically stable at 5 GPa and 0 GPa, respectively, indicating a high possibility to be quenched to ambient condition or synthesized using the large volume press.</jats:p>

<jats:p>Tunnel oxide passivated contact solar cells have evolved into one of the most promising silicon solar cell concepts of the past decade, achieving a record efficiency of 25%. We study the transport mechanisms of realistic tunnel oxide structures, as encountered in tunnel oxide passivating contact (TOPCon) solar cells. Tunneling transport is affected by various factors, including oxide layer thickness, hydrogen passivation, and oxygen vacancies. When the thickness of the tunnel oxide layer increases, a faster decline of conductivity is obtained computationally than that observed experimentally. Direct tunneling seems not to explain the transport characteristics of tunnel oxide contacts. Indeed, it can be shown that recombination of multiple oxygen defects in <jats:italic>a</jats:italic>-SiO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> can generate atomic silicon nanowires in the tunnel layer. Accordingly, new and energetically favorable transmission channels are generated, which dramatically increase the total current, and could provide an explanation for our experimental results. Our work proves that hydrogenated silicon oxide (SiO<jats:sub> <jats:italic>x</jats:italic> </jats:sub>:H) facilitates high-quality passivation, and features good electrical conductivity, making it a promising hydrogenation material for TOPCon solar cells. By carefully selecting the experimental conditions for tuning the SiO<jats:sub> <jats:italic>x</jats:italic> </jats:sub>:H layer, we anticipate the simultaneous achievement of high open-circuit voltage and low contact resistance.</jats:p>

<jats:p>We report a systematic investigation on the evolution of the structural and physical properties, including the charge density wave (CDW) and superconductivity of the polycrystalline CuIr<jats:sub>2</jats:sub>Te<jats:sub>4−<jats:italic>x</jats:italic> </jats:sub>I<jats:sub> <jats:italic>x</jats:italic> </jats:sub> for 0.0 ≤ <jats:italic>x</jats:italic> ≤ 1.0. X-ray diffraction results indicate that both of <jats:italic>a</jats:italic> and <jats:italic>c</jats:italic> lattice parameters increase linearly when 0.0 ≤ <jats:italic>x</jats:italic> ≤ 1.0. The resistivity measurements indicate that the CDW is destabilized with slight <jats:italic>x</jats:italic> but reappears at <jats:italic>x</jats:italic> ≥ 0.9 with very high <jats:italic>T</jats:italic> <jats:sub>CDW</jats:sub>. Meanwhile, the superconducting transition temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> enhances as <jats:italic>x</jats:italic> increases and reaches a maximum value of around 2.95 K for the optimal composition CuIr<jats:sub>2</jats:sub>Te<jats:sub>1.9</jats:sub>I<jats:sub>0.1</jats:sub> followed by a slight decrease with higher iodine doping content. The specific heat jump (Δ<jats:italic>C</jats:italic>/<jats:italic>γT</jats:italic> <jats:sub>c</jats:sub>) for the optimal composition CuIr<jats:sub>2</jats:sub>Te<jats:sub>3.9</jats:sub>I<jats:sub>0.1</jats:sub> is approximately 1.46, which is close to the Bardeen–Cooper–Schrieffer value of 1.43, indicating that it is a bulk superconductor. The results of thermodynamic heat capacity measurements under different magnetic fields [<jats:italic>C</jats:italic> <jats:sub>p</jats:sub>(<jats:italic>T</jats:italic>, <jats:italic>H</jats:italic>)], magnetization <jats:italic>M</jats:italic>(<jats:italic>T</jats:italic>, <jats:italic>H</jats:italic>) and magneto-transport <jats:italic>ρ</jats:italic>(<jats:italic>T</jats:italic>, <jats:italic>H</jats:italic>) measurements further suggest that CuIr<jats:sub>2</jats:sub>Te<jats:sub>4−<jats:italic>x</jats:italic> </jats:sub>I<jats:sub> <jats:italic>x</jats:italic> </jats:sub> bulks are type-II superconductors. Finally, an electronic phase diagram for this CuIr<jats:sub>2</jats:sub>Te<jats:sub>4−<jats:italic>x</jats:italic> </jats:sub>I<jats:sub> <jats:italic>x</jats:italic> </jats:sub> system has been constructed. The present study provides a suitable material platform for further investigation of the interplay of the CDW and superconductivity.</jats:p>

<jats:p>We report transport measurements on Josephson junctions consisting of Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> topological insulator (TI) thin films contacted by superconducting Nb electrodes. For a device with junction length <jats:italic>L</jats:italic> = 134 nm, the critical supercurrent <jats:italic>I</jats:italic> <jats:sub>c</jats:sub> can be modulated by an electrical gate which tunes the carrier type and density of the TI film. <jats:italic>I</jats:italic> <jats:sub>c</jats:sub> can reach a minimum when the TI is near the charge neutrality regime with the Fermi energy lying close to the Dirac point of the surface state. In the p-type regime the Josephson current can be well described by a short ballistic junction model. In the n-type regime the junction is ballistic at 0.7 K &lt; <jats:italic>T</jats:italic> &lt; 3.8 K while for <jats:italic>T</jats:italic> &lt; 0.7 K the diffusive bulk modes emerge and contribute a larger <jats:italic>I</jats:italic> <jats:sub>c</jats:sub> than the ballistic model. We attribute the lack of diffusive bulk modes in the p-type regime to the formation of p–n junctions. Our work provides new clues for search of Majorana zero mode in TI-based superconducting devices.</jats:p>

<jats:p>We report the discovery of superconductivity and detailed normal-state physical properties of RbV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> single crystals with V kagome lattice. RbV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> single crystals show a superconducting transition at <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> ∼ 0.92 K. Meanwhile, resistivity, magnetization and heat capacity measurements indicate that it exhibits anomalies of properties at <jats:italic>T</jats:italic> <jats:sup>*</jats:sup> ∼ 102–103 K, possibly related to the formation of charge ordering state. When <jats:italic>T</jats:italic> is lower than <jats:italic>T</jats:italic> <jats:sup>*</jats:sup>, the Hall coefficient <jats:italic>R</jats:italic> <jats:sub>H</jats:sub> undergoes a drastic change and sign reversal from negative to positive, which can be partially explained by the enhanced mobility of hole-type carriers. In addition, the results of quantum oscillations show that there are some very small Fermi surfaces with low effective mass, consistent with the existence of multiple highly dispersive Dirac band near the Fermi energy level.</jats:p>

<jats:p>Twisted van der Waals bilayers provide an ideal platform to study the electron correlation in solids. Of particular interest is the 30° twisted bilayer honeycomb lattice system, which possesses an incommensurate moiré pattern, and uncommon electronic behaviors may appear due to the absence of phase coherence. Such a system is extremely sensitive to further twist and many intriguing phenomena will occur. Based on first-principles calculations we show that, for further twist near 30°, there could induce dramatically different dielectric behaviors of electron between left and right-twisted cases. Specifically, it is found that the left and right twists show suppressed and amplified dielectric response under vertical electric field, respectively. Further analysis demonstrate that such an exotic dielectric property can be attributed to the stacking dependent charge redistribution due to twist, which forms twist-dependent pseudospin textures. We will show that such pseudospin textures are robust under small electric field. As a result, for the right-twisted case, there is almost no electric dipole formation exceeding the monolayer thickness when the electric field is applied. Whereas for the left case, the system could even demonstrate negative susceptibility, i.e., the induced polarization is opposite to the applied field, which is very rare in the nature. Such findings not only enrich our understanding on moiré systems but also open an appealing route toward functional 2D materials design for electronic, optical and even energy storage devices.</jats:p>

<jats:p>Compared to AgNbO<jats:sub>3</jats:sub> based ceramics, the experimental investigations on the single crystalline AgNbO<jats:sub>3</jats:sub>, especially the ground state and ferroic domain structures, are not on the same level. Here, based on successfully synthesized AgNbO<jats:sub>3</jats:sub> single crystal using a flux method, we observed the coexistence of ferroelastic and ferroelectric domain structures by a combination study of polarized light microscopy and piezoresponse force microscopy. This finding may provide a new aspect for studying AgNbO<jats:sub>3</jats:sub>. The result also suggests a weak electromechanical response from the ferroelectric phase of AgNbO<jats:sub>3</jats:sub>, which is also supported by the transmission electron microscope characterization. Our results reveal that the AgNbO<jats:sub>3</jats:sub> single crystal is in a polar ferroelectric phase at room temperature, clarifying its ground state which is controversial from the AgNbO<jats:sub>3</jats:sub> ceramic materials.</jats:p>

<jats:p>Brucite Mg(OH)<jats:sub>2</jats:sub> is an archetypal hydrous mineral and it has attracted a great deal of attention. However, little is known about the evolution of hydroxyl groups in brucite with respect to subduction fluids. We carried out Raman measurements up to 15.4 GPa and 874 K via an externally heated diamond anvil cell, investigating the stability of brucite under the conditions relevant to subducting slabs. The hydroxyl vibration mode <jats:italic>A</jats:italic> <jats:sub>1_g</jats:sub>(I) of brucite is weakened under simultaneous high pressure-temperature conditions. Meanwhile, the presence of carbonated solution can destabilize the hydroxyl groups of brucite at low pressure. Our results suggest that brucite releases water when reacting with hydrogen carbonate ion to form magnesite MgCO<jats:sub>3</jats:sub> in subduction zones. This implies that the global water cycle is largely coupled with the deep carbon cycle in Earth’s interior.</jats:p>