Magnetic field filtering of the boundary supercurrent in unconventional metal NiTe2-based Josephson junctions.

Topological materials with boundary (surface/edge/hinge) states have attracted tremendous research interest. Additionally, unconventional (obstructed atomic) materials have recently drawn lots of attention owing to their obstructed boundary states. Experimentally, Josephson junctions (JJs) constructed on materials with boundary states produce the peculiar boundary supercurrent, which was utilized as a powerful diagnostic approach. Here, we report the observations of boundary supercurrent in NiTe2-based JJs. Particularly, applying an in-plane magnetic field along the Josephson current can rapidly suppress the bulk supercurrent and retain the nearly pure boundary supercurrent, namely the magnetic field filtering of supercurrent. Further systematic comparative analysis and theoretical calculations demonstrate the existence of unconventional nature and obstructed hinge states in NiTe2, which could produce hinge supercurrent that accounts for the observation. Our results reveal the probable hinge states in unconventional metal NiTe2, and demonstrate in-plane magnetic field as an efficient method to filter out the bulk contributions and thereby to highlight the hinge states hidden in topological/unconventional materials.

Technology and Integration Roadmap for Optoelectronic Memristor.

Optoelectronic memristors (OMs) have emerged as a promising optoelectronic Neuromorphic computing paradigm, opening up new opportunities for neurosynaptic devices and optoelectronic systems. These OMs possess a range of desirable features including minimal crosstalk, high bandwidth, low power consumption, zero latency, and the ability to replicate crucial neurological functions such as vision and optical memory. By incorporating large-scale parallel synaptic structures, OMs are anticipated to greatly enhance high-performance and low-power in-memory computing, effectively overcoming the limitations of the von Neumann bottleneck. However, progress in this field necessitates a comprehensive understanding of suitable structures and techniques for integrating low-dimensional materials into optoelectronic integrated circuit platforms. This review aims to offer a comprehensive overview of the fundamental performance, mechanisms, design of structures, applications, and integration roadmap of optoelectronic synaptic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review seeks to provide insights into emerging technologies and future prospects that are expected to drive innovation and widespread adoption in the near future.

Stepwise Alloying in Liquid-like Solid Solutions to Achieve Crystallographic Distortion for Regulating Thermoelectric Transport Behavior.

With the surge of energy consumption, environmental-protection Cu2-xSe thermoelectric materials are increasingly attracting attention. In this work, multilayered structures are constructed in Cu2-xSe solid solutions by alloying (SnSe)0.75(AgBiSe2)0.25, which strongly scatters full-wavelength phonons by carefully regulating the crystallographic distortion. By using the stepwise alloying strategies, crystallographic distortion and the resultant strain fields presented in microstructure were strengthened markedly, which enhanced the phonon scattering. Meanwhile, by adjusting the coalloying content of Ag, Bi, and Sn elements, the carrier and phonon transports were well decoupled in p-type Cu2-xSe, and the thermoelectric performance was significantly enhanced. By optimized power factor as well as depressed heat transport originating from the moderate coalloying, the maximum zT of 1.23 at 750 K was achieved in Cu1.9Se - 1 wt % (SnSe)0.75(AgBiSe2)0.25. This study indicated that the stepwise alloying strategy was a suitable method for optimizing zT of Cu2-xSe.

Enhanced Thermoelectric Properties of Nb-Doped Ti(FeCoNi)Sb Pseudo-Ternary Half-Heusler Alloys Prepared Using the Microwave Method.

Pseudo-ternary half-Heusler thermoelectric materials, which are formed by filling the B sites of traditional ternary half-Heusler thermoelectric materials of ABX with equal atomic proportions of various elements, have attracted more and more attention due to their lower intrinsic lattice thermal conductivity. High-purity and relatively dense Ti1-xNbx(FeCoNi)Sb (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1) alloys were prepared via microwave synthesis combined with rapid hot-pressing sintering, and their thermoelectric properties are investigated in this work. The Seebeck coefficient was markedly increased via Nb substitution at Ti sites, which resulted in the optimized power factor of 1.45 µWcm-1K-2 for n-type Ti0.93Nb0.07(FeCoNi)Sb at 750 K. In addition, the lattice thermal conductivity was largely decreased due to the increase in phonon scattering caused by point defects, mass fluctuation and strain fluctuation introduced by Nb-doping. At 750 K, the lattice thermal conductivity of Ti0.97Nb0.03(FeCoNi)Sb is 2.37 Wm-1K-1, which is 55% and 23% lower than that of TiCoSb and Ti(FeCoNi)Sb, respectively. Compared with TiCoSb, the ZT of the Ti1-xNbx(FeCoNi)Sb samples were significantly increased. The average ZT values of the Nb-doped pseudo-ternary half-Heusler samples were dozens of times that of the TiCoSb prepared using the same process.

Chirality selective magnon-phonon hybridization and magnon-induced chiral phonons in a layered zigzag antiferromagnet.

Two-dimensional (2D) magnetic systems possess versatile magnetic order and can host tunable magnons carrying spin angular momenta. Recent advances show angular momentum can also be carried by lattice vibrations in the form of chiral phonons. However, the interplay between magnons and chiral phonons as well as the details of chiral phonon formation in a magnetic system are yet to be explored. Here, we report the observation of magnon-induced chiral phonons and chirality selective magnon-phonon hybridization in a layered zigzag antiferromagnet (AFM) FePSe3. With a combination of magneto-infrared and magneto-Raman spectroscopy, we observe chiral magnon polarons (chiMP), the new hybridized quasiparticles, at zero magnetic field. The hybridization gap reaches 0.25 meV and survives down to the quadrilayer limit. Via first principle calculations, we uncover a coherent coupling between AFM magnons and chiral phonons with parallel angular momenta, which arises from the underlying phonon and space group symmetries. This coupling lifts the chiral phonon degeneracy and gives rise to an unusual Raman circular polarization of the chiMP branches. The observation of coherent chiral spin-lattice excitations at zero magnetic field paves the way for angular momentum-based hybrid phononic and magnonic devices.

Recent progress in the synthesis of novel two-dimensional van der Waals materials.

The last decade has witnessed the significant progress of physical fundamental research and great success of practical application in two-dimensional (2D) van der Waals (vdW) materials since the discovery of graphene in 2004. To date, vdW materials is still a vibrant and fast-expanding field, where tremendous reports have been published covering topics from cutting-edge quantum technology to urgent green energy, and so on. Here, we briefly review the emerging hot physical topics and intriguing materials, such as 2D topological materials, piezoelectric materials, ferroelectric materials, magnetic materials and twistronic heterostructures. Then, various vdW material synthetic strategies are discussed in detail, concerning the growth mechanisms, preparation conditions and typical examples. Finally, prospects and further opportunities in the booming field of 2D materials are addressed.

Mimicking Neuroplasticity via Ion Migration in van der Waals Layered Copper Indium Thiophosphate.

Artificial synaptic devices are the essential components of neuromorphic computing systems, which are capable of parallel information storage and processing with high area and energy efficiencies, showing high promise in future storage systems and in-memory computing. Analogous to the diffusion of neurotransmitter between neurons, ion-migration-based synaptic devices are becoming promising for mimicking synaptic plasticity, though the precise control of ion migration is still challenging. Due to the unique 2D nature and highly anisotropic ionic transport properties, van der Waals layered materials are attractive for synaptic device applications. Here, utilizing the high conductivity from Cu+ -ion migration, a two-terminal artificial synaptic device based on layered copper indium thiophosphate is studied. By controlling the migration of Cu+ ions with an electric field, the device mimics various neuroplasticity functions, such as short-term plasticity, long-term plasticity, and spike-time-dependent plasticity. The Pavlovian conditioning and activity-dependent synaptic plasticity involved neural functions are also successfully emulated. These results show a promising opportunity to modulate ion migration in 2D materials through field-driven ionic processes, making the demonstrated synaptic device an intriguing candidate for future low-power neuromorphic applications.

Lipase-Catalyzed Reactive Extrusion: Copolymerization of ε-Caprolactone and ω-Pentadecalactone.

This study assesses the use of immobilized lipase catalyst N435 during reactive extrusion (REX) versus magnetically stirred bulk and solution reaction conditions for the copolymerization of ε-caprolactone with ω-pentadecalactone (CL/PDL 1:1 molar). N435-catalyzed REX for reaction times from 1 to 3 h results in total %-monomer conversion, Mn , and D values increase from 92.7% to 98.8%, 36.1 to 51.3 kDa, and 1.85 to 1.96, respectively. Diad fraction analysis by quantitative 13 C NMR reveals that, after just 1 h, rapid N435-catalyzed transesterification reactions occur that give random copolyesters. In contrast, for bulk polymerization with magnetic stirring in round bottom flasks, reaction times from 1 to 3 h result in the following: Mn  increases from 12.4 to 25.6 kDa, D decreases from 2.98 to 1.87, and the randomness index increases from 0.74 and 0.86 as PDL*-PDL diads are dominant. These results highlight that REX avoids problems associated with internal batch mixing that are encountered in bulk polymerizations. In sharp contrast to a previous study of 1:1 molar PDL/δ-valerolactone (VL) copolymerizations by N435-catalyzed REX, VL %-conversion increases to just 40.1% in 1 h whereas CL reaches 94.7%.

Toward 2D Magnets in the (MnBi2 Te4 )(Bi2 Te3 )n Bulk Crystal.

2D magnets and their engineered magnetic heterostructures are intriguing materials for both fundamental physics and application prospects. On the basis of the recently discovered intrinsic magnetic topological insulators (MnBi2 Te4 )(Bi2 Te3 )n , here, a new type of magnet, in which the magnetic layers are separated by a large number of non-magnetic layers and become magnetically independent, is proposed. This magnet is named as a single-layer magnet, regarding the vanishing interlayer exchange coupling. Theoretical calculations and magnetization measurements indicate that, the decoupling of the magnetic layers starts to emerge from n = 2 and 3, as revealed by a unique slow-relaxation behavior below a ferromagnetic-type transition at Tc = 12-14 K. Magnetization data analysis shows that the proposed new magnetic states have a strong uniaxial anisotropy along the c-axis, forming an Ising-type magnetic structure, where Tc is the ordering temperature for each magnetic layer. The characteristic slow relaxation, which exists only along the c-axis but is absent along the ab plane, can be ascribed to interlayer coherent spin rotation and/or intralayer domain wall movement. The present results will stimulate further theoretical and experimental investigations for the prototypical magnetic structures, and their combination with the topological surface states may lead to exotic physical properties.

Roles of Polyethylenimine Ethoxylated in Efficiently Tuning the Thermoelectric Performance of Poly(3,4-ethylenedioxythiophene)-Rich Nanocrystal Films.

The regulation of oxidation levels is of great importance as an efficient way to optimize the thermoelectric (TE) performance of conducting polymers. Many efforts have been devoted to the acquisition of a high TE performance for poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by oxidation/reduction post treatment to achieve an effective compromise. However, a strong oxidant/reductant is usually employed to tune the TE performance of PEDOT:PSS with high electrical conductivity (σ) and Seebeck coefficient ( S), and it also presents a number of operational challenges depending on a fast reaction rate. Herein, nontoxic polyethylenimine ethoxylated (PEIE) served as a reductant to successfully realize an enhanced S for PEDOT:PSS, besides playing a significant anion-blocking role in enabling the efficient modulation of the oxidation level by sulfuric acid (H2SO4) with a longer operating time. Eventually, a good PEDOT-rich nanocrystal is achieved by a sequential dipping process in PEIE/ethylene glycol and H2SO4 solutions. The large TE power factor of 133 µW m-1 K-2 can be ascribed to the good formation of PEDOT-rich nanocrystals and an effective compromise between σ and S of PEDOT:PSS films. A mechanism was elucidated for the efficient regulation of σ and S enabling high performance of organic TE materials.

Highly Conductive Hydrogel Polymer Fibers toward Promising Wearable Thermoelectric Energy Harvesting.

The requirement of a portable electron is functioning as a driving force for a wearable energy instrument. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), as one of the most promising organic electron materials, has been widely studied in energy conversion devices. However, the efforts for PEDOT:PSS fibers are insufficient to boost the development of wearable thermoelectric energy harvesting. Here, a highly conductive p-type PEDOT:PSS fiber was produced by gelation process, which was 3 orders of magnitude higher than that of previous hydrogel fibers. Surprisingly, a post-treatment with organic solvents such as ethylene glycol and dimethyl sulfoxide tripled their electrical conductivity with an only 5% decreased Seebeck coefficient, consequently leading to an optimized thermoelectric power factor. Furthermore, we assembled a p-n-type thermoelectric device connecting five pairs of p-type PEDOT:PSS fibers and n-type carbon nanotube fibers. This fiber-based device displayed an acceptable output voltage of 20.7 mV and a power density of 481.2 µW·cm-2 with a temperature difference of ∼60 K, which might pave the way for the development of organic thermoelectric fibers for wearable energy harvesting.

Dual-functional aniline-assisted wet-chemical synthesis of bismuth telluride nanoplatelets and their thermoelectric performance.

The wet-chemical approach is of great significance for the synthesis of two-dimensional (2D) bismuth telluride nanoplatelets as a potential thermoelectric (TE) material. Herein, we proposed a simple and effective solution method with the assistance of aniline for the fabrication of bismuth telluride nanoplatelets at a low temperature of 100 °C. The choice of aniline with its dual function avoided the simultaneous use of a capping regent and a toxic reductant. The as-synthesized nanoplatelets have a large size of more than 900 × 500 nm2 and a small thickness of 15.4 nm. The growth of bismuth telluride nanoplatelets are related to the Bi/Te ratio of precursors indicating that a larger content of the Bi precursor is more conducive to the formation of 2D nanoplatelets. The bismuth telluride nanoplatelets pressed into a pellet show a smaller electrical resistivity (∼6.5 × 10-3 Ω · m) and a larger Seebeck coefficient (-135 µV K-1), as well as a lower thermal conductivity (0.27 W m-1 K-1) than those of nanoparticles. The next goal is to further reduce the electrical resistivity and optimize the TE performance by disposing of the residual reactant of aniline adsorbed on the surface of the nanoplatelets.

Solution-processed two-dimensional layered heterostructure thin-film with optimized thermoelectric performance.

Graphene-based two-dimensional (2D) heterostructures have ignited intensive interest in recent years because of their excellent physical performance. However, the most common method to prepare them uses chemical vapor deposition, which has the drawback of a complex process unsuitable for large-scale production. In this respect, reduced graphene oxide and transitional metal dichalcogenides (rGO-TMDs) composite thin-films were fabricated by a simple solution-processing method and their thermoelectric performance was investigated systematically. Addition of rGO nanosheets (NSs) efficiently improved the electrical conductivity of MoS2 and WS2 (MS2) NSs, due to the excellent electron transport performance of rGO. Furthermore, it should be noted that an optimized content of rGO can effectively avoid direct contact between TMDs NSs by forming a rGO-TMDs heterojunction, leading to significantly increased electrical conductivity and a slight variation in its Seebeck coefficient. Our work obtained high thermoelectric performance heterostructures by inducing two kinds of layered materials using a simple method that may potentially be applied to other 2D layered materials to construct heterostructures for energy conversion.

Thermoelectric performance of restacked MoS2 nanosheets thin-film.

MoS2 has been predicted to be an excellent thermoelectric material due to its large intrinsic band gap and high carrier mobility. In this work, we exfoliated bulk MoS2 by the assistance of lithium intercalation and fabricated the restacked MoS2 thin-film using a simple filtration technique. These MoS2 thin-films with different thickness showed different thermoelectric performance. It was found that with the increase of thickness, carrier concentration, electrical conductivity and Seebeck coefficient all showed an increasing trend. In particular, the maximum Seebeck coefficient was able to reach 93.5 µV K(-1). This high thermopower indicates that MoS2 will have ideal thermoelectric performance in the future through optimizing its structure. The highest figure of merit (ZT = 0.01) is calculated in this experiment.