Jiuxiang Dai

Author(s): F. Balduini, L. Rocchino, A. Molinari, T. Paul, G. Mariani, V. Hasse, C. Felser, C. Zota, H. Schmid, and B. Gotsmann

Combining quantum oscillations and transverse-electron focusing experiments enables the measurement of the Weyl Fermi surface and separation between Weyl points in NbP.

[Phys. Rev. Lett. 133, 096601] Published Wed Aug 28, 2024

This article reviews the latest research advancements in the critical interplay between 2D ferroelectricity and magnetic, valleytronic, mechanical, and optical phenomena. It elucidates the role of fundamental degrees of freedom-charge, spin, valley, lattice, and excitation-in driving these interactions, and offers an in-depth analysis of theoretical insights, highlighting the unique properties of 2D ferroelectric materials.

Abstract

2D ferroelectric materials present promising applications in information storage, sensor technology, and optoelectronics through their coupling with magnetics/valleytronics, mechanics, and optics, respectively. The integration of 2D ferroelectrics with magnetism enhances data storage density in memory devices by enabling electric-field-controlled magnetic states. Ferroelectric-valley coupling holds promise for high-speed, low-energy electronics by leveraging the electrical control of valley polarization. Ferroelectric-strain coupling results in various polar topologies, with potential applications in high-density data storage technologies and sensor devices. Moreover, the coupling between ferroelectrics and optics facilitates the development of nonlinear photonics based on ferroelectric materials. This review summarizes the latest theoretical progress in the coupling mechanisms, including the Dzyaloshinskii-Moriya-interaction-induced magnetoelectric coupling, symmetry-linked ferroelectric-valley coupling, ferroelectric-strain-coupling-generated polar topologies, and second-harmonic generation through ferroelectric-light interactions. The current challenges and future opportunities in harnessing the coupling in 2D ferroelectric materials for multifunctional applications are provided.

In misfit layer compound (LaSe)_1.14(NbSe₂), LaSe layers effectively reduce the dimensionality of NbSe₂ layers, which makes spin-orbit coupling become apparent. The weak antilocalization effect and spin fluctuations caused by spin-orbit coupling are detected through transport and NMR experiments. This study proves that MCLs are a suitable platform for exploring exotic physical properties of transition metal dichalcogenides within the 2D limit.

Abstract

Spin-orbit coupling (SOC) has significant effects on the superconductivity and magnetism of transition metal dichalcogenides (TMDs) at the 2D limit. Although 2D TMD samples possess many exotic properties different from those of bulk samples, experimental characterization in this field is still limited, especially for magnetism. Recent studies have revealed that bulk misfit layer compounds (MLCs) with (LaSe)_1.14(NbSe₂)_{n = 1,2} exhibit an Ising superconductivity similar to that of heavily electron-doped NbSe₂ monolayers. This offers an opportunity to study the effect of SOC on the magnetism of 2D TMDs. Here, the possible SOC effect in (LaSe)_1.14(NbSe₂) is investigated by measuring nuclear magnetic resonance (NMR) and electrical transport. It is found that the LaSe layer not only functions as a charge reservoir for transferring electrons into the NbSe₂ layer but also remarkably influences the local electronic environment around the ⁹³Nb nuclei. More importantly, the significant SOC induces both a weak antilocalization (WAL) effect and anisotropic spin fluctuations in noncentrosymmetric NbSe₂ layers. The present work contributes to a deep understanding of the role of the SOC effect in 2D TMDs and supports MCLs as an intriguing platform for exploring exotic physical properties within the 2D limit.

Through in situ high-energy synchrotron-radiation XRD and molecular dynamic growth simulations, the nanosecond and even picoseconds switching behavior of elemental Te is enabled by the narrow bandgap of Te and, respectively, a decrease (increase) in the interchain atomic distances (intrachain bond lengths) after electronic excitation.

Abstract

Elemental tellurium, a prototypical one-dimensional van der Waals material, has recently been found to crystallize quickly from the liquid on a nanosecond timescale, yet the inherent mechanism is not clear. Here, by combining in situ high-energy synchrotron radiation X-ray diffraction with ab initio molecular-dynamics simulation, it is found that trigonal crystalline Te completely melts into the liquid phase at 450 °C, and recrystallizes into the trigonal phase for temperatures lower than 380 °C without the formation of any other phase. This directly confirms the recent proposal of a crystal-liquid-crystal phase transition in this material underlying the observed electrical-switching process. Atomic-scale, melt-quench computer simulations show that liquid Te is capable of crystallizing within a time of 25 ps in the vicinity of templating crystallization interfaces. This ultrafast crystallization ability of Te can be understood as being due to delayed Peierls distortions during a quench and therefore a high atomic mobility over a wide range of temperature. This finding opens the way to develop a crystal-liquid-crystal, phase-transition-based selector switch with an ultrafast switching speed.

In this review, the physicochemical principles of mechanochemistry are first clarified. Based on this foundation, the research basis and cutting-edge scientific achievements in four areas are introduced: solid-state organic chemistry, polymers, interface science, and biomechanochemistry. Special emphasis is placed on the applications of mechanochemistry in materials science. Furthermore, the perspectives and insights on the research challenges and potential future directions are offered.

Abstract

Mechanochemistry is an emerging research field at the interface of physics, mechanics, materials science, and chemistry. Complementary to traditional activation methods in chemistry, such as heat, electricity, and light, mechanochemistry focuses on the activation of chemical reactions by directly or indirectly applying mechanical forces. It has evolved as a powerful tool for controlling chemical reactions in solid state systems, sensing and responding to stresses in polymer materials, regulating interfacial adhesions, and stimulating biological processes. By combining theoretical approaches, simulations and experimental techniques, researchers have gained intricate insights into the mechanisms underlying mechanochemistry. In this review, the physical chemistry principles underpinning mechanochemistry are elucidated and a comprehensive overview of recent significant achievements in the discovery of mechanically responsive chemical processes is provided, with a particular emphasis on their applications in materials science. Additionally, The perspectives and insights into potential future directions for this exciting research field are offered.

A large-sized single-crystalline 2D COFs with enhanced structural integrity and exceptional chemical and electrochemical stability was prepared. Through a simple composite process with CNTs, the resultant COF-CNT core–shell hybrids exhibit outstanding performance as lithium-ion storage materials in lithium-ion batteries.

Abstract

A large-sized single crystalline 2D COFs with excellent crystallinity and stability was prepared through the traditional thermal solvent method. The electrochemical performance can be significantly enhanced using a straightforward hybrid approach that involves in situ growth of the 2D COFs on multi-walled carbon nanotubes (MWCNTs). Both the advantages of COFs and CNTs are mutually enhanced. The single-crystalline feature of the obtained COFs improves the structural integrity and brings excellent chemical and electrochemical stabilities for lithium-ion battery applications. The resultant COF-CNT core–shell hybrids greatly improved the conductivity and demonstrated excellent lithium-ion storage performance with a high capacity of 228 mAh g⁻¹ (0.2 A g⁻¹).

Nature Reviews Materials, Published online: 27 August 2024; doi:10.1038/s41578-024-00719-5

An article in Nature reports the observation of giant terahertz magnetoelectric oscillations in a van der Waals multiferroic and presents a theoretical model that elucidates their origin.

Nature Electronics, Published online: 28 August 2024; doi:10.1038/s41928-024-01241-w

The further development of transistors based on two-dimensional transition metal dichalcogenides faces various issues, starting with the high density of defects typically found in the materials.

Nature, Published online: 28 August 2024; doi:10.1038/s41586-024-07872-5

Chemical lithiation of two-dimensional transition metal dichalcogenides can be accelerated by up to six orders of magnitude using low-power illumination and a variety of phase transition agents.

Highly crystalline borophene nanosheets were successfully synthesized on an aluminum foil substrate, exhibiting two characteristic borophene structures: β₁₂-borophene and α‘-4H-borophene. The anisotropic memory behavior of quasi-continuous borophene nanosheet films has been observed, which is characterized by volatile memory in the vertical direction and non-volatile memory in the horizontal direction.

Abstract

Neuromorphic computing, marked by its parallel computational abilities and low power usage, has become pivotal in advancing artificial intelligence. However, the advancement of neuromorphic computing has faced significant obstacles due to the performance limitations of traditional memory devices struggling with high power consumption and limited reliability. Two-dimensional (2D) materials have been extensively investigated as high-performance memristive materials, but they are often restricted by fixed memristive properties, which complicate circuit design and limit flexibility. Here, we report that multilayer borophene nanosheets represent a breakthrough material, displaying anisotropic variable memristive properties. The nanosheets, comprising semiconductor α’-4H-borophene sheets and metal β₁₂-borophene sheets, have been synthesized on aluminum foil surface through chemical vapor deposition method. The multilayer borophene nanosheets exhibit volatile memory behavior in the vertical direction and non-volatile memory behavior in the planar direction. This innovative class of 2D nanosheets not only overcomes the limitations of conventional memory devices but also expands the potential applications of borophene-based memories in information storage and in-memory computing.

Nature Materials, Published online: 27 August 2024; doi:10.1038/s41563-024-01987-w

A metastable pentagonal PdTe2 monolayer has been synthesized through symmetry-driven epitaxy, utilizing lattice matching with a Pd(100) substrate. The lattices, phonons and electronic structures of this phase have been studied.

Nature Materials, Published online: 27 August 2024; doi:10.1038/s41563-024-01985-y

The authors experimentally demonstrate twist-angle modulation of the spin texture in graphene-based heterostructures.

Nature Materials, Published online: 28 August 2024; doi:10.1038/s41563-024-01986-x

New two-dimensional semiconductors may exhibit properties beyond inherent semiconducting attributes. Here the authors report protonated semiconducting III–V-derived van der Waals crystals with memristive properties.

Nature Nanotechnology, Published online: 29 August 2024; doi:10.1038/s41565-024-01755-6

The third-order nonlinear Hall effect is observed in the quantum Hall states in graphene.

Nature Materials, Published online: 30 August 2024; doi:10.1038/s41563-024-01999-6

Inspired by non-trivial band topology and the variety of correlated electronic phases in moiré superlattices formed in van der Waals materials, scientists are finding alternative material platforms to exploit the rich phenomena arising from the twist-angle degree of freedom.

Nature Materials, Published online: 30 August 2024; doi:10.1038/s41563-024-01983-0

Evolving materials

npj 2D Materials and Applications, Published online: 02 September 2024; doi:10.1038/s41699-024-00493-6

Magnetic tunnel junction based on bilayer LaI₂ as perfect spin filter device

Nature Communications, Published online: 01 September 2024; doi:10.1038/s41467-024-51612-2

Exciton-polaritons result from the strong coupling of excitons and photons, exhibiting strong nonlinearity. Here, Zhao et al demonstrate room-temperature optical polariton spin-switching in a tungsten disulfide superlattice.

Nature Communications, Published online: 01 September 2024; doi:10.1038/s41467-024-51843-3

Spontaneous parametric down-conversion in thin films should allow to realise extremely compact entangled photon sources. Here, the authors generate entangled photon pairs from a 3R-MoS2 flake, characterize them via quantum state tomography, and show how to tune between different Bell state outputs by changing the pump polarization.