Progressive Control of Rashba State on Topological Dirac Semimetal KZnBi.

Rashba states have been actively revisited as a platform for advanced applications such as spintronics and topological quantum computation. Yet, access to the Rashba state is restricted to the specific material sets, and the methodology to control the Rashba state is not established. Here, we report the Rashba states on the (001) surface of KZnBi, a 3D Dirac semimetal.

Topological Fermi-arc surface state covered by floating electrons on a two-dimensional electride.

Two-dimensional electrides can acquire topologically non-trivial phases due to intriguing interplay between the cationic atomic layers and anionic electron layers. However, experimental evidence of topological surface states has yet to be verified. Here, via angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM), we probe the magnetic Weyl states of the ferromagnetic electride [GdC]·2e.

Pressure-Dependent Superconductivity in Topological Dirac Semimetal SrCuBi.

The discovery of superconducting states in diverse topological materials generates a burgeoning interest to explore a topological superconductor and to realize a fault-tolerant topological quantum computation. A variety of routes to realize topological superconductors are proposed, and many types of topological materials are developed. However, a pristine topological material with a natural superconducting state is relatively rare as compared to topological materials with artificially induced superconductivity.

Magnetic quasi-atomic electrons driven reversible structural and magnetic transitions between electride and its hydrides.

In electrides, interstitial anionic electrons (IAEs) in the quantized energy levels at cavities of positively charged lattice framework possess their own magnetic moment and interact with each or surrounding cations, behaving as quasi-atoms and inducing diverse magnetism. Here, we report the reversible structural and magnetic transitions by the substitution of the quasi-atomic IAEs in the ferromagnetic two-dimensional [GdC]·2e electride with hydrogens and subsequent dehydrogenation of the canted antiferromagnetic GdCH (y > 2.0).

Real-space imaging and control of chiral anomaly induced current at room temperature in topological Dirac semimetal.

Chiral fermions (CFs) in condensed matters, distinguished by right (+) or left (-) handedness, hold a promise for emergent quantum devices. Although a chiral anomaly induced current, = (+) - (-), occurs in Weyl semimetals due to the charge imbalance of the CFs, monitoring spatial flow and temporal dynamics of has not been demonstrated yet. Here, we report real-space imaging and control of on the topological Dirac semimetal KZnBi at room temperature (RT) by near-field terahertz (THz) spectroscopy, establishing a relation for an electromagnetic control of .

Boosted Heterogeneous Catalysis by Surface-Accumulated Excess Electrons of Non-Oxidized Bare Copper Nanoparticles on Electride Support.

Engineering active sites of metal nanoparticle-based heterogeneous catalysts is one of the most prerequisite approaches for the efficient production of chemicals, but the limited active sites and undesired oxidation on the metal nanoparticles still remain as key challenges. Here, it is reported that the negatively charged surface of copper nanoparticles on the 2D [Ca N] ∙e electride provides the unrestricted active sites for catalytic selective sulfenylation of indoles and azaindoles with diaryl disulfides. Substantial electron transfer from the electride support to copper nanoparticles via electronic metal-support interactions results in the accumulation of excess electrons at the surface of copper nanoparticles.

Quantum electron liquid and its possible phase transition.

Purely quantum electron systems exhibit intriguing correlated electronic phases by virtue of quantum fluctuations in addition to electron-electron interactions. To realize such quantum electron systems, a key ingredient is dense electrons decoupled from other degrees of freedom. Here, we report the discovery of a pure quantum electron liquid that spreads up to ~3 Å in a vacuum on the surface of an electride crystal.

Non-Oxidized Bare Metal Nanoparticles in Air: A Rational Approach for Large-Scale Synthesis via Wet Chemical Process.

Metal nanoparticles (MeNPs) have been used in various industrial applications, owing to their unique physical and chemical properties different from the bulk counterparts. However, the natural oxidation of MeNPs is an imminent hindrance to their widespread applications despite much research efforts to prevent it. Here, a rational approach for non-oxidized bare MeNPs in air, which requires no additional surface passivation treatment is reported.

Identifying the Correlation between Structural Parameters and Anisotropic Magnetic Properties in IMnV Semiconductors: A Possible Room-Temperature Magnetism.

Layer-structured materials are of central importance in a wide range of research fields owing to their unique properties originating from their two dimensionality and anisotropy. Herein, quasi-2D layer-structured IMnV (I: alkali metals and V: pnictogen elements) compounds are investigated, which are potential antiferromagnetic (AFM) semiconductors. Single crystals of IMnV compounds are successfully grown using the self-flux method and their electronic and magnetic properties are analyzed in correlation with structural parameters.

Chemically Stable Low-Dimensional Electrides in Transition Metal-Rich Monochalcogenides: Theoretical and Experimental Explorations.

Electrides, which are ionic crystals composed of excess anionic electrons, are of great interest as an exotic material for fundamental research and practical applications in broad fields of science and technology. However, an inherent chemical instability under ambient conditions at room temperature has been a fatal drawback to be addressed. Here, we report that transition metal-rich monochalcogenides are an emerging class of low-dimensional electrides with excellent chemical and thermal stability in air and water at room temperature through a comprehensive exploration of theoretical prediction and experimental verification.

Non-oxidized bare copper nanoparticles with surface excess electrons in air.

Copper (Cu) nanoparticles (NPs) have received extensive interest owing to their advantageous properties compared with their bulk counterparts. Although the natural oxidation of Cu NPs can be alleviated by passivating the surfaces with additional moieties, obtaining non-oxidized bare Cu NPs in air remains challenging. Here we report that bare Cu NPs with surface excess electrons retain their non-oxidized state over several months in ambient air.

Boosting Photoredox Catalysis Using a Two-Dimensional Electride as a Persistent Electron Donor.

Electrides, which have excess anionic electrons, are solid-state sources of solvated electrons that can be used as powerful reducing agents for organic syntheses. However, the abrupt decomposition of electrides in organic solvents makes controlling the transfer inefficient, thereby limiting the utilization of their superior electron-donating ability. Here, we demonstrate the efficient reductive transformation strategy which combines the stable two-dimensional [GdC]·2e electride electron donor and cyclometalated Pt(II) complex photocatalysts.

Antiperovskite Gd SnC: Unusual Coexistence of Ferromagnetism and Heavy Fermions in Gd Lattice.

Inverted structures of common crystal lattices, referred to as antistructures, are rare in nature due to their thermodynamic constraints imposed by the switched cation and anion positions in reference to the original structure. However, a stable antistructure formed with mixed bonding characters of constituent elements in unusual valence states can provide unexpected material properties. Here, a heavy-fermion behavior of ferromagnetic gadolinium lattice in Gd SnC antiperovskite is reported, contradicting the common belief that ferromagnetic gadolinium cannot be a heavy-fermion system due to the deep energy level of localized 4f-electrons.

Ti Addition Effect on the Grain Structure Evolution and Thermoelectric Transport Properties of HfZrNiSnSb Half-Heusler Alloy.

Compositional tuning is one of the important approaches to enhance the electronic and thermal transport properties of thermoelectric materials since it can generate point defects as well as control the phase evolution behavior. Herein, we investigated the Ti addition effect on the grain growth during melt spinning and thermoelectric transport properties of HfZrNiSnSb half-Heusler compound. The characteristic grain size of melt-spun ribbons was reduced by Ti addition, and very low lattice thermal conductivity lower than 0.

Weighted Mobility Ratio Engineering for High-Performance Bi-Te-Based Thermoelectric Materials via Suppression of Minority Carrier Transport.

Thermoelectrics, which can generate electricity from a temperature difference, or vice versa, is a key technology for solid-state cooling and energy harvesting; however, its applications are constrained owing to low efficiency. Since the conversion efficiency of thermoelectric devices is directly obtained via a figure of merit of materials, zT, which is related to the electronic and thermal transport characteristics, the aim here is to elucidate physical parameters that should be considered to understand transport phenomena in semiconducting materials. It is found that the weighted mobility ratio of the majority and minority carrier bands is an important parameter that determines zT.

Stoner enhancement from interstitial electrons in YC toward a spontaneous ferromagnetic electride.

The evolutionary magnetism associated with the interlayer spacing in two-dimensional (2D) YC electrides has been investigated by first-principles total-energy calculations based on density functional theory. Several structures with different c-axis parameters around the optimized value were taken into our consideration. Mapping of the electron localization function shows that the interstitial electron is strongly localized at the body center position (denoted as the X-site) in the primitive rhombohedral unit cell, serving as an anion which is ionically bonded with the cationic framework of the YC layer.

Symmetry Dictated Grain Boundary State in a Two-Dimensional Topological Insulator.

Grain boundaries (GBs) are ubiquitous in solids and have been of central importance in understanding the nature of polycrystals. In addition to their classical roles, topological insulators (TIs) offer a chance to realize GBs hosting distinct topological states that can be controlled by their crystal symmetries. However, such roles of crystalline symmetry in two-dimensional (2D) TIs have not been definitively measured yet.

Improvement in the thermoelectric performance of highly reproducible n-type (Bi,Sb)Se alloys by Cl-doping.

(Bi,Sb)Se alloys are promising alternatives to commercial n-type Bi(Te,Se) ingots for low-mid temperature thermoelectric power generation due to their high thermoelectric conversion efficiency at elevated temperatures. Herein, we report the enhanced high-temperature thermoelectric performance of the polycrystalline Cl-doped Bi Sb Se ( = 0.8, 1.

Author Correction: Ferromagnetic quasi-atomic electrons in two-dimensional electride.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Ferromagnetic quasi-atomic electrons in two-dimensional electride.

An electride, a generalized form of cavity-trapped interstitial anionic electrons (IAEs) in a positively charged lattice framework, shows exotic properties according to the size and geometry of the cavities. Here, we report that the IAEs in layer structured [GdC]·2e electride behave as ferromagnetic elements in two-dimensional interlayer space and possess their own magnetic moments of ~0.52 μ per quasi-atomic IAE, which facilitate the exchange interactions between interlayer gadolinium atoms across IAEs, inducing the ferromagnetism in [GdC]·2e electride.

Probing Multiphased Transition in Bulk MoS by Direct Electron Injection.

Structural phase transitions in layered two-dimensional (2D) materials are of significant interest owing to their ability to exist in multiple metastable states with distinctive properties. However, phase transition in bulk MoS by nondestructive electron infusion has not yet been realized. In this study, we report the 2H to 1T' phase transition and in-between intermediates in bulk MoS using MoS/[CaN]·e heterostructures, in which kinetic free electrons were directly injected into MoS.

Proximity Engineering of the van der Waals Interaction in Multilayered Graphene.

The van der Waals (vdW) interaction in two-dimensional (2D)-layered materials affects key characteristics of electronic devices, such as the contact resistance, with a vertical heterostructure geometry. While various functionalizations to manipulate the properties of 2D materials have shown issues such as defect generation or have a limited spatial range for the methods, engineering the vdW interaction in nondestructive ways for device applications has not been tried or properly achieved yet. Here, we introduce the proximity engineering of the vdW interaction in multilayered graphene, which is observed as modified interlayer distances and deviated stacking orders by Raman spectroscopy.

Creation of two-dimensional layered Zintl phase by dimensional manipulation of crystal structure.

The discovery of new families, beyond graphene, of two-dimensional (2D) layered materials has always attracted great attention. However, it has been challenging to artificially develop layered materials with honeycomb atomic lattice structure composed of multicomponents such as hexagonal boron nitride. Here, through the dimensional manipulation of a crystal structure from sp-hybridized 3D-ZnSb, we create an unprecedented layered structure of Zintl phase, which is constructed by the staking of sp-hybridized honeycomb ZnSb layers.

Lowering the Schottky Barrier Height by Graphene/Ag Electrodes for High-Mobility MoS Field-Effect Transistors.

2D transition metal dichalcogenides (TMDCs) have emerged as promising candidates for post-silicon nanoelectronics owing to their unique and outstanding semiconducting properties. However, contact engineering for these materials to create high-performance devices while adapting for large-area fabrication is still in its nascent stages. In this study, graphene/Ag contacts are introduced into MoS devices, for which a graphene film synthesized by chemical vapor deposition (CVD) is inserted between a CVD-grown MoS film and a Ag electrode as an interfacial layer.