We present a density functional theory study of 3d transition-metal (TM) atoms (Sc–Zn) adsorbed on a phosphorene sheet. We show that due to the existence of lone pair electrons on P atoms in phosphorene, all the TM atoms, except the closed-shell Zn atom, can bond strongly to the phosphorene with sizable binding energies. Moreover, the TM@phosphorene systems for TM from Sc to Co exhibit interesting magnetic properties, which arise from the exchange splitting of the TM 3d orbitals. We also find that strain is an effective way to control the magnetism of TM@phosphorene systems by tuning the interaction of the TM with phosphorene and, thus, the relative positions of in-gap TM 3d orbitals. In particular, a small biaxial strain could induce a magnetic transition from a low-spin to a high-spin state in phosphorene decorated by Sc, V, or Mn. These results clearly establish the potential for phosphorene utilization in innovative spintronic devices.

A key challenge in manipulating the magnetization in heavy-metal/ferromagnetic bilayers via the spin-orbit torque is to identify materials that exhibit an efficient charge-to-spin current conversion. Ab initio electronic structure calculations reveal that the intrinsic spin Hall conductivity (SHC) for pristine β-W is about sixty percent larger than that of α-W. More importantly, we demonstrate that the SHC of β-W can be enhanced via Ta alloying. This is corroborated by spin Berry curvature calculations of W 1−x Ta x (x ∼ 12.5%) alloys which show a giant enhancement of spin Hall angle of up to ≈ −0.5. The underlying mechanism is the synergistic behavior of the SHC and longitudinal conductivity with Fermi level position. These findings, not only pave the way for enhancing the intrinsic spin Hall effect in β-W, but also provide new guidelines to exploit substitutional alloying to tailor the spin Hall effect in various materials.

it has been demonstrated recently that the residual water would exist ubiquitously within the ionic liquid (IL) when experiments performed in the air. [11][12][13][14] The water molecular would facilitate the electrochemical reaction through electrolysis into H + and O 2ions, which would then be inserted into materials depending on the polarity of the gating bias [11][12][13][14][15][16][17] (as shown in Figure 1a). Clearly, the electrochemical reaction related modulation is a bulk effect, and therefore its associated charge modulation should not be confined by the 2D limit as the conventional ILG, which is about 10 15 cm −2 at the sample surface. [2][3][4][5][6][7][8] Along these studies, the H + (proton) ion, the smallest and lightest ion, emerges as an ideal candidate to incorporate into materials for the manipulation of band filling via charge neutrality induced electron doping with positively charged proton. [13,18] Besides, protonated materials have tremendous application potential in hydrogen storage [18] and fuel cells. [19][20][21][22] So the study of ILG induced protonation is significant for both fundamental physics (realizing electron doping and phase control) and industry application (discovering new protonated functional materials). It is important to note that although the ILG induced protonation Ionic-liquid-gating-(ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO 2.5 , VO 2 , WO 3 , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo 2 O 4 , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo 2 O 4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution. Electron Doping

Topological semimetals (TSMs) in which conduction and valence bands cross at zero-dimensional (0D) Dirac nodal points (DNPs) or 1D Dirac nodal lines (DNLs), in 3D momentum space, have recently drawn much attention due to their exotic electronic properties. Here we generalize the TSM state further to a higher-dimensional Dirac nodal sphere (DNS) or pseudo DNS (PDNS) state, with the band crossings forming a 2D closed or approximate sphere at the Fermi level. This new TSM state can exhibit unique electronic properties, making DNS/PDNS a new type of fermion beyond DNP/DNL paradigm. In the realistic crystals, we demonstrate two possible types of PDNS states underlied by different crystalline symmetries, which are characterized with a spherical backbone consisting of multiple DNLs and approximate band degeneracy in between the DNLs. We identify all the possible band crossings with pairs of 1D irreducible representations to form the PDNS states in 32 point groups. Importantly, we discover that strained M H3 (M = Y, Ho, Tb, Nd) and Si3N2 are materials candidates to realize these two types of PDNS states, respectively. As a high-symmetryrequired state, the PDNS semimetal can be regarded as the "parent phase" for other topological gapped and gapless states.

Plasmon opens up the possibility to efficiently couple light and matter at sub-wavelength scales.In general, the plasmon frequency is dependent of carrier density. This dependency, however, renders fundamentally a weak plasmon intensity at low frequency, especially for Dirac plasmon (DP) widely studied in graphene. Here we demonstrate a new type of DP, excited by a Dirac nodal-surface state, which exhibits an anomalously density-independent frequency. Remarkably, we predict realization of anomalous DP (ADP) in 1D topological electrides, such as Ba 3 CrN 3 and Sr 3 CrN 3 , by first-principles calculations. The ADPs in both systems have a density-independent frequency and high intensity, and their frequency can be tuned from terahertz to mid-infrared by changing the excitation direction. Furthermore, the intrinsic weak electron-phonon coupling of anionic electrons in electrides affords an added advantage of ultra-low phonon-assisted damping and hence a long lifetime of the ADPs. Our work paves the way to developing novel plasmonic and optoelectronic devices by combining topological physics with electride materials. *

Materials with large magnetocrystalline anisotropy and strong electric field effects are highly needed to develop new types of memory devices based on electric field control of spin orientations. Instead of using modified transition metal films, we propose that certain monolayer transition metal dichalcogenides are the ideal candidate materials for this purpose. Using density functional calculations, we show that they exhibit not only a large magnetocrystalline anisotropy (MCA), but also colossal voltage modulation under external field. Notably, in some materials like CrSe2 and FeSe2, where spins show a strong preference for in-plane orientation, they can be switched to out-of-plane direction. This effect is attributed to the large band character alteration that the transition metal dstates undergo around the Fermi energy due to the electric field. We further demonstrate that strain can also greatly change MCA, and can help to improve the modulation efficiency while combined with an electric field.

Triply degenerate points (TDPs) in band structure of a crystal can generate novel TDP fermions without high-energy counterparts. Although identifying ideal TDP semimetals, which host clean TDP fermions around the Fermi level (E_{F}) without coexisting with other quasiparticles, is critical to explore the intrinsic properties of this new fermion, it is still a big challenge and has not been achieved up to now. Here, we disclose an effective approach to search for ideal TDP semimetals via selective band crossing between antibonding s and bonding p orbitals along a line in the momentum space with C_{3v} symmetry. Applying this approach, we have successfully identified the NaCu_{3}Te_{2} family of compounds to be ideal TDP semimetals, where two, and only two, pairs of TDPs are located around the E_{F}. Moreover, we demonstrate a fundamental mechanism to modulate energy splitting between a pair of TDPs, and we illustrate the intrinsic features of TDP Fermi arcs in these ideal TDP semimetals.

Ordered atomic-scale superlattices on a surface hold great interest both for basic science and for potential applications in advanced technology. However, controlled fabrication of superlattices down to the atomic scale has proven exceptionally challenging. Here we develop a segregation method to realize self-organization of S superlattices at the interface of graphene and S-rich Cu substrates. Via scanning tunneling microscope measurements, we directly image well-ordered identical nanocluster superlattices and atomic superlattices under the cover of graphene. Scanning tunneling spectra show that the superlattices in turn could modulate the electronic structure of top-layer graphene. Importantly, a special-ordered S monatomic superlattice commensurate with a graphene lattice is found to drive semimetal graphene into a symmetry-broken phasethe electronic Kekulé distortion phasewhich opens a bandgap of ∼245 meV.