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Lieb lattice, a two-dimensional edge-centered square lattice, has attracted considerable interest due to its exotic electronic and topological properties. Although various optical and photonic Lieb lattices have been experimentally demonstrated, it remains challenging for an electronic Lieb lattice to be realized in real material systems. Here, based on first-principles calculations and tight-binding modeling, a silver sulfide (Ag2S) monolayer is reported as a long-sought-after inorganic electronic Lieb lattice. This Lieb-lattice Ag2S is further found to be ultrasoft, which enables its electronic properties and topological states near the Fermi level to be finely tuned, as evidenced by the strain-induced topologically non-trivial edge states near the valence band edge. These results not only provide an ideal platform to further explore and harvest interesting quantum properties but also pave a way to pursue other inorganic electronic Lieb lattices in a broader material domain.

The degree of buckling of two-dimensional (2D) materials can have a dramatic impact on their corresponding electronic structures. Antimonene (β-phase), a new 2D material with air stability and promising electronic properties, has been engineered to adopt flat or two-heights-buckling geometries by employing different supporting substrates for epitaxial growth. However, studies of the antimonene monolayer with a more buckled configuration are still lacking. Here, we report the synthesis of an antimonene monolayer with a three-heights-buckling configuration overlaid on SbAg2 surface alloy-covered Ag(111) by molecular beam epitaxy, in which the underlying surface alloy provides interfacial interactions to modulate the structure of the antimonene monolayer. The atomic structure of the synthesized antimonene has been precisely identified through a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. The successful fabrication of a buckled antimonene monolayer could provide a promising way to modulate the structures of 2D materials for future electronic and optoelectronic applications.

Lieb lattice, a two-dimensional edge-centered square lattice, has attracted considerable interest due to its exotic electronic and topological properties. Although various optical and photonic Lieb lattices have been experimentally demonstrated, it remains challenging for an electronic Lieb lattice to be realized in real material systems. Here, based on first-principles calculations and tight-binding modeling, a silver sulfide (Ag

We study the origin of the strong spin Hall effect (SHE) in a recently discovered family of Weyl semimetals, $\mathrm{LaAl}X$ ($X$ = Si, Ge) via first-principles with maximally localized Wannier functions. We show that the strong intrinsic spin Hall effect in $\mathrm{LaAl}X$ originates from the multiple slight anticrossings of nodal lines and points near to the Fermi energy due to their high-mirror symmetry and large spin-orbit interaction. It is further found that hole doping and increasing the temperature can enhance the spin Hall conductivity (${\ensuremath{\sigma}}_{\mathrm{SH}}$). However, the former also increases the electrical conductivity (${\ensuremath{\sigma}}_{c}$), while the latter decreases it. As a result, the independent tuning of ${\ensuremath{\sigma}}_{\mathrm{SH}}$ and ${\ensuremath{\sigma}}_{c}$ by increasing the temperature can enhance the spin Hall angle (proportional to $\frac{{\ensuremath{\sigma}}_{\mathrm{SH}}}{{\ensuremath{\sigma}}_{c}}$), a figure of merit of charge-to-spin current interconversion of spin-orbit torque devices. The underlying physics of such independent changes of the spin Hall and electrical conductivities by thermal means is revealed through the band-resolved and $k$-resolved spin Berry curvature. Our finding offers a way in the search of high spin Hall angle materials for room temperature spin-orbitronics applications.

The complex oxide heterostructures such as LaAlO3/SrTiO3 (LAO/STO) interface are paradigmatic platforms to explore emerging multi-degrees of freedom coupling and the associated exotic phenomena. In this study, we reveal the effects of multiorbital and magnetic ordering on Rashba spin-orbit coupling (SOC) at the LAO/STO (001) interface. Based on first-principles calculations, we show that the Rashba spin splitting near the conduction band edge can be tuned substantially by the interfacial insulator-metal transition due to the multiorbital effect of the lowest t_2g bands. We further unravel a competition between Rashba SOC and intrinsic magnetism, in which the Rashba SOC induced spin polarization is suppressed by the interfacial magnetic ordering. These results deepen our understanding of intricate electronic and magnetic reconstruction at the perovskite oxide interfaces and shed light on the engineering of oxide heterostructures for all-oxides-based spintronic devices., 24 pages, 4 figures

This work explores the mechanism of interfacial coupling in LaMnO${}_{3}$/SrIrO${}_{3}$ superlattices by x-ray spectroscopies and first-principles calculations. The superlattice-period dependent properties of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital.

Materials with flat bands are considered as ideal platforms to explore strongly correlated physics such as the fractional quantum hall effect, high-temperature superconductivity, and more. In theory, a Kagome lattice with only nearest-neighbor hopping can give rise to a flat band. However, the successful fabrication of Kagome lattices is still very limited. Here, we provide a new design principle to construct the Kagome lattice by trapping atoms into Kagome arrays of potential valleys, which can be realized on a potassium-decorated phosphorus-gold surface alloy. Theoretical calculations show that the flat band is less correlated with the neighboring trivial electronic bands, which can be further isolated and dominate around the Fermi energy with increased Kagome lattice parameters of potassium atoms. Our results provide a new strategy for constructing Kagome lattices, which serve as an ideal platform to study topological and more general flat band phenomena.

The ability to tune magnetic orders, such as magnetic anisotropy and topological spin texture, is desired to achieve high-performance spintronic devices. A recent strategy has been to employ interfacial engineering techniques, such as the introduction of spin-correlated interfacial coupling, to tailor magnetic orders and achieve novel magnetic properties. We chose a unique polar–nonpolar LaMnO3/SrIrO3 superlattice because Mn (3d)/Ir (5d) oxides exhibit rich magnetic behaviors and strong spin–orbit coupling through the entanglement of their 3d and 5d electrons. Through magnetization and magnetotransport measurements, we found that the magnetic order is interface-dominated as the superlattice period is decreased. We were able to then effectively modify the magnetization, tilt of the ferromagnetic easy axis, and symmetry transition of the anisotropic magnetoresistance of the LaMnO3/SrIrO3 superlattice by introducing additional Mn (3d) and Ir (5d) interfaces. Further investigations using in-depth first-principles calculations and numerical simulations revealed that these magnetic behaviors could be understood by the 3d/5d electron correlation and Rashba spin–orbit coupling. The results reported here demonstrate a new route to synchronously engineer magnetic properties through the atomic stacking of different electrons, which would contribute to future applications in high-capacity storage devices and advanced computing. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version X.R.W. acknowledges support from the Nanyang Assistant Professorship grant from Nanyang Technological University and Academic Research Fund Tier 1 (Grant Nos. RG108/17 and RG177/18) and Tier 3 (Grant No. MOE2018-T3-1-002) from the Singapore Ministry of Education. L.S. acknowledges support from Singapore MOE Tier 1 (Grant No. R-265-000-615-114). N.S. and P.S. acknowledge the support of Grant No. MOE2014-T2-2-112 from the Ministry of Education, Singapore, and the computational resources of the NSCC ASPIRE1 cluster in Singapore. D.Q. acknowledges the support of the Australian Research Council (Grant No. FT160100207). C.P. acknowledges financial support from the Academic Research Fund Tier 3 (Reference No. MOE5093) and the National Research Foundation (Reference No. NRF-NRFI2015-04). C.W.N. acknowledges support from the Basic Science Center Program of NSFC (Grant No. 51788104). Part of this research was undertaken on the soft X-ray spectroscopy beamline at the Australian Synchrotron, part of ANSTO, and the rest of the soft X-ray spectroscopy measurements were performed at beamline 6.3.1 of Advanced Light Source, which is an Office of Science User Facility operated for the U.S. DOE Office of Science by Lawrence Berkeley National Laboratory and supported by the DOE under Contract No. DEAC02-05CH11231.

As an effort to identify van der Waals heterostructures for efficient excitonic solar cell application, high-throughput computational screening was carried out to study the band alignments of 1540 vertical heterostructures formed by 56 two-dimensional semiconducting/insulating materials. More than 90 heterostructures with estimated power conversion efficiency (PCE) higher than 15% have been identified, of which 17 heterostructures are predicted to have PCE higher than the best value (20%) reported or proposed in the literature.

Polymorph engineering of 2H-MoS2, which can be achieved by alkali metal intercalation to obtain either the mixed 2H/1T′ phases or a homogeneous 1T′ phase, has received wide interest recently, since this serves as an effective route to tune the electrical and catalytic properties of MoS2. As opposed to an idealized single crystal-to-single crystal phase conversion, the 2H to 1T′ phase conversion results in crystal domain size reduction as well as strained lattices, although how these develop with composition is not well understood. Herein, the evolution of the phonon modes in Li-intercalated 1T′-MoS2 (LixMoS2) are investigated as a function of different 1T′-2H compositions. We observed that the strain evolution in the mixed phases is revealed by the softening of four Raman modes, Bg (J1), Ag (J3), E12g, and A1g, with increasing 1T′ phase composition. Additionally, the first-order temperature coefficients of the 1T′ phonon mode vary linearly with increasing 1T′ composition, which is explained by increased e...

A large bulk band gap and tunable Dirac carriers are desired for practical device applications of topological insulators. However, most known topological insulators are narrow gap materials and the manipulation of their Dirac surface states is limited by residual bulk charge carriers originating from intrinsic defects. In this study, via density functional theory based first-principles calculations, we predict that a layered hexagonal structure of Bi2S3 is stable, and it becomes a topological insulator under a moderate compressive pressure of about 5.3 GPa. Interestingly, we find that the strength of the spin–orbit interaction in Bi2S3 can be effectively enhanced by the applied pressure. This leads to an increased inverted band gap with pressure, which can reach 0.4 eV with a pressure of 13.7 GPa. Compared to Bi2Se3, intrinsic defects are suppressed in Bi2S3 under both cation- and anion-poor growth conditions. Our calculations predict a new Bi-based topological insulator, and also shed light on control over spin–orbit interactions in Bi2S3 and tuning of its topological properties.

A long-lasting puzzle of the conducting $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ (LAO/STO) interface is that the excess electron density counted in the transport measurements is much less than 0.5 electrons per unit cell as predicted by the polar catastrophe model. In this study, via first-principles calculations, we show that the excess electrons at the LAO/STO interface favor the formation of small polarons. These electrons interact strongly with the interfacial Ti ions, forming localized midgap states, which make an insignificant contribution to the conductivity. We also find that the interaction between the neighboring spin-polarized small polarons is weak and does not lead to long-range magnetic ordering. Compared with bulk STO, the formation of the polarons is more favorable at the LAO/STO interface, which is ascribed to the reduced symmetry of the crystal field and the increased lattice distortion. Our results suggest that a large number of the excess electrons at the LAO/STO interface are localized in the form of small polarons, which can partially explain the unexpected fewer electrons in the transport measurements, and also shed light on understanding various properties of other complex perovskite oxide interfaces.

Flexible and recyclable zinc-based batteries have been hot research topics due to their high discharge platform, safety, and low cost. However, most research on zinc-based batteries put their attention on metal oxides as the cathode, such as manganese dioxide (MnO2), cobaltosic oxide (Co3O4), nickel oxide (NiO), etc. Very few studies use metal sulfides as electrode materials and focus on its mechanism based on theoretical analysis. Hence, in this work, we firstly used cobaltosic sulfide (Co3S4) nanosheets grown on Ni foam (CSNSs/NF) as an electrode material for zinc-based batteries. Both first-principles calculations and experimental results reveal that S plays a crucial role in the capacitive activity and electrical conductivity enhancement for Co-based materials. The Zn//CSNSs/NF battery provides a high specific capacity of 317 mA h g−1 at a current density of 1 A g−1. Furthermore, it also displays an impressive energy density of 507 Wh kg−1 and a long cycling performance. Impressively, the Zn//CSNSs/NF battery has high flexibility and can work well under different deformations. This work not only provides a new member of cathode materials in zinc-based batteries, but also opens new opportunities for powering portable and wearable electronics.

There is a huge demand for magnetoresistance (MR) sensors with high sensitivity, low energy consumption, and room temperature operation. It is well-known that spatial charge inhomogeneity due to impurities or defects introduces mobility fluctuations in monolayer graphene and gives rise to MR in the presence of an externally applied magnetic field. However, to realize a MR sensor based on this effect is hampered by the difficulty in controlling the spatial distribution of impurities and the weak magnetoresistance effect at the monolayer regime. Here, we fabricate a highly stable monolayer graphene-on-black phosphorus (G/BP) heterostructure device that exhibits a giant MR of 775% at 9 T magnetic field and 300 K, exceeding by far the MR effects from devices made from either monolayer graphene or few-layer BP alone. The positive MR of the G/BP device decreases when the temperature is lowered, indicating a phonon-mediated process in addition to scattering by charge impurities. Moreover, a nonlocal MR of10 000% is achieved for the G/BP device at room temperature due to an enhanced flavor Hall effect induced by the BP channel. Our results show that electron-phonon coupling between 2D material and a suitable substrate can be exploited to create giant MR effects in Dirac semimetals.

A large bulk band gap and tunable Dirac carriers are desired for practical device applications of topological insulators. However, most known topological insulators are narrow gap materials and the manipulation of their Dirac surface states is limited by residual bulk charge carriers originating from intrinsic defects. In this study, via density functional theory based first-principles calculations, we predict that a layered hexagonal structure of Bi

In this paper, the manipulative effect of N doping on topological insulator Bi 2 Se 3 was investigated by using density functional theory (DFT). The computational results reveal that the van der Waals (vdW) correction is necessary when calculating the geometric structure of Bi 2 Se 3 . Taking into account the spin–orbit coupling(SOC), the electronic structure of Bi 2 Se 3 can be accurately described, especially for the energy bands near the Fermi level. The N doping at anion sites can produce an impurity band which appeared at Fermi energy. Comparing with pure Bi 2 Se 3 , the electronic structure of N doping Bi 2 Se 3 changed obviously at Fermi energy. The valence band and conduction band meet when N doped on Se1 sites, the insulating properties of Bi 2 Se 3 system are damaged. The indirect gaps between the valence band and conduction band are 0.135 eV and 0.115 eV with N doping on Se2 sites with the doping levels 6.67% and 1.67%, respectively. On the other hand, the N doping at Se sites of Bi 2 Se 3 can induce magnetic moments. The magnetic moments are related to the covalent bond length between N atom and Bi atom. Furthermore, the real and imaginary parts of dielectric functions have been computed. The static dielectric constant e 1 (0) becomes significantly larger and the peaks in the imaginary part of dielectric constant e 2 ( ω ) spectra move toward low energy. The intensity of the peak is gradually enhanced and there is a small bump in Bi 6 Se 8 N2 at 0.38 eV. The N doping paves a prospective way to tune the topological properties and may find change to potential spintronic applications and electronic devices.