The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI3, are reported (A = Cs, organic cation). systematic study this reaction system led to isolation 6 new semiconductors. Using CsGeI3 (1) as prototype compound, we have prepared methylammonium, CH3NH3GeI3 (2), formamidinium, HC(NH2)2GeI3 (3), acetamidinium, CH3C(NH2)2GeI3 (4), guanidinium, C(NH2)3GeI3 (5), trimethylammonium, (CH3)3NHGeI3 (6), isopropylammonium, (CH3)2C(H)NH3GeI3 (7) analogues....

The potential of graphene to impact the development next generation electronics has renewed interest in its growth and structure. graphitization hexagonal SiC surfaces provides a viable alternative for synthesis graphene, with wafer-size epitaxial on SiC(0001) now possible. Despite this recent progress, exact nature graphene-SiC interface whether even semiconducting gap remain controversial. Using scanning tunneling microscopy functionalized tips density functional theory calculations, here...

While noncentrosymmetric ${\mathrm{MoS}}_{2}$ monolayer is known to exhibit efficient second-harmonic generation (SHG), there currently no agreement on its absolute nonlinear susceptibility ${\ensuremath{\chi}}^{(2)}$, varying over three orders of magnitude according recent experiments. In order resolve this conflicting issue, we have studied the optical properties grown by chemical vapor deposition. The polycrystalline nature was directly probed SHG polarization dependence across grain...

SnSe single crystals have recently been found to exhibit excellent thermoelectric performance with an extremely high figure of merit (ZT) value 2.6. Although this ZT has attracted considerable attention, the microscopic origin p-type characteristics is not yet clearly understood. Here, we directly observed and identified intrinsic point defects existing on via scanning tunneling microscopy (STM) investigated effect electronic properties using density functional theory (DFT) calculations. Our...

We report the observation of coherent lattice vibrations in mono- and few-layer WSe2 time domain, which were obtained by performing time-resolved transmission measurements. Upon excitation ultrashort pulses with energy resonant to that A excitons, oscillations A1g optical phonon longitudinal acoustic at M point Brillouin zone (LA(M)) impulsively generated monolayer WSe2. In multilayer flakes, interlayer breathing mode (B1) is found be sensitive number layers, demonstrating its usefulness...

The electronic structures and properties of heterointerfaces in the perovskite oxide superlattices ${\mathrm{LaAlO}}_{3}∕{\mathrm{SrTiO}}_{3}\phantom{\rule{0.3em}{0ex}}[001]$ are presented using first-principles all-electron full-potential linearized augmented plane-wave (FLAPW) method. Superlattices with three types interfaces, (i) electron-doped, (ii) hole-doped, (iii) both electron- studied compared. For electron-doped interface, mixed valency Ti along Jahn-Teller effect found to explain...

As silicon-based electronics are reaching the nanosize limits of semiconductor roadmap, carbon-based nanoelectronics has become a rapidly growing field, with great interest in tuning properties materials. Chemical functionalization is proposed route, but syntheses graphene oxide (G-O) produce disordered, nonstoichiometric materials poor electronic properties. We report synthesis an ordered, stoichiometric, solid-state carbon that never been observed nature and coexists graphene. Formation...

We have investigated strong optical nonlinearity of monolayer MoS2(1–x)Se2x across the exciton resonance, which is directly tunable by Se doping. The quality alloys prepared chemical vapor deposition verified atomic force microscopy, Raman spectroscopy, and photoluminescence analysis. crystal symmetry all our essentially D3h, as confirmed polarization-dependent second-harmonic generation (SHG). spectral structure resonance sampled wavelength-dependent SHG (λ = 1000–1800 nm), where red-shifts...

A key challenge in manipulating the magnetization heavy-metal/ferromagnetic bilayers via spin-orbit torque is to identify materials that exhibit an efficient charge-to-spin current conversion. Ab initio electronic structure calculations reveal intrinsic spin Hall conductivity (SHC) for pristine $\ensuremath{\beta}$-W about 60% larger than of $\ensuremath{\alpha}$-W. More importantly, we demonstrate SHC can be enhanced Ta alloying. This corroborated by Berry curvature...

In clean inversion symmetric materials, spin-orbit coupling is not thought to have a pronounced effect on spin-singlet superconductivity. Here we show that, for the recently discovered pnictide superconductor SrPtAs, this case. particular, superconductivity in strong leads significant enhancement of both spin susceptibility and paramagnetic limiting field with respect that usually expected superconductors. The underlying reason while SrPtAs has center symmetry, it contains weakly coupled...

Non-centrosymmetric superconductors have attracted much interest in the context of heavy Fermion and interface superconductivity. Here we show that a sublattice structure staggered subunits without inversion center can important implications for superconductivity even globally centrosymmetric system. After discussing general aspects systems with alternating non-centrosymmetric layers, two concrete examples are studied: (1) artificially grown superlattices CeCoIn5/YbCoIn5 (2) pnictide...

The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms valleytronics. In this study, high-quality MoSe2-WSe2 lateral HSs are grown by pulsed-laser-deposition-assisted selenization method. sharp interface the HS is verified morphological and optical characterizations. Intriguingly, photoluminescence spectra acquired from show rather clear signatures pristine MoSe2 WSe2 with...

The emergence of topologically protected conducting states with the chiral spin texture is most prominent feature at surface topological insulators. On application side, large band gap and high resistivity to distinguish from bulk degrees freedom should be guaranteed for full usage states. Here, we suggest that oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional insulator exhibiting both resistivity. Based on first-principles calculations varying...

Significant enhancement of the magnetocrystalline anisotropy (MCA) an Fe(001) surface capped by 4$d$ and 5$d$ transition metal monolayers is presented in this study using first principles density functional calculations. In particular, extremely large perpendicular MCA $+$10 meV/Ir was found Ir-capped Fe(001), which originates not from Fe but spin-orbit coupling Ir atoms. From spin-channel decomposition matrix electronic structure analyses, we find that strong 3$d$--5$d$ band hybridization...

Field-effect transistor-based conductance gas sensors are attracting considerable research interest because of their miniaturized size, high sensitivity, and portability. Here, we propose statistical thermodynamics models to analytically characterize monolayer molecule adsorption on crystalline amorphous solid surfaces in terms density coverage, respectively, which critical for sensing applications. By testing the molecules, such as CO, NO, NH3 NO2, graphene reduced oxide (rGO), found that...

Dynamic second-order nonlinear susceptibilities, $χ^{(2)}(2ω,ω,ω)\equiv χ^{(2)}(ω)$, are calculated here within a fully first-principles scheme for monolayered molybdenum dichalcogenides, $2H$-MoX$_2$ (X=S,Se,Te). The absolute values of $χ^{(2)}(ω)$ across the three chalcogens critically depend on band gap energies upon uniform strain, yielding highest $χ^{(2)}(0)\sim$ 140 pm/V MoTe$_2$ in static limit. Under this in-plane stress, can undergo direct-to-indirect transition gaps, which turn...

Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated highly anisotropic, and agree well experiment. Changes in presented, when strain applied along b c direction strength -3% to +3%, where influence gaps dispersions significant. Moreover, for compressive strains, sign change at...

Abstract Dzyaloshinskii–Moriya interaction (DMI) is considered as one of the most important energies for specific chiral textures such magnetic skyrmions. The keys generating DMI are absence structural inversion symmetry and exchange energy with spin–orbit coupling. Therefore, a vast majority research activities about mainly limited to heavy metal/ferromagnet bilayer systems, only focusing on their interfaces. Here, we report an asymmetric band formation in superlattices (SL) which arises...

Density functional theory calculations reveal that the interfacial 6$\sqrt{3}$ \ifmmode\times\else\texttimes\fi{} structure [a warped graphene layer with periodic inclusions of pentagon-hexagon-heptagon (H${}_{5,6,7}$) defects] facilitates a Si diffusion path vertically through interface during epitaxial growth on SiC(0001). The calculated barrier is 4.7 eV, competitive interstitial \ensuremath{\sim}3.5 eV in SiC [M. Bockstedte et al., Phys. Rev. B 68, 205201 (2003)]. Scanning tunneling...

Magnetism of FeRh (001) films strongly depends on film thickness and surface terminations. While magnetic ground state bulk is G-type antiferromagnetism, the Rh-terminated exhibit ferromagnetism with strong perpendicular MCA whose energy +2.1 meV/$\Box$ two orders magnitude greater than 3$d$ metals, where $\Box$ area two-dimensional unit cell. Goodenough-Kanamori-Anderson rule superexchange interaction crucial in determining phases thin films, are results interplay competition between three...

Optical properties, such as the imaginary part of dielectric function, index refraction, reflectivity, and absorption coefficient, $[{\ensuremath{\epsilon}}_{2}(\ensuremath{\omega}),n(\ensuremath{\omega}),k(\ensuremath{\omega}),R(\ensuremath{\omega}),\ensuremath{\alpha}(\ensuremath{\omega})]$ some III-V semiconductors (InAs, InSb, GaSb, AlSb), are determined using our highly precise full-potential linearized augmented plane wave method with screened-exchange local density approximation...

Using first-principles calculations we demonstrate the feasibility of band-gap engineering in two-dimensional crystalline graphene monoxide (GMO), a recently reported graphene-based material with 1:1 carbon/oxygen ratio. The band gap GMO, which can be switched between direct and indirect, is tunable over large range (0--1.35 eV) for accessible strains. Electron hole transport occurs predominantly along zigzag armchair directions (armchair both) when GMO direct- (indirect-) semiconductor. A...