Showing papers on "Fermi energy published in 2013"
TL;DR: In this article, density functional theory is used to systematically study the electronic properties of doped MoS2 monolayers, wherethedopantsare incorporated both via S/Mosubstitution and ad-sorbates.
Abstract: Density functional theory is used to systematically study the electronic properties of doped MoS2 monolayers, wherethedopantsareincorporatedbothviaS/Mosubstitutionorasadsorbates.Amongthepossiblesubstitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS2 conduction band, making the system n type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n -a nd p-type conductivity, depending on the charge polarity of the adsorbed species.
480 citations
TL;DR: In this paper, theoretical and experimental developments for one-dimensional Fermi gases are discussed. But the exact results obtained for Bethe ansatz integrable models of this kind enable the study of the nature and microscopic origin of a wide range of quantum many-body phenomena driven by spin population imbalance, dynamical interactions, and magnetic fields.
Abstract: This article reviews theoretical and experimental developments for one-dimensional Fermi gases. Specifically, the experimentally realized two-component delta-function interacting Fermi gas-the Gaudin-Yang model-and its generalizations to multicomponent Fermi systems with larger spin symmetries is discussed. The exact results obtained for Bethe ansatz integrable models of this kind enable the study of the nature and microscopic origin of a wide range of quantum many-body phenomena driven by spin population imbalance, dynamical interactions, and magnetic fields. This physics includes Bardeen-Cooper-Schrieffer-like pairing, Tomonaga-Luttinger liquids, spin-charge separation, Fulde-Ferrel-Larkin-Ovchinnikov-like pair correlations, quantum criticality and scaling, polarons, and the few-body physics of the trimer state (trions). The fascinating interplay between exactly solved models and experimental developments in one dimension promises to yield further insight into the exciting and fundamental physics of interacting Fermi systems.
436 citations
TL;DR: Analysis of this large and tunable gap renormalization based on atomic charges obtained from density functional theory confirms and clarifies the dominant role of image-charge effects in single-molecule junctions.
Abstract: Metal/organic interfaces critically determine the characteristics of molecular electronic devices, because they influence the arrangement of the orbital levels that participate in charge transport. Studies on self-assembled monolayers show molecule-dependent energy-level shifts as well as transport-gap renormalization, two effects that suggest that electric-field polarization in the metal substrate induced by the formation of image charges plays a key role in the alignment of the molecular energy levels with respect to the metal's Fermi energy. Here, we provide direct experimental evidence for an electrode-induced gap renormalization in single-molecule junctions. We study charge transport through single porphyrin-type molecules using electrically gateable break junctions. In this set-up, the position of the occupied and unoccupied molecular energy levels can be followed in situ under simultaneous mechanical control. When increasing the electrode separation by just a few angstroms, we observe a substantial increase in the transport gap and level shifts as high as several hundreds of meV. Analysis of this large and tunable gap renormalization based on atomic charges obtained from density functional theory confirms and clarifies the dominant role of image-charge effects in single-molecule junctions.
275 citations
TL;DR: It is reported that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact, and identified in the energy domain with shot-noise spectroscopy and in the time domain with electronic Hong–Ou–Mandel noise correlations.
Abstract: The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the time domain. Finally, the generation technique could be applied to cold atomic gases, leading to the possibility of atomic levitons.
268 citations
TL;DR: In this article, the authors describe Li2O2 discharge experiments in a bulk electrolysis cell as a function of current density and temperature, which imply that charge transport through Li 2O2 in Li O2 batteries at practical current densities is based principally on hole tunneling, with hole polaron conductivity playing a significant role near the end of very low current discharges and at temperatures greater than 30 °C.
Abstract: We describe Li–O2 discharge experiments in a bulk electrolysis cell as a function of current density and temperature. In combination with a simple model, these imply that charge transport through Li2O2 in Li–O2 batteries at practical current densities is based principally on hole tunneling, with hole polaron conductivity playing a significant role near the end of very low current discharges and at temperatures greater than 30 °C. We also show that charge-transport limitations are much less significant during charging than those in discharge. A key element of the model that qualitatively explains all results is the alignment of the Li2O2 valence band maximum close to the electrochemical Fermi energy and how this alignment varies with overpotentials during discharge and charge. In fact, comparison of the model with the experiments allows determination of the alignment of the bands relative to the electrochemical Fermi level.
160 citations
TL;DR: It is shown that a TSF state with a single-component nonzero centre-of-mass momentum, called a topological Fulde-Ferrell (tFF) state, can be stabilized in a 2D Fermi gas with Rashba spin-orbit coupling and both in-plane and out- of-plane Zeeman fields.
Abstract: New quantum phenomena like Majorana fermions – particles that are their own anti-particles – could be demonstrated using cold atom systems. Zhang and Yi show how to stabilize a topological Fulde–Ferrell state in a two-dimensional Fermi gas, which might be able to support Majorana modes.
134 citations
TL;DR: In this paper, it was shown that the linear conductivity of icosahedral quasicrystals is characterized by two features not seen in ordinary metallic systems: there is an absence of the Drude peak and the interband conductivity rises linearly from a very low value up to normal metallic levels over a wide range of frequencies.
Abstract: The optical conductivity of quasicrystals is characterized by two features not seen in ordinary metallic systems. There is an absence of the Drude peak and the interband conductivity rises linearly from a very low value up to normal metallic levels over a wide range of frequencies. The absence of a Drude peak has been attributed to a pseudogap at the Fermi surface but a detailed explanation of the linear behavior has not been found. Here we show that the linear conductivity, which seems to be universal in all Al based icosahedral quasicrystal families, as well as their periodic approximants, follows from a simple model that assumes that the entire Fermi surface is gapped except at a finite set of Dirac points. There is no evidence of a semiconducting gap in any of the materials suggesting that the Dirac spectrum is massless, protected by topology leading to a Weyl semimetal. This model gives rise to a linear conductivity with only one parameter, the Fermi velocity. This picture suggests that decagonal quasicrystals should, like graphene, have a frequency independent conductivity, without a Drude peak. This is in accord with the experimental data as well.
133 citations
TL;DR: In this article, analytical expressions for the intraband conductivity tensor of graphene that includes spatial dispersion for arbitrarily wave-vector values and the presence of a nonzero Fermi energy are presented.
Abstract: Analytical expressions are presented for the intraband conductivity tensor of graphene that includes spatial dispersion for arbitrarily wave-vector values and the presence of a nonzero Fermi energy. The conductivity tensor elements are derived from the semiclassical Boltzmann transport equation under both the relaxation-time approximation and the Bhatnagar-Gross-Krook model (which allows for an extra degree of freedom to enforce number conservation). The derived expressions are based on linear electron dispersion near the Dirac points, and extend previous results that assumed small wave-vector values; these are shown to be inadequate for the very slow waves expected on graphene nanoribbons. The new expressions are also compared to results obtained by numericalintegrationoverthefirstBrillouinzoneusingtheexact(tight-binding)electrondispersionrelation.Very good agreement is found between the new analytical expressions and the exact numerical results. Furthermore, a comparison with the longitudinal random-phase conductivity is also made. It is shown analytically that these new expressions lead to the correct value of the quantum capacitance of a graphene sheet and that ignoring spatial dispersion leads to serious errors in the propagation properties of fundamental modes on graphene nanoribbons.
132 citations
TL;DR: The energy spectroscopy of emitted electrons indicates that at high magnetic field these electrons can be transported over several microns without inelastic electron-electron or electron-phonon scattering.
Abstract: We demonstrate the energy- and time-resolved detection of single-electron wave packets from a clock-controlled source transmitted through a high-energy quantum Hall edge channel. A quantum dot source is loaded with single electrons which are then emitted $\ensuremath{\sim}150\text{ }\text{ }\mathrm{meV}$ above the Fermi energy. The energy spectroscopy of emitted electrons indicates that at high magnetic field these electrons can be transported over several microns without inelastic electron-electron or electron-phonon scattering. Using a time-resolved spectroscopic technique, we deduce the wave packet size at picosecond resolution. We also show how this technique can be used to switch individual electrons into different electron waveguides (edge channels).
132 citations
TL;DR: In this paper, a density functional theory (DFT) calculation of the band structure of a Σ7 { 4 5 ¯ 1 0 } bicrystal boundary, for which the atomic structure of the boundary was known from an independent DFT energy-minimization calculation and comparisons with an atomic-resolution transmission electron micrograph of the same boundary.
129 citations
TL;DR: In this paper, a dimensional regularization scheme for quantum field theories with a Fermi surface was devised to study scaling behavior of non-Fermi liquid states in a controlled approximation.
Abstract: We devise a dimensional regularization scheme for quantum field theories with a Fermi surface to study scaling behavior of non-Fermi liquid states in a controlled approximation. Starting from two space dimensions, the co-dimension of the Fermi surface is extended to a general value while its dimension is fixed. When the Fermi surface is coupled with a critical boson centered at zero momentum, the interaction becomes marginal at a critical space dimension ${d}_{c}=5/2$. A deviation from the critical dimension is used as a small parameter for a systematic expansion. We apply this method to the theory where two patches of the Fermi surface are coupled with a critical boson, and show that the Ising-nematic critical point is described by a stable non-Fermi liquid state slightly below the critical dimension. Critical exponents are computed up to the two-loop order.
TL;DR: In this article, the anomalous Hall effect in ferromagnetic SrRuO_3 has been investigated in the context of Weyl semimetals, and it has been shown that even the nodes inside the Fermi sea have a significant effect on the physical properties of the material.
Abstract: We reconsider the problem of the anomalous Hall effect in ferromagnetic SrRuO_3, incorporating insights from the recently developed theory of Weyl semimetals. We demonstrate that SrRuO_3 possesses a large number of Weyl nodes, separated in momentum space, in its band structure. While the nodes normally do not coincide with the Fermi energy, unless the material is doped, we show that even the nodes inside the Fermi sea have a significant effect on the physical properties of the material. In particular, we show that the common belief that (the nonquantized part of) the intrinsic anomalous Hall conductivity of a ferromagnetic metal is entirely a Fermi-surface property, is incorrect: there generally exists a contribution to the anomalous Hall conductivity that arises from topological Fermi-arc surface states, associated with the Weyl nodes, which is of the same order of magnitude as the Fermi-surface contribution.
Journal Article•
TL;DR: It is demonstrated that strained or corrugated samples will have a space-dependent Fermi velocity in either approach that can affect the interpretation of local probe experiments in graphene.
Abstract: We investigate some apparent discrepancies between two different models for curved graphene: the one based on tight-binding and elasticity theory, and the covariant approach based on quantum field theory in curved space. We demonstrate that strained or corrugated samples will have a space-dependent Fermi velocity in either approach that can affect the interpretation of local probe experiments in graphene. We also generalize the tight-binding approach to general inhomogeneous strain and find a gauge field proportional to the derivative of the strain tensor that has the same form as the one obtained in the covariant approach.
TL;DR: The experimental measurement utilizes Bragg spectroscopy to obtain the dynamic and static structure factors of ultracold Fermi gases at high momentum in the unitarity and molecular Bose-Einstein condensate regimes and performs quantum Monte Carlo calculations of the static properties.
Abstract: We present a high-precision determination of the universal contact parameter in a strongly interacting Fermi gas. In a trapped gas at unitarity, we find the contact to be $3.06\ifmmode\pm\else\textpm\fi{}0.08$ at a temperature of 0.08 of the Fermi temperature in a harmonic trap. The contact governs the high-momentum (short-range) properties of these systems, and this low-temperature measurement provides a new benchmark for the zero-temperature homogeneous contact. The experimental measurement utilizes Bragg spectroscopy to obtain the dynamic and static structure factors of ultracold Fermi gases at high momentum in the unitarity and molecular Bose-Einstein condensate regimes. We have also performed quantum Monte Carlo calculations of the static properties, extending from the weakly coupled BCS regime to the strongly coupled Bose-Einstein condensate case, that show agreement with experiment at the level of a few percent.
TL;DR: A very thin graphene nanoribbon/polyvinyl alcohol (GNR/PVA) composite film has been developed which is light weight and requires a very low concentration of filler to achieve electromagnetic interference (EMI) shielding as high as 60 dB in the X band.
Abstract: A very thin graphene nanoribbon/polyvinyl alcohol (GNR/PVA) composite film has been developed which is light weight and requires a very low concentration of filler to achieve electromagnetic interference (EMI) shielding as high as 60?dB in the X band. Atomic force microscope studies show very well conjugated filler concentration in the PVA matrix for varying concentrations of GNR supported by Raman spectroscopy data. The films show 14 orders of increase in conductivity with a GNR concentration of 0.0075?wt% in PVA. This is possible because of the interconnected GNR network providing a very low percolation threshold as observed from the electrical measurements. Local density of states study of GNR using scanning tunnelling spectroscopy shows the presence of localized states near the Fermi energy. There are multiple advantages of GNR as an EMI shielding material in a polymer matrix. It has good dispersion in water, the conductive network in the composite shows very high electrical conductivity for a very low concentration of GNR and the presence of localized density of states near Fermi energy provides the spin states required for the absorbance of radiation energy in the X band.
TL;DR: Tuning spectroscopy shows that the superconducting behavior of graphene on Re is well described by the Bardeen-Cooper-Schrieffer theory and stands for a very good interface between the graphene and its metallic substrate.
Abstract: We report a new way to strongly couple graphene to a superconductor. The graphene monolayer has been grown directly on top of a superconducting Re(0001) thin film and characterized by scanning tunneling microscopy and spectroscopy. We observed a moir\'e pattern due to the mismatch between Re and graphene lattice parameters that we have simulated with ab initio calculations. The density of states around the Fermi energy appears to be position dependent on this moir\'e pattern. Tunneling spectroscopy performed at 50 mK shows that the superconducting behavior of graphene on Re is well described by the Bardeen-Cooper-Schrieffer theory and stands for a very good interface between the graphene and its metallic substrate.
TL;DR: In this paper, the authors studied the time evolution of continuous MERA under quantum quenches in free field theories and showed that it qualitatively agrees with its gravity dual given by a half of the AdS black hole spacetime.
Abstract: We study the time evolution of cMERA (continuous MERA) under quantum quenches in free field theories. We calculate the corresponding holographic metric using the proposal of arXiv:1208.3469 and confirm that it qualitatively agrees with its gravity dual given by a half of the AdS black hole spacetime, argued by Hartman and Maldacena in arXiv:1303.1080. By doubling the cMERA for the quantum quench, we give an explicit construction of finite temperature cMERA. We also study cMERA in the presence of chemical potential and show that there is an enhancement of metric in the infrared region corresponding to the Fermi energy.
TL;DR: The thermopower has little correlation with the conductance, but it decreases with the transition voltage, which is consistent with a theory based on Landauer's formula and shows that the thermopOWER provides valuable information about the relative alignment between the molecular energy levels and the electrodes' Fermi energy level.
Abstract: We have measured the thermopower as well as other important charge transport quantities, including conductance, current–voltage characteristics, and transition voltage of single molecules. The thermopower has little correlation with the conductance, but it decreases with the transition voltage, which is consistent with a theory based on Landauer’s formula. Since the transition voltage reflects the molecular energy level alignment, our finding also shows that the thermopower provides valuable information about the relative alignment between the molecular energy levels and the electrodes’ Fermi energy level.
TL;DR: The electron affinity of fluorine-terminated (100) diamond surfaces prepared by exposure to dissociated XeF2 has been determined using synchrotron-based photoemission.
Abstract: The work function and electron affinity of fluorine-terminated (100) diamond surfaces prepared by exposure to dissociated XeF2 have been determined using synchrotron-based photoemission. After vacuum annealing to 350 °C a clean, monofluoride terminated C(100):F surface was obtained for which an electron affinity of 2.56 eV was measured. This is the highest electron affinity reported for any diamond surface termination so far, and it exceeds the value predicted by recent density functional theory calculations by 0.43 eV. The work function of 7.24 eV measured for the same surface places the Fermi energy of 0.79 eV above the valence band maximum.
TL;DR: Detailed first-principles computations were performed on the geometric and electronic properties of the interfaces between graphene and ZnO polar surfaces, providing a theoretical explanation for the good performance of graphene/ZnO hybrid materials in photocatalysts and solar cells.
Abstract: Detailed first-principles computations were performed on the geometric and electronic properties of the interfaces between graphene and ZnO polar surfaces. A notable van der Waals force exists at the interface, and charge transfer occurs between graphene and ZnO as a result of the difference in their work functions. The Dirac point of graphene remains intact despite its adsorption on ZnO, implying that its interaction with ZnO does not affect the superior conductivity of graphene. Excited electrons within the energy range of 0?3?eV (versus Fermi energy) in the hybrid systems are mainly accumulated on graphene. The computations provide a theoretical explanation for the good performance of graphene/ZnO hybrid materials in photocatalysts and solar cells.
TL;DR: A general materials design approach that produces large orbital energy splittings (orbital polarization) in nickelate heterostructures, creating a two-dimensional single-band electronic surface at the Fermi energy that mimics that of the high temperature cuprate superconductors.
Abstract: We describe a general materials design approach that produces large orbital energy splittings (orbital polarization) in nickelate heterostructures, creating a two-dimensional single-band electronic surface at the Fermi energy. The resulting electronic structure mimics that of the high temperature cuprate superconductors. The two key ingredients are (i) the construction of atomic-scale distortions about the Ni site via charge transfer and internal electric fields, and (ii) the use of three-component (tricomponent) superlattices to break inversion symmetry. We use ab initio calculations to implement the approach, with experimental verification of the critical structural motif that enables the design to succeed.
TL;DR: In this article, the free energy of the quantum uniform electron gas for temperatures from near 0 to 100 times the Fermi energy, approaching the classical limit, was calculated using an extension of the Vashista-Singwi theory to finite temperatures.
Abstract: We calculate the free energy of the quantum uniform electron gas for temperatures from near 0 to 100 times the Fermi energy, approaching the classical limit. An extension of the Vashista-Singwi theory to finite temperatures and a self-consistent compressibility sum rule is presented. Comparisons are made to other local-field correction methods, as well as recent quantum Monte Carlo simulation and classical map-based results. Accurate fits to the exchange-correlation free energy from both theory and simulation are given for future practical applications.
TL;DR: The estimated superconducting gap Δ and Fermi energy indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-cOUpling BCS-like super conductivity in the hole band, and the study identifies the possible route to B CS-BECsuperconductivity.
Abstract: Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe$_{0.6}$Se$_{0.4}$($T_c$ = 14.5 K $\sim$ 1.2 meV) in an accessible range below and above the Fermi level($E_F$) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV ($\sim$ 8 K) above $E_F$ at the $\Gamma$-point, which shows a sharp superconducting coherence peak with gap formation below $T_c$. The estimated superconducting gap $\Delta$ and Fermi energy $\epsilon_F$ indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.
TL;DR: In this paper, the authors studied the electron transmission through the domain boundary on bilayer graphene separating the AB and BA stacking regions using the effective continuum model and calculated the transmission probability as a function of the electron energy and the incident angle for several specific boundary structures.
Abstract: We study the electron transmission through the domain boundary on bilayer graphene separating $\mathit{AB}$ and $\mathit{BA}$ stacking regions. Using the effective continuum model, we calculate the electron transmission probability as a function of the electron energy and the incident angle, for several specific boundary structures. The transmission strongly depends on the crystallographic direction of the boundary and also on the atomic configuration inside. At low energy, the boundary is either insulating or highly transparent depending on the structure. In insulating cases, the transmission sharply rises when the Fermi energy is increased to a certain level, suggesting that the electric current through the boundary can be controlled by the field effect. The boundary parallel to the zigzag direction generally has different transmission properties between the two different valleys, and this enables one to generate the valley polarized current in a certain configuration. We show that those characteristic features can be qualitatively explained by the transverse momentum conservation in the position-dependent band structure in the intermediate region.
TL;DR: In this paper, the ground state of an interacting fermionic system is characterized by a Fermi surface in momentum space, and the low energy excitations are weakly interacting fermanionic quasiparticles near the surface.
Abstract: For over fifty years our understanding of the lowtemperature properties of metals has been based on Laudau’s theory of Fermi liquids. In Fermi liquid theory, the ground state of an interacting fermionic system is characterized by a Fermi surface in momentum space, and the low energy excitations are weakly interacting fermionic quasiparticles near the Fermi surface. This picture of well-defined quasiparticles close to the Fermi surface provides a powerful tool for obtaining low temperature properties of the system and has been very successful in explaining most metallic states observed in nature, from liquid 3 He to heavy fermion behavior in rare earth compounds.
TL;DR: In this article, the effect of La2O3 addition on electrical and optical properties of lithium borate glass has been studied in the present paper, where the authors measured the direct and indirect optical band gap, Urbach energy and Fermi energy were calculated from absorption spectra using functionality of extinction coefficient from Fermis-Dirac distribution function.
TL;DR: Numerical simulations show that the light absorbance can be controlled from near zero to 100% by tuning the Fermi energy and a set of periodically located absorption peaks is observed at near grazing incidence.
Abstract: Graphene is a two-dimensional material with exotic electronic, optical and thermal properties. The optical absorption in monolayer graphene is limited by the fine structure constant α. Here we demonstrated the strong enhancement of light absorption and thermal radiation in homogeneous graphene. Numerical simulations show that the light absorbance can be controlled from near zero to 100% by tuning the Fermi energy. Moreover, a set of periodically located absorption peaks is observed at near grazing incidence. Based on this unique property, highly directive comb-like thermal radiation at near-infrared frequencies is demonstrated.
TL;DR: In this paper, the authors demonstrate the electrical injection and detection of spin-polarized electrons in the Co2FeSi/GaAs hybrid system using lateral transport structures Spin valve signatures and characteristic Hanle curves are observed both in the nonlocal and the local configuration.
Abstract: We demonstrate the electrical injection and detection of spin-polarized electrons in the Co2FeSi/GaAs hybrid system using lateral transport structures Spin valve signatures and characteristic Hanle curves are observed both in the nonlocal and the local configuration The comparatively large magnitude of the local spin valve signal and the high signal-to-noise ratio are attributed to the large spin polarization at the Fermi energy of Co2FeSi in the well-ordered L21 phase
TL;DR: In this article, a Laplacian correction term in the electromagnetic wave equation was proposed to account for the non-local dynamics of the electron gas when exploring the true nanoscale.
Abstract: The plasmon response of metallic nanostructures is anticipated to exhibit nonlocal dynamics of the electron gas when exploring the true nanoscale. We extend the local-response approximation (based on Ohm's law) to account for a general short-range nonlocal response of the homogeneous electron gas. Without specifying further details of the underlying physical mechanism we show how this leads to a Laplacian correction term in the electromagnetic wave equation. Within the hydrodynamic model we demonstrate this explicitly and we identify the characteristic nonlocal range to be ξ NL ∼ v F / ω where v F is the Fermi velocity and ω is the optical angular frequency. For noble metals this gives significant corrections when characteristic device dimensions approach ∼1–10 nm, whereas at more macroscopic length scales plasmonic phenomena are well accounted for by the local Drude response.
TL;DR: A silicon germanide (SiGe) analog of silicene is proposed, which is stable and free from imaginary frequency in the phonon spectrum, making sublattice-selective hydrogenation and consequently electron spin-polarization possible.
Abstract: From first-principles calculations, we proposed a silicon germanide (SiGe) analog of silicene This SiGe monolayer is stable and free from imaginary frequency in the phonon spectrum The electronic band structure near the Fermi level can be characterized by Dirac cones with the Fermi velocity comparable to that of silicene The Ge and Si atoms in SiGe monolayer exhibit different tendencies in binding with hydrogen atoms, making sublattice-selective hydrogenation and consequently electron spin-polarization possible