meV Binding Energy Research Articles

Spectroscopic evidence of flat bands in breathing kagome semiconductor Nb3I8

Kagome materials have become solid grounds to study the interplay among geometry, topology, correlation, and magnetism. Recently, niobium halide semiconductors Nb3X8 (X = Cl, Br, I) have been predicted to be two-dimensional magnets and these materials are also interesting for their breathing kagome geometry. However, experimental electronic structure studies of these promising materials are still lacking. Here, we report the spectroscopic evidence of flat and weakly dispersing bands in breathing-kagome semiconductor Nb3I8 around 500 meV binding energy, which is well supported by our first-principles calculations. These bands originate from the breathing kagome lattice of niobium atoms and have niobium d-orbital character. They are found to be sensitive to the polarization of the incident photon beam. Our study provides insight into the electronic structure and flat band topology in an exfoliable kagome semiconductor, thereby providing an important platform to understand the interaction of geometry and electron correlations in two-dimensional materials.

Efficient generation of emissive many-body correlations in copper-doped colloidal quantum wells

Colloidal quantum wells (CQWs) provide an appealing platform to achieve emissive many-body correlations for novel optoelectronic devices, given that they act as hosts for strong carrier Coulomb interactions and present suppressed Auger recombination. However, the demonstrated high-order excitonic emission in CQWs requires ultrafast pumping with high excitation levels and can only be spectrally resolved at the single-particle level under cryogenic conditions. Here, through systematic investigation using static power-dependent emission spectroscopy and transient carrier dynamics, we show that Cu-doped CdSe CQWs exhibit continuous-wave-pumped high-order excitonic emission at room temperature with a large binding energy of ∼64 meV. We attribute this unique behavior to dopant excitons in which the ultralong lifetime and the highly localized wavefunction facilitate the formation of many-body correlations. The spectrally resolved high-order excitonic emission generated at power levels compatible with solar irradiation and electrical injection might pave the way for novel solution-processed solid-state devices. • Continuous-wave-pumped high-order excitonic emission at room temperature is shown • The excitation level is compatible with solar irradiation and electrical injection • 64 meV binding energy enables spectrally resolved high-order excitonic emission Yu et al. demonstrate continuous-wave-pumped high-order excitonic emission at room temperature in Cu-doped CdSe colloidal quantum wells. The properties of dopant excitons enable an ultra-low excitation level compatible with solar irradiation or electrical injection and a binding energy of ∼64 meV, which makes the high-order excitonic emission spectrally resolvable at room temperature.

Search for the Charmed Baryonium and Dibaryon Structures via the QCD Sum Rules

In the present work, we construct eight six-quark currents to study the Σ c Σ ¯ c baryonium and Σ c Σ c dibaryon states via the QCD sum rules. For either Σ c Σ ¯ c baryonium or Σ c Σ c dibaryon states, we construct four currents with the J P = 1 − , 1 + , 0 + and 0 − . Except the current 1 + of Σ c Σ c , we find the Borel windows for the other seven. There are two possible Σ c Σ ¯ c molecular states or compact six-quark states with the J P = 1 − and 0 − . The results of the current 0 + of Σ c Σ c show a possible Σ c Σ c molecular state with 20 MeV binding energy. We find two Σ c Σ ¯ c baryonium resonances states with the J P = 1 + , 0 + and two Σ c Σ c dibaryon resonances states with the J P = 0 − , 1 − , respectively. Pole residues of the seven states are also calculated.

Two-Step Chemical Vapor Deposition-Synthesized Lead-Free All-Inorganic Cs3Sb2Br9 Perovskite Microplates for Optoelectronic Applications.

Lead-based halide perovskites (APbX3, where A = organic or inorganic cation, X = Cl, Br, I) are suitable materials for many optoelectronic devices due to their many attractive properties. However, the concern of lead toxicity and the poor ambient and operational stability of the organic cation group greatly limit their practical utilization. Therefore, there has recently been great interest in lead-free, environment-friendly all-inorganic halide perovskites (IHPs). Sb and Sn are common species suggested to replace Pb for Pb-free IHPs. However, the large difference in the melting points of the precursor materials (e.g., CsBr and SbBr3 precursors for Cs3Sb2Br9) makes the chemical vapor deposition (CVD) growth of high-quality Pb-free IHPs a very challenging task. In this work, we developed a two-step CVD method to overcome this challenge and successfully synthesized Pb-free Cs3Sb2Br9 perovskite microplates. Cs3Sb2Br9 microplates ∼25 μm in size with the exciton absorption peak at ∼2.8 eV and a band gap of ∼2.85 eV were obtained. The microplates have a smooth hexagonal morphology and show a large Stokes shift of ∼450 meV and exciton binding energy of ∼200 meV. To demonstrate the applications of these microplates in optoelectronics, simple photoconductive devices were fabricated. These photodetectors exhibit a current on/off ratio of 2.36 × 102, a responsivity of 36.9 mA/W, and a detectivity of 1.0 × 1010 Jones with a fast response of rise and decay time of 61.5 and 24 ms, respectively, upon 450 nm photon irradiation. Finally, the Cs3Sb2Br9 microplates also show good stability in ambient air without encapsulation. These results demonstrate that the 2-step CVD process is an effective approach to synthesize high-quality all-inorganic lead-free Cs3Sb2Br9 perovskite microplates that have the potential for future high-performance optoelectronic device applications.

Unmasking the Origin of Kinks in the Photoemission Spectra of Cuprate Superconductors.

The origin of a ubiquitous bosonic coupling feature in the photoemission spectra of high-T_{c} cuprates, an energy-momentum dispersion "kink" observed at ∼70 meV binding energy, remains a two-decade-old mystery. Understanding this phenomenon requires an accurate description of the coupling between the electron and some collective modes. We report here abinitio calculations based on GW perturbation theory and show that correlation-enhanced electron-phonon interaction in cuprates gives rise to the strong kinks, which not only explains quantitatively the observations but provides new understanding of experiments. Our results reveal it is the electron density of states being the predominant factor in determining the doping dependence of the kink size, manifesting the multiband nature of the cuprates, as opposed to the prevalent belief of it being a measure of the mode-coupling strength.

Characterization and device applications of p-type ZnO films prepared by thermal oxidation of sputter-deposited zinc oxynitride

Formation of nitrogen-doped p-type ZnO (p-ZnO) and related homojunction devices has been reported extensively using a variety of techniques with the exception of thermal oxidation of ZnON that is a simple and less explored method. We converted sputter-deposited ZnON films to p-ZnO at relatively low oxidation temperatures (400–500 °C) as compared with other reports. Chemical bonding states of nitrogen in p-ZnO films were examined by XPS analysis and the mechanism of p-type doping was discussed. Films were characterized by XRD, SEM, photocurrent spectroscopy, and photoluminescence (PL) measurement. Films were composed from nano-size crystallites with (100) preferential orientation. A shallow acceptor level with a 70–90 meV binding energy and a 1.72-eV deep level were measured and identified. PL thermal quenching of the films had activation energy of 34 meV. Schottky barrier (SB) and homojunction diodes, with two different types of n-ZnO, were fabricated on films and their parameters were compared with the reported data. The SB and both types of homojunction diodes had high rectification factors (104-105) and good device parameters. The conductance of homojunction diode based on sputter-deposited n-ZnO showed thermal activation energies of 0.08–0.12 eV, 0.16–0.20 eV, and 0.40–0.50 eV. The homojunction diode based on n-ZnO nano-rods exhibited strong electroluminescence in the visible region from which two defect-related transition energies of 2.21 eV and 2.66 eV were obtained. In conclusion, good quality p-ZnO films and related devices can be prepared by thermal oxidation of ZnON films.

In-mediumη′mass andη′Ninteraction based on chiral effective theory

The in-medium ${\ensuremath{\eta}}^{\ensuremath{'}}$ mass and the ${\ensuremath{\eta}}^{\ensuremath{'}}N$ interaction are investigated in an effective theory based on the linear realization of the SU(3) chiral symmetry. We find that a large part of the ${\ensuremath{\eta}}^{\ensuremath{'}}$ mass is generated by the spontaneous breaking of chiral symmetry through the U${}_{A}$(1) anomaly. As a consequence of this observation, the ${\ensuremath{\eta}}^{\ensuremath{'}}$ mass is reduced in nuclear matter where chiral symmetry is partially restored. In our model, the mass reduction is found to be 80 MeV at the saturation density. Estimating the ${\ensuremath{\eta}}^{\ensuremath{'}}N$ interaction based on the same effective theory, we find that the ${\ensuremath{\eta}}^{\ensuremath{'}}N$ interaction in the scalar channel is attractive sufficiently to form a bound state in the ${\ensuremath{\eta}}^{\ensuremath{'}}N$ system with a several MeV binding energy. We discuss the origin of attraction by emphasizing the special role of the $\ensuremath{\sigma}$ meson in the linear sigma model for the mass generation of ${\ensuremath{\eta}}^{\ensuremath{'}}$ and $N$.

First-Principles Studies of Photoinduced Charge Transfer in Noncovalently Functionalized Carbon Nanotubes

We have studied the energetics, electronic structure, optical excitation, and electron relaxation of dinitromethane molecules (CH2N2O4) adsorbed on semiconducting carbon nanotubes (CNTs) of chiral index (n,0) (n = 7, 10, 13, 16, 19). Using first-principles density functional theory (DFT) with generalized gradient approximations and van der Waals corrections, we have calculated adsorption energies of dinitropentylpyrene, in which the dinitromethane is linked to the pyrene via an aliphatic chain, on a CNT. A 780 meV (18.0 kcal/mol) binding energy has been found, which explains why such aliphatic chain–pyrene units can be and have been used in experiments to bind functional molecules to CNTs. The calculated electronic structures show that the dinitromethane introduces a localized state inside the band gap of CNT systems of n = 10, 13, 16. and 19; such a state can trap an electron when the CNT is photoexcited. We have therefore investigated the dynamics of intraband relaxations using the reduced density matrix formalism in conjunction with DFT. For pristine CNTs, we have found that the calculated charge relaxation constants agree well with the experimental time scales. Upon adsorption, these constants are modified, but there is not a clear trend for the direction and magnitude of the change. Nevertheless, our calculations predict that electron relaxation in the conduction band is faster than hole relaxation in the valence band for CNTs with and without molecular adsorbates.

Angle-resolved photoemission spectroscopy study of BaCo2As2

We use angle-resolved photoemission spectroscopy and full-potential linearized augmented-plane-wave (FP-LAPW) calculations to study the electronic structure of BaCo${}_{2}$As${}_{2}$. The Fermi surface (FS) maps and the corresponding band dispersion data (at 90 and 200 K) reveal a small electron pocket at the center and a large electron pocket at the corner of the Brillouin zone. Therefore the nesting between electron and hole FS pockets is absent in this compound, in contrast to the parent compounds of FeAs-based high-$T$${}_{\mathrm{c}}$ superconductors. The electron pockets at the center of the zone are surrounded by two sets of four smaller electron pockets. The electronic structure at about 500 meV binding energy is very similar to features at the chemical potential in BaFe${}_{2}$As${}_{2}$. This indicates that complete substitution of Co for Fe causes a nearly rigid shift in the chemical potential by adding two electrons per formula unit at higher binding energies. However at lower binding energies $\ensuremath{\sim}$270 meV, the electron pocket at the center of the zone is absent, unlike in the Co-substituted Fe-based materials. This demonstrates that the rigid band picture is valid only at higher binding energies and breaks down closer to the chemical potential in BaCo${}_{2}$As${}_{2}$. We also observed the presence of a flat band near the Fermi energy that may have consequences for transport and thermodynamical properties. The experimental FS topology as well as band dispersion data are in reasonable agreement with the FP-LAPW calculations.

Photoluminescence study of Zn-doped wurtzite InP core-shell nanowires

In situ Zn doping of InP shells on nanowires in the wurtzite crystal structure has been investigated using diethyl zinc (DEZn) as a precursor. Photoluminescence measurements of single nanowires unexpectedly exhibit an acceptor-related peak at room temperature, in contrast to thin films grown at identical conditions. This peak is observable even using low DEZn molar fractions, which indicates efficient Zn incorporation at the InP wurtzite facets. The spectra indicate a 52 meV binding energy for the Zn acceptor in wurtzite, which is higher than that of bulk zinc blende. These results demonstrate that in situ Zn doping of wurtzite InP nanowire shells can be achieved.

Circumstantial evidence for hydrogen-induced surface magnetism on Pd(110)

The surface of clean and hydrogen-covered Pd(110) was investigated by angle-resolved photoemission spectroscopy. At a coverage of 1.5 ML, where the surface adapts a pairing-row reconstruction, the spectra show a peculiar peak splitting of the $\overline{S}$-surface resonance. The band dispersion of this satellite is parallel to the dispersion of the main resonance but shifted by 400 meV at $T=100$ K. An interpretation in terms of magnetic exchange splitting is supported by the appearance of a kink structure of the photoemission data around 350 meV binding energy. This unexpected behavior for H adsorption is attributed to the reduced coordination of the Pd atoms at the surface.

MICROSCOPIC OPTICAL POTENTIAL FROM ARGONNE INTER-NUCLEON POTENTIALS

In the present work we describe our results concerning the calculation of equation of state of symmetric zero temperature nuclear matter and the microscopic optical potential using the soft-core Argonne inter-nucleon potentials in first order Brueckner–Hartree–Fock (BHF) theory. The nuclear matter saturates at a density 0.228 nucleon/fm 3 with 17.52 MeV binding energy per nucleon for Argonne av-14 and at 0.228 nucleon/fm 3 with 17.01 MeV binding energy per nucleon for Argonne av-18. As a test case we present an analysis of 65 and 200 MeV protons scattering from 208 Pb . The Argonne av-14 has been used for the first time to calculate nucleon optical potential in BHF and analyze the nucleon scattering data. We also compare our reaction matrix results with those using the old hard-core Hamada–Johnston and the soft-core Urbana uv-14 and Argonne av-18 inter-nucleon potentials. Our results indicate that the microscopic potential obtained using av-14 gives marginally better agreement with the experimental data than the other three Hamiltonians used in the present work.

KK̄N and K̄K̄N Molecular States with I = 1/2, 3/2 and JP = 1/2+ Studied with Three-Body Faddeev Calculations

Using the Akaishi—Yannazaki (AY) and Hyodo—Weise (HW) effective KK̄, K̄N, K̄K̄ and KN interactions, we study possible existence of KK̄N and K̄K̄N molecule states with I = 1/2,3/2 and JP = 1/2+ by means of three-body Faddeev equations. We find that for HW potential, KK̄N and K̄K̄N systems with I = 1/2 both are bound hadron molecular states with about 10 MeV binding energy. The relativistic effects of kinetic energy are of the order of 4–5 MeV. AY potential would give larger binding energy because of overestimating K̄N interaction strength. Although there are attractive interactions in the case of I = 3/2, the interaction is too weak to bind the systems.

Interaction in a chiral quark model

The interaction is dynamically investigated in a chiral quark model by resolving the resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon–nucleon (NN) scattering phase shifts and the hyperon–nucleon (YN) cross sections. The results show that the S-wave isospin interaction is attractive, and in the extended chiral SU(3) quark model such attraction can make for a bound state with 3 MeV binding energy. Furthermore the behavior of the one-gluon exchange and the vector-meson exchange is examined and it is found that the one-gluon exchange is strongly repulsive while the vector-meson exchange offers weak attraction in the system.

Universal character of CoO 2 plane studied by high-resolution angle-resolved photoemission

We have performed high-resolution angle-resolved photoemission spectroscopy on M x CoO 2 (M: Na, K, Rb) to clarify the band dispersion and Fermi surface inherent to CoO 2 plane. We have found that a 1 g band which forms a large hexagonal Fermi surface centered at Γ (A) point shows a dispersion kink at approximately 100 meV binding energy, irrespective of the species of alkali metals and its content ( x). We discuss the origin of kink in the dispersion in terms of the strong mass renormalization due to electron–phonon interaction and/or the hybridization of a 1 g and e g ′ bands.

Nϕstates in a chiral quark model

The structures of $N\ensuremath{\phi}$ states with spin-parity ${J}^{p}=3/{2}^{\ensuremath{-}}$ and ${J}^{p}=1/{2}^{\ensuremath{-}}$ are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The channel coupling of $N\ensuremath{\phi}$ and $\ensuremath{\Lambda}{K}^{*}$ is considered, and the effect of the tensor force which results in the mixing of S and D waves is also investigated. The results show that the $N\ensuremath{\phi}$ state has an attractive interaction, and in the extended chiral SU(3) quark model such an attraction plus the channel coupling effect can consequently make for an $N\ensuremath{\phi}$ quasi-bound state with several MeV binding energy.

Structures of (ΩΩ)0+ and (ΞΩ)1+ in Extended Chiral SU(3) Quark Model**The project supported by National Natural Science Foundation of China

The structures of (ΩΩ)0+ and (ΞΩ)1+ are studied in the extended chiral SU(3) quark model in which vector meson exchanges are included. The effect from the vector meson fields is very similar to that from the one-gluon exchange (OGE) interaction. Both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model, di-omega (ΩΩ)0+ is always deeply bound, with over one hundred MeV binding energy, and (ΞΩ)1+'s binding energy is around 20 MeV. An analysis shows that the quark exchange effect plays a very important role for making di-omega (ΩΩ)0+ deeply bound.

Evidence for abrupt change in dispersion and scattering rate of quasiparticles in Bi 2Sr 2CaCu 2O 8

We report high-resolution ARPES data from Bi 2Sr 2CaCu 2O 8 superconductors as a function of doping and temperature. A clear break in the quasiparticle dispersion near 50±10 meV binding energy has been observed, resulting in a change of the quasiparticle velocity up to a factor of two or more. This break is present at various points of the momentum space, and the magnitude of the dispersion change decreases with temperature and with doping.

Evidence for an energy scale for quasiparticle dispersion in Bi2Sr2CaCu2O8

Quasiparticle dispersion in Bi2Sr2CaCu2O8 is investigated with improved angular resolution as a function of temperature and doping. Unlike the linear dispersion predicted by the band calculation, the data show a sharp break in dispersion at 50+/-15 meV binding energy where the velocity changes by a factor of 2 or more. This change provides an energy scale in the quasiparticle self-energy. This break in dispersion is evident at and away from the d-wave node line, but the magnitude of the dispersion change decreases with temperature and with increasing doping.

Near-Band Gap Selective Photoluminescence in Wurtzite GaN

Selective photoluminescence (SPL) experiments are performed at low temperature on n-type GaN layers obtained by epitaxial lateral overgrowth on sapphire. A significant impurity electronic Raman scattering (ERS) effect is observed when excited in the spectral range of excited states of A and B free excitons, giving an accurate determination of the transition energies to the n = 2 states and a straightforward estimation of the A and B Rydberg. From the donor transition energy measured on the ERS spectra we deduce a 30.5 meV binding energy for the main residual donor in our epitaxial layers. In addition, SPL experiments have been used to analyse the neutral donor bound exciton (I2) spectra. It is shown that a laser tuned near the A free exciton induces strong and narrow resonant peaks superimposed to I2. It is concluded that such effect is due to the selective excitation of inhomogeneously broadened I2 excited states. Up to five rotational I2 excited states are identified.