Results 1 - 10 of 836
Results 1 - 10 of 836. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] Graphene is characterized by chiral electronic excitations. As such it provides a perfect testing ground for the production of Klein pairs (electron/holes). If confirmed, the standard results for barrier phenomena must be reconsidered with, as a byproduct, the accumulation within the barrier of holes. (paper)
[en] The possibility of coexistence of ferromagnetic ordering and superconductivity in a two-band model of a semimetal with an isotopic current carrier spectrum is investigated in detail. It is shown that for unequal electron and hole concentrations triplet electron-hole and triplet cooper pairings with weak electron coupling may coexist. In this case a nonvanishing mean magnetic moment appears. (author). 9 refs., 4 figs
[en] Complete text of publication follows. Recent developments in solid-state semiconductor devices have made it possible to prepare a layer of electrons and a layer of holes in close proximity (∼ 10-20 nm), comparable to the excitonic Bohr radius of the host semiconductor (Gallium Arsenide). The physics of this system is driven by the attractive interlayer (electron-hole) Coulomb interaction and the in-plane repulsive interaction between the electrons (holes) themselves. But the binding energy scales (few meV) and the mass ratio of the positive and negative charges are very different from those in ionized Hydrogen plasmas. The electron and hole densities of this 2-component plasma can be individually controlled by gate voltages, set by the experimenter. Electrical current can be passed through each layer by independent ohmic contacts. The primary transport based tool for probing the interlayer scattering rate in these devices is the 'Coulomb drag' method, in which a current is passed through one layer and Coulomb interaction mediated momentum transfer to the other layer is measured. The interesting physics in these bilayers can be observed at T ∼ 1K or lower - readily accessible in liquid helium cooled cryostats. A rich phase diagram of the ground state of the electron-hole bilayer, consisting of excitonic phases, Charge density waves, Wigner crystals, excitonic condensates has been anticipated for many years. Recent data from two experimental groups have clearly shown that at low temperatures the interlayer scattering rate can no longer be correctly described by Fermi liquid theory. I will discuss the design concepts behind these devices, results of the ongoing experiments and several interesting open questions that have come up. Experimentally we have reached a strongly interacting regime, where the electron and hole densities can be tuned down to ∼ 5 x 1010cm-2 (rs ∼ 10 for holes, rs ∼ 2 for electrons) at an interlayer separation of 10-20 nm. This is a regime where the finite thickness of the wavefunctions are comparable to their separation and the intra-layer separation between the similarly charge particles are larger than the interlayer separation. The interlayer scattering and possible binding/density modulations must both be driven by the screened Coulomb interaction under these conditions. The behaviour of the dynamic bilayer dielectric screening ε(q; ω) in presence of disorder would be crucial in understanding the results.
[en] Herein, Fe is loaded into g-C3N4 nanosheets (Fe@g-C3N4) to form a photoactive system for H2 evolution. The loaded Fe species are present in the +3 oxidation state in the form of amorphous clusters. Upon loading 0.4 atomic% of Fe into g-C3N4, the H2 evolution rate under visible light increases from 2.19 μmol/g · h (g-C3N4) to 17.39 μmol/g · h (0.4Fe@g-C3N4). Meanwhile, the population of photoexcited electrons increases by 10.6 times in 0.4Fe@g-C3N4. The improved separation of electron-hole is behind the enhanced photoactivity for H2 evolution with Fe@g-C3N4. (paper)
[en] The authors determine the quantum phase diagram of the Hubbard chain with electron-hole symmetric correlated hopping at 1/2- and 1/4-filling using geometric concepts and continuum limit field theory. The long distance behavior of various correlation functions show a very rich phase diagram with several insulating, metallic, and superconducting phases, which might be relevant to (TMTSF)2X compounds. The closing of charge and spin gaps are accurately resolved as topological transitions (jumps in π of Berry phases). The metallic or insulating character of each thermodynamic phase is obtained from the ground-state expectation value of a displacement operator in reciprocal space
[en] Mott excitons in ferrodielctrics are investigated. It is shown that the two-particle equations for these excitons are different. These differences lead to the splitting of excitonic states. The generation of these excitons by electron beams is also discussed. (Author)
[en] The evolution of both vibration and electronic spectra of insulating La2CuO4+x single crystals upon charge-transfer gap photoexcitation has been studied by means of photoinduced reflection spectroscopy. Interaction of self-localized hole with some of the Ag, B2g(B3g), B3u optical phonons has been observed. Formation of self-localized hole state and its multiparticle complexes is supposed. Photoinduced absorption in C60 thin films has been found to differ essentially from that in cuprates
[en] Complete text of publication follows. In order to better understand the collective mode behavior of electronic bilayers actually realized in laboratory quantum well structures, there is a need to take into account the mass asymmetry. For example, in electron-hole bilayers (EHBs), one can hardly ignore the marked disparity in the electron and hole masses. So, with the aid of the quasilocalized charge approximation (QLCA), we have calculated the longitudinal sound speeds and long-wavelength finite-frequency (energy) gaps for closely spaced mass asymmetric EHB and electron bilayer (EBL) systems. The present study generalizes our earlier QLCA collective mode studies in symmetric EBLs and EHBs. Concentrating here on the closely spaced equal-density EHB in its dipole liquid phase, we find that for d/a < 1 (d is the layer spacing and a is the 2D Wigner-Seitz radius), the small-k behavior of the 'inphase' mode is acoustic with slope s + ∞ω0d, where √ω0 = 4e2/(m1+m2)a3. This is in marked contrast to the √d dependence exhibited by the RPA acoustic speed s+ =ω0 √ad; this latter is entirely suppressed in the strongly coupled dipole liquid. Note the decidedly different in-phase dispersion of the strongly coupled EBL liquid, ω+ (k→0) ∼ ω0√2ka. The 'out of phase' collective mode spectrum of the EHB dipole liquid features the k = 0 finite-frequency energy gap formula which is dominated by the prominent Gaussian-like peak in the interlayer pair distribution function at r = 0; thus the emergence of the Kepler frequency ΩK (d) = √(e2 / πd3)(m1+1/m2). Here, in contrast to the in-phase acoustic speed, it is the lighter particles (the electrons) that play the dominant role. Our calculated sound speed for the closely spaced asymmetric EHB is in perfect agreement with the sound speed reported for the strongly coupled 2D dipole liquid with repulsive interaction potential φ(r) = e2d2 / r3.
[en] The photoelectrochemical (PEC) water splitting properties can be enhanced by broadening the light absorption region and improving the separation of photogenerated carriers. In this paper, a novel ZnO/In2S3/Co–Pi ternary composite photoanode system is provided, by building the ZnO/In2S3 heterojunction to broaden the light absorption region and improve the separation and transfer of photogenerated electron–hole pairs in bulk, and by using the Co–Pi cocatalyst to increase the separation of photogenerated electron–hole pairs between the ZnO/In2S3 heterojunction surface and electrolyte. This ternary composite photoanode system exhibits a negative shifted onset potential and a higher photocurrent density of about 2.4 mA/cm2 at 1.23 V (vs. RHE), which is 3 and 2.18 times compared with bare ZnO nanorod and ZnO/In2S3 heterojunction, respectively. The results show that the ZnO/In2S3/Co–Pi ternary composite photoanode has an excellent potential application for PEC water splitting.
[en] The physical chemistry of the silver photography processes, exposure, development and fixing, is briefly summarized. The mechanism of the autocatalytic development by the developer of the clusters produced in silver bromide crystals during the exposure which is controlled by the critical nuclearity of these clusters was understood from pulse radiolysis studies. The effective quantum yield PHIeff of photoinduced silver cluster formation in silver halide microcrystals is usually much lower than the photoionization theoretical limit PHItheor=1 electron-hole pair per photon absorbed, owing to a subsequent very fast intra-crystal recombination of a part of the electron-hole pairs. In order to inhibit this recombination and favor the silver reduction by photo-electrons, the AgX crystals were doped with the formate HCO2- as a specific hole scavenger. First, the dopant scavenges the photoinduced hole, thus enhancing the electron escape from the pair recombination. Second, the CO2·- radical so formed transfers an electron to another silver cation, so that the PHIeff limit may be of 2Ag0 per photon. This Photoinduced Bielectronic Transfer mechanism is strictly proportional to the light quanta absorbed and induces an exceptional efficiency for enhancing the radio- or photographic sensitivity insofar as it totally suppresses the electron-hole recombination