ترغب بنشر مسار تعليمي؟ اضغط هنا

Many-body effects in porphyrin-like transition metal complexes embedded in graphene

85   0   0.0 ( 0 )
 نشر من قبل Adrian E. Feiguin
 تاريخ النشر 2019
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We introduce a new computational method to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce GGA+U results when ignoring inter-orbital Coulomb repulsion $U$ and Hund exchange $J$. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra, and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN$_4$ centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore, $U$ changes the relative position of the peaks in the density of states, particularly on the iron $d_{z^2}$ orbital, which is expected to greatly affect the binding of ligands.



قيم البحث

اقرأ أيضاً

The low-energy (intraband) range of the third harmonic generation of graphene in the terahertz regime is governed by the damping terms induced by the interactions. A controlled many-body description of the scattering processes is thus a compelling an d desirable requirement. In this paper, using a Kadanoff-Baym approach, we systematically investigate the impact of many-body interaction on the third-harmonic generation (THG) of graphene, taking elastic impurity scattering as a benchmark example. We predict the onset in the mixed inter-intraband regime of novel incoherent features driven by the interaction at four- and five-photon transition frequencies in the third-harmonic optical conductivity with a spectral weight proportional to the scattering rate.We show also that, in spite of the complex many-body physics, the purely intraband term governing the limit $omega to 0$ resembles the constraints of the phenomenological model. We ascribe this agreement to the fulfilling of the conservation laws enforced by the conserving approach. The overlap with novel incoherent features and the impact of many-body driven multi-photon vertex couplings limit however severely the validity of phenomenological description.
We develop the plasmon-pole approximation (PPA) theory for calculating the carrier self-energy of extrinsic graphene as a function of doping density within analytical approximations to the $GW$ random phase approximation ($GW$-RPA). Our calculated se lf-energy shows excellent quantitative agreement with the corresponding full $GW$-RPA calculation results in spite of the simplicity of the PPA, establishing the general validity of the plasmon-pole approximation scheme. We also provide a comparison between the PPA and the hydrodynamic approximation in graphene, and comment on the experimental implications of our findings.
We present magneto-Raman spectroscopy measurements on suspended graphene to investigate the charge carrier density-dependent electron-electron interaction in the presence of Landau levels. Utilizing gate-tunable magneto-phonon resonances, we extract the charge carrier density dependence of the Landau level transition energies and the associated effective Fermi velocity $v_mathrm{F}$. In contrast to the logarithmic divergence of $v_mathrm{F}$ at zero magnetic field, we find a piecewise linear scaling of $v_mathrm{F}$ as a function of charge carrier density, due to a magnetic field-induced suppression of the long-range Coulomb interaction. We quantitatively confirm our experimental findings by performing tight-binding calculations on the level of the Hartree-Fock approximation, which also allow us to estimate an excitonic binding energy of $approx$ 6 meV contained in the experimentally extracted Landau level transitions energies.
We investigate the many-body properties of graphene on top of a piezoelectric substrate, focusing on the interaction between the graphene electrons and the piezoelectric acoustic phonons. We calculate the electron and phonon self-energies as well as the electron mobility limited by the substrate phonons. We emphasize the importance of the proper screening of the electron-phonon vertex and discuss the various limiting behaviors as a function of electron energy, temperature, and doping level. The effect on the graphene electrons of the piezoelectric acoustic phonons is compared with that of the intrinsic deformation acoustic phonons of graphene. Substrate phonons tend to dominate over intrinsic ones for low doping levels at high and low temperatures.
We make use of micro-magneto Raman scattering spectroscopy to probe magneto-phonon resonances (MPR) in suspended mono- to penta-layer graphene. MPR correspond to avoided crossings between zone-center optical phonons (G-mode) and optically-active inte r Landau level (LL) transitions and provide a tool to perform LL spectroscopy at a fixed energy ($approx 197~rm{meV}$) set by the G-mode phonon. Using a single-particle effective bilayer model, we readily extract the velocity parameter associated with each MPR. A single velocity parameter slightly above the bulk graphite value suffices to fit all MPR for $Ngeq2$ layer systems. In contrast, in monolayer graphene, we find that the velocity parameter increases significantly from $(1.23pm 0.01) times 10^6~mathrm{m.s^{-1}}$ up to $(1.45pm0.02) times 10^6~mathrm{m.s^{-1}}$ as the first to third optically-active inter LL transition couple to the G-mode phonon. This result is understood as a signature of enhanced many-body effects in unscreened graphene.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا