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Register a new userCharge Kondo Effect in Thermoelectric Properties of Lead Telluride doped with Thallium Impurities
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We investigate the thermoelectric properties of PbTe doped with a small concentration $x$ of Tl impurities acting as acceptors and described by Anderson impurities with negative on-site (effective) interaction. The resulting charge Kondo effect naturally accounts for a number of the low temperature anomalies in this system, including the unusual doping dependence of the carrier concentration, the Fermi level pinning and the self-compensation effect. The Kondo anomalies in the low temperature resistivity at temperatures $Tleq 10, {rm K}$ and the $x$-dependence of the residual resistivity are also in good agreement with experiment. Our model also captures the qualitative aspects of the thermopower at higher temperatures $T>300, {rm K}$ for high dopings ($x>0.6%$) where transport is expected to be largely dominated by carriers in the heavy hole band of PbTe.
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We report results of low-temperature thermodynamic and transport measurements of Pb_{1-x}Tl_{x}Te single crystals for Tl concentrations up to the solubility limit of approximately x = 1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T_K ~ 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high T_c values.
The effect of magnetic impurities on the ballistic conductance of nanocontacts is, as suggested in recent work, amenable to ab initio study cite{naturemat}. Our method proceeds via a conventional density functional calculation of spin and symmetry dependent electron scattering phase shifts, followed by the subsequent numerical renormalization group solution of Anderson models -- whose ingredients and parameters are chosen so as to reproduce these phase shifts. We apply this method to investigate the Kondo zero bias anomalies that would be caused in the ballistic conductance of perfect metallic (4,4) and (8,8) single wall carbon nanotubes, ideally connected to leads at the two ends, by externally adsorbed Co and Fe adatoms. The different spin and electronic structure of these impurities are predicted to lead to a variety of Kondo temperatures, generally well below 10 K, and to interference between channels leading to Fano-like conductance minima at zero bias.
The recent discovery of excellent thermoelectric properties and topological surface states in SnTe-based compounds has attracted extensive attention in various research areas. Indium doped SnTe is of particular interest because, depending on the doping level, it can either generate resonant states in the bulk valence band leading to enhanced thermoelectric properties, or induce superconductivity that coexists with topological states. Here we report on the vapor deposition of In-doped SnTe nanowires and the study of their surface oxidation and thermoelectric properties. The nanowire growth is assisted by Au catalysts, and their morphologies vary as a function of substrate position and temperature. Transmission electron microscopy characterization reveals the formation of amorphous surface in single crystalline nanowires. X-ray photoelectron spectroscopy studies suggest that the nanowire surface is composed of In2O3, SnO2, Te and TeO2 which can be readily removed by argon ion sputtering. Exposure of the cleaned nanowires to atmosphere yields rapid oxidation of the surface within only one minute. Characterizations of electrical conductivity {sigma}, thermopower S, and thermal conductivity k{appa} were performed on the same In-doped nanowire which shows suppressed {sigma} and k{appa} but enhanced S yielding an improved thermoelectric figure of merit ZT than the undoped SnTe.
We report the existence of the charge density wave (CDW) in the ground state of 1D Kondo lattice model at the filling of n=0.75 in the weak coupling region. The CDW is driven by the effective Coulomb repulsion mediated by the localized spins. Based on our numerical results using the density matrix renormalization group method, we show that the CDW phase appears in the paramagnetic region previously known as the Tomonaga-Luttinger liquid. The emergence of this phase serves as an example of CDW phase induced without bare repulsive interactions, and enriches the phase diagram of the 1D Kondo lattice model.
Last few years have witnessed significant enhancement of thermoelectric figure of merit of lead telluride (PbTe) via nanostructuring. Despite the experimental progress, current understanding of the electron transport in PbTe is based on either band structure calculation using first principles with constant relaxation time approximation or empirical models, both relying on adjustable parameters obtained by fitting experimental data. Here, we report parameter-free first-principles calculation of electron and phonon transport properties of PbTe, including mode-by-mode electron-phonon scattering analysis, leading to detailed information on electron mean free paths and the contributions of electrons and phonons with different mean free paths to thermoelectric transport properties in PbTe. Such information will help to rationalize the use and optimization of nanosctructures to achieve high thermoelectric figure of merit.
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