Browsing by Author "Radonjić, Miloš"

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    Manifestation of strong correlations in transport in ultraclean SiGe/Si/SiGe quantum wells
    Shashkin, Alexander A.; Melnikov, Mikhail; Dolgopolov, Valeri; Radonjić, Miloš; Dobrosavljević, Vladimir; Huang, S.; Liu, Chi-Wu; Zhu, Amy Y. X.; Kravchenko, Sergey
    We observe that in a strongly interacting two-dimensional electron system in ultraclean SiGe/Si/SiGe quantum wells, the resistivity on the metallic side near the metal-insulator transition increases with decreasing temperature, reaches a maximum at some temperature, and then decreases by more than one order of magnitude. We scale the resistivity data in line with expectations for the transport of strongly correlated Fermi systems and find a nearly perfect agreement with theory over a wide range of electron densities.
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    Phonon anomalies in FeS
    Baum, Andreas; Milosavljević, Ana; Lazarević, Nenad; Radonjić, Miloš; Nikolić, Božidar; Mitschek, Merlin; Maranloo, Z. Inanloo; Šćepanović, Maja; Grujić-Brojčin, Mirjana; Stojilović, Nenad; Opel, Matthias; Wang, Aifeng; Petrović, Čedomir; Popović, Zoran; Hackl, Rudi U.
    We present results from light scattering experiments on tetragonal FeS with the focus placed on lattice dynamics. We identify the Raman active A1g and B1g phonon modes, a second order scattering process involving two acoustic phonons, and contributions from potentially defect-induced scattering. The temperature dependence between 300 and 20 K of all observed phonon energies is governed by the lattice contraction. Below 20 K the phonon energies increase by 0.5-1 cm-1, thus indicating putative short range magnetic order. Along with the experiments we performed lattice-dynamical simulations and a symmetry analysis for the phonons and potential overtones and find good agreement with the experiments. In particular, we argue that the two-phonon excitation observed in a gap between the optical branches becomes observable due to significant electron-phonon interaction.
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    Predicting the conductance of strongly correlated molecules: the Kondo effect in perchlorotriphenylmethyl/Au junctions
    Appelt, Wilhelm H.; Droghetti, Andrea; Chioncel, Liviu; Radonjić, Miloš; Muñoz, Enrique T.; Kirchner, Stefan; Vollhardt, Dieter; Rungger, Ivan
    Stable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule-metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized.
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    Quantum critical scaling for finite-temperature Mott-like metal-insulator crossover in few-layered MoS2
    Moon, Byoung Hee; Han, Gang Hee; Radonjić, Miloš; Ji, Hyunjin; Dobrosavljević, Vladimir
    The dominant role of strong electron-electron interactions in driving two-dimensional metal-insulator transitions has long been debated, but its clear experimental demonstration is still not available. Here, we examine the finite-temperature transport behavior of few-layered MoS2 material in the vicinity of the density-driven metal-insulator transition, revealing previously overlooked universal features characteristic of strongly correlated electron systems. Our scaling analysis, based on the Wigner-Mott theoretical viewpoint, conclusively demonstrates that the transition is driven by strong electron-electron interactions and not disorder, in striking resemblance to what is seen in other Mott systems. Our results provide compelling evidence that transition-metal dichalcogenides provide an ideal testing ground, and should open an exciting avenue for the study of strong correlation physics.
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    Superconducting nature of the Bi-II phase of elemental bismuth
    Khasanov, Rustem; Radonjić, Miloš; Luetkens, Hubertus; Morenzoni, Elvezio; Simutis, Gediminas; Schönecker, Stephan; Appelt, Wilhelm H.; Östlin, Andreas; Chioncel, Liviu; Amato, Alex
    The superconductivity in the Bi-II phase of elemental bismuth (transition temperature Tc≃3.92 K at pressure p≃2.80 GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with density functional theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field Bc(0)≃31.97 mT. The Eliashberg theory approach provides a good agreement with the experimental Tc and the temperature evolution of Bc. The estimated value for the retardation (coupling) parameter kBTc/ωln≈0.07 (ωln is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately coupled superconductor.