Results 1 - 10 of 7613
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[en] Dy adatom adsorption and penetration on defected graphene were studied using first-principles calculations. We show that adsorption of Dy adatom on defect is energetically more favorable than on pristine graphene. Strong covalent bonding between Dy and C atoms at the defect sites is confirmed by interaction charge density analysis. We also found that the pathways for Dy penetration through defects with 1 and 2 missing carbon atoms are different from those through larger holes in graphene due to strong spatial confinement effects. The larger size of the hole is, the smaller barrier for Dy penetration. (paper)
[en] An axion insulator is a correlated topological phase, predicted to arise from the formation of a charge density wave in Weyl semimetals. The accompanying sliding mode in the charge density wave phase, the phason, is an axion. It is expected to cause anomalous magneto-electric transport effects. However, this axionic charge density wave has so far eluded experimental detection. In this paper, we report for the first time the observation of a large, positive contribution to the magneto-conductance in the sliding mode of the charge density wave Weyl semimetal (TaSe)I for collinear electric and magnetic fields (EB). The positive contribution to the magneto-conductance originates from the anomalous axionic contribution of the chiral anomaly to the phason current, and is locked to the parallel alignment of E and B. By rotating B, we show that the angular dependence of the magneto-conductance is consistent with the anomalous transport of an axionic charge density wave.
[en] The coupling of phonons with collective modes and single-particle gap excitations associated with one (1d) and two-directional (2d) electronically-driven charge-density wave (CDW) ordering in metallic RTe3 is investigated as a function of rare-earth ion chemical pressure (R = Tb, Dy, Ho) using femtosecond pump-probe spectroscopy. From the T-dependence of the CDW gap ΔCDW and the amplitude mode (AM) we find that while the transition to a 1d-CDW ordered state at Tc1 initially proceeds in an exemplary mean-field (MF)-like fashion, below Tc1, ΔCDW is depressed and departs from the MF behavior. The effect is apparently triggered by resonant mode-mixing of the amplitude mode (AM) with a totally symmetric phonon at 1.75 THz. At low temperatures, when the state evolves into a 2d-CDW ordered state at Tc2 in the DyTe3 and HoTe3, additional much weaker mode mixing is evident but no soft mode is observed.
[en] Highlights: • A piezoelectrochemical reaction is theoretically investigated. • The reaction takes place within a molecular compression chamber (MCC). • Molecular hydrogen is formed in situ and stored inside the MCC cage. • Besides H2 the MCC cage can also host F2 or a monoatomic gas. Nitrogen-containing molecular compression chambers (MCCs) undergo stepwise protonation followed by a 2-electron reduction step which affords molecular hydrogen in situ. This piezoelectrochemical reaction is favored by the high compression that characterizes the molecular skeleton of MCC and its fluorinated analogue. Besides H2, the MCCs are also capable of trapping molecular fluorine and the small monoatomic gases helium and neon. A topological analysis of the electronic charge density reveals the presence of closed-shell interactions between hosts and guests.
[en] We present a method for charge mixing in self-consistent density functional calculations which uses the Thomas-Fermi-von Weizsaecker equation to solve implicitly for the charge density response function to the potential. This approach has significant improvements over existing methods, particularly for inhomogeneous systems with large unit cells which commonly suffer from poor convergence due to charge sloshing
[en] The DC resistivity of charge density waves weakly-pinned by disorder is controlled by diffusive, incoherent processes rather than slow momentum relaxation. The corresponding incoherent conductivity can be computed in the limit of zero disorder. We compute this transport coefficient in holographic spatially modulated breaking translations spontaneously. As a by-product of our analysis, we clarify how the boundary heat current is obtained from a conserved bulk current, defined as a suitable generalization of the Iyer-Wald Noether current of the appropriate Killing vector.
[en] The effects of carbon (C) on hydrogen (H) trapping in tungsten (W) have been investigated by using a first-principles method, C exhibits a weak attractive interaction with H at a distance of ∼2.5 A in intrinsic W. H is energetically favorable to be far away from C, and prefers to bind onto an isosurface of an optimal charge density of 0.10 electrons/A3 at the vacancy with C. Such optimal charge density region shrinks when more H atoms are added, and disappears with the addition of a sixth H, which bonds strongly with C characterized by a much higher C-H charge density. The presence of C increases the trapping energy of H at the vacancy, indicating a strong effect of C on H trapping in W.