22 research outputs found
Transfer matrix approach for the Kerr and Faraday rotation in layered nanostructures
To study the optical rotation of the polarization of light incident on
multilayer systems consisting of atomically thin conductors and dielectric
multilayers we present a general method based on transfer matrices. The
transfer matrix of the atomically thin conducting layer is obtained using the
Maxwell equations. We derive expressions for the Kerr (Faraday) rotation angle
and for the ellipticity of the reflected (transmitted) light as a function of
the incident angle and polarization of the light. The method is demonstrated by
calculating the Kerr (Faraday) angle for bilayer graphene in the quantum
anomalous Hall state placed on the top of dielectric multilayers. The optical
conductivity of the bilayer graphene is calculated in the framework of a
four-band model.Comment: 10 pages, 6 figure
Voltage-time dilemma and stochastic threshold voltage variation in pure silver atomic switches
The formation and dissolution of silver nanowires plays a fundamental role in
a broad range of resistive switching devices, fundamentally relying on the
electrochemical metallization phenomenon. It was shown, however, that resistive
switching may also appear in pure metallic nanowires lacking any
silver-ion-hosting embedding environment, but this pure atomic switching
mechanism fundamentally differs from the conventional
electrochemical-metallization-based resistive switching. To facilitate the
quantitative description of the former phenomenon, we investigate broad range
of Ag atomic junctions with a special focus on the frequency-dependence and the
fundamentally stochastic cycle-to-cycle variation of the switching threshold
voltage. These devices are established in an ultra-high purity environment
where electrochemical metallization can be excluded. The measured
characteristics are successfully described by a vibrational pumping model,
yielding consistent predictions for the weak frequency dependence and the large
variance of the switching threshold voltage. We also demonstrate that
electrochemical-metallization-based resistive switching and pure atomic
switching may appear in the same device structure, and therefore the proper
understanding of the pure atomic switching mechanism has a distinguished
importance in silver-based electrochemical metallization cells
Protected edge states in silicene antidots and dots in magnetic field
Silicene systems, due to the buckled structure of the lattice, manifest remarkable intrinsic spin- orbit interaction triggering a topological phase transition in the low-energy regime. Thus, we found that protected edge states are present in silicene antidots and dots, being polarized in valley-spin pairs. We have also studied the effect of the lattice termination on the properties of the single electron energy levels and electron density distribution of silicene antidots and dots situated in a perpendicular magnetic field. Our calculations confirmed that the topological edge states are prop- agating over the perimeter of the antidot/dot for both ideal or realistic edge termination containing roughness on the atomic length scale. The valley polarization and the slope of the energy line as a function of the magnetic field is, however, reduced when the antidot or dot has a rough edge
Diverging dc conductivity due to a flat band in disordered pseudospin-1 Dirac-Weyl fermions
Several lattices, such as the dice or the Lieb lattice, possess Dirac cones and a flat band crossing
the Dirac point, whose effective model is the pseudospin-1 Dirac-Weyl equation. We investigate
the fate of the flat band in the presence of disorder by focusing on the density of states (DOS)
and dc conductivity. While the central hub-site does not reveal the presence of the flat band, the
sublattice resolved DOS on the non-central sites exhibits a narrow peak with height 1/pg with
g the dimensionless disorder variance. Although the group velocity is zero on the flat band, the
dc conductivity diverges as ln(1/g) with decreasing disorder due to interband transitions around
the band touching point between the propagating and the flat band. Generalizations to higher
pseudospin are given
Smectite appearance in the footwall of the Úrkút manganese ore deposit, Bakony Mts., Hungary
The Úrkút manganese ore deposit (Transdanubian Range, Hungary) is one of the largest manganese accumulations to be formed during the Toarcian Oceanic Anoxic Event. In the past 60 years, the area was investigated intensively. The core storage facility of the manganese mine had more than 20,000 sample pieces. Most of these samples have never been investigated. During this study, which is the first widespread clay mineral study in the footwall of the Úrkút manganese ore deposit, we investigated 40 samples from seven boreholes (footwall rocks, black/gray shales below and above the first ore bed, and manganese carbonate ores). Although previous studies assumed that smectite is associated only with the ore beds, our research revealed its appearance in the footwall (Pliensbachian) as well. Simultaneously, tripoli (the local name of completely bleached chert) can also be found in the footwall. Based on the investigated samples, a sharp geochemical difference was detected between Pliensbachian and Toarcian sediments. In this paper, we try to trace the relationship between the smectite content of the footwall and the ore bed and compare these results with the observed geochemical changes. Based on the new data, we assume that the ore accumulation was caused by a flow system (upwelling-controlled ore formation)
Stress-induced rearrangements of cellular networks: consequences for protection and drug design
The complexity of the cells can be described and understood by a number of
networks such as protein-protein interaction, cytoskeletal, organelle,
signalling, gene transcription and metabolic networks. All these networks are
highly dynamic producing continuous rearrangements in their links, hubs,
network-skeleton and modules. Here we describe the adaptation of cellular
networks after various forms of stress causing perturbations, congestions and
network damage. Chronic stress decreases link-density, decouples or even
quarantines modules, and induces an increased competition between network hubs
and bridges. Extremely long or strong stress may induce a topological phase
transition in the respective cellular networks, which switches the cell to a
completely different mode of cellular function. We summarize our initial
knowledge on network restoration after stress including the role of molecular
chaperones in this process. Finally, we discuss the implications of
stress-induced network rearrangements in diseases and ageing, and propose
therapeutic approaches both to increase the robustness and help the repair of
cellular networks.Comment: 9 pages, 1 table, 2 figures, invited paper of FEBS Letters Cellular
Stress special issu