Showing papers by "Irina V. Grigorieva published in 2011"
TL;DR: Graphene's linear dispersion relation makes its charge carriers behave as if they were massless, however, near the Dirac point where graphene's valence and conduction bands meet, electron-electron interactions cause this relation to diverge, such that it becomes strongly nonlinear and the effective carrier velocity doubles.
Abstract: Graphene’s linear dispersion relation makes its charge carriers behave as if they were massless. However, near the Dirac point where graphene’s valence and conduction bands meet, electron–electron interactions cause this relation to diverge, such that it becomes strongly nonlinear and the effective carrier velocity doubles.
674 citations
TL;DR: In this paper, the authors reported a strong Anderson localization and the corresponding metal-insulator transition in ultra-high-quality graphene, where the transition is controlled externally, by changing the carrier density in another graphene layer placed at a distance of several nm and decoupled electrically.
Abstract: Disordered conductors with resistivity above the resistance quantum h/e(2) should exhibit an insulating behaviour at low temperatures, a universal phenomenon known as a strong (Anderson) localization(1-3). Observed in a multitude of materials, including damaged graphene and its disordered chemical derivatives(4-10), Anderson localization has not been seen in generic graphene, despite its resistivity near the neutrality point reaching approximate to h/e(2) per carrier type(4,5). It has remained a puzzle why graphene is such an exception. Here we report a strong localization and the corresponding metal-insulator transition in ultra-high-quality graphene. The transition is controlled externally, by changing the carrier density in another graphene layer placed at a distance of several nm and decoupled electrically. The entire behaviour is explained by electron-hole puddles that disallow localization in standard devices but can be screened out in double-layer graphene. The localization that occurs with decreasing rather than increasing disorder is a unique occurrence, and the reported double-layer heterostructures presents a new experimental system that invites further studies.
501 citations
TL;DR: The molecular signaling pathways that are involved in determining the differentiation of the pharyngeal pouch endoderm into parathyroid cells are being elucidated by studies of patients with hypoparathyroidism and appropriate mouse models.
Abstract: Parathyroid developmental anomalies, which result in hypoparathyroidism, are common and may occur in one in 4,000 live births. Parathyroids, in man, develop from the endodermal cells of the third and fourth pharyngeal pouches, whereas, in the mouse they develop solely from the endoderm of the third pharyngeal pouches. In addition, neural crest cells that arise from the embryonic mid- and hindbrain also contribute to parathyroid gland development. The molecular signaling pathways that are involved in determining the differentiation of the pharyngeal pouch endoderm into parathyroid cells are being elucidated by studies of patients with hypoparathyroidism and appropriate mouse models. These studies have revealed important roles for a number of transcription factors, which include Tbx1, Gata3, Gcm2, Sox3, Aire1 and members of the homeobox (Hox) and paired box (Pax) families.
45 citations
TL;DR: In this paper, the Abrikosov vortex patterns in thin Nb films with random, periodic (triangular), and quasiperiodic (Penrose) arrays of antidots were visualized by Bitter decoration for a range of applied fields.
Abstract: We imaged Abrikosov vortex patterns in thin Nb films with random, periodic (triangular), and quasiperiodic (Penrose) arrays of antidots. Vortex positions were visualized by Bitter decoration for a range of applied fields $B$, antidot radii $r$, and densities ${n}_{p}$ after field-cooling through the transition temperature ${T}_{c}$ to a base temperature $T\ensuremath{\approx}2\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The observed vortex patterns correspond to snapshots of vortex positions at the time of decoration. The effectiveness of antidots as artificial pinning sites for vortices is found to be sensitive to several factors: array geometry, antidot size and density, and applied field. Overall, the triangular lattice provides the most effective pinning landscape, with antidots trapping the highest proportion of vortices, but for a wide range of parameters the Penrose lattice is equally effective. For a quantitative analysis, we determined the occupation number $n$ (average number of vortices trapped per antidot) from each image. This revealed a significantly more complicated dependence of antidot occupation on applied field and/or antidot density than that predicted by simple models considering pinning by an isolated antidot. In particular, upon increasing the antidot density ${n}_{p}$, we find a marked increase in $n$ for triangular arrays, which we attribute to the additional repulsion from interstitial vortices, pushing more vortices into antidots with decreasing antidot separation. This effect is also present but less pronounced for Penrose arrays, which can be explained by the variation of antidot spacing inherent to the Penrose geometry and accordingly more options for accommodating interstitial vortices.
13 citations