Two-pulse excitation at a graphene p-n junction generates a time-dependent photocurrent response that we show functions as a novel ultrafast thermometer of the hot electron temperature, Te(t). The extracted hot electron cooling rates are consistent with heat dissipation near the Fermi level of graphene occurring by an acoustic phonon supercollision mechanism. © Owned by the authors, published by EDP Sciences, 2013.

In cells, RNA polymerase (RNAP) must transcribe supercoiled DNA, whose torsional state is constantly changing, but how RNAP deals with DNA supercoiling remains elusive. We report direct measurements of individual Escherichia coli RNAPs as they transcribed supercoiled DNA. We found that a resisting torque slowed RNAP and increased its pause frequency and duration.

Graphene, a two-dimensional material with a high mobility and a tunable conductivity, is uniquely suited for plasmonics. The frequency dispersion of plasmons in bulk graphene has been studied both theoretically and experimentally, but no theoretical models have been reported and tested against experiments for confined plasmon modes in graphene microstructures. In this Rapid Communication, we present measurements as well as analytical and computational models for such confined modes. We show that plasmon modes can be described by an eigenvalue equation.

Despite much interest in engineering new topological surface (edge) states using structural defects, such topological surface states have not been observed yet. We show that recently imaged tilt boundaries in gated multilayer graphene should support topologically protected gapless edge states. We approach the problem from two perspectives: the microscopic perspective of a tight-binding model and an ab initio calculation on a bilayer, and the symmetry-protected topological (SPT) state perspective for a general multilayer.

We investigate the bilayer Ruddlesden-Popper iridate Sr3Ir 2O7 by temperature-dependent angle-resolved photoemission. At low temperatures, we find a fully gapped correlated insulator, characterized by a small charge gap and narrow bandwidths. The low-energy spectral features show a pronounced temperature-dependent broadening and non-quasiparticle-like Gaussian line shapes. Together, these spectral features provide experimental evidence for a polaronic ground state.

The phase diagram of Sr3Ru2O7 shows hallmarks of strong electron correlations despite the modest Coulomb interaction in the Ru 4d shell. We use angle-resolved photoelectron spectroscopy measurements to provide microscopic insight into the formation of the strongly renormalized heavy d-electron liquid that controls the physics of Sr 3Ru2O7. Our data reveal itinerant Ru 4d-states confined over large parts of the Brillouin zone to an energy range of <6 meV, nearly three orders of magnitude lower than the bare band width.

We explore the time evolution of correlations in a homogeneous gas of lattice bosons with filling factor n0, following a sudden reduction in the lattice depth to a regime where the interactions are weak. In the limit of vanishing interactions, we find a simple closed-form expression for the static structure factor. The corresponding real-space density-density correlation function shows multiple spatial oscillations which disperse linearly in time. By perturbatively including the effect of interactions, we study the evolution of boson quasimomentum distribution following the quench.

We demonstrate the continuous tuning of the electronic structure of atomically thin MoS2 on flexible substrates by applying a uniaxial tensile strain. A redshift at a rate of ∼70 meV per percent applied strain for direct gap transitions, and at a rate 1.6 times larger for indirect gap transitions, has been determined by absorption and photoluminescence spectroscopy. Our result, in excellent agreement with first principles calculations, demonstrates the potential of two-dimensional crystals for applications in flexible electronics and optoelectronics. © 2013 American Chemical Society.

We study the quantum phase transition of interacting electrons in quantum wires from a one-dimensional (1D) linear configuration to a quasi-1D zigzag arrangement using quantum Monte Carlo methods. As the density increases from its lowest values, first, the electrons form a linear Wigner crystal, then, the symmetry about the axis of the wire is broken as the electrons order in a quasi-1D zigzag phase, and, finally, the electrons form a disordered liquidlike phase.

In heteroepitaxy, lattice mismatch between the deposited material and the underlying surface strongly affects nucleation and growth processes. The effect of mismatch is well studied in atoms with growth kinetics typically dominated by bond formation with interaction lengths on the order of one lattice spacing.