David Cubero

Like many one-dimensional systems, carbon nanotubes are known to exhibit a divergent thermal conductivity as the length of the nanotube is increased, but the precise form of this divergence has so far been disputed, some even arguing for a final convergent conductivity. In this work, the solution given by mode-coupling theory, which precisely describes the heat divergence as a power law for sufficiently large lengths, is clearly revealed in molecular dynamics simulations where the tubes' ends are kept at different temperatures. The precise localization of such an asymptotic power law explains why it has not been found before and helps resolve a long-standing puzzle in nanoscale heat transport. It is estimated to show up in carbon nanotubes of macroscopic lengths, currently achievable experimentally.

We propose a generalized Fourier's law, based on recent mode-coupling calculations, for one-dimensional nonlinear lattices in nonequilibrium simulations, where the boundaries are kept at different temperatures. Though not useful for the typical textbook numerical examples, we are able to demonstrate numerically the theory for an anharmonic lattice with force field parameters similar to those of realistic low-dimensional structures such as covalently bonded molecular chains or carbon nanotubes, specifically showing that the asymptotic heat conductivity is described by the mode-coupling theory in good approximation, without any adjustable parameter. Published by the American Physical Society 2024

Randomly diffusing atoms confined in a dissipative optical lattice are illuminated by a weak probe of light. The probe transmission spectrum reveals directed atomic propagation that occurs perpendicular to the direction of probe beam propagation. Resonant enhancement of this directed propagation is observed as we vary the random photon scattering rate. We experimentally characterize this stochastic resonance as a function of probe intensity and lattice well depth. A simple model reveals how the probe-excited atomic density waves and optical pumping rates conspire to create directed atomic propagation within a randomly diffusing sample.

An exact series expansion of the average velocity of cold atoms in dissipative optical lattices under probe driving, based on the amplitudes of the excited atomic density waves, is derived from the semiclassical equations for the phase space densities of the Zeeman ground-state sublevels. This expansion permits the identification of the precise contribution to the current of a propagating atomic wave for the specific driving, as well as providing the general threshold for the transition into the regime of infinite density.

Boron nitride nanotubes are added to polyethylene with coupling agents to enhance heat transport. They boost heat transfer in nano-fabricated electrical insulators, with the possibility for controlling the direction of heat conduction via the nanotube orientation.

An excess electron in amorphous and crystalline polyethylene-vacuum interfaces. A precise reaction-field method is used to compute the surface states.