Hot electron relaxation in Type-II quantum wells.

A photovoltaic device fabricated with conventional zincblende materials can use the Type-II quantum well structure, which spatially separates electrons and holes, to reduce their recombination rate. In order to obtain higher power conversion efficiency, it is desirable to preserve more energetic carriers by engineering a phonon "bottleneck," a mismatch between the gaps in the well and barrier phonon structure. Such a mismatch leads to poor phonon transport and therefore prevents energy from leaving the system in the form of heat.

Quantum-electrodynamical time-dependent density functional theory within Gaussian atomic basis.

Inspired by the formulation of quantum-electrodynamical time-dependent density functional theory (QED-TDDFT) by Rubio and co-workers [Flick et al., ACS Photonics 6, 2757-2778 (2019)], we propose an implementation that uses dimensionless amplitudes for describing the photonic contributions to QED-TDDFT electron-photon eigenstates. This leads to a Hermitian QED-TDDFT coupling matrix that is expected to facilitate the future development of analytic derivatives.

Automatic learning of topological phase boundaries.

Topological phase transitions, which do not adhere to Landau's phenomenological model (i.e., a spontaneous symmetry breaking process and vanishing local order parameters), have been actively researched in condensed matter physics.

Line of Dirac Nodes in Hyperhoneycomb Lattices.

We propose a family of structures that have "Dirac loops," closed lines of Dirac nodes in momentum space, on which the density of states vanishes linearly with energy. Those lattices all possess the planar trigonal connectivity present in graphene, but are three dimensional. We show that their highly anisotropic and multiply connected Fermi surface leads to quantized Hall conductivities in three dimensions for magnetic fields with toroidal geometry.

Using normal modes to calculate and optimize thermal conductivity in functionalized macromolecules.

The quest for high thermal conductivity materials has led to nanocomposites incorporating macromolecular materials with excellent thermal conductivity, such as carbon nanotubes and graphene nanoribbons, in a matrix of poorer thermal conductivity. To minimize the interface thermal resistance the stiff, incorporated materials can be chemically functionalized with various side chains. We report here an efficient theoretical method using normal modes to calculate the thermal conductivity of such systems and show how the participation ratio of these modes can be used to evaluate different choices for functionalization.

Computational modeling of the thermal conductivity of single-walled carbon nanotube-polymer composites.

A computational model was developed to study the thermal conductivity of single-walled carbon nanotube (SWNT)-polymer composites. A random walk simulation was used to model the effect of interfacial resistance on the heat flow in different orientations of SWNTs dispersed in the polymers. The simulation is a modification of a previous model taking into account the numerically determined thermal equilibrium factor between the SWNTs and the composite matrix material.

Atomic-scale observation of temperature and pressure driven preroughening and roughening.

Preroughening and roughening transitions are observed on the GaAs(001) surface using scanning tunneling microscopy. By tuning the substrate temperature or As4 pressure the surface morphology can be made free of islands, covered with one monolayer high islands or covered with islands on top of islands forming a wedding-cake-type structure. These three distinct surface morphologies are classified as ordered flat (OF), disordered flat (DOF), and rough within the restricted solid-on-solid model.