Thermal transport plays a crucial role in performance and reliability of semiconductor electronic devices, where heat is mainly carried by phonons. Phonon transport in crystalline semiconductor materials, such as Si, Ge, GaAs, GaN, etc, has been extensively studied over the past two decades. In fact, study of phonon physics in crystalline semiconductor materials in both bulk and nanostructure f...

Positronium (Ps), a bound state of an electron and a positron, forms in various dielectric crystals [1]. Being a light impurity atom in a crystal lattice, Ps is extremely sensitive to its local surroundings and phonon lattice vibrations. In crystal lattices of non-cubic symmetry, the Ps atom may exhibit effective quadrupole interactions even in spite of the fact that it is completely electroneu...

Energy Transfer About the time this issue of Los Alamos Science was going to press, we obtained new experimental results on atomic vibrations in uranium. These results help answer questions raised when Andrew Lawson and coworkers of Los Alamos rediscovered vibrational softening in the early 1990s. Although softening had been observed at least three times earlier, the most important questions ab...

Theoretical analysis of Raman scattering spectra (RS) for single-crystal MoS2 sample and atomically thin MoS2 sample consisting from one to few layers was performed in order to explain the change of MoS2 vibrations at transition from a monoatomic layer to a bulk crystal. Experiments have shown that changes of frequencies of the most intensive bands arising from the in-plane, [Formula: see text]...

In the past five years enormous progress has been made in the ab initio calculations of the optical response of electrons in semiconductors. The calculations include the Coulomb interaction between the excited electron and the hole left behind, as well as local field effects. However, they are performed under the assumption that the atoms occupy fixed equilibrium positions and do not include ef...

Non-metallic crystalline materials conduct heat by the transport of quantized atomic lattice vibrations called phonons. Thermal conductivity depends on how far phonons travel between scattering events-their mean free paths. Due to the breadth of the phonon mean free path spectrum, nanostructuring materials can reduce thermal conductivity from bulk by scattering long mean free path phonons, wher...

of the vibrations of the magnetic ion alone, AO, at 2’ = 0 is 1.2% of the observed zero-field splitting. Similarly, we find AO/D = 0.027 at room temperatures. For 54Fe3+, 66Fe3+, and 67Fe3+ in calcite, we use TD = 4’70oK [a], and obtain AO/D = 0.007 at T = O°K and 0.03 at 300°K. We fail to account for the temperature independence of 6AO from 4.2’K as found experimentally [l]. Instead, our calcu...

The low-frequency vibrational and low-temperature thermal properties of amorphous solids are markedly different from those of crystalline solids. This situation is counterintuitive because all solid materials are expected to behave as a homogeneous elastic body in the continuum limit, in which vibrational modes are phonons that follow the Debye law. A number of phenomenological explanations for...

Abstract We investigate how collective behaviors of vibrations such as cooperativity and interference can enhance energy transfer in a nontrivial way, focusing on an example donor–bridge–acceptor trimeric chromophore system coupled to two vibrational degrees freedom. Employing parameters selected provide overall uphill from donor acceptor, we use numerical calculations dynamics exciton–vibratio...

Abstract Paramagnetic defects in diamond and hexagonal boron nitride possess a combination of spin optical properties that make them prototypical solid-state qubits. Despite the coherence these qubits being critically limited by spin-phonon relaxation, full understanding this process is not yet available. Here we apply ab initio dynamics simulations to problem quantitatively reproduce experimen...