#phonons

Swapping one atom can cut heat flow through a molecule by half

Swapping a single atom can fine-tune the thermal conductance of single-molecule junctions without affecting their electrical conductance, according to a study led by University of Michigan Engineering with collaborators at the University of Augsburg published in Nature Materials. To study heat flow through single molecules, the researchers trapped a small organic molecule between two gold electrodes and systematically replaced one hydrogen atom with progressively heavier halogens: fluorine, chlorine, bromine and iodine. Each swap to a heavier atom resulted in further reduction of heat transport through the junction, which cuts heat flow in half upon iodine substitution. "This is a powerful demonstration that heat flow can be controlled with atomic precision—a capability that could transform how we design thermoelectric devices and molecular materials for thermal management," said Pramod Reddy, a professor of mechanical engineering and materials science and engineering at U-M and co-corresponding author of the study.

Physicists explore optical launch of hypersound pulses in halide perovskites

A German-French team of physicists from TU Dortmund University, University of Würzburg, and Le Mans Université has succeeded in launching shear hypersound pulses with exceptionally large amplitudes in metal halide perovskites using pulsed optical excitation. This discovery is published in the journal Science Advances. Whereas the material has been of high interest for photovoltaics so far, the new results turn it into a candidate to be used for optically driven devices capable of generating and detecting sound waves at sub-terahertz frequencies, with potential applications across electronic, photonic, magnetic, and biomedical devices.

New method uses spin motion to control heat flow in magnetic materials

NIMS, in joint research with the University of Tokyo, AIST, the University of Osaka, and Tohoku University, have proposed a novel method for actively controlling heat flow in solids by utilizing the transport of magnons—quasiparticles corresponding to the collective motion of spins in a magnetic material—and demonstrated that magnons contribute to heat conduction in a ferromagnetic metal and its junction more significantly than previously believed. The creation of new principles "magnon engineering" for modulating thermal transport using magnetic materials is expected to lead to the development of thermal management technologies. This research result is published in Advanced Functional Materials. Thermal conductivity is a fundamental parameter characterizing heat conduction in a solid. The primary heat carriers are known to be electrons and phonons, quasiparticles corresponding to lattice vibrations. In current thermal engineering, efforts are underway to modulate thermal conductivity and interfacial thermal resistance by elucidating and controlling the transport properties of heat carriers. In particular, heat conduction modulation focusing on the transport and scattering of phonons has been actively studied over the past decades as "phonon engineering."

Q&A: Chiral phonons research offers new ways to control materials

The rapidly growing field of research on chiral phonons is giving researchers new insights into the fundamental behaviors and structures of materials. The chirality of phonons could pave the way for new methods to control material properties and to encode information at the quantum level, which has implications for, among other areas, quantum technologies, electronics, energy transport, and sensor technology. A recently published perpsective article in Nature Physics describes the development of this emerging research area, presents a framework for the classification of phonons, and provides a comprehensive overview of the materials in which chiral phonons have been studied or may be discovered in the future. This work is helping accelerate progress in one of today's fastest-growing areas of quantum materials. Matthias Geilhufe, Assistant Professor at the Department of Physics, conducts research on chiral phonons and is one of the main authors of the article.

When heat flows backwards: A neat solution for hydrodynamic heat transport

When we think about heat traveling through a material, we typically picture diffusive transport, a process that transfers heat from high-temperature to low-temperature as particles and molecules bump into each other, losing kinetic energy in the process. But in some materials, heat can travel in a different way, flowing like water in a pipeline that—at least in principle—can be forced to move in a direction of choice. This second regime is called hydrodynamic heat transport. Heat conduction is mediated by movement of phonons, which are collective excitations of atoms in solids, and when phonons spread in a material without losing their momentum in the process, you have phonon hydrodynamics. The phenomenon has been studied theoretically and experimentally for decades, but is becoming more interesting than ever to experimentalists because it features prominently in materials like graphene, and could be exploited to guide heat flow in electronics and energy storage devices.

Electron microscopy technique captures nanoparticle organizations to forge new materials

A research team including members from the University of Michigan have unveiled a new observational technique that's sensitive to the dynamics of the intrinsic quantum jiggles of materials, or phonons. This work will help scientists and engineers better design metamaterials—substances that possess exotic properties that rarely exist in nature—that are reconfigurable and made from solutions containing nanoparticles that self-assemble into larger structures, the researchers said. These materials have wide-ranging applications, from shock absorption to devices that guide acoustic and optical energy in high-powered computer applications.

Using phononic bandgap materials to suppress decoherence in quantum computers

Quantum computers have the potential of outperforming classical computers on some optimization and computational tasks. Compared to classical systems, however, quantum systems are more prone to errors, as they are more sensitive to noise and prone to so-called decoherence. Decoherence is a process via which a quantum system loses its quantum properties due to interactions with its surrounding environment, causing a loss of quantum information and errors. This loss of coherence can be caused by a range of external disturbances, including material defects, temperature fluctuations and electromagnetic fields. In recent years, physicists and engineers worldwide have been trying to devise effective methods to reduce decoherence and thus improve the reliability of quantum computers. The sources of decoherence in solid-state systems include so-called two-level systems (TLSs), which are a class of material defects that arise from the random switching between two energy states, which can disrupt the stability of qubits.