Phonon–phonon scattering selection rules and control: an application to nanofriction and thermal transport

Abstract

Symmetry-based selection rules are a guide on how to switch on or off multi-phonon scattering processes.

Effect of electric fields in low-dimensional materials: Nanofrictional response as a case study

“…( 2) we can infer that, if the effect of the electric field is to halve the frequency, the resulting frictional force is four times smaller than the initial one. We are aware that this is an approximation because phonon coupling should be taken into account explicitly [52][53][54]64]. A rigorous derivation of the force in terms of phonon contributions requires the explicit expression of the energy in terms of single phonons and the relative coupling, also including the effect of the temperature; however, this falls out of the scope of the present discussion and we plan to investigate it in a future work.…”

Control of energy dissipation in sliding low-dimensional materials

“…where h is the reduced Planck's constant, N is the number of unit cells, ω λ is the eigenfrequency of the mode λ, m k is the mass of the kth atom, r kl (r k l , r k l ) is the position of the kth (k th, k th) atom in the lth (l th, l th) cell replica, e α λ (r k ) is the αth Cartesian component of the eigenvector associated to the mode λ and to the kth atom, and αβγ is the third-rank Cartesian tensor of the cubic anharmonic force constants. We already observed [38] that it is possible to turn off or on any λ + λ = λ scattering process by controlling the symmetries of the system; in fact, if e λ , e λ , and e λ are irreducible representations for which the eigenvectors e λ , e λ , e λ are, respectively, a basis, then…”

“…In what follows, we show that an other way to control the value of λλ λ is to act on the subtle relation between the electronic density and the dynamic properties of the system. In all the MX -nL systems, the sliding modes with main contribution to relative layer shift have wave vector q = (0, 0, 0) ≡ and band indices which depend on n [38] (see Fig. 2 as an example; a schematic representation of the sliding modes at different n can be found in the Supporting Material of Ref.…”

“…2 as an example; a schematic representation of the sliding modes at different n can be found in the Supporting Material of Ref. [38]). The number of sliding modes depends on the number of layers: the higher n, the higher the number of modes effectively contributing to the sliding, the higher the number of dissipative modes and corresponding dissipation channels.…”

Phonon confinement and interface lattice dynamics of ultrathin high-k rare earth sesquioxide films: the case of Eu2O3 on YSZ(001)

“…14 The spatial connement of atoms in nano-and subnanometer-thick layers profoundly alters their vibrational dynamics. 15 Via phonon-phonon, 16 electron-phonon 17 and spin-phonon 18 interactions, these size effects impact important properties of nanomaterials like thermal conductivity, superconductivity, charge mobility, spin polarization and others, manifesting themselves in phenomena such as self-heating, 19 increase of the critical temperature of superconductors [20][21][22] and spin relaxation, 23 which play a crucial role in micro-, optoelectronic and spintronic device technologies. [24][25][26] Common features of the phonon density of states (PDOS) of thin lms are enhancement of the number of states at low and high energy as well as broadening and shi of the peaks.…”