Orbital magnetic moments of phonons

Juraschek, Dominik M.; Spaldin, Nicola A.

doi:10.1103/physrevmaterials.3.064405

Cited by 119 publications

(119 citation statements)

References 51 publications

(65 reference statements)

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“…Note that magnetic circular dichroism [82], as well as interactions with the Zeeman-split atomic states [83,84], have been successfully employed to detect nontrivial local polarization and spin properties in inhomogeneous optical fields. Moreover, various magneto-acoustic interactions involving angular momentum of phonons in solids were recently intensively explored [25][26][27]85]. This marks magneto-acoustics as one of the most promising directions for future studies of acoustic spin-related phenomena.…”

Section: Discussionmentioning

confidence: 99%

Spin and orbital angular momenta of acoustic beams

2019

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We analyze spin and orbital angular momenta in monochromatic acoustic wave fields in a homogeneous medium. Despite being purely longitudinal (curl-free), inhomogeneous acoustic waves generically possess nonzero spin angular momentum density caused by the local rotation of the vector velocity field. We show that the integral spin of a localized acoustic wave vanishes in agreement with the spin-0 nature of longitudinal phonons. We also show that the helicity or chirality density vanishes identically in acoustic fields. As an example, we consider nonparaxial acoustic Bessel beams carrying well-defined integer orbital angular momentum, as well as nonzero local spin density, with both transverse and longitudinal components. We describe the nontrivial polarization structure in acoustic Bessel beams and indicate a number of observable phenomena, such as nonzero energy density and purely-circular transverse polarization in the center of the first-order vortex beams.

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Section: Discussionmentioning

confidence: 99%

Spin and orbital angular momenta of acoustic beams

2019

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“…This process allows the coherent excitation of both Raman-active and silent phonon modes in contrast to conventional difference and sum-frequency ionic Raman scattering that only allow coupling of Raman-active to IR-active phonons. The energy conversion efficiency of the parametric excitation thereby outperforms ionic Raman scattering, in which only a fraction of the energy is transferred to other modes [41,[66][67][68], and is at par with predictions for the transfer of energy in the resonant phonon upconversion process sum-frequency ionic Raman scattering [41,42,69].…”

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confidence: 66%

Parametric Excitation of an Optically Silent Goldstone-Like Phonon Mode

2020

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It has recently been indicated that the hexagonal manganites exhibit Higgs-and Goldstone-like phonon modes that modulate the amplitude and phase of their primary order parameter. Here, we describe a mechanism by which a silent Goldstone-like phonon mode can be coherently excited, which is based on nonlinear coupling to an infrared-active Higgs-like phonon mode. Using a combination of first-principles calculations and phenomenological modeling, we describe the coupled Higgs-Goldstone dynamics in response to the excitation with a terahertz pulse. Besides theoretically demonstrating coherent control of crystallographic Higgs and Goldstone excitations, we show that the previously inaccessible silent phonon modes can be excited coherently with this mechanism.Order parameters are physical observables that are used to quantify the different states of matter. Their amplitudes and phases can be excited by external stimuli, such as a laser pulse, leading to exotic states of matter that cannot be accessed in equilibrium [1]. Two particular excitations are Higgs and Goldstone modes, which correspond to the modulation of the amplitude and phase of an order parameter that breaks a continuous symmetry. Originally discussed in the context of particle physics [2] and superconductivity [3], Higgs and Goldstone excitations were found in cold atom systems, such as superfluids [4][5][6][7][8] or supersolids [9]. Higgs and Goldstone modes are well-studied in superconductors today [10][11][12][13][14][15][16][17][18][19][20][21], and similar manifestations have recently been reported in charge density wave (CDW) systems [22][23][24], antiferromagnets [25][26][27], and excitonic insulators [28]. It has been debated whether the optical and acoustic vibrational modes of solids can be considered Higgs and Goldstone excitations of the crystal lattice [29]. Several complex transition metal oxide compounds have shown signatures of optical Goldstone-like phonon modes that live in their symmetry-broken potential energy landscape [30][31][32][33][34].Coherent control over Raman-active phonons via impulsive stimulated Raman scattering using visible light pulses is well-established [35,36]. Recently, the excitation of infrared (IR)-active phonons with large amplitudes via IR absorption has become feasible through the development of high intensity terahertz and mid-IR sources. This progress has enabled selective control over the dynamics of the crystal lattice through nonlinear phonon interactions using ionic Raman scattering [37-39] and two-particle absorption mechanisms [40][41][42][43][44][45]. In contrast, phonon modes that do not respond to IR absorption or Raman scattering techniques, so called silent modes, can only be detected through hyper-Raman scattering. As hyper-Raman scattering is a third-order interaction of the electric field component of light with a * djuraschek@seas.harvard.edu † prineha@seas.harvard.edu phonon mode, it is inefficient and no coherent excitation has been achieved yet. Higgs and Goldstone modes, similar to silent p...

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“…Theories address the phonon spin induced by Raman spin-phonon interactions [17], by the relaxation of magnetic impurities [11,18], by temperature gradients in magnets with broken inversion symmetry [19], and phonon spin pumping into nonmagnetic contacts by ferromagnetic resonance dynamics [20]. The phonon Zeeman effect has also been considered [21]. The quantum dynamics of magnetic rigid rotors has been investigated recently in the context of levitated nanoparticles [22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Angular momentum conservation and phonon spin in magnetic insulators

et al. 2020

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We develop a microscopic theory of spin-lattice interactions in magnetic insulators, separating rigid-body rotations and the internal angular momentum, or spin, of the phonons, while conserving the total angular momentum. In the low-energy limit, the microscopic couplings are mapped onto experimentally accessible magnetoelastic constants. We show that the transient phonon spin contribution of the excited system can dominate over the magnon spin, leading to nontrivial Einstein-de Haas physics.

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Orbital magnetic moments of phonons

Cited by 119 publications

References 51 publications

Spin and orbital angular momenta of acoustic beams

Spin and orbital angular momenta of acoustic beams

Parametric Excitation of an Optically Silent Goldstone-Like Phonon Mode

Angular momentum conservation and phonon spin in magnetic insulators

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