27 research outputs found
Quadrature skyrmions in two-dimensionally arrayed parametric resonators
Skyrmions are topological solitons in two-dimensional systems and have been
observed in various physical systems. Generating and controlling skyrmions in
artificial resonator arrays lead to novel acoustic, photonic, and electric
devices, but it is a challenge to implement a vector variable with the chiral
exchange interaction. Here, we propose to use quadrature variables, where their
parametric coupling enables skyrmions to be stabilized. A finite-element
simulation indicates that a stable acoustic skyrmion would exist in a realistic
structure consisting of a piezoelectric membrane array.Comment: 22 pages, 10 figure
Cavity magnomechanical coupling with coupled magnon modes in a synthetic antiferromagnet
On-chip cavity magnomechanics is an emerging field exploring acoustic and
magnonic functionalities of various ferromagnetic materials and structures
using strongly confined phonons. It is expected that such cavity magnomechanics
can be extended to multilayer ferromagnets, especially synthetic
antiferromagnets (SAFs) that exhibit zero net magnetization through interlayer
exchange coupling. However, the conventional theoretical framework for a single
ferromagnet cannot be used directly because of the antiferromagnetic
magnetization dynamics associated with the interlayer exchange coupling. In
this paper, we theoretically investigate phonon-magnon coupling with a
three-layer SAF. Our formulation of the phonon-magnon coupling constants
reveals that the acoustic (optical) magnon mode dominantly couples to the
cavity phonon when the magnetization angles in the two ferromagnetic layers are
antiparallel (orthogonal). Moreover, numerical calculations including the
effects of dipole-dipole interactions and in-plane uniaxial magnetic anisotropy
allow us to predict phonon frequency shifts and linewidth broadening that can
be detected in experiments. These theoretical insights would greatly help us to
make a strategy for bringing the system into the strong coupling regime and to
devise novel control protocols in analogy to cavity quantum electrodynamics and
cavity optomechanics
Evanescently coupled topological ring-waveguide systems for chip-scale ultrahigh frequency phononic circuits
Topological phononics enabling backscattering-immune transport is expected to
improve the performance of electromechanical systems for classical and quantum
information technologies. Nonetheless, most of the previous demonstrations
utilized macroscale and low-frequency structures and thus offered little
experimental insight into ultrahigh frequency phonon transport, especially in
chip-scale circuits. Here, we report microwave phonon transmissions in a
microscopic topological ring-waveguide coupled system, which is an important
building block for wave-based signal processing. The elastic waves in the
topological waveguide evanescently couple to the ring resonator, while
maintaining the valley pseudospin polarization. The resultant waves are robust
to backscattering even in the tiny hexagonal ring, generating a resonant phonon
circulation. Furthermore, the evanescently coupled structure allows for a
critical coupling, where valley-dependent ring-waveguide interference enables
blocking of the topological edge transmission. Our demonstrations reveal the
capability of using topological phenomena to manipulate ultrahigh frequency
elastic waves in intricate phononic circuits for classical and quantum
signal-processing applications.Comment: 13 pages, 9 figure
Impedance-matched High-overtone Bulk Acoustic Resonator
A high-overtone bulk acoustic resonator (HBAR), in which a piezoelectric
transducer is set on an acoustic cavity, has been attracting attention in both
fundamental research and RF applications due to its scalability, high
frequency, and high quality factor. The acoustic impedance matching in HBARs is
crucial for efficient acoustic power transfer from the piezoelectric transducer
to the cavity. However, impedance mismatch remains in most HBARs due to the
metal layer insertion between the piezoelectric layer and cavity substrate. In
this study, we fabricated a nearly impedance-matched high-quality HBAR using an
epitaxial AlN piezoelectric layer directly grown on a conductive SiC cavity
substrate with no metal layer insertion. The small impedance mismatch was
verified from the variation in the free spectral range (FSR), which is
comparable to the best value in previously reported HBARs. The experimentally
obtained FSR spectra was greatly reproduced by using the Mason model. Broadband
phonon cavity modes up to the K-band (26.5 GHz) were achieved by reducing the
thickness of the AlN layer from 800 to 200 nm. The high figure of merit of
at 10 GHz was also
obtained. Our nearly impedance-matched high-quality HBAR will enable the
development of RF applications, such as low-phase noise oscillators and
acoustic filters, as well as research on high-frequency acoustic systems
hybridized with electric, optical, and magnetic systems