Koji Onomitsu

Coherent phonon manipulation in coupled mechanical resonators

It is now shown that phonons can be coherently transferred between two nanomechanical resonators, it is now shown. The technique of controlling the coupling between nanoscale oscillators using a piezoelectric transducer is useful for manipulating classical oscillations, but if extended to the quantum regime it could also enable entanglement of macroscopic mechanical objects.

Edge channel transport in the InAs/GaSb topological insulating phase

Transport in InAs/GaSb heterostructures with different InAs layer thicknesses is studied using a six-terminal Hall bar geometry with a 2-

Phonon waveguides for electromechanical circuits

\mu

Improved resonance characteristics of GaAs beam resonators by epitaxially induced strain

m edge channel length. For a sample with a 12-nm-thick InAs layer, non-local resistance measurements with various current/voltage contact configurations reveal that the transport is dominated by edge channels with negligible bulk contribution. Systematic non-local measurements allow us to extract the resistance of individual edge channels, revealing sharp resistance uctuations indicative of inelastic scattering. Our results show that the InAs/GaSb system can be tailored to have conducting edge channels while keeping a gap in the bulk region and provide a way of studying 2D topological insulators even when quantized transport is absent.

Optical Tuning of Coupled Micromechanical Resonators

Nanoelectromechanical systems (NEMS), utilizing localized mechanical vibrations, have found application in sensors, signal processors and in the study of macroscopic quantum mechanics. The integration of multiple mechanical elements via electrical or optical means remains a challenge in the realization of NEMS circuits. Here, we develop a phonon waveguide using a one-dimensional array of suspended membranes that offers purely mechanical means to integrate isolated NEMS resonators. We demonstrate that the phonon waveguide can support and guide mechanical vibrations and that the periodic membrane arrangement also creates a phonon bandgap that enables control of the phonon propagation velocity. Furthermore, embedding a phonon cavity into the phonon waveguide allows mobile mechanical vibrations to be dynamically switched or transferred from the waveguide to the cavity, thereby illustrating the viability of waveguide-resonator coupling. These highly functional traits of the phonon waveguide architecture exhibit all the components necessary to permit the realization of all-phononic NEMS circuits.

Two-mode thermal-noise squeezing in an electromechanical resonator.

Micromechanical-beam resonators were fabricated using a strained GaAs film grown on relaxed In0.1Ga0.9As∕In0.1Al0.9As buffer layers. The natural frequency of the fundamental mode was increased 2.5–4 times by applying tensile strain, showing good agreement with the model calculation assuming strain of 0.35% along the beam. In addition, the Q factor of 19 000 was obtained for the best sample, which is one order of magnitude higher than that for the unstrained resonator. This technique can be widely applied for improving the performance of resonator-based micro-/nanoelectromechanical devices.

An electromechanical membrane resonator

Frequency tuning of two mechanically coupled microresonators by laser irradiation is demonstrated. The eigenfrequency of a doubly clamped GaAs beam shifts downward in proportion to laser power due to optically induced thermal stress, which modifies the spring constant of the resonator. This frequency tuning enables the control of the coupling efficiency and thus the realization of perfect coupling between the micromechanical resonators, i.e., purely symmetric and anti-symmetric coupled vibration. This optical tuning is a valuable method for the study of physics in coupled resonators as well as for expanding the applications of micromechanical resonators for sensors, filters, and logics.

Anomalous hall effect in Mn δ-doped GaAs/In0.17Ga0.83As/GaAs quantum wells with high hole mobility

An electromechanical resonator is developed in which mechanical nonlinearities can be dynamically engineered to emulate the nondegenerate parametric down-conversion interaction. In this configuration, phonons are simultaneously generated in pairs in two macroscopic vibration modes, resulting in the amplification of their motion. In parallel, two-mode thermal squeezed states are also created, which exhibit fluctuations below the thermal motion of their constituent modes as well as harboring correlations between the modes that become almost perfect as their amplification is increased. The existence of correlations between two massive phonon ensembles paves the way towards an entangled macroscopic mechanical system at the single phonon level.

High-sensitivity charge detection using antisymmetric vibration in coupled micromechanical oscillators

An electrically active membrane-based mechanical resonator was fabricated from a GaAs/AlGaAs heterostructure. The mechanical motion of the membrane was piezoelectrically excited and detected. The piezoelectric transducer could also excite a range of resonance modes in the membrane that were identified and mapped via optical interferometry. Furthermore, the various mode shapes combined with the piezoelectric transduction could be used to execute mechanical-logic-gates. The development of an electrically active membrane-based mechanical resonator paves the way towards responsive electromechanical detectors and highly functional opto-electro-mechanical systems.

A phonon transistor in an electromechanical resonator array

Magnetic and magnetotransport properties of GaAs(δ〈Mn〉)/In0.17Ga0.83As/GaAs quantum wells with different Mn concentrations are studied. The delta-doped manganese layer has been separated from the GaAs quantum well with a spacer with an optimal thickness (3 nm), which has provided a sufficiently high hole mobility (≥103 cm2V−1 s−1) in the quantum wells and their effective exchange with Mn atoms. It is found that the anomalous Hall effect (AHE) is exhibited only in a restricted temperature range above and below the Curie temperature, while the AHE is not observed in quantum wells with quasi-metallic conductivity. Thus, it is shown that the use of the AHE is inefficient in studying magnetic ordering in semiconductor systems with high-mobility carriers. The features observed in the behavior of the resistance, magnetoresistance, and Hall effect are discussed in terms of the interaction of holes with magnetic Mn ions with regard to fluctuations of their potential, hole transport on the percolation level, and hopping conduction.