Why quantum phononics?
-The paradigm shift from conventional electronics to heat manipulation: In recent decades, major innovations have been based on manipulations of two particles, electrons and photons, while the limits of heated devices from the engineering standpoint, such as the low quantum efficiency of optoelectronics and velocity saturation in electronic devices, have been passively accepted. In addition to electrons and photons, another technologically important particle is the phonon, which is responsible for the transmission of sound and heat. Given the many applications of electronics/optoelectronics, it would be valuable to achieve a similar degree of control over phonons. Sound and heat can respectively be thought of as atomic vibrations in the low-frequency "sound spectrum” (< 1 GHz) and in the high-frequency "heat spectrum" (1 GHz–100 THz).
-Practical importance of phononics: Understanding and controlling the phononic properties of materials and devices open up opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity, and develop earthquake protection. Although some sonics (e.g., medical ultrasound imaging) and thermal devices (e.g., thermal insulation materials) are well known, further applications in the "heat spectrum" (1 GHz–100 THz) could be heralded on the basis of our research, quantum phononics, as a way to integrate the electronics with phononics, advancing the next revolution in manipulating heats.
Purpose of the research
Development and clear elucidation of unprecedented heat manipulation technologies, or phononics, by controlling phononic wave properties, such as 1) Amplitude, 2) Mode, and 3) Phase.
-Amplitude of acoustic phonons can be controlled by external bias, Vz, in a piezoelectric quantum structure.
-To generate and measure THz acoustic waves, laser ultrasonic methods were utilized instead of 'low frequency' electrical generation scheme.
-The acoustic wave generation mechanism was dominated by the ultrafast screening of the piezoelectric field, where the photocarrier absorption via the Franz-Keldysh effect strongly depends on the applied bias.
-Full details can be found in 'Control of coherent acoustic phonon generation with external bias in InGaN/GaN multiple quantum wells', C. S. Kim et al.,, Appl. Phys. Lett. 100, 101105.
-We experimentally and theoretically investigate the correlation between electrically-controlled crystal symmetry and the generation of different acoustic phonon modes, LA or TA.
-When transverse symmetry was broken with lateral bias, Vx, TA mode could be initiated even in isotropic planes of wurtzite structures. In addition, the detection sensitivity of TA mode was significantly enhanced, which could be explained in terms of nonlinear photoelasticity (arXiv:1803.02105v2).
-Full details can be found in Here and in 'Electrical Manipulation of Crystal Symmetry for Switching Transverse Acoustic Phonons', H. Jeong et al., Phys. Rev. Lett. 114, 043603 (2015); 'Electrical Modulation and Switching of Acoustic Phonons', H. Jeong et al., Phys. Rev. B 94, 024307 (2016).
-By selectively exciting oppositely strained quantum layers, the strain polarity of acoustic phonons can be controlled under external bias.
-Depending on the strain polarity, the phase of probe beam is shifted by 180o. Starting from this nature of phonon-photon interaction, phonon scattering mechanisms can be explored in the presence of nonliear photoelasticity in nanoscale structures.
-Full details can be found in Here and in 'External Manipulation of Acoustic Phonon Wave Properties under Nonlinear Photoelasticity', Y. D. Jho et al., Phonons 2018 & PTES 2018 Joint Conference, 30 May - 03 June 2018, Nanjing, China (Invited lecture); 'Nonlinear Photoelasticity to Explicate Acoustic Phonon Phase under Anharmonic and Extrinsic Decay', H. Jeong et al., arXiv:1803.02105v2.