Nano-acoustic resonator with ultralong phonon lifetime

The energy damping time in a mechanical resonator is critical to many precision metrology applications, such as timekeeping and force measurements. We present measurements of the phonon lifetime of a microwave-frequency, nanoscale silicon acoustic cavity incorporating a phononic bandgap acoustic shield. Using pulsed laser light to excite a colocalized optical mode of the cavity, we measured the internal acoustic modes with single-phonon sensitivity down to millikelvin temperatures, yielding a phonon lifetime of up to τph,0≈1.5 seconds (quality factor Q=5×1010) and a coherence time of τcoh,0≈130 microseconds for bandgap-shielded cavities. These acoustically engineered nanoscale structures provide a window into the material origins of quantum noise and have potential applications ranging from tests of various collapse models of quantum mechanics to miniature quantum memory elements in hybrid superconducting quantum circuits.

Light–matter interactions in two-dimensional layered WSe2 for gauging evolution of phonon dynamics

Phonon dynamics is explored in mechanically exfoliated two-dimensional WSe2 using temperature-dependent and laser-power-dependent Raman and photoluminescence (PL) spectroscopy. From this analysis, phonon lifetime in the Raman active modes and phonon concentration, as correlated to the energy parameter E 0, were calculated as a function of the laser power, P, and substrate temperature, T. For monolayer WSe2, from the power dependence it was determined that the phonon lifetime for the in-plane vibrational mode was twice that of the out-of-plane vibrational mode for P in the range from 0.308 mW up to 3.35 mW. On the other hand, the corresponding relationship for the temperature analysis showed that the phonon lifetime for the in-plane vibrational mode lies within 1.42× to 1.90× that of the out-of-plane vibrational mode over T = 79 K up to 523 K. To provide energy from external stimuli, as T and P were increased, peak broadening in the PL spectra of the A-exciton was observed. From this, a phonon concentration was tabulated using the Urbach formulism, which increased with increasing T and P; consequently, the phonon lifetime was found to decrease. Although phonon lifetime decreased with increasing temperature for all thicknesses, the decay rate in the phonon lifetime in the monolayer (1L) material was found to be 2× lower compared to the bulk. We invoke a harmonic oscillator model to explain the damping mechanism in WSe2. From this it was determined that the damping coefficient increases with the number of layers. The work reported here sheds fundamental insights into the evolution of phonon dynamics in WSe2 and should help pave the way for designing high-performance electronic, optoelectronic and thermoelectric devices in the future.

Laser induced Fano scattering, electron–phonon coupling, bond length and phonon lifetime changes in α-Fe2O3 nanostructures

We have extensively studied the laser-induced Fano scattering, electron–phonon coupling, bond length and phonon lifetime of the α-Fe2O3 nanostructure prepared through a simple co-precipitation method.

Numerical investigation of the dependence of stimulated Brillouin scattering threshold on the pump intensity fluctuation

In this paper, the dependence of stimulated Brillouin scattering (SBS) threshold on the sinusoidal modulated properties of pump pulse is studied. A 527-nm-wavelength, 5 ns square laser pulse with sinusoidal temporal modulation is used as the pump source, and a 600 mm liquid heavy fluorocarbon material FC-40 is used as the Brillouin medium. The numerically calculated results indicate that the SBS threshold increases with the increase of both temporal intensity modulation index and modulation frequency of the pump pulse. However, when the intensity distortion criterion is below 30% or the duration of modulation peaks below three times the phonon lifetime, the SBS threshold tends to remain stable. The numerical results provide assistance to judge the SBS threshold for unsmoothed pump pulses, especially for high power laser applications.