TY  - JOUR
A1  - Bojahr, Andre
A1  - Gohlke, Matthias
A1  - Leitenberger, Wolfram
A1  - Pudell, Jan-Etienne
A1  - Reinhardt, Matthias
A1  - Reppert, Alexander von
A1  - Rössle, Matthias
A1  - Sander, Mathias
A1  - Gaal, Peter
A1  - Bargheer, Matias
T1  - Second Harmonic Generation of Nanoscale Phonon Wave Packets
JF  - Physical review letters
N2  - Phonons are often regarded as delocalized quasiparticles with certain energy and momentum. The anharmonic interaction of phonons determines macroscopic properties of the solid, such as thermal expansion or thermal conductivity, and a detailed understanding becomes increasingly important for functional nanostructures. Although phonon-phonon scattering processes depicted in simple wave-vector diagrams are the basis of theories describing these macroscopic phenomena, experiments directly accessing these coupling channels are scarce. We synthesize monochromatic acoustic phonon wave packets with only a few cycles to introduce nonlinear phononics as the acoustic counterpart to nonlinear optics. Control of the wave vector, bandwidth, and consequently spatial extent of the phonon wave packets allows us to observe nonlinear phonon interaction, in particular, second harmonic generation, in real time by wave-vector-sensitive Brillouin scattering with x-rays and optical photons.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.115.195502
SN  - 0031-9007
SN  - 1079-7114
VL  - 115
IS  - 19
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Maerten, Lena
A1  - Bojahr, Andre
A1  - Gohlke, Mathias
A1  - Rössle, Matthias
A1  - Bargheer, Matias
T1  - Coupling of GHz Phonons to Ferroelastic Domain Walls in SrTiO3
JF  - Physical review letters
N2  - We study the linear and nonlinear acoustic response of SrTiO3 across its ferroelastic transition at T-a = 105 K by time domain Brillouin scattering. Above T-a we observe that for a strain amplitude of similar to 0.18% the sound velocity for compressive strain exceeds the tensile strain velocity by 3%. Below T-a we find a giant slowing down of the sound velocity by 12% and attribute this to the coupling of GHz phonons to ferroelastic twin domain walls. We propose a new mechanism for this coupling on the ultrafast time scale, providing an important new test ground for theories used to simulate atomic motion in domain forming crystals.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.047401
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  -