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Impact of strong picosecond THz pulses on dielectrics and semiconductors

Date Fr, 12.07.2019 - Fr, 12.07.2019
Time 14:00h
Speaker Prof. Elena Mishina, MIREA – Russian Technological University - Moscow, Russia
Location ETH Hönggerberg, HPF G-6
Program Direct manipulation of the atomic lattice using high power single-period THz pulses allows to create new states of matter in complex materials. This is possible due to strong anharmonicity of ionic potential due to excitation by strong transient electric field of THz pulse, which ranges up to tens of MV/cm. This pulse can dynamically alter the lattice structure and provide through phonon-phonon coupling coherent control over specific phonons including soft modes. Two types of unharmonic processes were reported so far. The first one is to resonantly excite high frequency vibrational mode and to modify the lattice structure through indirect coupling of this infrared-active phonon to other, lower frequency lattice modulations. The second one is opposite: to drive the lowest frequency optical phonon in the into the anharmonic regime with a strong terahertz pulse and transfer energy to higher frequency phonon modes through nonlinear coupling. In semiconductors, high electric fields produces electrical breakdown due to avalanche of electrons generated by impact ionization. This effect has been studied for decades in electronic devices in CW or low frequency field. Ultrashort THz pulse gives birth to absolutely new effects, when impact ionization takes place but it does not lead to breakdown because of high localization in time and space.
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