Type of Thesis
High-temperature superconductivity has attracted a lot of attention. Since 1986 when the first high-temperature superconductor was discovered by researchers of IBM, scientists never give up to increase the transition temperature so that superconductors can be applied widely in industries. However, it remains an enigma that what causes the superconductivity of the high -temperature superconductor. The study of conventional superconductors suggest that the possible cause of superconductivity is electron-phonon coupling. Vast research have been devoted into this direction. But generally stimulating phonons is not efficient enough to see how phonons of exact mode affect the properties of a certain material. In this work, we will investigate a method to resonantly stimulate phonons with an optical pulse train generator. By setting the position of each lens and mirror, we can match the frequency of the output pulses with the frequency of phonons and then stimulate them resonantly.
Then we will collect data with Angle Resolved Photoemission Spectroscopy. This allowed us to analyze the behaviors of electrons inside the sample after the excitation of phonons. We find that resonant stimulation indeed increase the intensity of vibration of phonons of corresponding frequency and decrease the intensity of phonons of other mode. This provides us a helpful tool to precisely stimulate phonons of certain mode and study the properties of material.
Huang, Yongyang, "Stimulating Coherent Phonons in CaFe2As2 With Laser" (2016). Undergraduate Honors Theses. 1080.