DEGENERATE SECOND ORDER NONLINEAR OPTICAL SPECTROSCOPY OF CHIRAL WEYL SEMIMETALS
type: CreativeWork
description: This thesis focuses on the development of nonlinear optical techniques and the measurement of topological properties of the Weyl semimetals. The first portion of this thesis describes technical developments of the nonlinear optical spectroscopic probes rotational anisotropy second harmonic generation (RA-SHG) and transient grating. In our work on SHG, we describe a fast-reflective optic-based rotational anisotropy nonlinear harmonic generation spectrometer built upon synchronization of stepper motors and a voice-coil fast turning motor with data recorded by a data acquisition card. This device enables fast accumulation of significantly more data points than traditional SHG spectrometers and further allows spectral measurement over a broad wavelength range to be performed without optical realignment. We then describe the Fourier domain RA-SHG, allows direct measurements of the RA-SHG signal components of Cn symmetry. This method is based on the fast scanning RA-SHG device described above and operates by recording the nth harmonics of the fast scanning signal using a lock-in amplifier. Finally, we describe a novel method of performing transient grating measurements based on low power laser diodes, a laser diode pulser, a digital delay generator, and a data acquisition card. The RA-SHG technique was applied to the chiral Weyl semimetal RhSi, where a spectrum of the sole SHG tensor element χ(2) i jk was measured over the unprecedented 0.275-1.5 eV incoming photon energy range. Our data shows evidence of a strong surface state response and are detailed enough to reveal the second order corrections to the linear band structure as well as the Pauli blocking condition which was observed to occur at ∼630 meV. We also describe measurements of the linear photogalvanic effect (LPGE) and circular photogalvanic effect (CPGE) in RhSi deriving from topological Fermi arc states. While the magnitude of the CPGE response broadly matched theoretical predictions, the data also exhibit a…
abstract: This thesis focuses on the development of nonlinear optical techniques and the measurement of topological properties of the Weyl semimetals. The first portion of this thesis describes technical developments of the nonlinear optical spectroscopic probes rotational anisotropy second harmonic generation (RA-SHG) and transient grating. In our work on SHG, we describe a fast-reflective optic-based rotational anisotropy nonlinear harmonic generation spectrometer built upon synchronization of stepper motors and a voice-coil fast turning motor with data recorded by a data acquisition card. This device enables fast accumulation of significantly more data points than traditional SHG spectrometers and further allows spectral measurement over a broad wavelength range to be performed without optical realignment. We then describe the Fourier domain RA-SHG, allows direct measurements of the RA-SHG signal components of Cn symmetry. This method is based on the fast scanning RA-SHG device described above and operates by recording the nth harmonics of the fast scanning signal using a lock-in amplifier. Finally, we describe a novel method of performing transient grating measurements based on low power laser diodes, a laser diode pulser, a digital delay generator, and a data acquisition card. The RA-SHG technique was applied to the chiral Weyl semimetal RhSi, where a spectrum of the sole SHG tensor element χ(2) i jk was measured over the unprecedented 0.275-1.5 eV incoming photon energy range. Our data shows evidence of a strong surface state response and are detailed enough to reveal the second order corrections to the linear band structure as well as the Pauli blocking condition which was observed to occur at ∼630 meV. We also describe measurements of the linear photogalvanic effect (LPGE) and circular photogalvanic effect (CPGE) in RhSi deriving from topological Fermi arc states. While the magnitude of the CPGE response broadly matched theoretical predictions, the data also exhibit a…
author: Lu, Baozhu
language: eng
keywords: Condensed matter physics, Optics, Physics, CPGE, Fermi arc surface states, Linear band structure, RA-SHG, Topology, Weyl semimetals
license: http://rightsstatements.org/vocab/InC/1.0/
date published: 2020
date modified: 2026-07-27T21:20:03Z
provider: Temple University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Temple University. Libraries

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property ID: Handle
value: http://hdl.handle.net/20.500.12613/6435