Deepu George | Searcharxiv

arXiv2016

Soft Phonon Mode Dynamics in Aurivillius Type Structures

We report the dynamics of soft phonon modes and their role towards the various structural transformations in Aurivillius materials by employing terahertz frequency-domain spectroscopy, atomic pair distribution function analysis, and first-principles calculations. We have chosen Bi4Ti3O12 as a model system and identified soft phonon modes associated with the paraelectric tetragonal to the ferroelectric monoclinic transition. Three soft phonon modes have been discovered which exhibit a strong temperature dependence. We have determined that the anharmonicity in Bi-O bonds plays a significant role in phonon softening and that Bi cations play an important role in the emergence of ferroelectricity.

cond-mat.mtrl-sci↗

arXiv2015

A Tunable Terahertz Detector Based On Self Assembled Plasmonic Structure on a GaAs 2DEG

Plasmonic detectors have the potential to provide a method of rapid spectroscopy without the need of moving mirrors or gratings. Previous measurements have demonstrated frequency tunable detection based on plasmonic excitations, however these devices were either small area, polarization dependent and/or required e-beam lithography. We demonstrate that large area high sensitivity THz plasmonic detection can be achieved using self-assembly nanosphere lithography. We achieve a submicron feature size grid covering a detector area of 4 mm^2. The absorbance at the fundamental, third and 5th harmonics of plasmon resonances are observed. Measurements at 80 K show a large transmission change of 25%. We also confirmed a magneto plasmon dispersion of this device. In this paper we will discuss the frequency dependence of the radiative damping effect which affects enhanced absorption at the higher harmonics mode relative to fundamental.

cond-mat.mtrl-sci↗