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BEGIN:VEVENT
DTSTAMP:20261021T161830Z
LAST-MODIFIED:20140407T205525Z
DTSTART:20140410T163000Z
DTEND:20140410T173000Z
UID:event1220@bu.edu
URL:http://physics.bu.edu/internal/events/show/1220
SUMMARY:Electronic and Structural Dynamics of Vanadates and Nickelates: Eff
	ect of Temperature\, Strain and Photoexcitation
DESCRIPTION:Featuring Elsa Caroline Souto Gonçalves de Abreu \n\nPart of t
	he PhD Final Oral Exams.\n\nExamining Committee:  Richard Averitt\, Claudio
	 Chamon\, Kevin Smith\, Shyam Erramilli\, Robert Carey\n\nABSTRACT\nThe sci
	entific relevance and potential for technological applications of complex m
	aterials have made them the focus of active investigation in order to fully
	 characterize the competition and interactions between their electronic\, s
	tructural\, orbital\, and spin degrees of freedom. Optical and terahertz (T
	Hz) spectroscopy provide access to electronic and low frequency quasipartic
	le responses\, and therefore play a key role in understanding the fundament
	al mechanisms which dictate the macroscopic properties of complex materials
	. Time-resolved experiments\, in turn\, have the potential to disentangle t
	he various coexisting energy scales through a careful selection of the pump
	 and probe characteristics. This work investigates the role played by the e
	lectronic\, structural and magnetic excitations in the insulator-to-metal t
	ransitions (IMT) of VO2\, V2O3 and NdNiO3\, through studies under different
	 conditions of temperature\, strain\, doping and photoexcitation. \n\nOur w
	ork shows that a complete understanding of the IMT in VO2 requires several 
	length scales and time scales to be considered. Indeed\, epitaxial strain l
	eads to anisotropy in the IMT characteristics of thin films of (100) and (1
	10) VO2/TiO2\, measured using THz spectroscopy\, which can be explained by 
	strain induced modifications both in the (microscopic) V3d orbitals and in 
	the geometry of mesoscopic metallic domains. On the other hand\, ultrafast 
	studies which track\, with femtosecond resolution\, the electronic and stru
	ctural dynamics of VO2 thin films following THz excitation reveal a delay i
	n the onset of the structural response with respect to the electronic one\,
	 lending support to the correlation rather than Peierls driven picture of t
	he IMT in this material.\n\nAs for V2O3\, the IMT is seen to occur via nucl
	eation and growth of metallic domains\, as previously reported in VO2. Howe
	ver\, a scaling of the photoinduced conductivity dynamics rise time is furt
	her identified\, which reveals the temperature and fluence dependence of th
	e nucleation and growth process.\n\nFinally\, strained NdNiO3 films exhibit
	 a two step dynamical conductivity response following optical excitation\, 
	different from that of the vanadates with which they share a complex\, albe
	it more tunable\, phase diagram. This hints at a significant role being pla
	yed by the magnetic structure during the IMT in NdNiO3.\n\n![Elsa](/resourc
	es/event-image/1220/8c39ecf_small)
LOCATION:PRB 595\, 3 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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