Show document

A+ | A- | | SLO | ENG

Title: ULTRAFAST ELECTRON DYNAMICS IN CORRELATED SYSTEMS PROBED BY TIME-RESOLVED PHOTOEMISSION SPECTROSCOPY Authors: ID Saha, Tanusree, University of Nova Gorica (Author) ID De Ninno, Giovanni, University of Nova Gorica (Mentor) More about this mentor... Files: PhD_Thesis_Tanusree_Saha.pdf (13,34 MB) MD5: 97CC7EC454E642D312CE441069A9EC9B   Language: English Work type: Doctoral dissertation Typology: 2.08 - Doctoral Dissertation Organization: FPŠ - Graduate School Abstract: Complex systems in condensed matter are characterized by strong coupling between different degrees of freedom constituting a solid. In materials described by many-body physics, these interactions may lead to the formation of new ground states such as excitonic insulators, Mott insulators, and charge and spin density waves. However, the inherent complexity in such materials poses a challenge to identifying the dominant interactions governing these phases using equilibrium studies. Owing to the distinct timescales associated with the elementary interactions, such complexities can be readily addressed in the non-equilibrium regime. Additionally, these materials might also show the emergence of new, metastable “hidden“ phases under non-equilibrium. The thesis investigates the ultrafast timescales of fundamental interactions in candidate systems by employing time-and angle-resolved photoemission spectroscopy in the femtosecond time domain. In the (supposed) excitonic insulator model system Ta2NiSe5, the timescale of band gap closure and the dependence of rise time (of the photoemission signal) on the photoexcitation strength point to a predominantly electronic origin of the band gap at the Fermi level. The charge density wave (CDW) - Mott insulator 1T-TaS2 undergoes photoinduced phase transition to two different phases. The initial one is a transient phase which resembles the systems’s high temperature equilibrium phase, followed by a long-lived “hidden“ phase with a different CDW amplitude and is primarily driven by the CDW lattice order. For the spin density wave system CaFe2As2 where multiple bands contribute in the formation of Fermi surfaces, selective photoexcitation was used to disentangle the role played by different electron orbitals. By varying the polarization of photoexcitation pulses, it is observed that dxz/dyz orbitals primarily contribute to the magnetic ordering while the dxy orbitals have dominant role in the structural order. The findings of the present study provide deeper perspectives on the underlying interactions in complex ground phases of matter, therefore, initiating further experimental and theoretical studies on such materials. Keywords: complex systems, charge density wave, excitonic insulator, metastable phase, Mott insulator, non-equilibrium, spin density wave, timescales, time- and angle-resolved photoemission, ultrafast dynamics Publication status: Published Place of publishing: University of Nova Gorica Year of publishing: 2023 PID: 20.500.12556/RUNG-8233  COBISS.SI-ID: 154203395  NUK URN: URN:SI:UNG:REP:3ORD7CQH Publication date in RUNG: 01.06.2023 Views: 3223 Downloads: 42 Metadata:    Cite this work Plain text BibTeX EndNote XML EndNote/Refer RIS ABNT ACM Ref AMA APA Chicago 17th Author-Date Harvard IEEE ISO 690 MLA Vancouver : SAHA, Tanusree, 2023, ULTRAFAST ELECTRON DYNAMICS IN CORRELATED SYSTEMS PROBED BY TIME-RESOLVED PHOTOEMISSION SPECTROSCOPY [online]. Doctoral dissertation. University of Nova Gorica. [Accessed 21 April 2025]. Retrieved from: https://repozitorij.ung.si/IzpisGradiva.php?lang=eng&id=8233 Copy citation

Average score: 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 (0 votes) Your score: Voting is allowed only for logged in users. Share: Similar works from our repository: NSCLC molecular testing in Central and Eastern European countries Access to novel drugs for non-small cell lung cancer in Central and Southeastern Europe Trans-esophageal endobronchial ultrasound-guided needle aspiration (EUS-B-NA) Treatment patterns, testing practices, and outcomes in the pre-FLAURA era for patients with EGFR mutation-positive advanced NSCLC Multicenter evaluation of the fully automated PCR-based Idylla EGFR Mutation Assay on formalin-fixed, paraffin-embedded Q1 tissue of human lung cancer Similar works from other repositories: Vpliv izražanja receptorja za inzulinu podoben rastni dejavnik 1 (IGF1R) na preživetje pri razsejanem nedrobnoceličnem raku pljuč Pomen tumorskih matičnih celic in epitelno-mezenhimskega prehoda pri napredovanju nedrobnoceličnega raka pljuč Gene expression levels of the prolyl hydroxylase domain proteins PHD1 and PHD2 but not PHD3 are decreased in primary tumours and correlate with poor prognosis of patients with surgically resected non-small-cell lung cancer Širitev Evropske unije: ali navdušenje hlapi? Demografski problemi tranzicijskih držav Hover the mouse pointer over a document title to show the abstract or click on the title to get all document metadata.

Secondary language

Language:	Slovenian
Title:	PREUČEVANJE ULTRA HITRE DINAMIKE ELEKTRONOV V KORELIRANIH SISTEMIH S POMOČJO ČASOVNO LOČLJIVE FOTOEMISIJE
Abstract:	Za kompleksne sisteme v kondenzirani snovi je značilna močna sklopitev med različnimi prostostnimi stopnjami, ki to snov tvorijo. V materialih, ki jih opisuje fizika več teles, lahko takšne interakcije vodijo v nastanek novih osnovnih stanj, kot so ekscitonski in Mottovi izolatorji ter valovi gostote naboja in spina. Zaradi zapletene narave takšnih sistemov lahko z ravnovesnimi študijami le stežka prepoznamo prevladujoče interakcije v omenjenih fazah. Po drugi strani pa lahko zaradi prisotnosti različnih karakterističnih časovnih skal kompleksne materiale lažje obravnavamo z nerovnovesnimi tehnikami. Poleg tega lahko v neravnovesju v omenjenih materialih pride do pojava novih, metastabilnih t.i. skritih stanj. V disertaciji smo raziskali ultra hitre časovne skale osnovnih interakcij v omenjenih sistemih z uporabo femtosekundne kotno ločljive fotoemisijske spektroskopije. V (domnevnem) ekscitonskem izolatorju Ta2NiSe5 karakteristični čas, v katerem se zapre energijska vrzel, ter odvisnost karakteristi čnega časa dviga fotoemisijskega signala od jakosti svetlobnega vzbujanja kažeta na to, da je energijska vrzel v omenjenem materialu elektronskega izvora. V Mottovem izolatorju 1T-TaS2, v katerem so prisotni valovi gostote naboja (ang. charge density wave - CDW) pride pri fotovzbujanju do prehoda v različne neravnovesne faze in sicer najprej v neravnovesno stanje, ki je podobno visoko temperaturnem ravnovesnem stanju in nato v dolgoživo “skrito“ stanje z manjšo CDW amplitudo, pričemer je gonilna sila teh prehodov kristalni red CDW. V vzorcih CaFe2As2, za katere so značilni valovi gostote spina in kjer več energijskih pasov prispeva k nastanku Fermijeve površine, smo s selektivnim fotovzbujanjem ugotavljali kakšna je vloga različnih orbital. S spreminjanjem polarizacije vzbujevalnih sunkov smo opazili, da dxz/dyz orbitale primarno prispevajo k magnetnemu urejanju, medtem ko imajo dxy orbitale glavno vlogo v strukturnem redu. Ugotovitve te študije ponujajo nov vpogled v temeljne interakcije v kompleksnih materialih in predstavljajo osnovo za nadaljnje eksperimentalne in teoretične raziskave.
Keywords:	kompleksni sistemi, val gostote naboja, ekscitonski izolator, metastabilna faza, Mottov izolator, neravnovesje, val gostote spina, asovne skale, časovno in kotno ločljiva fotoemisija, ultrahitra dinamika

Back