Elektronska svojstva i fazni prijelazi jako koreliranih sustava

doctoral thesis

• Title: Elektronska svojstva i fazni prijelazi jako koreliranih sustava : organski vodiči i manganiti
• Title (english): Electronic properties and phase transitions of strongly correlated systems : organic conductors and manganites
• Author: Matija Čulo
• Mentor: Bojana Hamzić (mentor)
• Committee member: Ivo Batistić (predsjednik povjerenstva)
• Committee member: Silvia Tomić (član povjerenstva)
• Committee member: Mihael Srđan Grbić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2015-04-20, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

U fokusu ove doktorske disertacije su sustavi s bogatim faznim dijagramima, jakim elektronskim korelacijama i dimenzionalnosti od 3D do kvazi-1D: 3D manganiti La1−xCaxMnO3 (x > 0.5) kod kojih se pojavljuje faza uređenja naboja (CO), 2D organski vodiči α-(BEDT-TTF)2I3 koji pokazuje CO s nabojnim prugama i κ-(BEDT-TTF)2Cu2(CN)3 gdje faza CO vjerojatno ne postoji te kvazi-1D organski vodič TTF-TCNQ karakterističan po uzastopnim faznim prijelazima u stanje vala gustoće naboja. Uzorci su karakterizirani uglavnom magnetotransportnim tehnikama (otpornost, magnetootpor, anizotropija magnetootpora i Hallov efekt). U manganitima su detektirani fazni prijelazi iz paramagnetske u CO fazu, prisustvo mehanizma vodljivosti preskakanjem (VRH) ovisnog o spinu i koncentraciji x u CO fazi te smanjivanje magnetootpora i anizotropije magnetootpora s povećanjem x. Ovi rezultati su interpretirani pomoću koegzistencije feromagnetske i antiferomagnetske faze za 0, 5 < x ≤ 0, 58. Za κ-(BEDT-TTF)2Cu2(CN)3 naši rezultati, kao i mnogi drugi, pokazali su izostanak faznog prijelaza. Predložen je 2D VRH mehanizam vodljivosti, a njegovo porijeklo je pripisano neredu u anionskom podsustavu. Za α-(BEDT-TTF)2I3 naši rezultati mjerenja su pokazali prisustvo CO prijelaza, dominaciju šupljina u semimetalnom stanju te izostanak VRH mehanizma ispod CO faznog prijelaza. U TTF-TCNQ po prvi put su dobiveni rezultati Hallovog efekta na nižim temperaturama te su detektirana sva tri fazna prijelaza. Razriješeno je i otvoreno pitanje starih rezultata te je ponuđena interpretacija da elektroni i šupljine podjednako doprinose metalnom tipu vodljivosti na visokim temperaturama

Abstract (english)

This thesis focuses on systems which are known for rich phase diagrams, strong electronic correlations and dimensionality from 3D to quasi-1D: 3D manganites La1−xCaxMnO3 (x > 0.5) with a charge order phase (CO), quasi-2D organic conductors α-(BEDT-TTF)2I3 which has a CO phase with charge stripes and κ-(BEDT-TTF)2Cu2(CN)3 where a CO phase probably does not exist and quasi-1D organic conductor TTF-TCNQ known for successive phase transitions to a charge density wave state. The samples were characterized by magnetotransport techniques (resistivity, magnetoresistance, anisotropy of magnetoresistance and Hall effect). In manganites we detected phase transitions from a paramagnetic to the CO phase, the presence of spin and concentration x dependent variable range hopping mechanism (VRH) and decreasing of magnetoresistance and anisotropy of magnetoresistance with increasing x. These results were interpreted by a coexistence of a ferromagnetic and an antiferromagnetic phase for 0, 5 < x ≤ 0, 58. Our results, like many others, show that there are no phase transitions in κ-(BEDT-TTF)2Cu2(CN)3. We proposed 2D VRH mechanism whose origin is ascribed to disorder in the anion network. In α-(BEDT-TTF)2I3 our results show the presence of the CO phase, the dominance of holes in the semimetalic state and the absence of VRH mechanism below the CO phase transition. Hall effect results in TTF-TCNQ were obtained for the first time at low temperatures and they showed the presence of all three phase transitions. We resolved open questions of old results and suggested that at high temperatures electrons and holes equally contribute to the conductivity

• Keywords: elektronske korelacije; reducirana dimenzionalnost; uredenje naboja; val gustoće naboja; magnetotransport; preskakanje promjenjivog dosega; nered
• Keywords (english): electronic correlations; reduced dimensionality; charge order; charge density wave; magnetotransport; variable range hopping; disorder
• Language: croatian
• URN:NBN: urn:nbn:hr:217:605144
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 163 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-21 12:09:41