Charge ordering in strongly correlated systems

doctoral thesis

• Title (croatian): Uređenja naboja u jako koreliranim sustavima
• Author: Tomislav Ivek
• Mentor: Silvia Tomić (mentor)
• Committee member: Amir Hamzić (predsjednik povjerenstva)
• Committee member: Silvia Tomić (član povjerenstva)
• Committee member: Slaven Barišić (član povjerenstva)
• Committee member: Martin Dressel (član povjerenstva); strani drzavljanin: Nije dostupno
• Committee member: Bojana Hamzić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2011-06-14, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

At the focus of this thesis are systems with strong correlations and reduced dimensionality: the inorganic quasi-1D chain compound BaVS3 with itinerant and localized charges, spin chain and ladder composite (La,Y,Sr,Ca)14Cu24O41, and the quasi-2D organic conductor α-(BEDT-TTF)2I3 with the so-called horizontal stripe charge order. Samples have been characterized by transport and optical methods used in solid state and low-temperature physics: anisotropy of dc conductivity, nonlinear conductivity and low-frequency dielectric response as well as terahertz and infrared spectroscopy. In the orbitally ordered phase of BaVS3 evidence is presented of collective excitations below the Peierls-like metal-insulator transition. Further, in (La,Y)y(Sr,Ca)14-yCu24O41 a crossover in charge transport is demonstrated at y ≈ 2 from a one-dimensional hopping along the chain subsystem to a quasi-two-dimensional charge conduction in the ladder planes. It is found that an interdependent formation of long-range orders takes place in the two subsystems: an antiferromagnetic dimer order in chains and a charge-density wave in ladders. Lastly, electrodynamic response in the organic conductor α-(BEDT-TTF)2I3 has been investigated. Optical spectra show a sudden appearance of long-range charge order below the phase transition. Rather than a fully localized Wigner crystal, our results favor an interesting interpretation of horizontal stripes as a cooperative bond-charge density wave with a ferroelectric-like nature.

Abstract (croatian)

U fokusu ove doktorske disertacije nalaze se sustavi s jakim elektronskim korelacijama i reduciranom dimenzionalnošću: anorganski kvazi-1D lanačasti spoj BaVS3 s itinerantnim i lokaliziranim nabojima, kompozit kupratnih lanaca i ljestvica (La,Y,Sr,Ca)14Cu24O41, te kvazi-2D organski vodič α-(BEDT-TTF)2I3 koji pokazuje tzv. uređenje naboja s horizontalnim prugama. Uzorci su karakterizirani optičkim metodama i mjerenjem električnog transporta: anizotropija istosmjerne vodljivosti, niskofrekventni dielektrični odziv te terahertzna i infracrvena spektroskopija. U fazi orbitalnog uređenja BaVS3 nađeni su dokazi kolektivnih pobuđenja ispod faznog prijelaza iz metala u izolator sličnog Peierlsovom. Nadalje, u (La,Y)y(Sr,Ca)14-yCu24O41 je na y ≈ 2 pokazano postupno prebacivanje transporta naboja s jednodimenzionalnog preskakivanja duž lanaca na kvazi-dvodimenzionalno vođenje u ravninama ljestvica. Rezultati ukazuju na zanimljivu međuzavisnost stvaranja dugodosežnog uređenja u dva sustava: antiferomagnetskog dimerskog uređenja na lancima, te vala gustoće naboja na ljestvicama. Na kraju, ispitan je i elektrodinamički odziv α-(BEDT-TTF)2I3. U optičkim spektrima pronalazimo dokaze naglog dugodosežnog uređenja naboja. Kao najkonzistentniju sliku te uređene faze predlažemo zanimljiv pogled horizontalnih pruga kao kooperativnog vala gustoće veza i naboja feroelektrične prirode umjesto potpuno lokaliziranog Wignerovog kristala.

• Keywords: charge ordering; charge-density wave; orbital ordering; phase transition; strong correlations; conductivity; anisotropy; dielectric response; infrared spectroscopy
• Keywords (croatian): uređenje naboja; val gustoće naboja; orbitalno uređenje; fazni prijelaz; jake korelacije; vodljivost; anizotropija; dielektrični odziv; infracrvena spektroskopija
• Language: english
• URN:NBN: urn:nbn:hr:217:988646
• 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: 212 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-23 12:14:36