Fractional excitations in low-dimensional spin systems [Elektronische Ressource] / von Ronny Thomale

Fractional Excitations inlow–dimensional spin systemsZur Erlangung des akademischen Grades einesDOKTORS DER NATURWISSENSCHAFTENvon der Fakult¨at fu¨r Physik derUniversit¨at (TH) KarlsruhegenehmigteDISSERTATIONvonDipl.-Phys. Ronny Thomaleaus Mu¨nsterReferent: Prof. Dr. Peter W¨olfle, TKMKorreferent: Prof. Dr. Alexander Mirlin, INTDatum der Pru¨fung: 21. November 2008AcknowledgmentsQui dedit beneficium, taceat. Narret, qui accepit.–LuciusAnnaeusSenecaIt is hard to say in words how much I thank my advisor Martin Greiter.Since my first semester at University, he provided me help, advice, and guid-ance to find and subsequently follow the path of theoretical physics. Withgenerosityandpatiencehedidnotonlyteachmehowtothinkaboutphysics,but most importantly also how to live with it.I am grateful to Peter W¨olfle for his constant support and for giving methe opportunity to do this thesis at the Institut fu¨r Theorie der Konden-sierten Materie (TKM). I also thank Alexander Mirlin for taking over theco-refereeing of my thesis.I thank the Studienstiftung des deutschen Volkes forthe PhD scholarshipby which my work was predominantly financed.There aremanypeopleIhavebeendiscussing andworkingwithwhogaveme a lot of support and provided me important insights into various fieldsof physics. I especially wish to thank Bogdan A.