Crystal Growth and Magnetic Property Study of layered honeycomb materials with Kitaev like interactions

Abstract

Kitaev-like bond-directional exchange interactions are novel and quite diand#64256;erent from the newlineubiquitous Heisenberg interactions found in most magnets. These kind of interactions newlineopen up new possibilities in the exploration and designing of new quantum magnets newlinewhich can host novel quantum ground states like spin-liquids. However, Kitaev-like in- newlineteractions have remained only a theoretical construct until recently. Honeycomb iridates newlineA 2 IrO 3 (A = Na, Li), oand#64256;er potential realizations of such novel exchange coupling. In this newlinethesis I have synthesized single crystals of A 2 TO 3 (A = Na, Li, K, and T = Ir, Ru) and newlinestudied their electrical transport, magnetic, and thermal properties. Our work provides newlineseveral new results: (i) the and#64257;rst thermodynamic evidence of possible fractionalization of newlineelectrons in Na 2 IrO 3 because of proximity to the Kitaev spin-liquid state, (ii) evidence newlinethrough magnetic impurity doping, of fragile magnetic order and importance of nearest- newlineneighbour interactions and spin-orbit coupling in deciding the magnetic ground state newlinein Na 2 IrO 3 , (iii) a novel method (reactive ion etching) of surface doping Na 2 IrO 3 and newlinepossibly other layered oxides has been discovered. The surface conductivity of Na 2 IrO 3 newlinecrystals could be increased by 11 orders of magnitude by varying etching times. The newlinesamples which turned metallic show transport anomalies consistent with charge density newlinewave or structural instabilities, (iv) and#64257;rst crystal growth of Li 2 RuO 3 is reported where newlinethe Xtals crystallize in the P2 1 /m structure and show the expected high temperature newlinemagneto-structural transition, and (v) design and crystal growth of a new layered honey- newlinecomb lattice iridate K 2 IrO 3 with an interlayer separation between Ir honeycomb planes newlinewhich is more than a factor of 2 larger than in Na 2 IrO 3 . Magnetic measurements on crys- newlinetals reveal localized eand#64256;ective spin S = 1/2 interacting strongly and#952; = and#8722;210 K but without newlinemagnetic order down to 1.8 K. Thus K 2 IrO 3 is a new Kitaev spin liquid candidate. newline