Experimental Detection of a Quantum Spin LiquidJanša, Nejc (Avtor)
Klanjšek, Martin (Mentor)
quantum spin liquidKitaev modelquantum computationnuclear magnetic resonancenuclear quadrupole resonanceKitaev paramagnetα-RuCl3BaCo2(AsO4)2Majorana fermiongauge fluxfractionalizationanyonspin excitation gapQuantum spin liquids are disordered states which feature entanglement and fractional quasiparticles with a lot of potential for study of quantum physics and for technological applications, for example in topologically protected quantum computation. The Kitaev model predicts an exact realization of the quantum spin liquid ground state. We search for experimental evidence of such states in real materials predicted to host the necessary Kitaev interactions. Our studies are done primarily using magnetic resonance on the candidates α-RuCl3 and BaCo2(AsO4)2. We identify the observables which show a unique response characteristic of the Kitaev quantum spin liquid as simulated by theoretical calculations. Although the pure ground state is disturbed by magnetic order, we observe that properties of the quantum spin liquid persist at higher temperatures in the so called Kitaev paramagnetic phase. In α-RuCl3 we show the fractionalization of a spin-flip into two types of anyons, a Majorana fermion and a pair of gauge fluxes in a wide range of temperatures and fields. The identity of the particles is confirmed by matching the spin excitation gap to the predictions of the pure Kitaev model with a cubic field dependence. The sample is studied in depth determining the electric field gradient and hyperfine tensors, properties of the crystal structure and finding effects of additional interactions where the pure Kitaev picture breaks down. In BaCo2(AsO4)2 we also find characteristics of the Kitaev paramagnetic phase in a phase diagram that is more sensitive to the external magnetic field. The spin excitation gap is found to have a linear field dependence as expected for models with additional interactions. A region in the phase diagram is found, where a different type of fractionalization into pairs of Majorana fermions might be present.20222022-08-03 12:01:56Doktorsko delo/naloga138622sl