Impurities in triangular lattice spin 1/2 antiferromagnet

Abstract

We study effects of nonmagnetic impurities in a spin-1/2 frustrated triangular antiferromagnet with the aim of understanding the observed broadening of ${}^{13}$C NMR lines in the organic spin liquid material $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$. For high temperatures down to $J/3$, we calculate local susceptibility near a nonmagnetic impurity and near a grain boundary for the nearest neighbor Heisenberg model in high temperature series expansion. We find that the local susceptibility decays to the uniform one in few lattice spacings, and for a low density of impurities we would not be able to explain the line broadening present in the experiments already at elevated temperatures. At low temperatures, we assume a gapless spin liquid with a Fermi surface of spinons. We calculate the local susceptibility in the mean field and also go beyond the mean field by Gutzwiller projection. The zero temperature local susceptibility decays as a power law and oscillates at $2k_F$. As in the high temperature analysis we find that a low density of impurities is not able to explain the observed broadening of the lines. We are thus led to conclude that there is more disorder in the system. We find that a large density of point-like disorder gives broadening that is consistent with the experiment down to about 5K, but that below this temperature additional mechanism is likely needed.

15 pages, 13 figures

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• ^{63}Cu, ^{35}Cl, and ^{1}H NMR in the S=1/2 Kagomé Lattice ZnCu_{3}(OH)_{6}Cl_{2}
• Emergence of inhomogeneous moments from spin liquid in the triangular-lattice Mott insulator $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$
• Low temperature magnetization of the S=1/2 kagome antiferromagnet ZnCu_3(OH)_6Cl_2
• Transport Properties of a spinon Fermi surface coupled to a U(1) gauge field
• Theory of quantum impurities in spin liquids
• Spin-triplet pairing instability of the spinon Fermi surface in a U(1) spin liquid
• Determining ethylene group disorder levels in $\kappa$-(BEDT-TTF)${}_2$Cu[N(CN)${}_2$]Br
• Insulator-metal transition on the triangular lattice
• Studies of non-magnetic impurities in the spin-1/2 Kagome Antiferromagnet
• Susceptibility of a spinon Fermi surface coupled to a U(1) gauge field

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• Critical Spin Liquid versus Valence Bond Glass in Triangular Lattice Organic $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$
• Molecular Quantum Materials: Electronic Phases and Charge Dynamics in Two-Dimensional Organic Solids
• Quantum Spin Liquid State in the Disordered Triangular Lattice Sc2Ga2CuO7
• Emergent moments and random singlet physics in a Majorana spin liquid
• Low-temperature lattice effects in the spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$
• Effects of impurities in Spin Bose-Metal phase on a two-leg triangular strip
• Magnetic effects of non-magnetic impurities in gapped short-range resonating valence bond spin liquids