Ground state and excitation properties of the quantum kagom\'{e} system ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ investigated by local probes

Source: arXiv

ABSTRACT We characterize the ground state and excitation spectrum of the $S=1/2$, nominally pure and perfect kagom\'{e} system ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ using the following measurements: magnetization, muon spin rotation frequency shift $K$, transverse relaxation time $T_{2}^{\ast}$, and zero field relaxation, and Cl nuclear spin-lattice relaxation $T_{1}$. We found no sign of singlet formation, no long range order or spin freezing, and no sign of spin-Peierls transition even at temperatures as low as 60 mK. The density of states has $E^{1/4}$ energy dependence with a negligible gap to excitation.

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    ABSTRACT: We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase transition when the Dzyaloshinskii-Moriya coupling is increased. For DDc the system develops antiferromagnetic long-range order. The quantum critical point is found to be Dc~=0.1J using exact diagonalizations and finite-size scaling. This suggests that the kagome compound ZnCu3(OH)6Cl3 may be in a quantum critical region controlled by this fixed point.
    Physical review. B, Condensed matter 10/2008; 78. · 3.66 Impact Factor
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    ABSTRACT: A small value of the spin gap in quantum antiferromagnets with strong frustration makes them susceptible to nominally small deviations from the ideal Heisenberg model. One such perturbation, the anisotropic Dzyaloshinskii-Moriya (DM) interaction, is an important perturbation for the S=1/2 kagome antiferromagnet, one of the current candidates for a quantum-disordered ground state. We study the influence of the DM term in a related one-dimensional system, the sawtooth chain, which has valence-bond order in its ground state. Through a combination of analytical and numerical methods, we show that a relatively weak DM coupling, 0.115J, is sufficient to destroy the valence-bond order, close the spin gap, and turn the system into a Luttinger liquid with algebraic spin correlations. A similar mechanism may be at work in the kagome antiferromagnet.
    Physical review. B, Condensed matter 09/2011; 84. · 3.66 Impact Factor
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    ABSTRACT: Using series expansions around the dimer limit, we find that the ground state of the spin-1/2 Heisenberg antiferromagnet on the kagome lattice appears to be a valence bond crystal (VBC) with a 36 site unit cell, and ground-state energy per site E=-0.433±0.001J . It consists of a honeycomb lattice of ``perfect hexagons.'' The energy difference between the ground state and other ordered states with the maximum number of perfect hexagons, such as a stripe-ordered state, is of order 0.001J . The expansion is also done for the 36 site system with periodic boundary conditions; its energy per site is 0.005±0.001J lower than the infinite system, consistent with exact diagonalization results. Every unit cell of the VBC has two singlet states whose degeneracy is not lifted to sixth order in the expansion. We estimate this energy difference to be less than 0.001J . The dimerization order parameter is found to be robust. Two leading orders of perturbation theory give lowest triplet excitations to be dispersionless and confined to the perfect hexagons.
    Physical Review B 11/2007; 76. · 3.66 Impact Factor

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