Browsing Physics & Astronomy, Dept. of by Author "Batista, C. D."
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ItemPhase diagram and spin Hamiltonian of weakly-coupled anisotropic S=½ chains in CuCl2·2((CD3)2SO)(American Physical Society, 2007-06-01) Chen, Y.; Stone, M. B.; Kenzelmann, M.; Batista, C. D.; Reich, D.H.; Broholm, C.Field-dependent specific heat and neutron scattering measurements were used to explore the antiferromagnetic S=½ chain compound CuCl2·2((CD3)2SO). At zero field the system acquires magnetic long-range order below TN=0.93 K with an ordered moment of 0.44μB. An external field along the b axis strengthens the zero-field magnetic order, while fields along the a and c axes lead to a collapse of the exchange stabilized order at μ0Hc=6 T and μ0Hc=4 T (extrapolated to zero temperature) and the formation of an energy gap in the excitation spectrum. We relate the field-induced gap to the presence of a staggered g-tensor and Dzyaloshinskii-Moriya interactions, which lead to effective staggered fields for magnetic fields applied along the a and c axes. Competition between anisotropy, interchain interactions, and staggered fields leads to a succession of three phases as a function of field applied along the c axis. For fields greater than μ0Hc, we find a magnetic structure that reflects the symmetry of the staggered fields. The critical exponent, β, of the temperature driven phase transitions are indistinguishable from those of the three-dimensional Heisenberg magnet, while measurements for transitions driven by quantum fluctuations produce larger values of β. ItemS=½ chain in a staggered field: high-energy bound-spinon state and the effects of a discrete lattice(American Physical Society, 2005-03-01) Kenzelmann, M.; Batista, C. D.; Chen, Y.; Broholm, C.; Reich, D.H.; Park, S.; Qiu, Y.We report an experimental and theoretical study of the antiferromagnetic S=½ chain subject to uniform and staggered fields. Using inelastic neutron scattering, we observe a bound-spinon state at high energies in the linear chain compound CuCl2·2((CD3)2SO). The excitation is explained with a mean-field theory of interacting S=½ fermions and arises from the opening of a gap at the Fermi surface due to confining spinon interactions. The mean-field model also describes the wave-vector dependence of the bound-spinon states, particularly in regions where effects of the discrete lattice are important. We calculate the dynamic structure factor using exact diagonalization of finite length chains, obtaining excellent agreement with the experiments.