Magnetic field-induced quasiparticle instability and universal scaling behavior at finite fields in an S=1/2 quantum antiferromagnet
April 7, 2016 -
3:00pm to 4:00pm
Oak Ridge National Laboratory
Quasiparticles, such as phonons, magnons, rotons, and heavy electrons and holes, are ubiquitous in nature. Quasiparticles usually have a long lifetime due to the weak or absence of interactions between them. However, this picture breaks down in rare conditions. In this talk, I will describe the experimental realization of magnetic field-induced spontaneous (T=0) magnon decays in an S=1/2 quantum antiferromagnet C9H18N2CuBr4 using the neutron scattering techniques . The observed intriguing renormalization of one-magnon dispersion and magnon decays over a large region of the Brillouin Zone in the magnetic excitation specra can be well explained by the mechanism where the three-magnon interactions are present and the process of one-magnon decays into the two-magnon continuum is kinematically allowed . Moreover, I will show that a universal scaling of the field-dependence of the Zeeman energy behaves in the same way as the temperature dependence of the spin gap in one-dimensional quantum magnets and agrees well with the calculation by the non-linear sigma model . This result demonstrates the similarity between thermal and quantum fluctuations near the quantum critical point , where the intrinsic energy scales vanish.
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