Soft phonons and structural phase transition in superconducting Ba0.59K0.41BiO3 |
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| Authors: | HJ Kang YS Lee JW Lynn SV Shiryaev SN Barilo |
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| Institution: | 1. NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA;2. Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA;3. Department of Physics and Astronomy, Clemson University, SC 29634, USA;4. Department of Physics, and Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;5. Institute of Solid State and Semiconductor Physics, Academy of Science, Minsk 220072, Belarus |
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| Abstract: | We have observed a softening of phonons and a structural phase transition in a superconducting Ba0.59K0.41BiO3 (Tc = 31 K) single crystal using elastic and inelastic neutron scattering measurements. The soft phonon occurs for the 1 1 1] transverse acoustic mode at the zone boundary. The phonon energies in this vicinity are found to continuously decrease with decreasing temperature from above room temperature. This softening stops at a temperature close to Ts, where a structural phase transition from cubic to tetragonal symmetry occurs. The overall results are consistent with previous data that reported phonon softening and a (0.5, 0.5, 0.5) type superstructure in several Ba1?xKxBiO3 systems. However, we also find weaker (0.5, 0.5, 0) type superstructure peaks that reveal an additional component to the modulation. No significant change related to the superconductivity was observed for these soft phonon energies or linewidths. |
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