Quantum fluctuations of charge order induce phonon softening in a superconducting cuprate

Hsiao-Yu Huang^1*, A. Singh¹, C. Y. Mou^2,3, S. Johnston⁴, A. F. Kemper⁵, J. van den Brink⁶, P. J. Chen^7,8, T. K. Lee^9,10, J. Okamoto¹, Y. Y. Chu¹, J. H. Li^3,1, S. Komiya¹¹, A. C. Komarek¹², A. Fujimori^13,1, C. T. Chen¹, D. J. Huang¹

¹National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Center for Quantum Technology, National Tsing Hua University, Hsinchu, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
⁴Department of Physics and Astronomy, The University of Tennessee, Knoxville, USA
⁵Department of Physics, North Carolina State University, Raleigh, USA
⁶Institute for Theoretical Solid State Physics, IFW Dresden, Dresden, Germany
⁷Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, China
⁸Hong Kong Institute for Advanced Study, City University of Hong Kong, Hong Kong, China
⁹Institute of Physics, Academia Sinica, Taipei, Taiwan
¹⁰Department of Physics,, National Sun Yat-sen University, Kaohsiung, Taiwan
¹¹Central Research Institute of Electric Power Industry, Kanagawa, Japan
¹²Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
¹³Department of Applied Physics, Waseda University, Tokyo, Japan

* Presenter:Hsiao-Yu Huang, email:huang.hy@nsrrc.org.tw

Quantum phase transitions play an important role in shaping the phase diagram of high-temperature cuprate superconductors. These cuprates possess intertwined orders which interact strongly with superconductivity. However, the evidence for the quantum critical point associated with the charge order in the superconducting phase remains elusive. Here we show the short-range charge orders and the spectral signature of the quantum fluctuations in La_2-xSr_xCuO₄ (LSCO) near the optimal doping using high-resolution resonant inelastic X-ray scattering. On performing calculations through a diagrammatic framework, we discovered that the charge correlations significantly soften several branches of phonons. These results elucidate the role of charge order in the LSCO compound, providing evidence for quantum critical scaling and discommensurations associated with charge order.

Keywords: Charge density waves, Superconductivity, Phonons, Resonant inelastic X-ray scattering