Colloquium with Dr. Shang-Shun Zhang, Postdoctoral Associate,  University of Minnesota

The concept of quasiparticles forms the foundation for understanding the low-temperature properties of various quantum materials. The existence of quasiparticles has been identified in diverse systems, including magnon excitations in magnets, Bogoliugov excitations in superconductors, and more. In recent years, quasiparticle breakdown has been observed in the exploration of materials with strong correlations. Examples of this phenomenon include the decay of magnons into different species of excitations and the emergence of non-Fermi liquids in quantum critical metals. Consequently, these materials exhibit unconventional behaviors in thermodynamics and transport, such as linear-in-T resistivity in several high-Tc materials. Beyond mere scientific curiosity, these novel behaviors lay the groundwork for future technological advancements. Motivated by these prospects, the quest for materials without quasiparticles has attracted significant attention. In this talk, I will discuss the recent proposal of superconductors lacking Bogoliubov quasiparticles, arising from strong quantum fluctuations near a quantum critical point. Specifically, this finding offers an explanation for the photoemission spectrum of cuprates, a family of high-Tc superconducting materials. I will conclude with an outlook on future studies along this exciting line of research.