Probing electron quadrupling order through ultrasound

Recent experiments have pointed to the formation of a new state of matter, the electron quadrupling condensate in Ba$_{1-x}$K$_x$Fe$_2$As$_2$. The state spontaneously breaks time-reversal symmetry and is sandwiched between two critical points, separating it from the superconducting and normal-metal...

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Main Authors Halcrow, Chris, Shipulin, Ilya, Caglieris, Federico, Li, Yongwei, Wosnitza, Joachim, Klauss, Hans-Henning, Zherlitsyn, Sergei, Grinenko, Vadim, Babaev, Egor
Format Journal Article
LanguageEnglish
Published 03.04.2024
Subjects
Physics - Quantum Physics
Physics - Strongly Correlated Electrons
Physics - Superconductivity
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Summary:Recent experiments have pointed to the formation of a new state of matter, the electron quadrupling condensate in Ba$_{1-x}$K$_x$Fe$_2$As$_2$. The state spontaneously breaks time-reversal symmetry and is sandwiched between two critical points, separating it from the superconducting and normal-metal states. We report a theory of the acoustic effects of systems with an electron quadrupling phase based on ultrasound-velocity measurements of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals. The theoretical analysis suggests that the ultrasound data can be understood by considering a plain $s$+i$d_{xy}$ order parameter or an $s$+i$s$ order parameter with symmetry-breaking deformations in this material with enhanced nematic susceptibility for the [110] direction, or when the transition to the quartic state is a weakly first-order. Our work provides the theoretical basis and proposes the experimental strategy to study the order parameter symmetry of emerging quadrupling condensates in superconductors.
DOI:10.48550/arxiv.2404.03020