Quantum phase transition between weak itinerant ferromagnetism and superconductivity induced by interstitial localized electrons in Li7Pb

Quantum phase transitions are crucial for understanding emergent phenomena in quantum many-body systems, especially at zero temperature, where quantum fluctuations dominate. Here, we utilized the crystal structure searching method in conjunction with first-principles calculations to investigate the lithium-lead system, leading to the discovery of three exotic phases. Notably, the P -62 m Li 7 Pb emerges as an electride with distinct A- type and B- type interstitial anion electrons (IAEs). The bilayer Kagome lattice of Li 7 Pb accommodates weak itinerant ferromagnetism within the stable pressure range from 20 to 45 GPa, primarily attributed to the presence of B- type IAEs. On the contrary, A- type IAEs are sensitive to charge doping, impacting the modulation of ferromagnetism. Furthermore, electron doping led to the transition of Li 7 Pb into a superconductor as the magnetic moment diminished, and the transition temperature could be raised from 1.6 to 3.4 K as doping intensified. This transition was facilitated by the interaction between A- type IAEs and phonons from the surrounding lithium lattice, showcasing a unique quantum phase transition between itinerant ferromagnetism and superconductivity in electrides. Our study not only revealed novel structures in lithium-lead systems but also established a platform for exploring quantum phase transitions in electrides.