Physicists at Heidelberg University have developed a theory that unites two conflicting views on how impurities behave in quantum many-body systems. The framework explains how even extremely heavy particles can enable the formation of quasiparticles through tiny movements. This advance could impact experiments in ultracold gases and advanced materials.
Researchers at the Institute for Theoretical Physics at Heidelberg University have created a new theoretical framework addressing a decades-old puzzle in quantum many-body physics. The work focuses on the behavior of a single unusual particle, such as an exotic electron or atom, within a crowded environment of fermions, often termed a Fermi sea. Previously, scientists viewed such impurities in two incompatible ways: either as mobile entities forming quasiparticles called Fermi polarons or as nearly stationary disruptors in Anderson's orthogonality catastrophe, where heavy impurities alter surrounding wave functions and prevent quasiparticle emergence.
The Heidelberg team's model bridges these paradigms by showing that even very heavy impurities are not perfectly immobile. As the surrounding system adjusts, these particles make slight shifts that create an energy gap, allowing quasiparticles to form in strongly correlated environments. This insight also accounts for the transition from polaronic states to molecular quantum states.
"The theoretical framework we developed explains how quasiparticles emerge in systems with an extremely heavy impurity, connecting two paradigms that have long been treated separately," said Eugen Dizer, a doctoral candidate in the Quantum Matter Theory group led by Prof. Dr. Richard Schmidt.
The theory applies across various dimensions and interaction types, offering a versatile tool for describing quantum impurities. Prof. Schmidt noted, "Our research not only advances the theoretical understanding of quantum impurities but is also directly relevant for ongoing experiments with ultracold atomic gases, two-dimensional materials, and novel semiconductors."
Conducted under Heidelberg University's STRUCTURES Cluster of Excellence and the ISOQUANT Collaborative Research Centre 1225, the findings appear in Physical Review Letters under the title "Mass-Gap Description of Heavy Impurities in Fermi Gases" by Xin Chen, Eugen Dizer, Emilio Ramos Rodríguez, and Richard Schmidt.