Dual Spin Excitation Components in FeSe_{0.67}Te_{0.33}.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Iron chalcogenides (FeSe$_{1-x}$Ch$_{x}$) display complex superconducting phase diagrams with double domes.
• The microscopic origins of these superconducting properties, particularly the role of magnetism, are not fully understood.

Purpose of the Study:

• To investigate spin excitations in single-crystalline FeSe$_{0.67}$Te$_{0.33}$ at the superconducting transition temperature minimum.
• To elucidate the relationship between magnetic excitations and the superconducting phase diagram of iron chalcogenides.

Main Methods:

• Inelastic neutron scattering was employed to probe spin excitations in single-crystalline FeSe$_{0.67}$Te$_{0.33}$ across various temperatures.
• Analysis focused on energy and temperature dependence of spin excitation components and their wave vectors.

Main Results:

• Two distinct spin excitation components were identified, separated by a crossover energy of approximately 30 meV.
• Below this energy, excitations originated from stripe-type wave vectors and were strongly coupled to nematicity.
• Above this energy, excitations showed different temperature dependence and evolved towards incommensurate wave vectors at higher temperatures.

Conclusions:

• A competition between stripe and incommensurate magnetic excitations is proposed as a key factor influencing the reduced superconducting transition temperature (T$_{c}$) in iron chalcogenides.
• Tellurium (Te) substitution likely tunes the electronic structure, potentially reinforcing this magnetic competition and affecting superconductivity.