Spin dynamics of the block orbital-selective Mott phase

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Magnetism

Background:

• Iron-based superconductors exhibit complex magnetic phases due to competing electronic, orbital, and spin interactions.
• Theoretical models predicted an orbital-selective Mott phase (OSMP) with block spin order in one-dimensional multi-orbital Hubbard models.
• Recent inelastic neutron scattering (INS) experiments on BaFe2Se3 confirmed the OSMP and revealed unexpected spectral features.

Purpose of the Study:

• To theoretically predict the dynamical spin structure factor in the block-OSMP regime.
• To explain the origin of low-energy acoustic and high-energy optical modes observed in experimental INS spectra.
• To elucidate the role of Hund coupling in novel spin excitations.

Main Methods:

• Utilizing the density-matrix renormalization-group (DMRG) method for theoretical calculations.
• Analyzing the dynamical spin structure factor within the block-OSMP framework.
• Comparing theoretical predictions with experimental INS data from BaFe2Se3.

Main Results:

• Theoretical predictions align with experimental observations, identifying two dominant spectral features.
• Observed low-energy dispersive modes are attributed to spin-wave-like dynamics in ferromagnetic islands.
• High-energy dispersionless modes are identified as a novel type of local on-site spin excitation governed by Hund coupling.

Conclusions:

• The study validates the relevance of the block-OSMP in iron-based superconductors.
• It provides a theoretical explanation for the complex excitation spectrum observed experimentally.
• It highlights the significance of Hund coupling in generating unique spin dynamics.