Unusual spin dynamics in topological insulators

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Conventional materials with weak spin-orbit coupling (SOC) exhibit a Lorentzian dynamic spin susceptibility (DSS) where spectral width indicates spin relaxation rate.
• Topological insulators are characterized by strong SOC, leading to unique electronic properties.

Purpose of the Study:

• To investigate the form of dynamic spin susceptibility (DSS) in topological insulators.
• To explore how DSS reveals the spin texture of topological states.
• To understand the implications for spin relaxation rate measurements in these materials.

Main Methods:

• Theoretical analysis of dynamic spin susceptibility (DSS).
• Investigation of electron behavior in topological insulators, including surface states, Weyl semimetals, and helical edge states.
• Examination of spin-charge entanglement effects.

Main Results:

• Topological insulators display an unusual non-Lorentzian DSS, differing from conventional materials.
• The anisotropy of DSS provides information about the spin texture of topological states.
• At zero temperature, high-frequency DSS exhibits universal power-law behavior (ω(d-1)) for surface states and Weyl semimetals, and renormalized behavior for helical edge states.
• Spin relaxation rates cannot be directly determined from DSS in topological insulators due to strong spin-charge entanglement.

Conclusions:

• The non-Lorentzian DSS in topological insulators is a signature of strong SOC and spin-charge entanglement.
• DSS anisotropy serves as a probe for the spin texture in topological materials.
• Standard methods for deducing spin relaxation rates from DSS are not applicable to topological insulators.