Circular dichroism and superdiffusive transport at the surface of BiTeI

Area of Science:

• Condensed Matter Physics
• Materials Science
• Ultrafast Spectroscopy

Background:

• Bismuth Telluride Iodide (BiTeI) exhibits unique electronic properties due to its non-centrosymmetric crystal structure.
• Optical pumping with circularly polarized light can induce spin and orbital polarization in materials.
• Understanding carrier dynamics in photoexcited states is crucial for novel electronic applications.

Purpose of the Study:

• To investigate the ultrafast electronic and spin dynamics in BiTeI following optical excitation.
• To elucidate the mechanisms behind the relaxation of photoinduced polarization and the origin of persistent dichroism.
• To explore the role of non-centrosymmetry in carrier transport under non-equilibrium conditions.

Main Methods:

• Time-resolved optical spectroscopy using circularly polarized pump pulses.
• Measurement of transient absorption and dichroic contrast.
• Analysis of carrier thermalization and polarization decay dynamics on femtosecond timescales.

Main Results:

• Photoexcited electrons in BiTeI thermalize internally within 300 femtoseconds (fs).
• Circularly polarized light induces dichroic contrast that decays faster than 80 fs, indicating rapid loss of spin and orbital polarization.
• Persistent dichroism at longer delay times is attributed to helicity-dependent superdiffusive transport, linked to the material's lack of inversion symmetry.

Conclusions:

• The rapid decay of polarization highlights the significant role of many-body interactions in BiTeI.
• Helicity-dependent transport, enabled by the broken inversion symmetry, governs the long-lived dichroism.
• These findings offer insights into controlling spin and charge dynamics in non-centrosymmetric materials for advanced spintronic devices.