Exceptional degeneracies in non-Hermitian Rashba semiconductors

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Topological Materials

Background:

• Exceptional points (EPs) are spectral degeneracies in non-Hermitian (NH) systems where eigenvalues and eigenvectors coalesce.
• These degeneracies lead to unique topological phases absent in Hermitian systems.
• Rashba spin-orbit coupling (SOC) is a key phenomenon in condensed matter physics.

Purpose of the Study:

• To investigate the emergence and tunability of EPs in a 2D semiconductor coupled to a ferromagnet lead.
• To explore the role of Zeeman fields and non-Hermiticity in controlling EPs.
• To identify signatures for detecting EPs in such systems.

Main Methods:

• Theoretical modeling of a 2D semiconductor with Rashba SOC coupled to a ferromagnet lead.
• Analysis of eigenvalue and eigenvector coalescence in momentum space.
• Investigation of the effects of in-plane Zeeman fields on EP properties.

Main Results:

• Highly tunable EPs emerge along rings in momentum space.
• These EPs act as endpoints of eigenvalue coalescence lines at finite real energy, analogous to Fermi arcs.
• An in-plane Zeeman field controls EPs, requiring higher non-Hermiticity compared to the zero-field regime.
• Spin projections also coalesce at EPs, potentially exceeding Hermitian values.
• EPs induce large spectral weights, serving as a detection signature.

Conclusions:

• Systems with Rashba SOC offer a promising platform for realizing novel non-Hermitian bulk phenomena.
• Tunable EPs and their associated topological properties can be controlled via external fields.
• The identified spectral weight signature facilitates the experimental detection of EPs.