Hidden non-collinear spin-order induced topological surface states

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Rare-earth monopnictides exhibit complex magnetism, electronic correlation, and topological band structures.
• Emergent arc-like surface states in these materials are linked to multi-wave-vector antiferromagnetic order, but direct evidence was lacking.

Purpose of the Study:

• To provide direct experimental evidence of non-collinear antiferromagnetic order in rare-earth monopnictides.
• To elucidate the relationship between magnetic order and topological surface states.
• To investigate a hidden spin-rotation transition and its effect on electronic properties.

Main Methods:

• Spin-polarized scanning tunneling microscopy (SP-STM) to observe magnetic order.
• Angle-resolved photoemission spectroscopy (ARPES) to measure surface states.
• Theoretical calculations to analyze band structure and topological properties.

Main Results:

• Direct observation of non-collinear antiferromagnetic order with multiple modulations in NdSb.
• Discovery of a hidden spin-rotation transition 2 K below the Néel temperature, shifting from single to multiple modulations.
• Coincidence of the hidden transition with the onset of surface state splitting, as measured by ARPES.
• Calculations revealed single modulation induces topological surface states, while multiple modulations further split surface bands via spin tilting.

Conclusions:

• The non-collinear spin order in NdSb is the direct cause of emergent topological surface states.
• A hidden spin-rotation transition plays a crucial role in modulating these topological states.
• This work establishes a new approach for controlling and manipulating band topology using magnetism in quantum materials.