Six-state clock physics in an atomically thin antiferromagnet

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Spintronics

Background:

• Collective behavior and phase transitions in quantum matter are governed by symmetry breaking and topology.
• The 2D XY model exhibits the Berezinskii-Kosterlitz-Thouless (BKT) transition, crucial for understanding quasi-long-range order.
• Anisotropy fields can destabilize the BKT phase, leading to true long-range order at low temperatures.

Purpose of the Study:

• Investigate the BKT transition and topological dynamics in the van der Waals antiferromagnet NiPS3.
• Explore the transition from 3D to 2D magnetic behavior as NiPS3 is thinned to a monolayer.
• Examine the stability of the 2D BKT phase and its transformation at low temperatures.

Main Methods:

• Utilized nonlinear optical micropolarimetry to probe magnetic properties.
• Investigated the magnetic response of NiPS3 as it was thinned to a monolayer.
• Performed Monte Carlo simulations to corroborate experimental findings.

Main Results:

• Observed an abrupt switch from 3D XXZ behavior in multilayers to a 2D BKT-like state in monolayer NiPS3.
• Found the monolayer BKT phase becomes unstable upon further cooling.
• Identified a transformation into a pinned state with long-range order at low temperatures.

Conclusions:

• Monolayer NiPS3 exhibits a BKT state, which is unstable and transitions to long-range order at low temperatures.
• The study provides insights into topological dynamics and spin vortices in 2D antiferromagnets.
• Results open new avenues for exploring topological phase transitions in quantum materials.