Spin-orbit density wave induced hidden topological order in URu2Si2

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science
• Materials Chemistry

Background:

• Conventional order parameters in quantum matter typically involve spontaneous symmetry breaking.
• Emergent phases can arise from complex interactions between broken and invariant symmetries.
• The heavy fermion metal URu2Si2 exhibits a mysterious hidden-order phase, with its underlying order parameter unknown.

Purpose of the Study:

• To elucidate the nature of the hidden-order phase in the heavy fermion metal URu2Si2.
• To identify the specific order parameter responsible for the second-order phase transition at 17.5 K.
• To propose a new type of order parameter in quantum materials.

Main Methods:

• Ab-initio calculations were employed to investigate the electronic structure and properties of URu2Si2.
• An effective model was developed to capture the essential physics of the proposed order parameter.
• Topological indices were computed to characterize the topological properties of the hidden order.

Main Results:

• A novel spin-orbit density wave in the f-states is proposed as the order parameter for the hidden-order phase.
• This spin-orbit order breaks rotational and translational symmetries while preserving time-reversal symmetry.
• The order parameter is topologically invariant and immune to pressure but sensitive to magnetic fields, indicating a quantum critical point.

Conclusions:

• The hidden-order phase in URu2Si2 is attributed to a staggered spin-orbit density wave.
• This discovery offers a new paradigm for understanding emergent phases in quantum materials.
• The study presents verifiable predictions for future experimental investigations.