Spin-orbital entangled liquid state in the copper oxide Ba₃CuSb₂O₉

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Chemistry

Background:

• Orbital degeneracy in structures often leads to spontaneous distortions.
• Orbital correlations typically have higher energy scales than spin interactions, influencing magnetic transitions independently.
• When spin and orbital energy scales converge, novel entangled states like spin-orbital liquids can emerge.

Purpose of the Study:

• To investigate novel spin-orbital magnetism in the hexagonal perovskite oxide Ba3CuSb2O9.
• To understand the behavior of coupled spin and orbital degrees of freedom in this material.
• To identify the ground state of Ba3CuSb2O9 under specific conditions.

Main Methods:

• Comprehensive structural and magnetic measurements.
• Macroscopic and microscopic experimental techniques.
• Analysis of Jahn-Teller ion behavior (Cu2+) in a hexagonal perovskite structure.

Main Results:

• Ba3CuSb2O9 exhibits a self-organized short-range order of Cu2+ ions.
• No magnetic or Jahn-Teller transitions were observed down to the lowest temperatures.
• Cu spins and orbitals maintained hexagonal symmetry and a paramagnetic state.
• Evidence suggests fluctuating spins and orbitals forming a spin-orbital entangled liquid state.

Conclusions:

• Ba3CuSb2O9 hosts a unique spin-orbital entangled liquid state.
• The material avoids conventional magnetic or orbital ordering due to strong spin-orbital coupling.
• This finding opens avenues for exploring new quantum states in materials with coupled degrees of freedom.