Quantum Disorder Induced by Nuclear Tunneling in Lattice

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Materials Science

Background:

• Lattice degrees of freedom can induce quantum disorder (QD) where nuclear tunneling dominates over long-range order.
• Conventional phonon theory cannot adequately describe these quantum disorder phases.
• Understanding QD is crucial for novel quantum materials and phenomena.

Purpose of the Study:

• To develop a computational method capable of describing quantum disorder phases induced by lattice degrees of freedom.
• To investigate quantum order-disorder-order phase transitions in lattice systems.
• To identify the quantum disorder region using excitation spectra and entanglement entropy.

Main Methods:

• Development of a novel method based on path-integral molecular dynamics.
• Verification of the method's accuracy using a double-well chain model.
• Application of the method to a real material from first-principles calculations.

Main Results:

• Demonstration of a quantum order-disorder-order phase transition sequence by tuning quantum fluctuations via lattice constants.
• Identification of the quantum disorder region through analysis of excitation spectra and Rényi entanglement entropy.
• The developed method accurately describes quantum disorder phases.

Conclusions:

• The path-integral molecular dynamics method successfully describes quantum disorder phases and associated phase transitions.
• Quantum disorder is a general phenomenon in lattice systems with soft phonon modes.
• Novel entangled lattice motion and its coupling with other degrees of freedom are expected in these systems.