Tunneling-induced restoration of classical degeneracy in quantum kagome ice

TL;DR

This paper investigates how quantum processes in a frustrated kagome ice model can restore classical degeneracy despite quantum fluctuations, revealing a complex interplay that prevents topological order and maintains residual entropy.

Contribution

It demonstrates that quantum tunneling processes can restore classical degeneracy in a quantum kagome ice model, challenging expectations of quantum order at low temperatures.

Findings

No $Z_2$ topological order observed at low temperatures.

Quantum processes lead to quasi-degeneracy and residual entropy.

Classical kagome ice behavior persists despite quantum effects.

Abstract

Quantum effect is expected to dictate the behaviour of physical systems at low temperature. For quantum magnets with geometrical frustration, quantum fluctuation usually lifts the macroscopic classical degeneracy, and exotic quantum states emerge. However, how different types of quantum processes entangle wave functions in a constrained Hilbert space is not well understood. Here, we study the topological entanglement entropy (TEE) and the thermal entropy of a quantum ice model on a geometrically frustrated kagome lattice. We find that the system does not show a $Z_2$ topological order down to extremely low temperature, yet continues to behave like a classical kagome ice with finite residual entropy. Our theoretical analysis indicates an intricate competition of off-diagonal and diagonal quantum processes leading to the quasi-degeneracy of states and effectively, the classical degeneracy is restored.