Intertwined Orders in a Quantum-Entangled Metal

TL;DR

This study uncovers a highly entangled electronic phase near a metal-insulator transition in a quantum material, using advanced scattering techniques to reveal quantum fluctuations and coexistence of exotic orders, linking entanglement to emergent phenomena.

Contribution

The paper introduces a novel interferometry method to quantify entanglement spectra in complex quantum materials, revealing the coexistence of multiple symmetry-breaking orders.

Findings

Identification of a highly entangled phase near the metal-insulator transition.

Detection of quantum fluctuations in spin, orbital, and charge degrees of freedom.

Observation of symmetry-breaking magnetic and structural orders.

Abstract

Entanglement underpins quantum information processing and computing, yet its experimental quantification in complex, many-body condensed matter systems remains a considerable challenge. Here, we reveal a highly entangled electronic phase proximate to a quantum metal-insulator transition, identified by resonant inelastic x-ray scattering interferometry. This approach reveals that entanglement across atomic sites generates characteristic interference patterns, which our model accurately reproduces, enabling extraction of a full entanglement spectrum and resolution of the underlying quantum states. Our analysis of the pyrochlore iridate Nd2Ir2O7 demonstrates that the system undergoes pronounced quantum fluctuations in its spin, orbital and charge degrees of freedom, even in the presence of a long-range 'all-in-all-out' antiferromagnetic order. Importantly, the observed entanglement signatures facilitate the coexistence of multiple exotic symmetry-breaking orders. Complementary investigations using Raman spectroscopy corroborate the presence of these hidden orders and their emergent excitations. In particular, we observe a two-magnon-bound state below the lowest single-magnon excitation energy, which, together with split phonon modes, provides strong evidence for cubic symmetry-breaking orders of magnetic origin juxtaposed with the all-in-all-out order. Our work thus establishes a direct link between quantum entanglement and emergent unconventional orders, opening new avenues for investigating quantum materials.