Identification of structural motifs as tunneling two-level systems in amorphous alumina at low temperatures

Abstract

One of the most accepted models that describe the anomalous thermal behavior of amorphous materials at temperatures below 1 K relies on the quantum mechanical tunneling of atoms between two nearly equivalent potential energy wells forming a two-level system (TLS). Indirect evidence for TLSs is widely available. However, the atomistic structure of these TLSs remains an unsolved topic in the physics of amorphous materials. Here, using classical molecular dynamics, we found several hitherto unknown bistable structural motifs that may be key to understanding the anomalous thermal properties of amorphous alumina at low temperatures. We show through free energy profiles that the complex potential energy surface can be reduced to canonical TLSs. The predicted tunnel splittings from instanton theory, the number density, dipole moment, and coupling to external strain of the discovered motifs are consistent with experiments.

10 pages, 9 figures. Final version, accepted for publication in Physical Review B

References in corpus (8)

• Quantum two-level systems in Josephson junctions as naturally formed qubits
• Measuring the temperature dependence of individual two-level systems by direct coherent control
• Quantum Friction in Nanomechanical Oscillators at Millikelvin Temperatures
• Microscopic Model of Critical Current Noise in Josephson Junctions
• Quantum decoherence of a charge qubit in a spin-fermion model
• Delocalised oxygen as the origin of two-level defects in Josephson junctions
• Microscopic model of critical current noise in Josephson-junction qubits: Subgap resonances and Andreev bound states
• Influence of polarizability on metal oxide properties studied by molecular dynamics simulations