Quantum Phases in spin-orbit coupled honeycomb magnets: beyond 4d and 5d transition metal ions

Colorado State University, Fort Collins CO

Investigators

Abstract

Non-Technical Abstract: Quantum phases of matter are based on entanglement between electrons confined to crystal lattices. A familiar example of such a phase is superconductivity; this once-exotic phenomenon has now matured and is being used for technological applications such as Magnetic Resonance Imaging (MRI). Similarly, the new quantum phases of matter being explored in this research on honeycomb lattice magnets (i.e., magnets built from a lattice structure composed of hexagons) could provide dramatic technological consequences. One predicted quantum phase, the Kitaev Honeycomb Quantum Spin Liquid, supports special excited states that could form unusually robust "qubits" for quantum computations. This research project aims to produce such exotic phases in new honeycomb lattice materials, using previously unexplored choices of magnetic ions. Undergraduate researchers, who prepare samples and perform basic techniques for magnetic characterizations, carry out a large part of the exploratory aspects of the research. Graduate students involved in this project master techniques in single crystal growth, thermodynamic characterization, and inelastic neutron scattering. This project heavily relies on large-scale neutron science facilities in the United States. Technical Abstract: This research is designed to produce new quantum phases of matter using unconventional materials choices. Magnetic insulators with strong spin-orbit coupling are ideal targets for exploring a wide variety of interesting phases based on quantum entanglement, such as Quantum Spin Liquids. These exotic phases host potentially useful quasi-particle excitations; one example is the "anyon" excitation predicted for the Kitaev Honeycomb Quantum Spin Liquid. Anyons, once they are successfully produced in a real material, could be used for topologically protected quantum computations. The two key ingredients for exotic phases like this are 1) anisotropic magnetic interactions on the honeycomb lattice, obtainable from magnetic species with strong spin-orbit coupling, and 2) quantum fluctuations, which are a natural feature of correlated pseudo-spin ½ magnetic moments. These ingredients have previously been sought in honeycomb lattice materials based on 4d and 5d transition metal ions. The current research project extends the search to unconventional choices of magnetic species outside of these series, enabling a wider variety of characterization techniques while opening a new arena of materials to be explored. Solid-state synthesis methods, including intense crystal growth efforts, are combined with detailed characterizations of materials using thermodynamic probes and inelastic neutron scattering at temperatures as low as 50 mK. Undergraduate researchers, who prepare samples and perform basic techniques for magnetic characterizations, carry out a large part of the exploratory aspects of the research. Graduate students involved in this project master techniques in single crystal growth, thermodynamic characterization, and inelastic neutron scattering. This project heavily relies on large-scale neutron science facilities in the US.