The study of magnetism in lower dimensions has a long history with important fundamental questions, technical challenges and applications yet to be realized. 2D magnetic atomic crystals could solve . enabling studies in magnetism, superconductivity and topology, while opening the door to spintronic, sensing, optical and quantum information devices. This requires optimizing materials, fabrication, developing new techniques to probe the magnetism.

Our group was the first to measure changes in the magnetic excitation spectra in exfoliated high Tc superconductors, reveal fractional magnetic excitations in the van der Waals frustrated magnet RuCl3, magneto-elastic coupling and the proper exfoliation procedures of the ferromagnetic semiconductor Cr2Ge2Te6.

Emergent Properties

A long standing challenge has been the clear demonstration of the suppression of long range magnetic order due to enhanced fluctuations in 2D. If successful this can open the door to new magnetic, topological states and provide the fluctuations for mediating novel superconducting states. One exciting example is the Kiteav spin liquid, where the exchange between magnetic moments on the honeycomb lattice is bond dependent. This leads to a ground state that orders topologically with Majorana Fermions as the emergent particles. A key challenge is finding a materials with this bond dependent exchange that does not have magnetic order. We are working with one candidate (RuCl3) to see how the excitations change upon exfoliation. Using Raman spectroscopy, we have already shown the excitations have Fermionc rather than Bosonic response. We are also working to uncover how to manipulate those excitations in devices.

In addition we are working to develop optical techniques that are optimized to measure both the high energy excitations spectra, as well as the magnetic response at low energies. This is crucial both for understanding the magnetic dynamics and for changes in the magnetic order.

(Left) Raman intensity versus temperature for RuCl3. The data are fit well by a Fermi function squared, suggesting the creation of pairs of fermions. (Right) Raman response from Cr2Ge2Te6 showing splitting of the phonons well above Tc due to magneto-elastic coupling.

 

Magneto Elastic Coupling

An exciting opportunity with 2D materials results from their flexibility. As first shown by the Burch group, some 2D magnetic materials reveal strong coupling between the lattice and the magnetism. By exploring the phonons as the thickness is changed we hope to uncover how this magneto-elastic evolves with thickness. Ultimately this could lead to novel devices combining strain and/or novel substrate structures to manipulate the magnetism.