Condensed Matter Seminar Series

Dimensional Crossover, Long-Range Order, and Magnetic Plateaus in Sheets of Magentic Dimers

Sara Haravifard

University of Chicago and Argonne National Lab

Tuesday April 15,  11:30 am,  Room 298,  Physics Building

Abstract: SrCu₂(BO₃)₂ (SCBO) has corner-sharing Cu2⁺ spin-1/2 dimers lying on a square lattice, corresponding to the two-dimensional Shastry-Sutherland model. I will present the results of the first single-crystal neutron scattering measurements at high pressure at the Spallation Neutron Source, which combined with computer modeling, show how true antiferromagnetic order can emerge with a crossover into the third dimension. We find a subtle symmetry change as a function of temperature for pressures above 4.5 GPa, linked to antiferromagnetism and the tilting of the dimers out of the plane. The inclusion of Dzyaloshinskii-Moriya interactions in the Shastry-Sutherland Hamiltonian helps explain the observations. Additionally, interest has focused on finite magnetization of SCBO at low temperatures, wherein the lowest energy of the three triplet states is driven to zero energy.  This is related to Bose-Einstein condensation of the triplet excitations, which occurs for fields near 20 T and higher.  At higher magnetic fields, plateaus have been observed in the magnetization, which have been interpreted in terms of preferred filling of the singlet ground state with increasing densities of triplet excitations. I will present how pressure can be used as tuning parameter to drive the system across the quantum phase diagram and study the evolution of the quantized magnetic plateaus.