# 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: SrCu_{2}(BO_{3})_{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.

*Host: Harold Baranger*