Quantum Materials under High Pressure – New Capabilities at ORNL

Neutron scattering gives powerful insight into quantum materials under extreme conditions due to neutrons’ unique capabilities for magnetic diffraction as well as the possibility to fully characterize phonon states. A thermodynamic ‘tuning’ parameter of particular interest is thereby pressure. In the past, neutron scattering at high pressures has, however, been limited due to a comparatively low neutron flux which requires large samples. Pressures were typically limited to ~20 GPa in a Paris-Edinburgh cell for neutron diffraction and to ~2 GPa in clamp cells for neutron spectroscopy. Furthermore, large presses prevented simultaneous application of other extremes such as magnetic fields or ultra-low temperature limiting these studies to clamp cells.

At Oak Ridge National Laboratory, a large range of pressure cells is used ranging from gas pressure cells (up to 0.7 GPa), over clamp cells (up to 2 GPa), palm-cubic cells (up to 7 GPa) and Paris-Edinburgh cells (up to 20 GPa) to newly developed diamond anvil cells (up to 60 GPa). These cells are used in various combinations with cooling environments or magnets at a large number of beamlines of the Spallation Neutron Source and the High Flux Isotope Reactor for diffraction as well as inelastic neutron scattering. This large diversity in cells and applications allows for an unparalleled insight into the effect of pressure on quantum materials.

In this presentation, I will give an overview over the many ‘standard’ pressure cells and their application to hard condensed matter. I will then elaborate on the newly developed wide-angle diamond cells and the possibilities afforded by advanced collimation through 3D-printing. These new methods will significantly expand the pressure range for single crystal diffraction as well as the detection of ever smaller magnetic moments while allowing for simultaneous application of other extreme conditions.