About the Group
We are an experimental condensed matter physics group focused on investigating the structure and magnetism of fascinating--and often technologically promising--materials, such as superconductors, strongly correlated electron systems, multiferroics, magnetocalorics, molten salts for nuclear reactors, and more. We use beams of neutrons, x-rays, and muons produced at large-scale accelerator facilities to probe the atomic and magnetic correlations in these materials, together with advanced computational modeling to gain quantitative insight into the spatial arrangement of atoms and spins in a given material. Specific techniques include atomic and magnetic pair distribution function (PDF) analysis of neutron/x-ray total scattering data and muon spin relaxation/rotation (μSR). Interested and motivated undergraduate and prospective graduate students are encouraged to reach out to learn more about our research and find opportunities to participate.
Research Projects
Thermoelectrics, Magnetocalorics, and Multiferroics--Oh My!
This project focuses on the connection between the local atomic and magnetic structure and the energy-relevant properties of magnetocaloric, thermoelectric, and multiferroic materials. Magnetocaloric materials exhibit large temperature changes with the application and removal of a magnetic field, offering promising applications in solid-state refrigeration and waste heat harvesting. Thermoelectric materials experience an electrical voltage when subjected to a temperature gradient or vice versa, also providing novel routes for energy-efficient cooling and waste heat harvesting. Multiferroic materials show cross-order coupling between electric polarization and magnetic order, potentially enabling unique functionalities for energy transformation, information science, and signal processing. We are using combined atomic and magnetic pair distribution function analysis, together with muon spin spectroscopy, to establish the local atomic and magnetic structure of representative compounds for these material classes and better understand the origin of their outstanding properties. In the process, we are developing new experimental and computational methods for magnetic pair distribution function analysis, which will be widely applicable to many other materials, as well. Funding: US Department of Energy, Early Career program.
Promoting Many-Body Quantum Entanglement in Geometrically Frustrated Magnets with Disorder
Quantum information technologies rely on quantum entanglement, or the intrinsic linking of one quantum object to another. An important research objective is to gain a fundamental understanding of many-body quantum entanglement involving large numbers of quantum objects. Certain magnetic materials known as geometrically frustrated magnets provide a valuable platform for this topic of study because they may exhibit many-body-entanglement at low temperature. This project advances the search for promising quantum-entangled frustrated magnets through a systematic investigation of the role of atomic-scale disorder in promoting or hindering many-body entanglement. The results illuminate strategies for utilizing disorder to promote quantum-entangled ground states and contribute to a deeper understanding of many-body quantum entanglement in general. Funding: US National Science Foundation LEAPS Program.
Novel magnets, Magnetic Nanoparticles, Metal-Insulator Transitions, High-Entropy Materials, and More
We maintain broad interest and involvement in structural studies of numerous material systems where knowledge of the local atomic and magnetic structure can add value. We have ongoing projects on novel magnets such as altermagnets and low-dimensional magnets, magnetic nanoparticles, Mott insulator systems and materials with metal-insulator transitions, high-entropy alloys and oxides, and more. We are always open to collaborations on interesting material systems.
Selected Publications
(mPDF) defined in an earlier paper [Frandsen et al. (2014). Acta Cryst. A70, 3–
11] is presented for the first time. The mPDF was determined from neutron
powder diffraction data from a reactor and a neutron time-of-flight total
scattering source on a powder sample of the antiferromagnetic oxide MnO. A
description of the data treatment that allowed the measured mPDF to be
extracted and then modelled is provided and utilized to investigate the lowtemperature
structure of MnO. Atomic and magnetic co-refinements support
the scenario of a locally monoclinic ground-state atomic structure, despite the
average structure being rhombohedral, with the mPDF analysis successfully
recovering the known antiferromagnetic spin configuration. The total scattering
data suggest a preference for the spin axis to lie along the pseudocubic [101]
direction. Finally, r-dependent PDF refinements indicate that the local
monoclinic structure tends toward the average rhombohedral R3m symmetry
over a length scale of approximately 100 A ° .
(
μ
SR
)
to investigate the superconducting properties of the noncentrosymmetric superconductor
CaIrSi
3
. Measurements of single-crystal specimens confirm the development of a robust superconducting state below
T
c
=
3.55
±
0.1
K
with a ground-state magnetic penetration depth of
λ
L
=
288
±
10
nm
and a coherence length of
ξ
=
28.8
±
0.1
nm
. The temperature evolution of the superfluid density indicates a nodeless superconducting gap structure dominated by an isotropic spin-singlet component in the dirty limit with a carrier density of
n
=
(
4.6
±
0.2
)
×
10
22
cm
−
3
as determined by Hall resistance measurements. We find no evidence of spontaneous time-reversal symmetry breaking in the superconducting state within an accuracy of 0.05 G. These observations suggest that the influence of any spin-triplet pairing component or multiple gap structure associated with noncentrosymmetric physics is very weak or entirely absent in
CaIrSi
3
.
