Our group's research focuses on novel electron interactions in materials, including those exhibiting superconductivity, magnetism, and heavy fermion behavior, as well as quantum phase transitions, non-Fermi liquid behavior, and nontrivial topological states. Basically, we investigate the weird ways in which electrons organize themselves in complicated materials. This site will introduce you to our research projects and our people.
(US Citizens) Motivated researchers looking to work at the forefront of materials synthesis, electronic property characterization, and spectroscopy are invited to apply for a prestigious NRC postdocdoral fellowship. The postdoctoral positions are research-only positions that allow the successful candidate to pursue a self-driven research program making use of research facilities and opportunities to collaborate at both NIST and UMD. Please contact me if you are interested to discuss the application process. There are two competitions per year, with due dates in February and August.
Our paper reporting the halo shape of the high-field Lazarus superconducting phase recently appeared in Science. The pairing mechanism remains enigmatic, and UTe2’s specific magnetophilic superconducting tendencies seem incompatible with existing models for field-enhanced superconductivity.
S. K. Lewin, et al, Science 389, 51 (2025).
Steve Anlage's group performed resonant microwave cavity measurements on UTe2. They were able to perform a thorough analysis of the anisotropic surface impedance. They also found that the temperature dependence of the magnetic penetration depth follows a power law, but is inconsistent with an order parameter having one pair of point nodes or a line node, in the weak scattering limit.
A. Carlton-Jones, et al, Phys. Rev. B 112, 014519 (2025).
Our collaborators, led by Seamus Davis's group, performed scanning tunneling spectroscopy measurements on UTe2 using a superconducting tip. They observed a splitting of the zero-bias in-gap peak, which depended on the tunnel junction resistance. These effects are consistent with a nonchiral superconducting order parameter, with the B3u symmetry believed to be the most likely scenario.
Q. Gu, et al, Science 388, 938 (2025).
We measured the bounds of the high-field (but below 35T) superconducting and magnetic phases near the crystalline b axis of UTe2. There is no evidence of any symmetry-breaking quadrupolar or higher magnetic order. The angular boundaries of the superconducting phase are nearly field-independent and maintain an anisotropy between the ab and bc planes that is comparable to the anisotropy of the higher-field metamagnetic transition.
S. K. Lewin, et al, arXiv:2410.05137.
We performed an inelastic neutron scattering study on a mosaic of dozens of single crystals of UTe2 on the CAMEA spectrometer at PSI. We resolved the zone-edge dispersion of the low-temperature magnetic excitations, which are surprisingly insensitive to a magnetic field of 11 teslas. These results suggest (again) that the low-energy magnetic interactions in UTe2 are dominated by metallic, hybridized f-electrons.
T. Halloran, P. Czajka, G. Saucedo, C. Frank, et al, arXiv:2408.14619.
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