Sean E. Barrett (physicist)
Sean Eric Barrett is an American experimental condensed matter physicist and Professor of Physics and Applied Physics at Yale University. He is known for his work using nuclear magnetic resonance (NMR) techniques to study quantum Hall effect physics, including some of the first experimental evidence for skyrmions in quantum wells, as well as contributions to solid-state magnetic resonance imaging (MRI), discrete time crystals, and sparse-sampling reconstruction algorithms.
Education and career
Barrett earned his Ph.D. in physics from the University of Illinois at Urbana–Champaign in 1992, where he studied under Charles P. Slichter. He then held a postdoctoral position at AT&T Bell Laboratories. He joined the Yale faculty in 1994 and holds a joint appointment in the Department of Applied Physics. He is a member of the Yale Quantum Institute and the Yale Program in Physics, Engineering, and Biology.
Barrett has served as Director of Undergraduate Studies and Dean of Graduate Studies in the Yale Physics Department.
Quantum Hall skyrmions and OPNMR
Barrett developed and applied the technique of optically pumped nuclear magnetic resonance (OPNMR) to study two-dimensional electron systems in GaAs quantum wells in the quantum Hall effect regime. In a 1995 paper, Barrett and collaborators at Bell Labs provided experimental evidence for the existence of finite-size skyrmions as the charged excitations of the ν = 1 quantum Hall ferromagnetic ground state, by measuring the rapid drop in electron spin polarization on either side of filling factor ν = 1.
Subsequent OPNMR work by Barrett's group at Yale provided spectroscopic evidence for skyrmion localization near ν = 1 at low temperatures, and placed new experimental constraints on the composite fermion description of the ν = 1/2 state.
Spin echoes in dipolar solids
Barrett's group discovered spin echoes generated by strong π pulses in dipolar solids such as silicon, which revealed intrinsic coherence effects arising from the internal structure of hard pulses.
MRI of solids
Building on the quadratic echo technique, Barrett and collaborators demonstrated three-dimensional phosphorus-31 MRI of hard and soft solids, including ex vivo bone and soft tissue samples, published in the Proceedings of the National Academy of Sciences in 2012.
Discrete time crystals
In 2018, Barrett's group observed signatures of a discrete time crystal (DTC) using NMR in an ordered crystal of monoammonium phosphate (MAP), reported in Physical Review Letters and Physical Review B. This was the second known observation of a DTC signature in a solid, and the finding was in an ordered spatial crystal, challenging the prevailing assumption that disorder (via many-body localization) was a necessary condition for DTC formation. The group also demonstrated a novel "DTC echo" that revealed hidden coherence in the driven system. The results were highlighted by the American Physical Society and covered in Yale News and other media.
Sparse-sampling and spectral reconstruction
Barrett's group has developed algorithms for accelerating multidimensional NMR and MRI experiments using iterated maps and sparse-sampling techniques, enabling faster data acquisition without loss of spectral fidelity.
External links
- Barrett Lab Website at Yale University
- Faculty profile at Yale Department of Physics
- Faculty profile at Yale School of Engineering & Applied Science