Stephen in Washington DC, November 2010

Stephen in Washington DC, November 2010

Stephen Powell

I am a Postdoctoral Fellow of the Joint Quantum Institute at the University of Maryland, College Park. I am based in the Condensed Matter Theory Center, part of the Department of Physics.

Research

My research, in theoretical condensed-matter physics, concerns the diverse and remarkable phenomena that result from strong couplings between the many constituent parts of a physical system. In particular, I study frustrated magnetism and ultracold atomic gases, two areas where the elementary constituents and interactions can be understood in detail, allowing a direct appreciation of the emergent collective phenomena.

My work on Higgs transitions of spin ice was mentioned in New Scientist. Spin ice is a frustrated magnet that exhibits a “Coulomb phase”, with behavior that closely parallels that of electromagnetism in the vacuum. (More technically, the long-wavelength description is a noncompact U(1) gauge theory.) Applying external perturbations, such as a magnetic field, can cause it to form an ordered state; this work showed that in some cases the transition to order occurs through the same physical mechanism as the Higgs transition in the standard model.

Publications

Universal monopole scaling near transitions from the Coulomb phase, S. Powell, arXiv:1203.4564 (unpublished).

Order by disorder in spin-orbit coupled Bose-Einstein condensates, R. Barnett, S. Powell, T. Graß, M. Lewenstein, and S. Das Sarma, Phys. Rev. A 85, 023615 (2012) (also arXiv:1109.4945).

Higgs transitions of spin ice, S. Powell, Phys. Rev. B 84, 094437 (2011) (also arXiv:1106.6046).

Chiral Rashba spin textures in ultra-cold Fermi gases, J. D. Sau, R. Sensarma, S. Powell, I. B. Spielman, and S. Das Sarma, Phys. Rev. B 83, 140510(R) (2011) (also arXiv:1012.3170).

Bogoliubov theory of interacting bosons on a lattice in a synthetic magnetic field, S. Powell, R. Barnett, R. Sensarma, and S. Das Sarma, Phys. Rev. A 83, 013612 (2011) (also arXiv:1009.1389).

Interacting Hofstadter spectrum of atoms in an artificial gauge field, S. Powell, R. Barnett, R. Sensarma, and S. Das Sarma, Phys. Rev. Lett. 104, 255303 (2010) (also arXiv:1004.0701).

Classical to quantum mapping for an unconventional phase transition in a three-dimensional classical dimer model, S. Powell and J. T. Chalker, Phys. Rev. B 80, 134413 (2009) (also arXiv:0907.1564).

Magnetic phases and transitions of the two-species Bose-Hubbard model, S. Powell, Phys. Rev. A 79, 053614 (2009) (also arXiv:0902.1993).

SU(2)-invariant continuum theory for an unconventional phase transition in a three-dimensional classical dimer model, S. Powell and J. T. Chalker, Phys. Rev. Lett. 101, 155702 (2008) (also arXiv:0805.3698).

Classical to quantum mappings for geometrically frustrated systems: Spin-ice in a [100] field, S. Powell and J. T. Chalker, Phys. Rev. B 78, 024422 (2008) (also arXiv:0803.4204).

Spin dynamics across the superfluid-insulator transition of spinful bosons, S. Powell and S. Sachdev, Phys. Rev. A 76, 033612 (2007) (also cond-mat/0703011).

Excited state spectra at the superfluid-insulator transition out of paired condensates, S. Powell and S. Sachdev, Phys. Rev. A 75, 031601(R) (2007) (also cond-mat/0608611).

Depletion of the Bose-Einstein condensate in Bose-Fermi mixtures, S. Powell, S. Sachdev, and H. P. Büchler, Phys. Rev. B 72, 024534 (2005) (also cond-mat/0502299).

Quench dynamics across quantum critical points, K. Sengupta, S. Powell, and S. Sachdev, Phys. Rev. A 69, 053616 (2004) (also cond-mat/0311355).

Background: Close-packed dimers on a square lattice. For a large lattice with A sites, the number of allowed configurations approaches eGA/π, where G is Catalan's constant (see, for instance, Kasteleyn and Fisher and Stephenson). [Fast|Slow|Stop]

(The dimer animation is experimental, and is known not to work on Firefox earlier than version 3 and Internet Explorer earlier than version 7. If you have any problems with it, try reloading the page first, and then please .)