William P. Halperin John Evans Professor of Physics and Astronomy

Research Interests

Controlled nanostructures in silica aerogels

Halperin's group in applied physics grows ultra-porous aerogel glasses for a variety of applications: fundamental studies of impurity effects on superfluid 3He, controlled interactions between optically active grains in random lasers, dynamics of rare gas solid crystallization and micro avalanches, and novel supports for catalytically active nanoparticles, Pd, Ag and Au. The different layers shown here are for different nanoparticles isolated from each other and suspended in a 98% porous silica aerogel; colors correspond to the different plasmon resonances that absorb light. The silica aerogels are formed from 3 nm particles distributed in an extremely open network.

Crystal growth of high purity heavy fermion superconductors

Superconductive properties of the heavy fermion compound, UPt3, can be directly related to the unusual symmetry of the order parameter, an f-wave state, which is best studied with single crystals of high quality. The purest and most homogeneous crystals (in the world) are grown in our ultra-high vacuum crystal growth facility. Directional tunneling and Josephson interference experiments on these crystals have been performed by our collaborators at the University of Illinois. Growth of a single crystal in ultra-high vacuum at 1700 °C is shown in the figure using float-zone, electron beam heating.

Nuclear magnetic resonance studies of unconventional superconductors Bi-2212

We perform measurements on correlated electrons in high temperature superconductor, single-crystals of Bi2Sr2CaCu2O8 (Bi-2212) using 17O NMR up to very high magnetic fields, from 3 to 42 T. The crystals are obtained from collaborations with Argonne National Laboratory, Brookhaven National Laboratory, and the University of Tokyo. Our work includes NMR at the highest fields possible at the National High Magnetic Field Laboratory. Stability of quantized vortex structures in Bi-2212 is one focus of our work. Stability in the vortex solid phase is a key aspect of the eventual use of these materials for round-wire applications in order to construct a new generation of high magnetic field superconducting magnets. We determined the stable vortex solid region shown in the figure to the right. Additionally we have developed high field NMR spectroscopy to spatially resolve electronic excitations within the vortex unit cell which can be varied from 8 nm to 250 nm in size.

Nuclear magnetic resonance studies of unconventional superconductors Ba-122: Iron-Arsenic compounds

No one could have imagined that high temperature superconductivity could be found in compounds of iron and arsenic. Nevertheless this is what was discovered in Japan in 2008. We are studying this phenomenon using 75As NMR on high quality single crystals from Ames National Laboratory and the University of Tennessee. Based on our experience using NMR to study vortices we have discovered several new aspects of this problem which may be important for the eventual application of high critical current devices. We study both electron and hole doped superconductors.

High frequency acoustic cavities for studies of collective modes in superfluid 3He

Measurements in high quality acoustic cavities with dimensions between 25 to 300 microns permit the observation of transverse sound in superfluid 3He. It is amazing that this quantum liquid is the only known fluid in which transverse waves can propagate. Experimenting with these cavities we discovered an Acoustic Faraday Effect, directly analogous to the famous optical effect first seen by Michael Faraday in 1849, but in our case at 107 lower frequencies and therefore at much smaller length scales. Using this tool we recently uncovered a new collective mode of the superfluid order parameter.

Selected Publications

Stability of superfluid 3He-B in compressed aerogel, J.I.A. Li, A.M. Zimmerman, J. Pollanen, C.A. Collett, W.J. Gannon, and W.P. Halperin, Phys. Rev. Lett. 112, 115303 (2014).

Absence of static orbital current magnetism at the apical oxygen site in HgBa2CuO4+δ from NMR, A.M. Mounce, Sangwon Oh, Jeongseop A. Lee, W.P. Halperin, A.P. Reyes, P.L. Kuhns, M.K. Chan, C. Dorow, L. Ji, D. Xia, X. Zhao, M. Greven, Phys. Rev. Lett.111, 187003 (2013).

The Superfluid Glass Phase of 3He-A, J.I.A. Li, J. Pollanen, A.M. Zimmerman, C.A. Collett, W.J. Gannon, W.P. Halperin, Nature Physics 9, 775-779 (2013).

Microscopic coexistence of a two-component incommensurate spin density wave with superconductivity in underdoped NaFe0.983Co0.017As, S. Oh, A.M. Mounce, J.A. Lee, W.P. Halperin, C.L. Zhang, S. Carr, P. Dai, A.P. Reyes, P.L. Kuhns, Phys. Rev. B 88, 134518 (2013).

Spin pairing and penetration depth measurements from nuclear magnetic resonance in NaFe0.975Co0.025As, S. Oh, A.M. Mounce, J.A. Lee, W.P. Halperin, C.L. Zhang, S. Carr, P. Dai, Phys. Rev. B 87, 174517 (2013).

Nonlinear field dependence and f-wave interactions in superfluid 3He, C.A. Collett, J. Pollanen, J.I.A. Li, W.J. Gannon, W.P. Halperin, Phys. Rev. B 87, 024502 (2013).

Magnetization in the superconducting state of UPt3 from polarized neutron diffraction, W.J. Gannon, W.P. Halperin, C. Rastovski, M.R. Eskildsen, Pengcheng Dai, and A. Stunault, Phys. Rev. B 86, 104510 (2012).

Magnetic field dependence of spin-lattice relaxation in the s± state of Ba0.67K0.33Fe2As2, S. Oh, A.M. Mounce, W.P. Halperin, C.L. Zhang, P. Dai, A.P. Reyes, and P.L. Kuhns, Phys. Rev. B 85, 174508 (2012).

New chiral phases of superfluid 3He stabilized by anisotropic silica aerogel, J. Pollanen, J.I.A. Li, C.A. Collett, W.J. Gannon, W.P. Halperin and J.A. Sauls, Nature Physics 8, 317-320 (2012).

Modification of the 3He Phase Diagram by Anisotropic Disorder, R.G. Bennett, N. Zhelev, E.N. Smith, J. Pollanen, W.P. Halperin, J.M. Parpia, Phys. Rev. Lett. 107, 235504 (2011).

Nanoparticle-Loaded Aerogels and Layered Aerogels Cast from Sol-Gel Mixtures, Jiwon Kim, Kideyuki Nakanishi, Johannes Pollanen, Stoyan Smoukov, William P. Halperin, and Bartosz A. Grzybowski, Small, 7, 2568-2572 (2011).

Spin-density wave near the vortex cores in the high-temperature superconductor Bi2Sr2CaCu2O8+?, A.M. Mounce, S. Oh, S. Mukhopadhyay, W.P. Halperin, A.P. Reyes, P.L. Kuhns, K. Fujita, M. Ishikado, S. Uchida, Phys. Rev. Lett. 106, 057003 (2011).

Charge Induced Vortex Lattice Instability, A.M. Mounce, S. Oh, S. Mukhopadhyay, W.P. Halperin, A.P. Reyes, P.L. Kuhns, K. Fujita, M. Ishikado, S. Uchida, Nature Physics 7, 125 (2011).

The Transition Between Real and Complex Superconducting Order Parameter Phases in UPt3, J.D. Strand, D.J. Bahr, D.J. Van Harlingen, J.P. Davis, W.J. Gannon, W.P. Halperin, Science, 328 (5984), 1368 (2010).

Discovery of a New Excited Pair State in Superfluid 3He, J.P. Davis, J. Pollanen, H. Choi, J.A. Sauls and W.P. Halperin, Nature Physics 4, 571-575 (2008)

Two-dimensional vortices in superconductors, Bo Chen and W. P. Halperin, et. al., Nature Physics 3 239 (2007).

Spatially Resolved Electronic Structure Inside and Outside the Vortex Core of a High Temperature Superconductor, V. F. Mitrovic, E. E. Sigmund, M. Eschrig, H. N. Bachman, W.P. Halperin, A.P. Reyes, P. Kuhns, and W.G. Moulton, Nature 413, 501 (2001).

Discovery of the Acoustic Faraday Effect in Superfluid 3He -B, Y.Lee, T. Haard, W. P. Halperin, and J.A. Sauls, Nature, 400, 431 (1999).