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Sonier Research Group

µSR Studies of Quantum Condensed Matter

UTe2

Absence of Spontaneous Magnetic Fields due to Time-Reversal Symmetry Breaking in Bulk Superconducting UTe2
Muon spin relaxation measurements on a new generation of high-quality molten salt flux-grown single crystals suggest that the superconducting state of UTe2 does not break time-reversal symmetry.
Physical Review Letters 131, 226504 (2023)
UTe2

Ubiquitous Spin Freezing in the Superconducting State of UTe2
By way of µSR measurements on independently grown UTe2 single crystals we demonstrate the existence of magnetic clusters that gradually freeze into a disordered spin frozen state at low temperatures. Our findings suggest that inhomogeneous freezing of magnetic clusters is linked to the ubiquitous residual linear term in the temperature dependence of the specific heat (C) and the low-temperature upturn in C/T versus T. The omnipresent magnetic inhomogeneity has potential implications for experiments aimed at establishing the intrinsic low-temperature properties of UTe2.
Communications Physics 6, 24 (2023)


What do we do?

We apply µSR to investigate local magnetic and electronic properties of quantum materials. The research in our group is primarily directed towards understanding unconventional superconductivity and other novel quantum states of matter.

What is µSR?

The use of the muon as a sensitive local probe of matter forms a collection of techniques known as muon spin rotation/relaxation/resonance (µSR). As a spin 1/2 particle, the muon serves as a pure magnetic probe of internal magnetic fields and is ideally suited for investigations of novel and exotic forms of magnetism in quantum materials.

SFU and TRIUMF

We are located in the Department of Physics at Simon Fraser University. Much of our work is carried out at the Centre for Molecular and Materials Science (CMMS) at TRIUMF, which is home to several continuous spin-polarized muon beams.

Jeff Sonier

Jeff Sonier
Professor
jsonier@sfu.ca

Nasrin Azari

Nasrin Azari
PhD Candidate
naa60@sfu.ca

 Michael Yakovlev

Michael Yakovlev
MSc Candidate
yakovlev.michael@icloud.com
Sarah Dunsiger

Sarah Dunsiger
Adjunct Professor
TRIUMF BAE Scientist
dunsiger@triumf.ca
  1. Gap structure of the nonsymmorphic superconductor LaNiGa2 probed by µSR
    Shyam Sundar, M. Yakovlev, N. Azari, M. Abedi, D. M. Broun, H. U. Özdemir, S. R. Dunsiger, D. Zackaria, H. Bowman, P. Klavins, Y. Shi, V. Taufour, and J. E. Sonier
    Physical Review B 109, 104517 (2024)
     
  2. Absence of Spontaneous Magnetic Fields Due to Time-Reversal Symmetry Breaking in Bulk Superconducting UTe2
    N. Azari, M. Yakovlev, N. Rye, S. R. Dunsiger, S. Sundar, M. M. Bordelon, S. M. Thomas, J. D. Thompson, P. F. S. Rosa, and J. E. Sonier
    Physical Review Letters 131, 226504 (2023)
     
  3. µ+ Knight shift in UTe2: Evidence for relocalization in a Kondo lattice
    N. Azari, M. R. Goeks, M. Yakovlev, M. Abedi, S. R. Dunsiger, S. M. Thomas, J. D. Thompson, P. F. S. Rosa, and J. E. Sonier
    Physical Review B 108, L081103 (2023)
     
  4. Ubiquitous Spin Freezing in the Superconducting State of UTe2
    Shyam Sundar, N. Azari, M. R. Goeks, S. Gheidi, M. Abedi, M. Yakovlev, S. R. Dunsiger, J. M. Wilkinson, S. J. Blundell, T. E. Metz, I. M. Hayes, S. R. Saha, S. Lee, A. J. Woods, R. Movshovich, S. M. Thomas, N. P. Butch, P. F. S. Rosa, J. Paglione, and J. E. Sonier
    Communications Physics 6, 24 (2023)
     
  5. Two-gap time reversal symmetry breaking superconductivity in non-centrosymmetric LaNiC2
    Shyam Sundar, S. R. Dunsiger, S. Gheidi, K. S. Akella, A. M. Côté, H. U. Özdemir, N. R. Lee-Hone, D. M. Broun, E. Mun, F. Honda, Y. J. Sato, T. Koizumi, R. Settai, Y. Hirose, I. Bonalde, and J. E. Sonier
    Physical Review B 103, 014511 (2021)
     
  6. Long-range magnetic order in the anisotropic triangular lattice system CeCd3As3
    S. R. Dunsiger, J. Lee, J. E. Sonier, and E. D. Mun
    Physical Review B 102, 064405 (2020)
     
  7. Absence of µSR evidence for magnetic order in the pseudogap phase of Bi2+xSr2-xCaCu2O8+δ
    S. Gheidi, K. Akintola, A. C. Y. Fang, Shyam Sundar, A. M. Côté, S. R. Dunsiger, G. D Gu, and J. E. Sonier
    Physical Review B 101, 184511 (2020)
     
  8. Intrinsic low-temperature magnetism in SmB6
    S. Gheidi, K. Akintola, K. S. Akella, A. M. Côté, S. R. Dunsiger, C. Broholm, W. T. Fuhrman, S. R. Saha, J. Paglione, and J. E. Sonier
    Physical Review Letters 123, 197203 (2019)
     
  9. Coexistence of ferromagnetic fluctuations and superconductivity in the actinide superconductor UTe2
    Shyam Sundar, S. Gheidi, K. Akintola, A. M. Côté, S. R. Dunsiger, S. Ran, N. P. Butch, S. R. Saha, J. Paglione, and J. E. Sonier
    Physical Review B 100, 140502(R) (2019)
     
  10. Magnetic field induced effects in the quasikagome Kondo lattice system CePtPb
    A. C. Y. Fang, S. R. Dunsiger, A. Pal, K. Akintola, J. E. Sonier, and E. Mun
    Physical Review B 100, 024404 (2019)
     
  11. A beamline for fundamental neutron physics at TRIUMF
    S. Ahmed, T.Andalib, M. J.Barnes, C. B. Bidinosti, Y. Bylinsky, J.Chak, M. Das, C. A. Davis, B. Franke, M. T. W. Gericke, P. Giampa, M. Hahn, S. Hansen-Romu, K. Hatanaka, B.Jamieson, D. Jones, K. Katsika, S. Kawasaki, W. Klassen, A. Konaka, E. Korkmaz, F. Kuchler, L. Kurchaninov, M. Lang, L. Lee, T. Lindner, K. Madison, J. Mammei, R. Mammei, J. Martin, R. Matsumiya, R. Picker, E. Pierre, W. Ramsay, Y. Rao, W. Rawnsley, L. Rebenitsch, C. Remon, W. Schreyer, A. Sikora, S. Sidhu, J. Sonier, B. Thorsteinson, S. Vanbergen, W. van Oers, Y. Watanabe, and D. Yosifov
    Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 927, 101-108 (2019)
     
  12. Freezing out of a low-energy bulk spin exciton in SmB6
    K. Akintola, A. Pal, S. R. Dunsiger, A. C. Y. Fang, M. Potma, S. R. Saha, X. F. Wang, J. Paglione, and J. E. Sonier
    npj Quantum Materials 3:36 (2018)
     
  13. Quasistatic internal magnetic field detected in the pseudogap phase of Bi2+xSr2-xCaCu2O8+δ
    A. Pal, S. R. Dunsiger, K. Akintola, A. C. Y. Fang, A. Elhosary, M. Ishikado, H. Eisaki, and J. E. Sonier
    Physical Review B 97, 060502(R) (2018)
     
  14. Quantum spin fluctuations in the bulk insulating state of pure and Fe-doped SmB6
    K. Akintola, A. Pal, M. Potma, S. R. Saha, X. F. Wang, J. Paglione, and J. E. Sonier
    Physical Review B 95, 245107 (2017)
     
  15. Superconducting correlations induced by charge ordering in cuprate superconductors and Fermi-arc formation
    E. V. L. de Mello and J. E. Sonier
    Physical Review B 95, 184520 (2017)
     
  16. Investigation of potential fluctuating intra-unit cell magnetic order in cuprates by µSR
    A. Pal, K. Akintola, M. Potma, M. Ishikado, H. Eisaki, W. N. Hardy, D. A. Bonn, R. Liang, and J. E. Sonier
    Physical Review B 94, 134514 (2016)
     
  17. µSR studies of cuprate superconductors
    J.E. Sonier
    Journal of the Physical Society of Japan 85, 091005 (2016)
     
  18. Signatures of new d-wave vortex physics in overdoped Tl2Ba2CuO6+x revealed by TF-µ+SR
    J. H. Brewer, S. L. Stubbs, R. Liang, D. A. Bonn, W. N. Hardy, J. E. Sonier, W. A. MacFarlane, and D. C. Peets
    Scientific Reports 5, 14156 (2015)
     
  19. Magnetic properties of the helimagnet Cr1/3NbS2 observed by µSR
    D. Braam, C. Gomez, S. Tezok, E. V. L. de Mello, L. Li, D. G. Mandrus, Hae-Young Kee, and J. E. Sonier
    Physical Review B 91, 144407 (2015)
     
  20. Partially ordered vortex lattices in the high-field low-temperature mixed state of quasi-two-dimensional organic superconductors
    A. Maniv, V. Zhuravlev, T. Maniv, O. Ofer, R. Rommel, J. Müller, and J. E. Sonier
    Physical Review B 91, 134506 (2015)
     
  21. Charge order, superconducting correlations, and positive muons
    J. E. Sonier
    Journal of Magnetism and Magnetic Materials 376, 20-24 (2015)
     
  22. Charge segregation model for superconducting correlations in cuprates above Tc
    E. V. L. de Mello and J. E. Sonier
    Journal of Physics: Condensed Matter 26, 492201 (2014)
     
  23. Zero-field µSR search for a time-reversal-symmetry-breaking mixed pairing state in superconducting Ba1-xKxFe2As2
    Z. Lotfi Mahyari, A. Cannell, C. Gomez, S. Tezok, A. Zelati, E. V. L. de Mello, J.-Q. Yan, D. G. Mandrus, and J. E. Sonier
    Physical Review B 89, 020502(R) (2014)
     
  24. Universal inhomogeneous magnetic-field response in the normal state of cuprate high-Tc superconductors
    Z. Lotfi Mahyari, A. Cannell, E.V.L. de Mello, M. Ishikado, H. Eisaki, Ruixing Liang, D.A. Bonn, and J.E. Sonier
    Physical Review B 88, 144504 (2013)
     
  25. Muon spin rotation studies of niobium for superconducting rf applications
    A. Grassellino, C. Beard, P. Kolb, R. Laxdall, N.S. Lockyer, D. Longuevergne, and J.E. Sonier
    Physical Review Special Topics - Accelerators and Beams 16, 062002 (2013)
     
  26. Curie-like paramagnetism due to incomplete Zhang-Rice singlet formation in La2-xSrxCuO4
    C.V. Kaiser, W. Huang, S. Komiya, N.E. Hussey, T. Adachi, Y. Tanabe, Y. Koike, and J.E. Sonier
    Physical Review B 86, 054522 (2012)
     
  27. Precision search for magnetic order in the pseudogap regime of La2-xSrxCuO4 by muon spin relaxation
    W. Huang, V. Pacradouni, M.P. Kennett, S. Komiya, and J.E. Sonier
    Physical Review B 85, 104527 (2012)
     
  28. Magnetism and disorder effects on muon spin rotation measurements of the magnetic penetration depth in iron-arsenic superconductors
    J.E. Sonier, W. Huang, C.V. Kaiser, V. Pacradouni, S.A. Sabok-Sayr, M.D. Lumsden, B.C. Sales, M.A. McGuire, A.S. Sefat, and D. Mandrus
    Physical Review Letters 106, 127002 (2011)
     
  29. Damping of de Haas-van Alphen oscillations and vortex-lattice disorder in the peak-effect region of extreme type-II borocarbide superconductors
    A. Maniv, T. Maniv, V. Zhuravlev, B. Bergk, J. Wosnitza, A. Kohler, G. Behr, P.C. Canfield, and J.E. Sonier
    Physical Review B 83, 104505 (2011)
     
  30. Magnetic properties of isostructural M(H2O)4[Au(CN)4]2-based coordination polymers (M = Mn, Co, Ni, Cu, Zn) by SQUID and µSR studies
    A.R. Geisheimer, W. Huang, V. Pacradouni, S.A. Sabok-Sayr, J.E. Sonier, and D.B. Leznoff
    Dalton Transactions 40, 7505-7516 (2011)
     
  31. Direct search for a ferromagnetic phase in a heavily overdoped nonsuperconducting copper oxide
    J.E. Sonier, C.V. Kaiser, V. Pacradouni, S.A. Sabok-Sayr, C. Cochrane, D.E. MacLaughlin, S. Komiya, and N.E. Hussey
    Proceedings of the National Academy of Sciences 107, 17131-17134 (2010)
     
  32. Topical Review: High-field µSR studies of superconducting and magnetic correlations in cuprates above Tc
    J.E. Sonier
    Journal of Physics: Condensed Matter 22, 203202 (2010)
     
  33. Field-induced coupled superconductivity and spin density wave order in the heavy fermion compound CeCoIn5
    J. Spehling, R.H. Heffner, J.E. Sonier, N. Curro, C.H. Wang, B. Hitti, G. Morris, E.D. Bauer, J.L. Sarrao, F.J. Litterst, and H.-H. Klauss
    Physical Review Letters 103, 237003 (2009)
     
  34. Detection of the unusual magnetic orders in the pseudogap region of a high-temperature superconducting YBa2Cu3O6.6 crystal by muon-spin relaxation
    J.E. Sonier, V. Pacradouni, S.A. Sabok-Sayr, W.N. Hardy, D.A. Bonn, R. Liang, and H.A. Mook
    Physical Review Letters 103, 167002 (2009)
     
  35. Magnetic frustration and spin disorder in isostructural M(µ-OH2)2[Au(CN)2]2 (M = Mn, Fe, Co) coordination polymers containing double aqua-bridged chains: SQUID and µSR studies
    J. Lefebvre, P. Tyagi, S. Trudel, V. Pacradouni, C.V. Kaiser, J.E. Sonier, and D.B. Leznoff
    Inorganic Chemistry 48, 55-67 (2009)
     
  36. Inhomogeneous magnetic-field response of YBa2Cu3Oy and La2-xSrxCuO4 persisting above the bulk superconducting transition temperature
    J.E. Sonier, M. Ilton, V. Pacradouni, C.V. Kaiser, S.A. Sabok-Sayr, Y. Ando, S. Komiya, W.N. Hardy, D.A. Bonn, R. Liang, and W.A. Atkinson
    Physical Review Letters 101, 117001 (2008)
     
  37. Role of CuO chains in vortex core structure in YBa2Cu3O7-δ
    W.A. Atkinson and J.E. Sonier
    Physical Review B 77, 024514 (2008)
     
  38. Muon spin rotation studies of electronic excitations and magnetism in the vortex cores of superconductors
    J.E. Sonier
    Reports on Progress in Physics 70, 1717-1755 (2007)
     
  39. Hole-doping dependence of the magnetic penetration depth and vortex core size in YBa2Cu3Oy: Evidence for stripe correlations near 1/8 hole doping
    J.E. Sonier, S.A. Sabok-Sayr, F.D. Callaghan, C.V. Kaiser, V. Pacradouni, J.H. Brewer, S.L. Stubbs, W.N. Hardy, D.A. Bonn, R. Liang, and W.A. Atkinson
    Physical Review B 76, 134518 (2007)
     
  40. Spin-glass state of individual magnetic vortices in YBa2Cu3Oy and La2-xSrxCuO4 below the metal-to-insulator crossover
    J. E. Sonier, F. D. Callaghan, Yoichi Ando, R. F. Kiefl, J. H. Brewer, C. V. Kaiser, V. Pacradouni, S. A. Sabok-Sayr, X. F. Sun, S. Komiya, W. N. Hardy, D. A. Bonn, and R. Liang
    Physical Review B 76, 064522 (2007)
     
  41. Muon spin rotation measurements of the vortex state in vanadium: A comparative analysis using iterative and analytical solutions of the Ginzburg-Landau equations
    M. Laulajainen, F.D. Callaghan, C.V. Kaiser, and J.E. Sonier
    Physical Review B 74, 054511 (2006)
     
  42. A new basic motif in cyanometallate coordination polymers: Structure and magnetic behavior of M(µ-OH2)2[Au(CN)2]2 (M=Cu, Ni)
    J. Lefebvre, F. Callaghan, M.J. Katz, J.E. Sonier, and D.B. Leznoff
    Chemistry - A European Journal 26, 6719 (2006)
     
  43. Magnetic field dependence of muon spin relaxation in geometrically frustrated Gd2Ti2O7
    S.R. Dunsiger, R.F. Kiefl, J.A. Chakhalian, J.E. Greedan, W.A. MacFarlane, R.I. Miller, G.D. Morris, A.N. Price, N.P. Raju, and J.E. Sonier
    Physical Review B 73, 172418 (2006)
     
  44. Coexistence of magnetism and superconductivity in ultraclean underdoped YBa2Cu3O6.37
    R.I. Miller, R.F. Kiefl, J.H. Brewer, F.D. Callaghan, J.E. Sonier, R. Liang, D.A. Bonn, and W. Hardy
    Physical Review B 73, 144509 (2006)
     
  45. Effect of delocalized vortex core states on the specific heat of Nb
    J.E. Sonier, M.F. Hundley, and J.D. Thompson
    Physical Review B 73, 132504 (2006)
     
  46. Field dependence of the vortex core size in a multiband superconductor
    F.D. Callaghan, M. Laulajainen, C.V. Kaiser and J.E. Sonier
    Physical Review Letters 95, 197001 (2005)
     
  47. Shrinking magnetic vortices in V3Si due to delocalized quasiparticle core states: Confirmation of the microscopic theory for interacting vortices
    J. E. Sonier, F. D. Callaghan, R. I. Miller, E. Boaknin, L. Taillefer, R. F. Kiefl, J. H. Brewer, K. F. Poon and J. D. Brewer
    Physical Review Letters 93, 017002 (2004)
     
  48. Investigations of the core structure of magnetic vortices in type-II superconductors using muon spin rotation
    J.E. Sonier
    Journal of Physics: Condensed Matter 16, S4479-98 (2004).
     
  49. Superconductivity and field-induced magnetism in Pr2-xCexCuO4 single crystals
    J. E. Sonier, K. F. Poon, G. M. Luke, P. Kyriakou, R. I. Miller, R. Liang, C. R. Wiebe, P. Fournier and R. L. Greene
    Physical Review Letters 91, 147002 (2003)
     
  50. Local magnetic susceptibility of the positive muon in the quasi-one-dimensional S=1/2 antiferromagnet dichlorobis (pyridine) copper (II)
    J.A. Chakhalian, R.F. Kiefl, R.I. Miller, J.H. Brewer, S.R. Dunsiger, G.D. Morris, W.A. MacFarlane, J.E. Sonier, S. Eggert, I. Affleck, A. Keren and M. Verdaguer
    Physical Review Letters 91, 027202 (2003)
     
  51. Heat conduction in the vortex state of NbSe2: Evidence for multiband superconductivity
    E. Boaknin, M. A. Tanatar, J. Paglione, D. Hawthorn, F. Ronning, R. W. Hill, M. Sutherland, L. Taillefer, J.E. Sonier, S.M. Hayden and J.W. Brill
    Physical Review Letters 90, 117003 (2003)
     
  52. Muon spin relaxation and isotropic pairing in superconducting PrOs4Sb12
    D. E. MacLaughlin, J. E. Sonier, R. H. Heffner, O. O. Bernal, Ben-Li Young, M. S. Rose, G. D. Morris, E. D. Bauer, T. D. Do and M. B. Maple
    Physical Review Letters 89, 157001 (2002)
     
  53. Temperature dependence of the magnetic penetration depth in the vortex state of the pyrochlore superconductor, Cd2Re2O7
    M. D. Lumsden, S. R. Dunsiger, J. E. Sonier, R. I. Miller, R. F. Kiefl, R. Jin, J. He, D. Mandrus, S. T. Bramwell and J. S. Gardner
    Physical Review Letters 89, 147002 (2002)
     
  54. Evidence for static magnetism in the vortex cores of ortho-II YBa2Cu3O6.50
    R.I. Miller, R.F. Kiefl, J.H. Brewer, J.E. Sonier, J. Chakhalian, S. Dunsiger, G.D. Morris, A.N. Price, D.A. Bonn, W.N. Hardy and R. Liang
    Physical Review Letters 88, 137002-137005 (2002)
     
  55. Evidence for local moment formation around a positive muon in graphite
    J. A. Chakhalian, R. F. Kiefl, S. R. Dunsiger, W. A. MacFarlane, R. Miller, J. E. Sonier and J. E. Fischer
    Physical Review B 66, 155107 (2002)
     
  56. Correlations between charge ordering and local magnetic fields in overdoped YBa2Cu3O6+x
    J.E. Sonier, J.H. Brewer, R.F. Kiefl, R.H. Heffner, K.F. Poon, S.L. Stubbs, G.D. Morris, R.I. Miller, W.N. Hardy, R. Liang, D.A. Bonn, J.S. Gardner, C.E. Stronach and N.J. Curro
    Physical Review B 66, 134501 (2002)
     
  57. Neutron elastic and inelastic scattering investigations of U0.965Th0.035Be13
    A. Hiess, R.H. Heffner, J.E. Sonier, G.H. Lander, J.L. Smith and J.C. Cooley
    Physical Review B 66, 064531 (2002)
     
  58. Anomalous vortex state of superconducting LuNi2B2C
    A.N. Price, R.I. Miller, R.F. Kiefl, J.A. Chakhalian, S.R. Dunsiger, G.D. Morris, J.E. Sonier and P.C. Canfield
    Physical Review B 65, 214520 (2002)
     
  59. Susceptibility inhomogeneity and non-Fermi-liquid behavior in Ce(Ru0.5Rh0.5)2Si2
    D.E. MacLaughlin, O.O. Bernal, J.E. Sonier, R.H. Heffner, T. Taniguchi and Y. Miyako
    Physical Review B 65, 184401 (2002)
     
  60. Nonlocal effects and shrinkage of the vortex core radius in YNi2B2C probed by muon spin rotation
    K. Ohishi, K. Kahuta, J. Akimitsu, W. Higemoto, R. Kadono, J.E. Sonier, A.N. Price, R.I. Miller, R.F. Kiefl, M. Nohara, H. Suzuki and H. Takagi
    Physical Review B 65, R140505-R140508 (2002)
     
  61. Glassy spin dynamics in non-Fermi-liquid UCu5-xPdx, x = 1.0 and 1.5
    D.E. MacLaughlin, O.O. Bernal, R.H. Heffner, G.J. Nieuwenhuys, M.S. Rose, J.E. Sonier, B. Andraka, R. Chau and M.B. Maple
    Physical Review Letters 87, 066402-066405 (2001)
     
  62. Anomalous weak magnetism in superconducting YBa2Cu3O6+x
    J.E. Sonier, J.H. Brewer, R.F. Kiefl, R.I. Miller, G.D. Morris, C.E. Stronach, J.S. Gardner, S.R. Dunsiger, D.A. Bonn, W.N. Hardy, R. Liang and R.H. Heffner
    Science 292, 1692-1695 (2001)
     
  63. Muon spin relaxation study of La1-xCaxMnO3
    R.H. Heffner, J.E. Sonier, D.E. MacLaughlin, G.J. Nieuwenhuys, G.M. Luke, Y.J. Uemura, William Ratcliff II, S.-W. Cheong and G. Balakrishnan
    Physical Review B 63, 0994408 (2001)
     
  64. µSR studies of the vortex state in type-II superconductors
    J.E. Sonier, J.H. Brewer and R.F. Kiefl
    Reviews of Modern Physics 72, 769-811 (2000)
     
  65. µ+-Knight Shift measurements in U0.965Th0.035Be13 single crystals
    J.E. Sonier, R.H. Heffner, D.E. MacLaughlin, G.J. Nieuwenhuys, O. Bernal, R. Movshovich, P.G. Pagliuso, J. Cooley, J.L. Smith and J.D. Thompson
    Physical Review Letters 85, 2821-2824 (2000)
     
  66. Low temperature spin dynamics of the geometrically frustrated antiferromagnetic garnet, Gd3Ga5O12
    S.R. Dunsiger, J.S. Gardner, J.A. Chakhalian, A.L. Cornelius, M. Jaime, R.F. Kiefl, R. Movshovich, W.A. MacFarlane, R.I. Miller, J.E. Sonier and B.D. Gaulin
    Physical Review Letters 85, 3504-3507 (2000)
     
  67. Positive muon studies of high temperature superconductors
    G.M. Luke and J.E. Sonier
    Physics in Canada 56, 263-266 (2000).
     
  68. Observation of two time scales in the ferromagnetic manganite La1-xCaxMnO3, x = 0.3
    R.H. Heffner, J.E. Sonier, D.E. MacLaughlin, G.J. Nieuwenhuys, G. Ehlers, F. Mezei, S.-W. Cheong, J.S. Gardner and H. Roder
    Physical Review Letters 85, 3285-3288 (2000)
     
  69. Low temperature limit of the vortex core radius and the Kramer-Pesch effect in NbSe2
    R.I. Miller, R.F. Kiefl, J.H. Brewer, J. Chakhalian, S. Dunsiger, G.D. Morris, J.E. Sonier and W.A. MacFarlane
    Physical Review Letters 85, 1540-1543 (2000)
     
  70. Melting and dimensionality of the vortex lattice in YBa2Cu3O6.60
    J.E. Sonier, J.H. Brewer, R.F. Kiefl, D.A. Bonn, J. Chakhalian, S.R. Dunsiger, W.N. Hardy, R. Liang, W.A. MacFarlane, R.I. Miller, D.R. Noakes, T.M. Riseman and C.E. Stronach
    Physical Review B 61, R890-R893 (2000)
     
  71. Field induced reduction of the low temperature superfluid density in YBa2Cu3O6.95
    J.E.Sonier, J.H. Brewer, R.F. Kiefl, G.D.Morris, R.I. Miller, D.A. Bonn, J. Chakhalian, W.N. Hardy, R.H. Heffner and R. Liang
    Physical Review Letters 83, 4156-4159 (1999)
     
  72. Low field anomaly in the specific heat of s-wave superconductors due to the expansion of the vortex cores
    J.E. Sonier, M.F. Hundley, J.D. Thompson and J.W. Brill
    Physical Review Letters 82, 4914-4917 (1999)
     
  73. Cooperative paramagnetism in the geometrically frustrated pyrochlore antiferromagnet Tb2Ti2O7
    J.S. Gardner, S.R. Dunsiger, B.D. Gaulin, M.J.P. Gingras, J.E. Greedan, R.F. Kiefl, M.D. Lumsden, W.A. MacFarlane, N.P. Raju, J.E.Sonier, I. Swainson and Z. Tun
    Physical Review Letters 82, 1012-1015 (1999)
     
  74. Expansion of the vortex Cores in YBa2Cu3O6.95 at low magnetic fields
    J.E.Sonier, R.F. Kiefl, J.H. Brewer, D.A. Bonn, S.R. Dunsiger, W.N. Hardy, R. Liang, R.I. Miller, D.R. Noakes and C.E. Stronach
    Physical Review B 59, R729-R732 (1999)
     
  75. Muon-spin-relaxational studies of the alkali-fulleride superconductors
    W.A. MacFarlane, R.F. Kiefl, S.R. Dunsiger, J.E.Sonier, J. Chakhalian, J.E. Fischer, T. Yildirim and K.H. Chow
    Physical Review B 58, 1004-1024 (1998)
     
  76. Measurement of the fundamental length scales in the vortex state of YBa2Cu3O6.60
    J.E.Sonier, J.H. Brewer, R. F. Kiefl, D.A. Bonn, S.R. Dunsiger, W.N. Hardy, Ruixing Liang, W.A. MacFarlane, R.I. Miller, T.M. Riseman, D.R. Noakes, C.E. Stronach and M.F. White Jr
    Physical Review Letters 79, 2875-2878 (1997)
     
  77. Muon spin-rotation measurements of the magnetic field dependence of the vortex-core radius and magnetic penetration depth in NbSe2
    J.E. Sonier, R.F. Kiefl, J.H. Brewer, J. Chakhalian, S.R. Dunsiger, W.A. MacFarlane, R.I. Miller, A. Wong, G.M. Luke and J.W. Brill
    Physical Review Letters 79, 1742-1745 (1997)
     
  78. Magnetic field dependence of the London penetration depth in the vortex state of YBa2Cu3O6.95
    J.E. Sonier, R.F. Kiefl, J.H. Brewer, D.A. Bonn, S.R. Dunsiger, W.N. Hardy, Ruixing Liang, W.A. MacFarlane, T. M. Riseman, D.R. Noakes and C.E. Stronach
    Physical Review B 55, 11789-11792 (1997)
     
  79. Muon spin relaxation investigation of the dynamics of geometrically frustrated antiferromagnets Y2Mo2O7and Tb2Mo2O7
    S.R. Dunsiger, R.F.Kiefel, K.H. Chow, B.D. Gaulin, M.J.P. Gingras, J.E. Greedan, A. Keran, K. Kojima, G.M. Luke, W.A. MacFarlane, N.P. Raju, J.E. Sonier, Y.J. Uemura and W.D. Wu
    Physical Review B 54, 9019-9022 (1996)
     
  80. Low temperature spin dynamics of geometrically frustrated antiferromagnets Y2Mo2O7 and Y2Mo1.6Tl0.4O7 Studied by Muon Spin Relaxation
    S.R. Dunsiger, R.F. Kiefl, K.H. Chow, B.D. Gaulin, M.J.P. Gingras, J.E. Greedan, A. Keren, K. Kojima, G.M. Luke, W.A. MacFarlane, N.P. Raju, J.E. Sonier, Y.J. Uemura and W.D. Wu
    Journal of Applied Physics 79, 6636-6638 (1996)
     
  81. Magnetism in RbC60 studied by muon-spin rotation
    W.A. MacFarlane, R.F. Kiefl, S. Dunsiger, J.E. Sonier and J.E. Fischer
    Physical Review B 52, R6995-R6998 (1995)
     
  82. New muon-spin-rotation measurement of the temperature dependence of the magnetic penetration depth in YBa2Cu3O6.95
    J.E. Sonier, R.F. Kiefl, J.H. Brewer, D.A. Bonn, J.F. Carolan, K.H. Chow, P. Dosanjh, W.N. Hardy, Ruixing Liang, W.A. MacFarlane, P. Mendels, G.D. Morris, T.M. Riseman and J.W. Schneider
    Physical Review Letters 72, 744-747 (1994)
     
  83. Bond-centered muonium in diamond: Resolved nuclear hyperfine structure
    J.W. Schneider, R.F. Kiefl, K.H. Chow, S. Johnston, J.E. Sonier, T.L. Estle, B. Hitti, R.L. Lichti, S.H. Connell, J.P.F. Sellschop, C.G. Smallman, T.R. Anthony and W.F. Banholzer
    Physical Review Letters 71, 557-560 (1993)
     
  84. Coherence peak and superconducting energy gap in Rb3C60 observed by muon spin relaxation
    R.F. Kiefl, W.A. MacFarlane, K.H. Chow, S. Dunsiger, T.L. Duty, T.M.S. Johnston, J.W. Schneider, J.E. Sonier, L. Brard, R.M. Strongin, J.E. Fischer and A.B. Smith
    Physical Review Letters 70, 3987-3990 (1993)