UCR

Department of Physics & Astronomy



Douglas MacLaughlin


Douglas MacLaughlin

Douglas E. MacLaughlin

Professor Emeritus

Office: Physics 3030/1033-7
Telephone:
951-827-5344
Alt. Phone: 951-827-5311
Email: douglas.maclaughlin@ucr.edu
Fax: (951) 827-4529

Research Interests:

  • Experimental Condensed Matter Physics
  • Magnetic Resonance in Novel Electronic Systems

Education:

Ph.D. 1966, University of California, Berkeley

Current Research:

My research interests center on understanding the behavior of certain exotic metals, alloys, and superconductors, in which the unifying thread is the importance of strong correlations between the conducting electrons. The so-called "heavy fermion" f-electron compounds comprise one class of strongly correlated electron materials. Electrons in the well-known high temperature superconductors are also strongly correlated. Viable explanations for much of the behavior of these materials continue to be elusive.

Our research uses magnetic resonance, principally nuclear magnetic resonance (NMR) and the related muon spin rotation (μSR) technique, as a local probe of magnetic phenomena. Both techniques sense static and dynamic magnetic behavior on the atomic scale, and yield important information on the effect of strong electron correlations. In the following I describe some of our magnetic resonance studies of correlated-electron physics.

Non-Fermi liquids. There is widespread interest in a recently discovered class of heavy fermion alloys which exhibit unconventional properties at low temperatures. Thermodynamic and transport measurements in these materials indicate that the standard "Fermi liquid" description appropriate to a conventional metal does not apply. (The "liquid" in this designation refers to the conducting electrons, which are free to move through the metal.) Now Fermi liquid theory occupies a position somewhat similar to that of the Standard Model in particle physics: it is remarkably successful, so successful that it exercises considerable intellectual tyranny over our ways of thinking about metals! It is therefore a good thing that cases have been found where Fermi liquid theory manifestly breaks down.

The origin of this unconventional "non-Fermi liquid" (NFL) behavior is highly controversial. One school of thought interprets NFL properties as arising from a novel form of band electron scattering from the f ions in the metal. An opposing view invokes quantum critical behavior at zero temperature, controlled by interactions between f-ion spins. Our NMR and μSR studies of NFL alloys suggest that a third mechanism, related to structural disorder in the alloy, can also give rise to NFL behavior, a result which has also proved to be controversial. Our work and that of several theoreticians has shown, however, that disorder-driven NFL behavior is present and in at least some cases dominant in random alloys. These exciting developments are all direct consequences of our experimental results.

Heavy-fermion superconductivity. Superconductivity has recently been discovered in the heavy-fermion compound PrOs4Sb12. A large carrier effective mass characterizes both the normal and superconducting states, and the transition temperature Tc = 1.85 K is relatively high for a heavy-fermion superconductor. Although a conventional spin-based mechanism has not been completely ruled out, thermodynamic properties of PrOs4Sb12 suggest a nonmagnetic praseodymium ground state.

Our group has initiated transverse-field μSR measurements in the vortex lattice of PrOs4Sb12. Initial results yield a temperature dependence of the magnetic penetration depth indicative of an isotropic or nearly isotropic energy gap. This is not seen to date in any other heavy-fermion superconductor, and is a signature of isotropic pairing symmetry, possibly related to a novel nonmagnetic quadrupolar Kondo HF mechanism in PrOs4Sb12.

The symmetry of the superconducting pairing in such a system is a fundamental question. Recently we have studied exotic properties of the superconducting transition in PrOs4Sb12 and its alloys, including the rare phenomenon of time-reversal symmetry breaking in the superconducting state. Unlike most heavy-fermion superconductors, PrOs4Sb12 does not lose its superconductivity with alloying; the transition temperature changes only modestly across the alloy series Pr(Os,Ru)4Sb12 and (Pr,La)Os4Sb12. Nevertheless, the spontaneous magnetic field observed in our experiments, which is an unambiguous signature of time-reversal symmetry breaking, is rapidly suppressed by Ru doping but much less affected by La doping. We are seeking an understanding of this unexpected behavior.

Collaborations. Working arrangements and relations with the research community are quite different for practitioners of μSR compared to NMR. μSR studies must be performed at large "meson factories", which are particle accelerators capable of producing copious numbers of muons. These are maintained at laboratories such as the Paul Sherrer Institute PSI (Switzerland) and TRIUMF (Canada). Teams of collaborators run the around-the-clock experiments, which are necessary to take advantage of limited "beam time". Although NMR equipment is quite sophisticated, the experiments require only small laboratory setups. We have a state-of-the-art NMR laboratory at U.C. Riverside, and we also carry out experiments at Los Alamos, where a 3He/4He dilution refrigerator is available for experiments at temperatures below 1 K. Both our NMR and μSR research programs involve collaboration with researchers at universities (U.C. San Diego, U. of Florida), and government laboratories (Los Alamos, National High Magnetic Field Laboratory). We also have ongoing collaborations with research groups abroad (Leiden University, Simon Fraser University (Canada), and PSI).

Selected Publications:

  1. D. E. MacLaughlin, M. S. Rose, J. E. Anderson, Lei Shu, R. H. Heffner, T. Kimura, G. D. Morris, O. O. Bernal, "Critical slowing down in the geometrically frustrated pyrochlore antiferromagnet Gd2Ti2O7," in Proc. 10th Int. Conf. on Muon Spin Rotation/Relaxation/Resonance, Oxford, August 2005; Physica B 374-375, 142-144 (2006).
  2. R. H. Heffner, G. D. Morris, M. J. Fluss, B. Chung, S. McCall, D. E. MacLaughlin, L. Shu, K. Ohishi, E. D. Bauer, J. L. Sarrao, W. Higemoto, and T. U. Ito, "Limits for ordered magnetism in Pu from muon spin rotation spectroscopy," Phys. Rev. B 73, 094453 (2006).
  3. D. E. MacLaughlin, R. H. Heffner, O. O. Bernal, K. Ishida, J. E. Sonier, G. J. Nieuwenhuys, M. B. Maple, and G. R. Stewart, "Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems, J. Phys.: Condens. Matter 16, S4479-S4498 (2004).
  4. (Invited) D. E. MacLaughlin, M. S. Rose, Ben-Li Young, O. O. Bernal, R. H. Heffner, G. D. Morris, K. Ishida, G. J. Nieuwenhuys and J. E. Sonier, "μSR and NMR in f-electron non-Fermi liquid materials," in Proc. 9th Int. Conf. on Muon Spin Rotation/Relaxation/Resonance, Williamsburg, Virginia, June 2002; Physica B 326}, 381--386 (2003).
  5. 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, "Muon relaxation and isotropic pairing in superconducting PrOs4Sb12," Phys. Rev. Lett. 89, 157001 (2002).
  6. O. O. Bernal, C. Rodrigues, A. Martinez, H. G. Lukefahr, D. E. MacLaughlin, A. A. Menovsky, and J. A. Mydosh, "29Si NMR and Hidden Order in URu2Si2," Phys. Rev. Lett. 87, 196402 (2001).
  7. 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, "Glassy spin dynamics in non-Fermi-liquid UCu5-xPdx , x = 1.0 and 1.5," Phys. Rev. Lett. 87, 066402 (2001).
  8. R. H. Heffner, J. E. Sonier, D. E. MacLaughlin, G. J. Nieuwenhuys, G. Ehlers, F. Mezei, S.-W. Cheong, J. S. Gardner, and H. Roeder, "Observation of Two Time Scales in the Ferromagnetic Manganite La1-xCaxMnO3, x < 0.3," Phys. Rev. Lett. 85, 3285 (2000).

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