Physics Department Personnel

Dr. Michael Graf

Associate Chairperson and Professor of Physics

617-552-4128
Higgins Hall 230B
grafm@bc.edu

Education

• Ph. D., Physics, Brown University, 1987
  
• B. S. Physics/Math minor, Rensselaer Polytechnic Institute, 1980
  

Awards

IBM Postdoctoral Fellowship, 1987
Boston College Distinguished Junior Faculty Award, 1991
Research Opportunity Award, Research Corporation, 1997

Areas of Research

My work focuses on the properties of condensed matter systems at low temperatures and in strong magnetic fields. Early in my career this included studies of the growth kinetics of helium crystals, electrical transport and optical properties of two-dimensional electron systems (GaAs-AlGaAs quantum wells, GaSb-InAs semi-metallic quantum wells), and optical properties of the semi-magnetic semiconductor Cd0.95Mn0.05Se:In near the metal-insulator transition. The recent emphasis of my research has been on novel electronic systems, which provide opportunities to further our understanding of fundamental physical principles as well as to develop unique electronic devices.

Research conducted by me and my collaborators at the University of Amsterdam (Dr. A. de Visser) on the heavy-fermion superconductor UPt3 (sponsored by grants from Petroleum Research Fund and Research Corporation) has an ultimate goal of understanding unconventional superconductivity, magnetism, and their interplay in these strongly-correlated systems. The U(Pt1-x,Pdx)3 system is particularly interesting, as Pd-substitution affects both the striking double superconducting transition — it is the only known way to increase the splitting — and the anomalous antiferromagnetic state observed in the pure compound. We pursue these goals through specific heat, resistance, muon spin rotation measurements (in collaboration with colleagues from the Paul Scherrer Institute and ETH-Zurich), cantilever magnetometry, and neutron scattering measurements for samples in zero and applied magnetic fields, and also under hydrostatic pressure (in collaboration with colleagues from the National High Magnetic Field Laboratory), with particular emphasis on delineating the temperature-Pd-concentration phase diagram, which dramatically demonstrates the competition between superconductivity and static antiferromagnetic order.

Another class of interesting materials is the composite formed by injecting metals into an ordered porous insulating host material, such as indium or bismuth into Vycor glass, or into sub-micron nanochannel arrays (in collaboration with colleagues from Howard University). In our most recent work we have tracked the effects of confinement on the Fermi surface through magnetoquantum oscillations (Shubnikov-de Haas and de Haas – van Alphen effects). The Bi-based compounds may have important technological applications in the area of solid-state thermoelectric cooling.

New projects, developed with colleagues at the NMR/NQR Group at the University of Pavia, include studies of strong magnetic fields on the quantum critical material CeCu5.9Au0.1, and probing quantum tunneling of magnetization in LiY0.998Ho0.002F4 through NMR and µSR spectroscopies.

Much of the work described above is carried out in my laboratory at Boston College, where I have a He-3 adsorption refrigerator and a He-4 recirculation refrigerator, used in conjunction with 10 T and 3 T superconducting magnets, respectively.

Recent Presentations

"Probing the interplay between magnetism and superconductivity in UPt3 via Pd substitution", presented at the Boston College Workshop on Magnetically Mediated Superconductivity and as an invited lecture at the 2001 APS March Meeting.

Selected Journal Publications

• "Probing spin dynamics and quantum relaxation in LiY0.998Ho0.002F4 via 19F NMR," M. J. Graf, A. Lascialfari, F. Borsa, A. M. Tkachuk, and B. Barbara Phys. Rev. B 73, 024403 (2006).



• "On the magnetic field dependence of the susceptibility at the quantum critical point in CeCu5.9Au0.1," P. Carretta, M. Giovannini, M.J. Graf, N. Papinutto, A. Rigamonti, and K. Sullivan, Physica B 378-380, 84 (2006).



• "Weak magnetism phenomena in heavy-fermion superconductors: selected μSR studies," A. Amato, M. J. Graf, A. de Visser, H. Amitsuka, D. Andreica, and A. Schenck, Journal of Physics: Condensed Matter 16, S4403-S4420 (2004) [Invited review article].



• "Magnetic anisotropy and de Haas - van Alphen oscillations in a Bi microwire array studied via cantilever magnetometry at low temperatures," M. J. Graf, C. P. Opeil, and T. E. Huber, Journal of Low Temperature Physics 143, 1055 (2004).



• "Crossover from anomalous to conventional antiferromagnetism in Pd-doped UPt3 studied via cantilever magnetometry," C. P. Opeil, A. de Visser, M. J. Naughton, and M. J. Graf, Journal of Magnetism and Magnetic Materials 272-276, 244 (2004).



• "Confinement Effects and Surface-Induced Charge Carriers in Bi Quantum Wires," T. E. Huber, A. Nikolaeva, D. Gitsu, L. Konopko, C. A. Foss, Jr., and M. J. Graf, Applied Physics Letters 84, 1326 (2004).



• "Onset of antiferromagnetism in UPt3 via Th-substitution studied by muon spin spectroscopy," M. J. Graf, A. de Visser, C. P. Opeil, J. C. Cooley, J. L. Smith, A. Amato, C. Baines, F. Gygax, and A. Schenck, Physical Review B 68, 224421 (2003).



• "Magnetoquantum oscillations and confinement effects in arrays of 270-nm diameter bismuth nanowires," T. E. Huber, K. Celestine, and M. J. Graf, Physical Review B 67, 245317 (2003).



• "Electronic transport in a 3-D network of 1-D Bi and Te-doped Bi quantum wires," M. J. Graf and T. E. Huber, Physica E 18, 260 (2003).



• "Evidence for the existence of a magnetic quantum critical point in U(Pt1-xPdx)3", C.P. Opeil and M. J. Graf, Physica B 319, 246 (2002).



• "Magnetic quantum critical point and superconductivity in UPt3 doped with Pd", A. de Visser, M. J. Graf, et al., Physical Review Letters 85, 3005 (2000).



• "Search for a quantum phase transition in U(Pt1-xPdx)3", M. J. Graf, R. J. Keizer, A. de Visser, and S. T. Hannahs, Physica B 284, 1281 (2000).



• "Processing and characterization of high-conductance bismuth wire array composites", T.E. Huber, M.J. Graf, C.A. Foss, Jr., and P. Constant, Journal of Materials Research 15, 1816 (2000).



• "Muon localization site in U(Pt,Pd)3", A. Schenck et al., Physica B 289-290, 455 (2000).



• "Suppression of superconductivity in single crystals of UPt3 by Pd substitution", M. J. Graf, R. J. Keizer, A. de Visser, and J. J. M. Franse, Physical Review B 60, 3056 (1999).



• "Superconductivity in heavy-fermion U(Pt,Pd)3 and its interplay with magnetism", R. J. Keizer, A. de Visser, M. J. Graf, A. A. Menovsky, and J. J. M. Franse, Physical Review B 60, 10527 (1999).



• "Electronic transport in a three-dimensional network of one-dimensional bismuth quantum wires," T. E. Huber and M. J. Graf, Physical Review B 60, 16880 (1999).



• "Studies of superconductivity in U(Pt1-x Pdx) 3", M. J. Graf, R. J. Keizer, A. de Visser, and J. J. M. Franse, Physica B 259-261, 666 (1999).



• "Physical dependence of the sensitivity and room-temperature stability of AuxGe1-x thin film resistive thermometers on annealing conditions", N. A. Fortune, M. J. Graf, and K. Murata, Reviews of Scientific Instruments 69, 133 (1998).



• "Specific heat of a superconducting indium nanostructured network", F. Dong, M. J. Graf, T. E. Huber, and C. I. Huber, Solid State Communications 101, 932 (1997).



• "Doping Dependence of the Critical Field and the Transition Temperature in YBa2(Cu1-xZnx)3O7-d", D. D. Lawrie, J. P. Franck, J. R. Beamish, E. B. Molz, W.-M. Chen, and M. J. Graf, Journal of Low Temperature Physics 107 (1997).



• "Anomalous zero-magnetic-field dissipation across YBCO thin-film microbridges in layered YBCO-BaF2-Sn devices at low temperatures", M. J. Graf and S. G. Wang, Physica C 235-240, 1787 (1994).



• "Superconducting properties of indium in the restricted geometry of porous Vycor glass", M. J. Graf, T. E. Huber, and C. A. Huber, Physical Review B 45, 3133 (1992).



• "Magnetoresistance of thoriated UBe13", B. A. Allor, M. J. Graf, J. L. Smith, and Z. Fisk, Physica B 165&166, 359 (1990).



• "Specific heat of pure and thoriated UBe13 at low temperatures in high magnetic fields", M. J. Graf, N. A. Fortune, J. S. Brooks, J. L. Smith, and Z. Fisk, Physical Review B 40, 9358 (1989).



• "Carrier screening effects in semi-metallic InAs single quantum wells", M. J. Graf, T. P. Smith, HI, H. Munekata, L. L. Chang. and J. S. Brooks, Physical Review B 40, 5852 (1989).



• "High-velocity growth of solid 4He", Michael J. Graf and Humphrey J. Maris, Physical Review B 35, 3142 (1987).