# Dr. Michael Graf

## associate chairperson and professor of physics

Phone: 617-552-4128

Higgins Hall 230B

E-mail: michael.graf@bc.edu

### Education

Ph.D., Physics, Brown University

B.S., Physics/Math minor, Rensselaer Polytechnic Institute

### 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 Publications

- "Observation of Three-Dimensional Behavior in Surface States of Bismuth Nanowires and the Evidence for Bulk-Bi Surface Quasiparticles," T.E. Huber, A. Nikolaeva, L. Konopko, and M.J. Graf,
*Phys. Rev. B***79**, 201304(R) (2009). [Rapid Communication, chosen as Editor’s Suggestion]. - "Spin Dynamics in the Negatively Charged Terbium(III) Bis-phthalocyaninato Complex," F. Branzoli, P. Carretta, M. Filibian, G. Zoppellaro, M. J. Graf, J. R. Galan-Mascaros, O. Fuhr, S. Brink, and M. Ruben,"
*J. Am. Chem. Soc.***131**, 4387 (2009). - "19F Nuclear Spin Relaxation and Spin Diffusion Effects in the Single Ion Magnet LiYF4:Ho3+," B.Z. Malkin, M.V. Vanyunin, M. J. Graf, J. Lago, F. Borsa, A. Lascialfari, A.M. Tkachuk, and B. Barbara,
*Eur. Phys. J. B***66**, 155 (2008). - "Role of Boundary Roughness in the Electronic Transport of Bi Nanowires," T. E. Huber, A. Nikolaeva, D. Gitsu, L. Konopko, and M. J. Graf,
*J. Appl. Phys*.**104**, 123704 (2008). - "Quantum Interference of Surface States in Bismuth Nanowires Probed by the Aharonov-Bohm Oscillatory Behavior of the Magnetoresistance," A. Nikolaeva, D. Gitsu, L. Konopko, M.J. Graf, T.E. Huber,
*Phys. Rev. B***77**, 075332 (2008). - "Muon Spin Rotation Studies of Spin Dynamics at Avoided Level Crossings in LiY0.998Ho0.002F4," M.J. Graf, J. Lago, A. Lascialfari, A. Amato, C. Baines, S. R. Giblin, J. S. Lord, A. M. Tkachuk, and B. Barbara,
*Phys. Rev. Lett.***99**, 267203 (2007). - "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,
*J. Phys.: Condens. 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,
*J. Low Temp. Phys.***143**, 1055 (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,
*Appl. Phys. Lett*.**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,
*Phys. Rev. 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,
*Phys. Rev. B***67**, 245317 (2003). - "Evidence for the Existence of a Magnetic Quantum Critical Ooint 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*.,*Phys. Rev. Lett.***85**, 3005 (2000). - "Processing and Characterization of High-Conductance Bismuth Wire Array Composites," T.E. Huber, M.J. Graf, C.A. Foss, Jr., and P. Constant,
*J. Mater. Res.***15**, 1816 (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,
*Phys. Rev. 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,
*Phys. Rev. B***60**, 10527 (1999). - "Electronic Transport in a Three-Dimensional Network of One-Dimensional Bismuth Quantum Wires," T. E. Huber, and M. J. Graf,
*Phys. Rev. B***60**, 16880 (1999). - "Studies of Superconductivity in U(Pt1-x Pdx)3 for x < 0.006," 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,
*Rev. Sci. Instrum.***69**, 133 (1998). - "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,*J. Low Temp. Phys.***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,
*Phys. Rev. B***45**, 3133 (1992). - "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,
*Phys. Rev. B***40**, 9358 (1989). - "Carrier Screening Effects in Semi-Metallic InAs Single Quantum Wells," M. J. Graf, T. P. Smith, III, H. Munekata, L. L. Chang, and J. S. Brooks,
*Phys. Rev. B***40**, 5852 (1989). - "High-Velocity Growth of Solid 4He," M. J. Graf, and H. J. Maris,
*Phys. Rev. B***35**, 3142 (1987). - "Effect of Interface Mobility on Heat Transfer from Solid 4He to 3He Quasiparticles in 3He-4He Mixtures," M. J. Graf, R. M. Bowley, and H. J. Maris,
*Phys. Rev. Lett.***53**, 1176 (1984).