Philip W. Phillips
Professor of Physics and Bliss Faculty Scholar
Professor Philip Phillips received his bachelor's degree in chemistry and mathematics from Walla Walla College in 1979 and his Ph.D. in physical chemistry from the University of Washington in 1982. After a Miller Fellowship at Berkeley, he joined the faculty in the Department of Chemistry at Massachusetts Institute of Technology (1984-1993). Professor Phillips came to the University of Illinois Department of Physics in 1993.
Professor Phillips is a theoretical condensed matter physicist who has an international reputation for his work on transport in disordered and strongly correlated low-dimensional systems. While he was at MIT, he developed a class of random 1-dimensional models which circumvent Anderson localization, the best-known of which is the random dimer model. The essence of the random dimer model is that Anderson localization fails even in 1-dimension anytime the defects possess a plane of symmetry. Since this initial observation, numerous researchers have applied this model to conducting polymers, semiconductor heterostructures, and Fibonacci lattices. Experiments confirming the random dimer model were published in 1998 in PRL.
More recently, Phillips has been working on quantum phase transitions and strongly correlated electrons. His work is motivated by experimental observations that challenge the standard paradigms of transport and magnetism in low-dimensionsional systems. To this end, he has focused on the experimental observations that 1) non-magnetic disorder suppresses the Kondo effect in thin films, 2) the resistivity on the 'superconducting' side of an insulator-superconductor transition levels at low temperatures rather than dropping to zero, 3) a dilute 2D electron gas exhibits a conducting phase as temperature tends to zero, in violation of the well-accepted theorem of Anderson's, and 4) the normal state of the cuprates appears to be a non-Fermi liquid. With his graduate student Ivar Martin, he showed that the suppression of the Kondo resistivity by non-magnetic scattering arises from an interplay between weak localization and the feedback effect that magnetic scattering has on localization.
Along with his student Denis Dalidovich, Phillips made the fundamental observation that destruction of superconductivity by phase fluctuations leads quite generally to a metal rather than an insulator, as had been thought previously. The Cooper pair metal is stable to weak disorder and hence constitutes the only proven example of an interaction-induced metal in 2D.
Research Areas: quantum critical phenomena, quantum magnetism, and strongly correlated electrons
Description of Current Research
Strongly Correlated Electrons
A key goal is to understand the competing order that transpires when the Coulomb interaction exceeds the kinetic energy. Experimental systems in which the physics of strong correlations dominates include the cuprates, vanadium oxide, the ruthenates, and wide classes of organic materials that become superconducting under pressure. In such systems, magnetism, charge-density waves, pairing, spin-denisty waves, Mott transitions, and phase separation all occur at some range of doping or applied pressure. Aside from the magnetic states, which generally arise at zero (or low) doping (or pressure), and certain types of charge density wave states, none of the other ordered states that are observed experimentally has ever been explained, particularly superconductivity. An unfortunate feature of strong-correlation physics is the inapplicability of perturbation theory. In fact, there is no agreed-upon analytical methodology for approaching such problems. Hence, experiments are essential. In the area of strong-correlation physics, I focus on two types of experiments: 1) those on the new conducting phase in a 2D electron gas and 2) superconductivity in the cuprates and organics. My emphasis here is on developing non-perturbative ways of understanding the strong-coupling limits of the Hubbard model and the dilute 2D electron gas.
Quantum Critical Phenomena
My work on quantum critical phenomena is motivated by the growing evidence that in 2D systems exhibiting insulator-superconductor transitions, as well as in quantum-Hall to insulator transitions (QHIT), the longitudinal resistivity levels, as opposed to dropping to zero, as temperature tends to zero. It has been proposed that in all of these systems, dissipation gives rise to the metallic phase. However, no microscopic model has been solved that produces metallic behaviour at zero temperature. As this problem centers on zero-temperature transport properties, the all-important question of the non-commutativity of the frequency and temperature tending to zero limits is of utmost importance. Further, in this context, the question of internal versus external dissipation also arises. We have recently shown that once Cooper pairs loose their global phase coherence, collisions between Cooper pairs creates a metallic rather than an insulating state. In our current work we are characterizing the bose metal phase as well as exploring how both internal and external dissipation affect the transport properties near QHIT.
Selected Publications
Choy, T-P and Phillips, PW. Doped Mott insulators are insulators: hole localization in the cuprates. Phys. Rev. Lett. 95, 196405-1 (2005).
Phillips, PW and Chamon, C. Breakdown of one-parameter scaling in quantum critical scenarios for high-temperature copper-oxide superconductors. Phys. Rev. Lett. 95, 107002-1 (2005).
Phillips, PW, Galanakis, D, and Stanescu, TD. Absence of asymptotic freedom in doped Mott insulators: Breakdown of strong coupling expansions. Phys. Rev. Lett 93, 267004-1-4 (2004).
Dalidovich, D and Phillips, PW. Nonlinear transport near a quantum phase transition in two dimensions. Phys. Rev. Lett. 93, 027004-1-4 (2004).
Chernyshev, AL, Galanakis, D, and Phillips, PW. Higher order corrections to effective low-energy theories for strongly correlated electron systems. Phys. Rev. B 70, 235111-1-12 (2004).
Misra, S, Vershinin, M, Phillips, PW, and Yazdani, A. Failure of scattering interface in the pseudogap state of cuprate superconductors. Phys. Rev. B 70, 220503-1-4 (2004).
Stanescu, TD and Phillips, PW. Nonperturbative approach to full Mott behavior. Phys. Rev. B 69, 245104-1-27 (2004).
P. Phillips, Advanced Solid State Theory (Westview Press, New York, 2002).
P. Phillips, "From insulator to superconductor," News and Views in Nature 406, 687 (2000).
P. Phillips and H-L. Wu, "Localization and its Absence: A New Metallic State for Conducting Polymers,'' Science 252 1805-1812 (1991).
Honors and awards
- General Councilor, American Physical Society
- Bliss Faculty Scholar, University of Illinois College of Engineering, 2005
- University Scholar, 2003
- Fellow, American Physical Society, 2002
- Edward A. Bouchet Award of the American Physical Society, 2000
- Beckman Associate, Center for Advanced Study, 1999
- Senior Xerox Faculty Research Award, University of Illinois College of Engineering, 1998
- Miller Postdoctoral Fellowship, University of California at Berkeley, 1981-1984
