A Collaborative Project of theoretical/computational research on strongly coupled plasmas will be continued by Boston College (BC; Dr. Gabor J. Kalman, Principal Investigator) and the University of Vermont (UVM; Dr. Kenneth I. Golden, Principal Investigator).
The coupling strength of a plasma is characterized by the ratio of the average Coulomb interaction energy to the average kinetic energy. The plasma is considered to be strongly coupled when this ratio is exceeds unity to the extent that the collection of charged particles is in the liquid or solid phase, exotic states of matter that are in marked contrast to the traditional gaseous plasmas studied in Tokamak fusion devices and space physics. Strong Coulomb interactions are exhibited by a variety of fascinating classical and quantum plasma systems, e.g., layered charged-particle systems in semiconductor quantum wells, layered charged particles confined in cryogenic traps, astrophysical plasmas (giant planetary interiors, white dwarf interiors, the outer crusts of neutron stars, etc.), and laboratory dusty plasmas.
The collaborative UVM/BC Project addresses issues central to the physics of strongly coupled plasma dynamics. Two general objectives for continued progress in this field are set forth. The first objective is to continue building up the theoretical framework for the description of the dynamics of strongly coupled plasma liquids. The second objective is the application of this understanding, gained in the study of strongly coupled plasmas, to novel physical systems that are in the forefront of condensed matter physics research. It is now recognized that the various guises of the quantum Coulomb liquid in semiconductors exhibit behavior that is to be understood within the framework of strongly coupled plasma dynamics while also presenting some unique ramifications of the original issues (formation of dipoles, ultra-relativistic-like behavior of graphene electrons, etc). The analysis of the collective modes (natural frequencies) and response functions pertaining to these novel semiconductor plasmas is the second main objective of the Project.
The proposed research, with its first-principles microscopic and simulation approaches to the determination of the dynamic properties of a wide variety of strongly coupled Coulomb systems, will substantially add to the fundamental knowledge base of plasma and condensed matter physics. This research will continue to provide new insights into the borderline area between these two disciplines by highlighting the similarity of the underlying physics that governs the behavior of plasma and condensed matter systems. The experiments that can be carried out along the predictions of this research can come from either discipline and are expected to be relevant to both.
The research program will continue to promote the teaching and training of participating undergraduate and graduate students at both academic institutions. It will also continue to provide cutting edge research and learning opportunities to scientists (including postdoctoral and graduate students) at foreign institutions (the Research Institute of Solid State Physics and Optics of the Hungarian Academy of Sciences; Polytechnic University of Valencia). The results of this research will continue to be presented at international conferences (such as the 2002, 2005, 2008 Strongly Coupled Coulomb Systems Conferences) and disseminated to the public through the major outreach efforts made by the conference organizers
The University of Vermont/Boston College (UVM/BC) collaborative Project addresses issues that are central to the physics of strongly coupled plasma dynamics. Two objectives have been set forth. The first was to further develop analytical/computational methods for the analysis of the dynamics of strongly coupled Coulomb and Coulomb-like liquids and solids. The second objective was the application of these methods to novel physical systems that are in the forefront of plasma/condensed matter physics: (i) charged-particle bilayers; (ii) the two-dimensional point dipole system; (iii) binary Coulomb and Yukawa systems. SIGNIFICANT OUTCOMES Charged-particle bilayers: The experiment [Publication 4] initiated by our long-time colleagues at the Institute of Solid State Physics and Optics of the Hungarian Academy of Sciences is the first laboratory observation of the collective mode spectrum of a charged-particle bilayer in its strongly coupled liquid or solid phase. The experiment verified the existence of the long-wavelength finite-frequency gap in the out-of-phase mode, theoretically predicted by the UVM/BC team some time ago [Physical Review Letters 82, 5293 (1999)]. We have established a comprehensive description of the long-wavelength mode dispersions in the electron-hole bilayer (EHB) in its Coulomb and dipole liquid phases [Publication 8]. Two-dimensional dipole system (2DDS): This model system, which emulates the closely spaced EHB, opens up a new avenue of research on bosonic superfluids. Publication [1] reports a remarkable likeness between our classical MD-generated dispersion curve and the dispersion curve for the zero-temperature superfluid phase generated from the Feynman relation with the input of quantum Monte Carlo static structure function data [Astrakharchik et al, Physical Review Letters 98, 060405 (2007)]. This likeness suggests that the celebrated roton minimum has a classical origin rooted in the strong correlations prevailing in the system [Publications 5, 6, 9]. Binary Yukawa systems: We have analyzed the collective mode dispersion of strongly coupled binary Yukawa systems for selected density, mass, and charge ratios, both in the strongly coupled liquid and solid phases. Publication [7] addresses the acoustic dispersion, whereas Publication [11] provides a wealth of new information about the full mode dispersions. REFEREED JOURNAL PUBLICATIONS (GRANT PHY-0812956) [1] Golden, KI; Kalman, GJ; Donko, Z; Hartman, P, "Collective excitations in a two-dimensional dipole system, Journal of Physics A: Mathematical and Theoretical, p. 214017, vol. 42, (2009). [2] Hartmann, P; Kalman. GJ; Golden KI; Donko, Z, "Collective excitations in strongly coupled ulra-relativistic plasmas", Journal of Physics A: Mathematical and Theoretical, p. 214018, vol. 42, (2009). [3] Golden, KI; Kalman, GJ; Donko, Z; Hartmann, P, [Physical Review B 78, 045304 (228)], "Erratum: Acoustic dispersion in a two-dimensional dipole system", Physical Review B, p. 239905, vol. 78, (2008). [4] Hartmann, P; Donko, Z; Kalman, GJ; Kyrkos, S; Golden, KI; Rosenberg, M, "Collective dynamics of complex plasma bilayers", Physical Review Letters, p. 245002, vol. 103 (2009). [5] Kalman, GJ; Hartmann, P; Golden, KI; Filinov, A; Donko, Z, "Correlational origin of the roton minimum", Europhysics Letters, p. 55002, vol. 90, (2010). [6] Golden, KI; Kalman, GJ; Hartmann, P; Donko, Z, "Dynamics of two-dimensional dipole systems", Physical Review E, p. 036402, vol. 82 (2010). [7] Kalman, GJ; Donko, Z; Hartmann, P; Golden, KI, "Strong coupling effects in binary Yukawa systems", Physical Review Letters, p. 175003, vol. 107, (2011). [8] Golden, KI; Kalman, GJ; Hartmann, P; Donko, Z, "Collective modes in classical mass-asymmetric bilayers", Contributions to Plasma Physics,p. 130, vol. 52, (2012). [9] Kalman, GJ; Kyrkos, S; Golden, KI; Hartmann, P; Donko, Z, "The roton minimum: Is it a general feature of strongly correlated liquids?", Contributions to Plasma Physics, p. 219, vol. 52, (2012). [10] Kalman, GJ; Donko, Z; Hartmann, P; Golden, KI; Kyrkos, S, "Collective modes in strongly coupled binary liquids", Contributions to Plamsa Physics, p. 234, vol. 52, (2012). [11] Kalman, GJ; Hartmann, P; Donko, Z; Golden, KI; Kyrkos, S, "Collective modes in two-dimensional binary Yukawa systems, Physical Review E, p. 043103, vol. 87, (2013). Intellectual merit of the outcomes: This Project has been pursuing a unique line of research in the area of strongly coupled plasma physics. The combination of analytic and advanced simulations methods has proved to be a cutting edge approach to the study of dynamics of many-body systems. The Principal Investigators have identified novel and entirely unexplored areas of research. Thus, there are transformative aspects of this research, both in the methodology and in its applications. Broader impacts of the outcomes: The project on strongly coupled plasmas is relevant to a variety of physical systems, either because they consist of strongly interacting charged particles or because, in their dynamical behavior, they emulate such systems. The most prominent of these systems are dusty laboratory plasmas, ionic mixtures in white dwarf and giant planetary interiors, electron-electron and electron-hole bilayers in semiconductors, and bosonic superfluids such as liquid helium. Clearly, in addition to strongly coupled plasma physics, the Project will have impact on condensed matter physics and astrophysics.
