Research
Research projects for Students:
Are you interested in working on a semester or a summer project? Please contact me.There are projects available both at the undergraduate and the graduate level.
No specialized knoweldge is required but enthusiasm and engagement are expected.
Fundings:
We are grateful to the following institutions for the support of our research:- National Science Foundation,
- Army High Performance Computing Research Center,
- Research Corporation,
- German Academic Exchange Services (DAAD),
- SCAC at CSU Long Beach.
Current activities:
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Grain size distribution in crystallization processes
The micromorphology of solids impacts in an essential way their mechanical, electronic,
optical or magnetic properties. It is thus an important task to characterize
quantitatively the granularity and homogeneity of materials. This allows in particular the
determination or tailoring of their functionality. One of the major physical observables
describing the microstructure is the grain size distribution as a function of time during
the crystallization and treatment process of solids. We propose a theory that offers
an analytical expression for the grain size distribution during the crystallization of an
amorphous solid. The project further develops the theory by studying scaling properties of
our partial differential equation, and by generalizing the model to anisotropic growth rates
and shapes of the crystallites.
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A. Bill and R.B.Bergmann, Mater. Res. Soc. Symp. Proc. 1308, DD03-01 (2011); doi:10.1557/opl.2011.506
(PDF)
Invited paper at the Symposium on Artificially Induced Crystalline Alignment in Thin Films and Nanostructures. - K.S. Lokovic, R.B.Bergmann, A.Bill, Mater. Res. Soc. Symp. Proc. 1245, A16-07 (2010) (PDF)
- A.V.Teran, R.B.Bergmann, A.Bill, Phys. Rev. B 81, 075319 (2010); cond-mat/1003.0143 (PDF); The figure above has been chosen for the front page (Kaleidoscope) of the Phys.Rev.B website, February 2010. Clicking on the figure will bring you there.
- A.V.Teran, R.B.Bergmann, A.Bill, Mater. Res. Soc. Symp. Proc. 1153, A05-3 (2009) (PDF)
- R.B.Bergmann, A.Bill, J. Cryst. Growth 310, 3135 (2008), cond-mat/0807.0396 (PDF)
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A. Bill and R.B.Bergmann, Mater. Res. Soc. Symp. Proc. 1308, DD03-01 (2011); doi:10.1557/opl.2011.506
(PDF)
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Interplay between superconductivity and magnetism at the nanoscale
Conventional wisdom claims that superconductivity and magnetism are mutually exclusive states of matter. This view has been challenged in recent years by the discovery of novel materials and the tailoring of nanostructures where new states of matter and cohabitation are thought to be observed. Next to heavy fermions and high-temperature superconductors where the reciprocal action of superconductivity and magnetism remains an intriguing phenomenon, ferromagnetic superconductors have been discovered. Artificially tailored multilayers with thicknesses at the nanoscale have also been predicted and found to display unusual ground states resulting from the interplay between superconductivity and ferromagnetism. The aim of the project is to study phase coexistence in the presence of inhomogeneities in the ferromagnet. Both fundamental properties of the ground state and envisioned electronic- and spintronics devices are investigated.In the context of this project we have studied and solved exactly analytically a 200 year old problem of classical mechanics: The Bead on the Hoop. This system has been used by James Watt to regulate the intake of heat into a steam engine. The mathematics used to describe all possible motions of the bead on a rotating hoop is also applicable to a variety of other physical systems outside the field of classical mechanics. Our findings are published as a featured article in the American Journal of Physics: Am.J.Phys. 80, 506 (2012); arXiv:1201.4201.
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Electronic properties of graphene multilayers
Graphene, a single layer of carbon atoms arranged on the nodes of a honeycomb lattice, has recently be singled out both on a substrate and in suspended form. Graphene is the basic constituent of graphite used in your pencils and other applications. This two-dimensional solid has surprising properties. It is a low-dimensional gapless semiconductor with linear bands near the Fermi energy. External perturbations such as a magnetic or electric field, impurities affect this system in ways that depart drastically from the behaviour of conventional metals and semiconductors. As one stacks graphene sheets, properties change until they reach those of the semi-metal graphite. In this project we investigate how electronic properties and size-quantization effects are affected by the stacking.
Further Topics:
These are topics I worked on in the past and keep interest for.- Collective excitations in layered superconductors,
- Magnetic Multilayers (exchange springs, exchange bias, etc.),
- Magnetic coherence effect and resonance in high-Tc superconductors,
- Isotope Effect in superconductors,
- Recovery of superconductivity due to magnetic impurity correlations,
- Long-range interactions and superconductivity,
- Phonon renormalization and order parameter anisotropy in unconventional superconductors.
- Intercalated superconductors : superconductivity in molecular crystals (fullerides, etc.).
New Developments in Physics:
The following site is one of several that displays novelties in Physics. It is by far not covering all interesting work in Physics, but it is a start to have an idea what is attracting attention in research presently. Enjoy the reading by clicking on the logo below!
