Oleg Tchernyshyov
Biographical sketch.Complete list of publications.
Geometrically frustrated magnets.
Research
I am a theorist working in the field of condensed matter. The main theme of my research is materials with strong correlations between electrons. This signifies physical systems whose state at low temperatures does not reduce to a simple Bose or Fermi liquid. A well understood strongly correlated system is the two-dimensional electron gas in magnetic field exhibiting the integer and fractional quantum Hall effects. Cuprate superconductors exhibit some strange behavior and are therefore also considered to be in this class.Most recently I have been working with frustrated magnets. These are spin systems with lots of conflicting interactions. The inability of the magnet to find a unique configuration minimizing the energy destroys magnetic order and sets the stage for a strongly correlated state. The ultimate example of such behavior is the Heisenberg antiferromagnet on the "pyrochlore" lattice realized in a series of spinels (e.g. ZnCr2O4). This magnet stays disordered down to very low temperatures (12 K). The spins remain liquid. However, unlike in a paramagnet at high temperatures, where spins fluctuate independently from one another, the spins in ZnCr2O4 move in a highly correlated fashion: in groups of six.
I am also a member of the Materials Research Science and Engineering Center (MRSEC) at Johns Hopkins. In collaboration with the group of C.L. Chien, I study topological defects in nanosized magnets. It turns out that the behavior of really small (submicron) magnets can duffer drastically from their conventionally-sized counterparts. Together with Gia-Wei Chern, we showed that domain walls in thin and narrow magnetic strips are composite objects made from integer and fractional vortices. Topological considerations place rather severe constraints on the structure of such domain walls. See this paper for more details.
A halfvortex near the edge of a magnetic film.
This image from our recent paper appeared in the May 2007 Kaleidoscope of Physical Review B. It shows magnetic stripes in a nanosized ferromagnetic disk separated by Bloch-type domain walls. In red and blue regions magnetization field M points into and out of the plane of the figure, respectively. Arrows show the in-plane direction of magnetization. A pair of half-skyrmions (merons) can be seen on two of the domain walls.
Featured articles:
- O. A. Tretiakov, D. Clarke, G.-W. Chern, Ya. B. Bazaliy, and O. Tchernyshyov, Dynamics of domain walls in magnetic nanostrips, Phys. Rev. Lett. 100, 127204 (2008); arXiv:0705.4463. Featured in the April 14, 2008, issue of VJNano.
- M. B. Stone, C. Broholm, D. H. Reich, P. Schiffer, O.
Tchernyshyov, P.
Vorderwisch, and N. Harrison, Field-driven
phase transitions in a quasi-two-dimensional quantum antiferromagnet,
New J. Phys 9, 31 (2007); cond-mat/0611463.
Featured in IOP Select.
- O. A. Tretiakov and O. Tchernyshyov, Vortices in thin ferromagnetic films and the skyrmion number, Phys. Rev. B 75, 012408 (2007); cond-mat/0611392. Featured in the February 5, 2007, issue of VJNano.
- A. Concha, J. W. McIver III, P. Mellado, D. Clarke, O. Tchernyshyov, and R. L. Leheny, Wrinkling of a bilayer membrane, Phys. Rev. E 75, 016609 (2007); cond-mat/0611507. Featured in the February 1, 2007, issue of VJBio.
- O. Tchernyshyov and G.-W. Chern, Fractional vortices and composite domain walls in flat nanomagnets, Phys. Rev. Lett. 95, 197204 (2005); cond-mat/0506744. Featured in the November 14, 2005, issue of VJNano.
- O. Tchernyshyov, R. Moessner, and S.L. Sondhi, Order by distortion and string modes in
pyrochlore antiferromagnet, Phys. Rev.
Lett. 88, 067203 (2002); cond-mat/0108505.
Featured in the February
2002 issue of Nature Physics Research Highlights.
Teaching
I have taught a number of courses in physics, both at the undergraduate and graduate levels. Here are some of the course web pages:- Condensed
Matter Physics I (171.621).
- Statistical Mechanics I (171.703).
- Introduction to Classical Physics I (171.105).
- Advanced
Statistical Mechanics II (171.704).
Jeff Wasserman and I have developed numerical simulations for classroom and homework use. Visit our Javalab to learn more. This project is sponsored by the Technology Fellowship Program at the JHU Center for Educational Resources and by the National Science Foundation.