Current Interests: First order phase transitions
To some extent first-order phase transitions, that is transitions where there are discontinuities (latent heat and jumps in density or volume) have been the poor cousins of continuous transitions (where there are no such jumps) when it comes to numerical investigations, in spite of their prevalence in nature. There are various reasons for this - they are harder to simulate, for instance, and there appear to be fewer distinct quantities to measure for the first order transitions compared with continuous transitions.
Recent research work along with Marco Mueller and Wolfhard Janke of Leipzig University has concentrated on several aspects of such first order transitions, in particular non-standard scaling behaviour at first order transitions when the low temperature phases are highly degenerate. As luck would have it, an old favorite - the Gonihedric Ising model - provides an example of this.
Collaborations with colleagues at Coventry University and a visitor from Sri Lanka, R.P.K.C.M. Ranasinghe, have also investigated the phase transitions of Potts models with so-called invisible states, which display unexpected first order transitions, clarifying why they occur.
(Fairly) recent papers:
- D. A. Johnston, M. Mueller and W. Janke, Plaquette Ising models, degeneracy and scaling, Eur. Phys. J. Special Topics,
226, Issue 4, 749–764 (2017)
- M. Mueller, W. Janke and D. A. Johnston, Exact solutions to plaquette Ising models with free and periodic boundaries, Nucl. Phys. B 914, 388-404 (2017)
- M. Mueller, W. Janke and D. A. Johnston, Macroscopic Degeneracy and Order in the 3d Plaquette Ising Model, MPLB Vol. 29 1550109 (2015)
- M. Mueller, W. Janke and D. A. Johnston, Planar ordering in the plaquette-only gonihedric Ising model, Nucl. Phys. B894, 1-14 (2015), [arxiv:1412.4426]
- M. Mueller, W. Janke and D. A. Johnston, Transmuted Finite-Size Scaling at First Order Phase Transitions, Physics Procedia Vol. 57, 68-72 (2014), [arxiv:1410.7928]
- D. A. Johnston, ℤ2 lattice gerbe theory,
Phys. Rev. D 90, 107701 (2014), [arXiv:1405.7890]
- M. Mueller, W. Janke and D. A. Johnston, Multicanonical analysis of the plaquette-only gonihedric Ising model and its dual, Nucl. Phys. B888, 214-235 (2014), [arXiv:1407.7252]
- M. Mueller, W. Janke and D. A. Johnston, Nonstandard Finite-Size Scaling at First Order Phase Transitions, Phys. Rev. Lett. 112, 200601 (2014), [arxiv 1312.5984]