Roger Haydock's research interests center on electronic structure, interatomic forces, and electronic processes in solids. The most challenging problems in this area concern surfaces, defects, alloys, and glasses.
His work on surfaces began with the discovery that electronic energy bands narrow at surfaces, an effect that was later observed in photoemission and helps to explain variations in the chemical reactivity of surfaces. This led to a theory of surface photoemission which takes the surface electronic structure into account explicitly. Nickel surfaces were studied in a series of calculations which elucidated charge transfer and the nature of oxygen chemisorption, leading to an explanation of oxygen overlayer structures on nickel. Another aspect of this is a theory of field evaporation from metals, which demonstrated that multiply-charged ions were produced by field ionization after evaporation. Recent work on surfaces includes an investigation of chemical reactivity near metals, and suggestions of mechanisms producing grain boundary embrittlement by impurities. The forces between helium atoms and metal surfaces were shown to involve significant effects of hybridization and image potentials. Recent projects include the effect of impurity atoms on surface plasticity, second harmonic generation of light from metal surfaces, and a study of surface tunnelling states.
Another theme of this research is structural phase stability of pure materials, compounds, and alloys. This began with a theory of the structural variations across the three rows of the transition series and went on to calculations of the structures of the Laves phases of transition metal compounds. Study of the formation of magnetic moments at iron sites in various compounds has led to theories of iron magnetism near the Curie temperature.
The effects of disorder in solids has fascinated physicists for over thirty years. A series of calculations of electronic states in random alloys has contributed to understanding electronic phase transitions which take place in various semiconductor structures at low temperatures. These ideas have also been applied to the formation of metal contacts on semiconductor surfaces. Recent work in this area has led to approximate conservation laws for electrons in covalent glasses and a related classification scheme for the structure of these materials.
Along side the work on specific systems, general mathematical methods have been developed for condensed matter theory. The main one is the recursion method, a way of calculating the quantum mechanical motion of electrons in complicated crystals, near defects and surfaces, or in random solids. Numerical versions of these methods have been implemented in the Recursion Library, which is used by research groups all over the world. Another version of this library has been developed specifically for the calculation of electronic characteristics of small devices. Current projects are to extend and optimize the Recursion Library for scalably parallel computers, to calculate the correlated electronic structure of transition metal oxides, and to develop methods for rapid calculation of the multidimensional integrals needed in many electronic structure calculations.
Consulting work includes the development of numerical methods for calculating electronic structure and the investigation of electronic states in disordered materials at the Xerox Palo Alto Research Center, and evaluation of switching phenomena for optical computing at the Lockheed Space and Missile Company, Inc. Professor Haydock is a regular visitor at the Cavendish Laboratory in Cambridge UK and at the International Centre for Theoretical Physics in Trieste, Italy
Papers and Research Links
Tight-Binding Energy Functionals (postscript file)
Phys. Rev. B 61, 7953 (2000)
Phys. Rev. E 59(5) 5292 (1999)
Numerical Evidence of an Electronic Localization Transition in a Disordered Layer of Metal Atoms published version Phys. Rev. B 57, p. 1.
Liouvillian Dynamics for Materials Simulation
Wolfram Arnold's Research Page and the Parallel Recursion Project
Vector continued fractions using a generalized inverse J. Phys. A: Math. Gen. 37 (2004) 161-172
Phase diagram for Anderson disorder: Beyond single-parameter scaling Phys. Rev. B 73, 045118 (2006)
Analytic trajectories for mobility edges in the Anderson model Phys. Rev. B 66, 155121 (2002)
Densities of states, moments, and maximally broken time-reversal symmetry Phys. Rev. B 74, 205121 (2006)