So-Young Pi

Materials Design from Nonequilibrium Steady States: Driven Graphene as a Tunable Semiconductor with Topological Properties

Controlling the properties of materials by driving them out of equilibrium is an exciting prospect that has only recently begun to be explored. In this Letter we give a striking theoretical example of such materials design: a tunable gap in monolayer graphene is generated by exciting a particular optical phonon. We show that the system reaches a steady state whose transport properties are the same as if the system had a static electronic gap, controllable by the driving amplitude. Moreover, the steady state displays topological phenomena: there are chiral edge currents, which circulate a fractional charge e/2 per rotation cycle, with the frequency set by the optical phonon frequency.

Point splitting regularization in a supersymmetric gauge field theory

Abstract Point splitting regularization is discussed in a supersymmetric Yang-Mills field theory. A supersymmetry and gauge invariant point-split supercurrent operator, along with the point-split lagrangian density, is constructed. A superconformal anomaly is computed.

The phase structure of the early universe in the minimal SU(5) grand unified theory

Abstract Using the most general, gauge invariant and renormalizable Higgs potential which avoids domain walls, we study the possible phases that can appear at high temperatures in the minimal SU(5) grand unified theory. We emphasize the important role of the fundamental representation of Higgs field for the phase structure at temperatures of 10 14 GeV.

Suppression of superheavy magnetic monopoles in grand unified theories

The superheavy magnetic monopoles predicted by grand unified theories would not be produced in significant numbers if electromagnetic gauge invariance is spontaneously broken when the temperature T is greater than Tc≳1 TeV.