Fundamentals on the Noncommutative Plane

We consider the addition of charged matter (``fundametals'') to noncommutative Yang-Mills theory and noncommutative QED, derive Feynman rules and tree-level potentials for them, and study the divergence structure of the theory. These particles behave very much as they do in the commutative theory, except that (1) they occupy bound-state wavefunctions which are essentially those of charged particles in magnetic fields, and (2) there is slight momentum nonconservation at vertices. There is no reduction in the degree of divergence of charged fermion loops like that which affects nonplanar noncommutative Yang-Mills diagrams.Comment: LaTeX, 25 pages, 8 figures; revised versio

Trends in ferromagnetism, hole localization, and acceptor level depth for Mn substitution in

We examine the intrinsic mechanism of ferromagnetism in dilute magnetic semiconductors by analyzing the trends in the electronic structure as the host is changed from GaN to GaP, GaAs and GaSb, keeping the transition metal impurity fixed. In contrast with earlier interpretations which depended on the host semiconductor, we found that a single mechanism is sufficient to explain the ferromagnetic stabilization energy for the entire series.Comment: 4 figures; To appear in Appl. Phys. Let

First-principles investigation of the assumptions underlying Model-Hamiltonian approaches to ferromagnetism of 3d impurities in III-V semiconductors

We use first-principle calculations for transition metal impurities V, Cr, Mn, Fe, Co and Ni in GaAs as well as Cr and Mn in GaN, GaP and GaSb to identify the basic features of the electronic structure of these systems. The microscopic details of the hole state such as the symmetry and the orbital character, as well as the nature of the coupling between the hole and the transition metal impurity are determined. This could help in the construction of model Hamiltonians to obtain a description of various properties beyond what current first-principle methods are capable of.Comment: 14 figure

Origin of room-temperature ferromagnetism in Mn doped semiconducting CdGeP2

CdGeP2 chalcopyrites doped with Mn have been recently found to exhibit room temperature ferromagnetism. Isovalent substitution of the Cd site is expected, however, to create antiferromagnetism, in analogy with the well-known CdTe:Mn (d^5) case. However, chalcopyrite semiconductors exhibit low-energy intrinsic defects. We show theoretically how ferromagnetism results from the interaction of Mn with hole-producing intrinsic defects.Comment: 4 pages, 4 figures. (To appear in Phys. Rev. Lett.