• Investigating the Effects of Magnetic Interaction on the Indirect Rixs Peak Location

      Stiwinter, Kenneth; Datta, Trinanjan; Department of Chemistry & Physics (2017-03)
      Resonant Inelastic X-ray scattering (RIXS) is a novel experimental technique to characterize the properties of magnetic materials. The goal of this research is to theoretically investigate the effect of spatial anisotropy and next-nearest neighbor interaction on the multiple peak location of the bimagnon RIXS spectrum. Utilizing a Green function approach within the Bethe-Salpeter scheme we wrote a python code to simulate the indirect RIXS spectrum. Using a spin wave theory magnetization phase diagram and the associated spatial anisotropy parameter (zeta) and next nearest neighbor interaction parameter (eta) we notice that the RIXS spectrum can develop multiple peaks. By fitting the location of the peaks we observe that a pattern emerges in how these peaks are affected by interaction. In the vast majority of the parameter space the peak of a fixed zeta with increasing eta combination shifts downward in frequency with each consecutive increase in eta. However, there are a couple of parameters where an upshift was observed. Based on our fits of the peak location we conclude that the pattern follows a non-linear (quadratic, cubic, or exponential) dependence on eta for a fixed zeta.
    • Spin wave Feynman diagram vertex computation package

      Price, Alexander; Javernick, Philip; Datta, Trinanjan; Department of Chemistry and Physics (2016-03-14)
      Spin wave theory is a well-established theoretical technique that can correctly predict the physical behavior of ordered magnetic states. However, computing the effects of an interacting spin wave theory incorporating magnons involve a laborious by hand derivation of Feynman diagram vertices. The process is tedious and time consuming. Hence, to improve productivity and have another means to check the analytical calculations, we have devised a Feynman Diagram Vertex Computation package. In this talk, we will describe our research group’s effort to implement a Mathematica based symbolic Feynman diagram vertex computation package that computes spin wave vertices. Utilizing the non-commutative algebra package NCAlgebra as an add-on to Mathematica, symbolic expressions for the Feynman diagram vertices of a Heisenberg quantum antiferromagnet are obtained. Our existing code reproduces the well-known expressions of a nearest neighbor square lattice Heisenberg model. We also discuss the case of a triangular lattice Heisenberg model where non collinear terms contribute to the vertex interactions.
    • Studying Quantum Magnets Using Ineracting Spin Wave Theory

      Mongan, Mongan; Department of Chemistry & Physics (2017-03)
      A magnon is a quantized magnetic excitation hosted in a condensed matter state caused by deviations of the electron spin. Quantum fluctuations of the magnetic wave results in a quantized spin wave. Using spin wave theory we present a derivation of the interaction that describes magnons in a 3D ferromagnetic crystal lattice and a 2D antiferromagnetic crystal. We use both the Holstein-Primakoff and Dyson-Maleev bosonization transformation scheme. As in the literature, we find higher order interaction terms within the Hamiltonian. We present a derivation of these interaction terms and subsequent representation from a Feynman diagram approach.