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Exact diagonalization RIXS studies of the doped 1d t1t2J model at the O KedgePrice, Gregory; Department of Chemistry & Physics; Datta, Trinanjan; Augusta University (20190213)Resonant inelastic xray scattering (RIXS) is a novel spectroscopic method for probing charge and spin excitations in quantum magnets. In one dimension, where quantum fluctuations are most prominent, a system of interacting electrons can support fractionalized spinless charge excitations (holons) and chargeless spin excitation (spinons). Currently, Xray spectroscopic techniques such as RIXS can excite the O Kedge core electrons of correlated quantum magnets to probe the physical nature of the above mentioned spincharge separated state. Using exact diagonalization we investigate the O Kedge RIXS response of the one dimensional antiferromagnetic spin chain compound with nearest and nextnearest neighbor hoppings. We also study the spinanisotropic version of the same model. Interaction of the core electrons with the Xrays generate multispinon excitations in the RIXS spectrum, for example in strontium copper oxide. We find that the RIXS spectrum of the t1t2J model with spin anisotropy presents a rich source of physical information, including allowing us to identify microscopic pathways for how the quantum spin fluctuations control the appearance of the four spinon excitations observed in the isotropic O Kedge spectrum.

Investigating the Effects of Magnetic Interaction on the Indirect Rixs Peak LocationStiwinter, Kenneth; Datta, Trinanjan; Department of Chemistry & Physics (201703)Resonant Inelastic Xray 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 nextnearest neighbor interaction on the multiple peak location of the bimagnon RIXS spectrum. Utilizing a Green function approach within the BetheSalpeter 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 nonlinear (quadratic, cubic, or exponential) dependence on eta for a fixed zeta.

A MATLAB GUI to study Ising model phase transitionThornton, CurtisLee; Datta, Trinanjan; Department of Chemistry and Physics (20160314)We have created a MATLAB based graphical user interface (GUI) that simulates the single spin flip Metropolis Monte Carlo algorithm. The GUI has the capability to study temperature and external magnetic field dependence of magnetization, susceptibility, and equilibration behavior of the nearestneighbor square lattice Ising model. Since the Ising model is a canonical system to study phase transition, the GUI can be used both for teaching and research purposes. The presence of a Monte Carlo code in a GUI format allows easy visualization of the simulation in real time and provides an attractive way to teach the concept of thermal phase transition and critical phenomena. We will also discuss the GUI implementation to study phase transition in a classical spin ice model on the pyrochlore lattice.

Spin wave Feynman diagram vertex computation packagePrice, Alexander; Javernick, Philip; Datta, Trinanjan; Department of Chemistry and Physics (20160314)Spin wave theory is a wellestablished 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 noncommutative algebra package NCAlgebra as an addon to Mathematica, symbolic expressions for the Feynman diagram vertices of a Heisenberg quantum antiferromagnet are obtained. Our existing code reproduces the wellknown 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.

Transport properties in Graphene BilayerTrowel, Alonte; Department of Chemistry & Physics; Datta, Trinanjan; Augusta University (20190213)Graphene is a single layer of carbon atoms arranged in a hexagonal pattern. It has many potential technological applications and provides a testbed to verify fundamental concepts in physics. Using quantum mechanical transmission and reflection amplitudes we study the transport properties of bilayer graphene. For the parameter range that We explored we find that the transmission probability is controlled by the applied bias. We also outline how this approach can be utilized to study oligomers and oligoacenes.