Polarization Dependent Angle Resolved Photoemission Spectroscopy for the Determination of Intrinsic Material Symmetries

In this thesis I investigate the utility of the polarization and angle dependence of the photoemission matrix element in angle resolved photoemission spectroscopy (ARPES). This technique is capable of determining internal symmetries of the electronic wave functions in crystalline solids and has been historically underutilized in the ARPES community. In Chapter 1, I introduce the ARPES technique, the established theory and models behind it, and the experimental considerations in performing the technique. It is my personal belief that the fastest way to build intuition for complex physical phenomena is through simulation, and a good portion of graduate school career was spent developing simulation toolkits for the photoemission process. This work will be covered in detail in chapter 2. The later chapters cover the application of this technique to various materials systems. Chapter 3 focuses on the use of this technique to observe a topological phase transition in the Lanthanum Monopnictides. Chapter 4 contains my work on the Cuprate high temperature superconductors, Bi2Sr2Ca1Cu2O8+x and La2-xSrxCuO2 and the use of tight binding simulations to approximate the single particle wave function in this material.</p

Author Correction: Fermiology and electron dynamics of trilayer nickelate La4Ni3O10.

The original version of this Article contained errors in Fig.&nbsp;2, Fig.&nbsp;3a-c and Supplementary Fig.&nbsp;2. In Fig.&nbsp;2g and Supplementary Fig.&nbsp;2, the band structure plot calculated from density function theory (DFT) had a missing band of mainly z2 character that starts at about - 0.25 eV at the Y point and disperses downwards towards the Γ point. This band was inadvertently neglected when transferring the lines from the original band plot to the enhanced version for publication. Also in Fig.&nbsp;2g, the points labelled M and Y were not exactly at (1/2 1/2 0) and (0 1/2 0), but rather (0.52 0.48 0) and (0 0.48 0) due to a bug in XCrysDen for low-symmetry structures that the authors failed to identify before publication. Thus, the bands presented were slightly off the true M-Y direction and additional splitting incorrectly appeared (in particular for the highly dispersive bands of x2-y2 character). The correct versions of Fig.&nbsp;2g&nbsp;(cited as Fig. 1) and Supplementary Fig.&nbsp;2&nbsp;(cited as Fig. 2) are:which replaces the previous incorrect version, cited here as Fig. 3 and Fig. 4:Neither of these errors in Fig.&nbsp;2g or Supplementary Fig.&nbsp;2 affects either the discussion or any of the interpretations of the ARPES data provided in the paper. The authors discussed the multilayer band splitting along the Γ-M direction (δ band and α band as assigned in the paper), and ARPES did not see any split band. The authors did not discuss the further splitting that arises due to back folding along the M-Y direction.In Fig.&nbsp;3a-c, the errors in the M and Y points in Fig.&nbsp;2g cause subtle changes to the DFT dispersions. The correct version of Fig.&nbsp;3a-c is&nbsp;cited here as Fig 5:which replaces the previous incorrect version&nbsp;(Fig. 6):However, the influence on the effective mass results of Fig.&nbsp;3d is negligible.These errors have now been corrected in both the PDF and HTML versions of the Article. The authors acknowledge James Rondinelli and Danilo Puggioni from Northwestern University for calling our attention to these issues

Author Correction: Fermiology and electron dynamics of trilayer nickelate La4Ni3O10.

The original version of this Article contained errors in Fig.&nbsp;2, Fig.&nbsp;3a-c and Supplementary Fig.&nbsp;2. In Fig.&nbsp;2g and Supplementary Fig.&nbsp;2, the band structure plot calculated from density function theory (DFT) had a missing band of mainly z2 character that starts at about - 0.25 eV at the Y point and disperses downwards towards the Γ point. This band was inadvertently neglected when transferring the lines from the original band plot to the enhanced version for publication. Also in Fig.&nbsp;2g, the points labelled M and Y were not exactly at (1/2 1/2 0) and (0 1/2 0), but rather (0.52 0.48 0) and (0 0.48 0) due to a bug in XCrysDen for low-symmetry structures that the authors failed to identify before publication. Thus, the bands presented were slightly off the true M-Y direction and additional splitting incorrectly appeared (in particular for the highly dispersive bands of x2-y2 character). The correct versions of Fig.&nbsp;2g&nbsp;(cited as Fig. 1) and Supplementary Fig.&nbsp;2&nbsp;(cited as Fig. 2) are:which replaces the previous incorrect version, cited here as Fig. 3 and Fig. 4:Neither of these errors in Fig.&nbsp;2g or Supplementary Fig.&nbsp;2 affects either the discussion or any of the interpretations of the ARPES data provided in the paper. The authors discussed the multilayer band splitting along the Γ-M direction (δ band and α band as assigned in the paper), and ARPES did not see any split band. The authors did not discuss the further splitting that arises due to back folding along the M-Y direction.In Fig.&nbsp;3a-c, the errors in the M and Y points in Fig.&nbsp;2g cause subtle changes to the DFT dispersions. The correct version of Fig.&nbsp;3a-c is&nbsp;cited here as Fig 5:which replaces the previous incorrect version&nbsp;(Fig. 6):However, the influence on the effective mass results of Fig.&nbsp;3d is negligible.These errors have now been corrected in both the PDF and HTML versions of the Article. The authors acknowledge James Rondinelli and Danilo Puggioni from Northwestern University for calling our attention to these issues

Fermiology and electron dynamics of trilayer nickelate La4Ni3O10

Exploration of the electronic structure of nickelates with similar crystal structure to cuprates may shed a light on the origin of high T c superconductivity. Here, Li et al. report strong resemblances and key differences of the electronic structure of trilayer nickelate La4Ni3O10 compared to the cuprate superconductors

Development of a Large Scale Asymmetric Synthesis of the Glucocorticoid Agonist BI 653048 BS H₃PO₄

The development of a large scale synthesis of the glucocorticoid agonist BI 653048 BS H₃PO₄ (<b>1·H</b>_<b>3</b><b>PO</b>_<b>4</b>) is presented. A key trifluoromethyl ketone intermediate <b>22</b> containing an <i>N</i>-(4-methoxyphenyl)­ethyl amide was prepared by an enolization/bromine–magnesium exchange/electrophile trapping reaction. A nonselective propargylation of trifluoromethyl ketone <b>22</b> gave the desired diastereomer in 32% yield and with dr = 98:2 from a 1:1 diastereomeric mixture after crystallization. Subsequently, an asymmetric propargylation was developed which provided the desired diastereomer in 4:1 diastereoselectivity and 75% yield with dr = 99:1 after crystallization. The azaindole moiety was efficiently installed by a one-pot cross coupling/indolization reaction. An efficient deprotection of the 4-methoxyphenethyl group was developed using H₃PO₄/anisole to produce the anisole solvate of the API in high yield and purity. The final form, a phosphoric acid cocrystal, was produced in high yield and purity and with consistent control of particle size

Process Development of the BACE Inhibitors BI 1147560 BS and BI 1181181 MZ

The development of large-scale syntheses of two beta-site amyloid precursor protein cleaving enzyme (BACE) inhibitors is described. New methodologies were discovered to overcome safety and scalability problems with existing procedures. The sterically hindered quaternary, neopentyl stereocenter was formed in high diastereoselectivity by the addition of a carbamoyl anion to an N-sulfinyl ketimine. An aryl nitrile was installed by a palladium- and cyanide-free electrophilic cyanation affected by transnitrilation of an arylmagnesium derivative with dimethylmalononitrile. A safe route to an oxetanylmethylamine side chain was devised based on diethyl malonate and dibenzylamine starting materials. A mild enamine fluorination was developed for the synthesis of a fluoroisobutylamine side chain