In this dissertation, I present experimental investigations on two materials of interest to the condensed matter community: the antiferromagnetic properties of Y2Co3 and the superconductivity and normal state properties of LaNiGa2. Both studies involve the development of single crystal growth methods and bulk magnetic and physical transport property measurements and analysis.The interest in Y2Co3 originates from its relatively high Néel temperature among the Co-based antiferromagnetic compounds, despite its high cobalt content. I developed, for the first time, the single-crystal growth method and reported its crystal structure belongs to the Cmce (No. 64) orthorhombic space group. The magnetic structure was also determined for the first time with single-crystal neutron diffraction to be an A-type antiferromagnet with almost collinear magnetic moments alignment, despite a seemingly non-collinear behavior observed in bulk magnetization measurements. Such discrepancy is attributed to the considerable temperature dependence of itinerant antiferromagnetic (AFM) exchange interactions, induced by thermal contraction along the b axis. Pressure study and high-field study revealed robust AMF ordering due to the compensating effect of lattice contraction on the ferromagnetic and AMF interactions. The high-field study revealed a spin-flop phase transition, offering further insight into the magnetocrystalline anisotropy.LaNiGa2 has attracted attention due to the evidence of time-reversal symmetry breaking in the superconducting state, alongside symmetry-enforced Dirac band crossings and anomalous pressure-dependent superconducting transition temperature. In this dissertation, I present a summary of the superconducting gap structure discussion based on recent works by our collaborators using our single-crystal samples, as well as the pressure studies. Furthermore, I discuss the normal state properties based on magnetization measurement and physical transport property measurement. The magnetization measurement indicates weak electron-electron interactions, making them unlikely to play a role in the unusual superconducting pairing. Transport measurements demonstrate multi-band behavior with both electron and hole carriers. The carrier densities remain nearly constant across the measured temperature range, with no evidence of sudden changes that might suggest electronic phase transitions. In particular, the magnetoresistance exhibits quadratic to linear field dependence, which deviates from conventional semiclassical transport behavior. Possible explanations including quantum transport effects resulting from small Fermi surface pockets and impeded circular motions are discussed. 

LaNiGa2 is superconductor that has been shown to break time-reversal symmetry in the superconducting state without any known nearby magnetism. Recently, single crystals of LaNiGa2 have been synthesized, revealing a nonsymmorphic Cmcm space group. Here, we report on measurements of the electronic structure of LaNiGa2 throughout the three-dimensional Brillouin zone (BZ) using angle-resolved photoemission spectroscopy. Our findings show broad consistency with density functional theory calculations and provide evidence for degeneracies in the electronic structure that are predicted from the space group symmetry. We report evidence for those predicted symmetry-enforced degeneracies as well as accidental near degeneracies throughout the BZ. These degeneracies and near degeneracies may play a role in the pairing mechanism of LaNiGa2. Our results provide insight into the interplay between structure, fermiology, and superconductivity in unconventional superconductors with nonsymmorphic space group.

1D organic metal halide hybrids (OMHHs) exhibit strongly anisotropic optical properties, highly efficient light emission, and large Stokes shift, holding promise for novel photodetection and lighting applications. However, the fundamental mechanisms governing their unique optical properties and in particular the impacts of surface effects are not understood. Herein, 1D C4N2H14PbBr4 by polarization-dependent time-averaged and time-resolved photoluminescence (TRPL) spectroscopy, as a function of photoexcitation energy, is investigated. Surprisingly, it is found that the emission under photoexcitation polarized parallel to the 1D metal halide chains can be either stronger or weaker than that under perpendicular polarization, depending on the excitation energy. The excitation-energy-dependent anisotropic emission is attributed to fast surface recombination, supported by first-principles calculations of optical absorption in this material. The fast surface recombination is directly confirmed by TRPL measurements, when the excitation is polarized parallel to the chains. The comprehensive studies provide a more complete picture for a deeper understanding of the optical anisotropy in 1D OMHHs.