skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 5:00 PM ET until 11:00 PM ET on Friday, June 21 due to maintenance. We apologize for the inconvenience.

Search for: All records

Creators/Authors contains: "Kumah, Divine P."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Free, publicly-accessible full text available August 9, 2024
  2. Abstract

    The structural and transport properties of vacancy‐ordered monoclinic superconducting titanium oxide (TiO) thin films grown by molecular beam epitaxy are investigated. The evolution of the crystal structure during growth is monitored by in situ synchrotron X‐ray diffraction. Long‐range ordering of Ti and O vacancies in the disordered cubic phase stabilizes the vacancy‐ordered monoclinic TiO phase. The reduced structural disorder arising from vacancy‐ordering is correlated with a superconductor‐metal transition (SMT) in contrast to the superconductor‐insulator transition (SIT) observed in cubic TiO, orthorhombicTi2O3, and the Magneli γ −Ti3O5and γ −Ti4O7phase. Magnetoresistance measurements for the SIT phases indicate superconducting fluctuations persisting in the normal phase. These results confirm the role of disorder related to Ti and O vacancies and structural inhomogeneity in determining the electronic properties of the normal state of titanium oxide‐based superconductors.

    more » « less
  3. Revealing anisotropic nature of 2D superconductivity in the context of electronic structure, orbital character, and spin texture. 
    more » « less
  4. The temperature-dependent layer-resolved structure of 3 to 44 unit cell thick SrRuO 3 (SRO) films grown on Nb-doped SrTiO 3 substrates is investigated using a combination of high-resolution synchrotron x-ray diffraction and high-resolution electron microscopy to understand the role that structural distortions play in suppressing ferromagnetism in ultra-thin SRO films. The oxygen octahedral tilts and rotations and Sr displacements characteristic of the bulk orthorhombic phase are found to be strongly dependent on temperature, the film thickness, and the distance away from the film–substrate interface. For thicknesses, t, above the critical thickness for ferromagnetism ( t > 3 uc), the orthorhombic distortions decrease with increasing temperature above T C . Below T C , the structure of the films remains constant due to the magneto-structural coupling observed in bulk SRO. The orthorhombic distortions are found to be suppressed in the 2–3 interfacial layers due to structural coupling with the SrTiO 3 substrate and correlate with the critical thickness for ferromagnetism in uncapped SRO films. 
    more » « less
  5. null (Ed.)
  6. The relationship between the sheet carrier concentration, $n_s$, of LaCrO$_3$(LCO)/SrTiO$_3$(STO) heterostructures and their structural properties has been investigated. Under low oxygen partial pressure, the STO substrate is reduced during growth as evidenced by a high $n_s$ of 10$^{16}$ cm$^{-2}$. By controlling the post-growth annealing conditions, heterostructures with $n_s$ of 10$^{13}$-10$^{16}$ cm$^{-2}$ are achieved. The atomic-scale structure of the samples are obtained using high-resolution synchrotron X-ray diffraction measurements. For heterostructures with $n_s$ at or below 3$\times 10^{13}$ cm$^{-2}$, polar distortions are present within the LCO layers and increase in magnitude with decreasing sheet carrier concentration. These distortions are absent for samples with $n_s$ on the order of 10$^{15}$-10$^{16}$ cm$^{-2}$ where interfacial carriers play a role in alleviating the polar discontinuity at the LCO/STO interface. These results suggest that interfacial charge carriers and polar distortions can act as complementary mechanisms to alleviate the polar discontinuity at polar/non-polar complex oxide interfaces. 
    more » « less