Recent Submissions

  • Strong ultrafast demagnetization due to the intraband transitions

    Zhang, G. P.; Murakami, Mitsuko (Institute of Physics, 2023-08)
    Demagnetization in ferromagnetic transition metals driven by a femtosecond laser pulse is a fundamental problem in solid state physics, and its understanding is essential to the development of spintronic devices. Ab initio calculation of time-dependent magnetic moment in the velocity gauge so far has not been successful in reproducing the large amount of demagnetization observed in experiments. In this work, we propose a method to incorporate intraband transitions within the velocity gauge through a convective derivative in the crystal momentum space. Our results for transition-element bulk crystals (bcc Fe, hcp Co and fcc Ni) based on the time-dependent quantum Liouville equation show a dramatic enhancement in the amount of demagnetization after the inclusion of an intraband term, in agreement with experiments. We also find that the effect of intraband transitions on each ferromagnetic material is distinctly different because of their band structure and spin property differences. Our finding has a far-reaching impact on understanding of ultrafast demagnetization.
  • Gentrification and HOPE VI in Chicago: Turning Points and Responses to Economic Crisis

    Sink, Todd; Ceh, Brian (2009-08-26)
    Public housing in Chicago, like many cities nationwide, has a history of poverty, crime, and disinvestments. In 1992 the HOPE VI program was created to change the development path of these neighborhoods. The objective of the program is to deconcentrate poverty and enrich prospects for gentrification and urban renewal in targeted neighborhoods by tearing down and replacing project-based public housing with mixed-income apartments. In the process condominium developments often arise on empty parcels of land that further accelerate neighborhood gentrification. Using data made available under the Home Mortgaged Disclosure Act of 1975 the study investigates gentrification in neighborhoods targeted by HOPE VI policy in Chicago from 1990-2007. We examine the following: (1) the extent to which mortgage financing is improving; (2) if changes vary at the intra-urban scale and; (3) the effect, if any, of the recent foreclosure crisis on areas of poverty and subsidized housing. It is found that housing investment was improving in HOPE VI neighborhoods prior to the foreclosure crisis. In these neighborhoods the rate of growth in housing investment was greater than in non-targeted HOPE VI neighborhoods and Chicago combined. The onset of the foreclosure crisis curtailed housing investment in both targeted and non-targeted HOPE VI neighborhoods. Yet, evidence suggests that targeted neighborhoods were most affected, especially those near the downtown where gentrification is more intense. Furthermore, results show that the intra-urban scale is important to consider in examining gentrification in HOPE VI neighborhoods.