Shivam Ghosh

Performance of Precast Concrete Building Structures

The Precast/Prestressed Concrete Institute (PCI) sent an assessment team to Chile, which visited the areas affected by the 27 February 2010 earthquake between 26 and 30 April 2010. This paper reports on the teams observations on the performance of precast/prestressed concrete structures. The precast concrete building systems observed by the PCI team generally performed well. In some cases, the lateral force-resisting system performed satisfactorily, but the absence or weakness of diaphragm framing resulted in local failures. Overall, the PCI team found a mature and sophisticated precast concrete industry that has successfully considered and solved issues of earthquake resistance without some of the constraints imposed on U.S. practice by restrictive building code provisions.

Phase diagram of the Kondo lattice model on the kagome lattice

We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the under-screened kagome Kondo lattice model. At weak coupling, we show that incommensurate non-coplanar multi-wave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduces competing interactions between the spins. At strong coupling, we find that such complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive degeneracy of states at infinite coupling. Finally, we show that at intermediate filling, only commensurate orders seem to survive. But these orders still include non-coplanar magnetism. So, the mere presence of both local moments and itinerant electrons enables complex orders to form unlike any currently observed in kagome materials.

Schwinger boson mean field perspective on emergent spins in diluted Heisenberg antiferromagnets

Using an adaptation of Schwinger boson mean field theory (SBMFT) for nonuniform systems, we study the nature of low-energy spin excitations on the square and Bethe lattice at their percolation threshold. The optimal SBMFT parameters are interpreted as on-site potentials and pairing amplitudes, which enables an explanation of why emergent local moments develop in this system on dilution [L. Wang and A. W. Sandvik, Phys. Rev. Lett. 97, 117204 (2006); H.J. Changlani et al., ibid 111, 157201 (2013)] and why the corresponding single particle frequencies are driven to anomalously low values. We discuss how our mean field calculations suggest the strong link between the presence of sublattice imbalance and long range antiferromagnetic order, and why linear spin wave theory is inadequate for capturing this relation. Within the SBMFT framework, we also extract an energy scale for the interaction between emergent moments, which show qualitative agreement with many-body calculations.