Sanjeev Kumar

Research Summary:

Over the last one year, we have developed and applied a numerical scheme to study coupled spin-fermion problems. This technique can prove to be of immense use in understanding the colossal magnetoresistance manganites, magnetic semiconductors and other strongly correlated materials. One can generalize it to incorporate any classical degrees of freedom coupling to quadratic fermions. We have compared this scheme against the exact scheme in various limiting cases. We studied the double-exchange model, in the presence of various additional interactions as the first test of the method. Our method allows access to system sizes an order of magnitude larger than previously possible. We can handle strong disorder and phase coexistence which was hitherto very difficult. Our basic results are documented in the papers cited below.

Publications/Preprints:

1. Anderson-Mott Transition Driven by Spin Disorder: Spin Glass Transition and Magnetotransport in Amorphous GdSi, Pinaki Majumdar and Sanjeev Kumar , cond-mat/0209579 (Phys. Rev. Lett. in press)

2. Double Exchange Models: Self Consistent Renormalisation, Sanjeev Kumar and Pinaki Majumdar , cond-mat 0305345

3. Inhomogeneous Ferromagnetism and Unconventional Charge Dynamics in Disordered Double Exchange Magnets, Sanjeev Kumar and Pinaki Majumdar, cond-mat 0305352

4. Nanoscale Phase Coexistence and Percolative Quantum Transport, Sanjeev Kumar and Pinaki Majumdar , cond-mat 0305645

5. Antilocalisation to Strong Localisation: the Interplay of Magnetic Scattering and Structural Disorder, Sanjeev Kumar and Pinaki Majumdar

Conferences/Schools Attended:

1. Regional Discussion Meeting on Strongly Correlated Electron Systems, Dec. 2002. HRI, Allahabad, India.
2. Summer College on Physics and Chemistry of Rare Earth Manganites, June-2003, ICTP, Trieste, Italy.

Invited Lectures/Seminars:

Nanoscale Phase Coexistence and Percolative Quantum Transport.
Poster at Manganites Conference in ICTP,Trieste.