My research focus is on theoretical and computational study of strongly interacting and disordered electron systems. Many of the transition-metal compounds belong to this catagory. Some examples are, the Cu-based high-Tc superconductors, the oxides of Mn, Co, Ni, etc., and the recently discovered Fe-based superconductors.
A microscopic understanding of the complex phenomena displayed by some of these systems is invariably obtained in terms of the relevant microscopic degrees of freedom, such as charge, spin and orbital. Taking into account the crystal structure, and the electronic structure at various levels of sophistication, one arrives at an effective Hamiltonian.Typically, such model Hamiltonians are rather complex with cross couplings between charge, spin, orbital and lattice variables. Moreover, the quantum many-body nature and the presence of disorder adds to the complexity.Therefore, to a large extent one has to rely on computational techniques to gain insight into the physics of such models.
I make use of Monte Carlo simulations and Exact Diagonalization methods to study the model Hamiltonians relevant to real materials. Some of the topics that I am working on at present are: (i) ferroelectricity in organic molecular crystals, (ii) spin models on frustrated geometries and (iii) development of exact-diagonalization methods for interacting fermionic systems.
- Sanjeev Kumar and Jeroen van den Brink, Phys. Rev. Lett. 105, 216405 (2010), Frustration-Induced Insulating Chiral Spin State in Itinerant Triangular-Lattice Magnets.
- Sanjeev Kumar, Jeroen van den Brink, and Arno P. Kampf, Phys. Rev. Lett. 104, 017201 (2010), Spin-Spiral States in Undoped Manganites: Role of Finite Hund’s Rule
- Gianluca Giovannetti, Sanjeev Kumar, Alessandro Stroppa, Jeroen van den Brink, and Silvia Picozzi, Phys. Rev. Lett. 103, 266401 (2009), Multiferroicity in TTF-CA Organic Molecular Crystals Predicted through Ab Initio Calculations.
- Frank Krüger, Sanjeev Kumar , Jan Zaanen, and Jeroen van den Brink, Phys. Rev. B 79, 054504 (2009),Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors.
- Sanjeev Kumar and Pinaki Majumdar, Phys. Rev. Lett. 96, 016602 (2006), Insulator-Metal Phase Diagram of the Optimally Doped Manganites from the Disordered Holstein-Double Exchange Model.