Diptiman Sen

Tuning the conductance of dirac fermions on the surface of a topological insulator.

We study the transport properties of the Dirac fermions with a Fermi velocity v{F} on the surface of a topological insulator across a ferromagnetic strip providing an exchange field J over a region of width d. We show that the conductance of such a junction, in the clean limit and at low temperature, changes from oscillatory to a monotonically decreasing function of d beyond a critical J. This leads to the possible realization of a magnetic switch using these junctions. We also study the conductance of these Dirac fermions across a potential barrier of width d and potential V0 in the presence of such a ferromagnetic strip and show that beyond a critical J, the criteria of conductance maxima changes from chi=eV{0}d/variant Plancks over v{F}=npi to chi=(n+1/2)pi for integer n. We point out that these novel phenomena have no analogs in graphene and suggest experiments which can probe them.

Density-matrix renormalization-group studies of the spin-1/2 Heisenberg system with dimerization and frustration

Using the density matrix renormalization group technique, we study the ground state phase diagram and other low-energy properties of an isotropic antiferromagnetic spin-half chain with both dimerization and frustration, i.e., an alternation

Majorana fermions in superconducting 1D systems having periodic, quasiperiodic, and disordered potentials.

\delta

Majorana Fermions in superconducting wires: effects of long-range hopping, broken time-reversal symmetry and potential landscapes

of the nearest neighbor exchanges and a next-nearest-neighbor exchange

Properties of low-lying states in some high-nuclearity Mn, Fe, and V clusters: Exact studies of Heisenberg models

J_2~

Floquet generation of Majorana end modes and topological invariants

. For

Quantum and statistical mechanics of anyons

\delta = 0

Defect production in nonlinear quench across a quantum critical point.

, the system is gapless for

A density matrix renormalization group study of low-energy excitations and low-temperature properties of alternating spin systems

J_2J_{2c} ~

Non-equilibrium Dynamics of Quantum Systems: Order Parameter Evolution, Defect Generation, and Qubit Transfer

where