Quantum phase transitions in skewed ladder systems.

In this brief review, we introduce a new spin ladder system called skewed spin ladders and discuss the exotic quantum phases of this system. The spin ladders studied are the 5/7, 3/4 and 3/5 systems corresponding to alternately fused 5 and 7 membered rings; 3 and 4 membered rings; and 3 and 5 membered rings. These ladders show completely different behaviour as the Hamiltonian model parameter is changed.

Haldane and dimer phases in a frustrated spin chain: an exact groundstate and associated topological phase transition.

A Heisenberg spin-chain with alternating ferromagnetic (FM) (-J1F<0) and antiferromagnetic (J1A>0) nearest-neighbor (NN) interactions, exhibits the dimer and spin-2Haldane phases in the limitsJ1F/J1A→0andJ1F/J1A→∞respectively. These two phases are understood to be topologically equivalent. Induction of the frustration through the next NN FM interaction (-J2F<0) produces a very rich quantum phase diagram.

Universality classes in Coulomb blockade conductance peak-height statistics.

We investigate, using exact diagonalization techniques, the distribution of conductance peak heights in Coulomb blockade regime of a quantum dot connected to two leads under generic dot conditions. The study reveals a three-parametric dependence of the distribution: (i) two dot-lead contact characteristics and (ii) the complexity parameter, mimicking the combined effect of all dot conditions. This also indicates the presence of an infinite range of universality classes of conductance statistics, dominantly characterized just by the complexity parameter and global symmetry constraints.