Subhendra D. Mahanti

Using a theoretical model that incorporates the full energy landscape of the electronic density of states of disordered arrays of quantum dots (DAQDs) with a realistic size distribution and non-uniform doping, we have examined the oscillatory behavior of electrical conductivity σ as a function of the average doping concentration ND. We find that Coulomb interactions between charged quantum dots suppress the magnitude of these oscillations, whereas increasing the temperature increases the magnitude of these oscillations. Furthermore, the magnitude of the oscillations increases with an increase of the localization length ξ. The observed oscillatory behavior of σ suggests the potential for optimizing the conductivity of DAQDs for application-specific purposes through controlled doping.

We study topological charge pumping in the Rice–Mele (RM) model with irreciprocal hopping. The non-Hermiticity gives rise to interesting pumping physics, owing to the presence of skin effect and exceptional points. In the static one-dimensional (1D) RM model, we find two independent tuning knobs that can drive the topological transition, namely, non-Hermitian parameter γ and system size N. To elucidate the system-size dependency, we use a finite-size generalized Brillouin zone scheme to show that the edge modes can be distinguished from the non-hermiticity induced skin modes. Moreover, this scheme can capture the state pumping of topological edge modes as a function of γ in the static 1D RM model and it further provides insight into engineering novel gapless exceptional edge modes with the help of adiabatic drive. Furthermore, we show that the standard topological pumping due to the adiabatic and periodic variation of the model parameters survives even with finite γ. However, we observe that it depends upon the driving protocols and strength of the non-Hermiticity (γ). With increasing γ, the adiabatic pumping for non-trivial protocols is destroyed first and then re-emerges as an anomalous pumping which does not have any Hermitian counterpart. Additionally, we observe that even a trivial adiabatic protocol can give rise to pumping as opposed to the Hermitian system. This is attributed to the inherent point gap physics of non-Hermitian system which we explain by reformulating a non-Bloch topological invariant for the 1+1D RM model. This invariant explains the number of pumped charges (in each period) for all the driving protocols.

Effect of A -site cationic ordering on structural, transport and magnetic properties of mixed-valent perovskite manganite NdBaMn 2 O 6 has been studied. Temperature ( T ) dependent x-ray diffraction data reveals that different types of phase transitions seen in this compound explicitly depend on the degree of ordering of the A -site cations Nd 3+ and Ba 2+ . For example, the ordered compound undergoes multiple structural phase transitions with decreasing T , whereas the disordered compound retains the high T crystal structure. Resistivity measurements show that although both the compounds are insulating, the mechanism of charge transport is different for the two compounds. Similarly the magnetic properties and colossal magnetoresistance also depend on the degree of ordering. Cationic disorder suppresses the long-range antiferromagnetic order and enhances ferromagnetic correlations at lower temperature; which (ferromagnetic correlation) is accompanied with larger value of saturation magnetic moment while ferromagnetic T C too shifts to higher temperature with increasing disorder. Disordered system also exhibits a larger value of magnetoresistance at low temperature compared to the ordered counterpart.