- Sudeshna Sen and N. S. Vidhyadhiraja,
Protocols for characterising quantum transport through nano-structures,
Applied Physics Letters
101, 133106 (2012).
- Monojit Bag, N. S. Vidhyadhiraja and K. S. Narayan,
Fluctuations in Photocurrent of Bulk Heterojunction Polymer Solar Cells – A Valuable Tool to Understand Microscopic and Degradation Processes,
Applied Physics Letters
101, 043903 (2012).
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Commentary: The first experimental observations of current noise in organic bulk-heterojunction solar cells are reported and analysed. The noise spectrum has a usual 1/fa form at low frequencies. At frequencies of ~ 8-10kHz, a broad maximum shows up. This intriguing feature is a direct evidence of hidden cyclostationary processes in the system. The maximum depends strongly on the background intensity, the extent of degradation and temperature. A kinetic Monte Carlo (KMC) simulation of charge transport in a disordered system has been carried out to understand the results. The inclusion of a transport level or a mobility edge is the new feature of simulations. The flicker noise is well reproduced, and the maximum is argued to arise from space-charge effects.
- Nagamalleswararao Dasari, P Mandal, A Sundaresan and N S Vidhyadhiraja,
Weak ferromagnetism and magnetization reversal in YFe1-xCrxO3,
Europhysics Letters
99, 17008 (2012).
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Commentary: YFe1-xCrxO3 is an unusual system. It is a solid solution of the Yttrium orthoferrite and orthochromite materials. The end points (YFeO3 and YCrO3) are boring canted anti-ferromagnets with a monotonic temperature dependent magnetization. The alloy, however, shows rich and unexpected behaviour such as magnetization reversal and compensation point(s). It turns out that the origin of such surprising behaviour is a three-way Dzyaloshinskii-Moriya interaction between Fe-Fe, Cr-Cr and Fe-Cr. Given that the first two are in the same direction, but the third is opposite, the whole range of experimental behaviour can be accounted for, in a quantitative way, using a simple minimalist theoretical approach. Read on.
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