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Mukherjee B.,Narasinha Dutt College
Optik | Year: 2017

A flexible organic field-effect transistor (OFET) and flexible phototransistor have been fabricated using self-assembled single crystals of a small molecule, viz, N,N’-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8). The solution processed single crystals of PTCDI-C8 with strong molecular ordering showed excellent OFET performances having mobility μ ∼ 0.2 cm2/Vs. The absence of grain boundaries, traps and intrinsically defect-free nature of the single crystals contributed to the improved device performances in PTCDI-C8 crystalline OFET. The device exhibited high sensitivity to photo-illumination with photoresponsivity value upto Ca. 3A/W and photo to dark current ratio ∼103. Both the transistor and photosensing characteristics of the OFET device were retained even under extreme bending of the flexible substrate, exhibiting robust mechanical flexibility of the OPT. To realize OFET based electro-optical logic circuits, we have suitably integrated the photo signal and electrical signal and demonstrated that binary NOT and OR operations could be performed on the OFET device with light as one of the input signal. The large area deposition of self-assembled organic single crystals with multifunctional activity, such as, photosensing with switching, signal amplification, and electro-optical logic operation opens up immense possibilities for flexible organic logic device and promises great potential for future low-cost plastic optoelectronic applications. © 2017 Elsevier GmbH


Maiti S.K.,Narasinha Dutt College | Chakrabarti A.,Kalyani University
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The Hubbard model on a Sierpinski gasket fractal is carefully examined within a Hartree-Fock mean-field approach. We examine the influence of a magnetic flux threading the gasket on its ground-state energy, persistent current and the Drude weight. Both an isotropic gasket and its anisotropic counterpart have been examined. The variance in the patterns of the calculated physical quantities are discussed for two situations, viz, at half filling and when the "band" is less than half filled. The phase reversal of the persistent currents and the change in the Drude weight as a function of the Hubbard interaction are found to exhibit interesting patterns that have so far remained unaddressed. © 2010 The American Physical Society.


Maiti S.K.,Saha Institute of Nuclear Physics | Maiti S.K.,Narasinha Dutt College
Solid State Communications | Year: 2010

We explore multi-terminal quantum transport through a single benzene molecule attached to metallic electrodes. A simple tight-binding model is used to describe the system and all the calculations are done based on the Green function formalism. With a brief description of two-terminal quantum transport, we present a detailed study of three-terminal transport properties through the benzene molecule to reveal the actual mechanism of electron transport. Here we address numerical results which describe multi-terminal conductances, reflection probabilities and currentvoltage characteristics. Most significantly we observe that, the molecular system where the benzene molecule is attached to three terminals can be operated as a transistor, and we call it a molecular transistor. This aspect can be utilized in designing nano-electronic circuits and our investigation may provide a basic framework to study electron transport in any complicated multi-terminal quantum system. © 2010 Elsevier Ltd. All rights reserved.


Maiti S.K.,Saha Institute of Nuclear Physics | Maiti S.K.,Narasinha Dutt College
Solid State Communications | Year: 2010

The present work proposes an idea to remove the long standing controversy between the calculated and measured current amplitudes carried by a small conducting ring upon the application of an AharonovBohm (AB) flux φ. Within a mean field HartreeFock (HF) approximation we numerically calculate persistent current, Drude weight, low-field magnetic susceptibility and related issues. Our analysis may be inspiring for studying magnetic response in nano-scale loop geometries. © 2010 Elsevier B.V. All rights reserved.


Majhi B.R.,Sn Bose National Center For Basic Science | Samanta S.,Narasinha Dutt College
Annals of Physics | Year: 2010

Applying the Hamilton-Jacobi method we investigate the tunneling of photon across the event horizon of a static spherically symmetric black hole. The necessity of the gauge condition on the photon field, to derive the semiclassical Hawking temperature, is explicitly shown. Also, the tunneling of photon and gravitino beyond this semiclassical approximation are presented separately. Quantum corrections of the action for both cases are found to be proportional to the semiclassical contribution. Modifications to the Hawking temperature and Bekenstein-Hawking area law are thereby obtained. Using this corrected temperature and Hawking's periodicity argument, the modified metric for the Schwarzschild black hole is given. This corrected version of the metric, up to ℏ order is equivalent to the metric obtained by including one loop back reaction effect. Finally, the coefficient of the leading order correction of entropy is shown to be related to the trace anomaly. © 2010 Elsevier Inc.


Banerjee R.,Sn Bose National Center For Basic Science | Modak S.K.,Sn Bose National Center For Basic Science | Samanta S.,Narasinha Dutt College
European Physical Journal C | Year: 2010

Black hole thermodynamics, confined to the semi-classical regime, cannot address the thermodynamic stability of a black hole in flat space. Here we show that inclusion of a correction beyond the semi-classical approximation makes a black hole thermodynamically stable. This stability is reached through a phase transition. By using Ehrenfest's scheme we further prove that this is a glassy phase transition with a Prigogine-Defay ratio close to 3. This value is well within the desired bound (2 to 5) for a glassy phase transition. Thus our analysis indicates a very close connection between the phase transition phenomena of a black hole and glass forming systems. Finally, we discuss the robustness of our results by considering different normalisations for the correction term. © 2010 Springer-Verlag / Società Italiana di Fisica.


Maiti S.K.,Saha Institute of Nuclear Physics | Maiti S.K.,Narasinha Dutt College
Physica Status Solidi (B) Basic Research | Year: 2011

The behavior of persistent current in a mesoscopic cylinder threaded by an Aharonov-Bohm flux φ{symbol} is carefully investigated within a Hartree-Fock mean field approach. We examine the combined effect of second-neighbor hopping integral and Hubbard correlation on the enhancement of persistent current in presence of disorder. A significant change in current amplitude is observed compared to the traditional nearest-neighbor hopping model and the current amplitude becomes quite comparable to experimental realizations. Our analysis is found to exhibit several interesting results which have so far remained unaddressed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Banerjee R.,Sn Bose National Center For Basic Science | Modak S.K.,Sn Bose National Center For Basic Science | Samanta S.,Narasinha Dutt College
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

We discuss a scheme based on Ehrenfest-like equations to exhibit and classify transitions between two phases (with "smaller" and "larger" masses) of Kerr-AdS black holes. We show that for fixed angular velocity this phase transition is of second order as both Ehrenfest's equations are satisfied. Finally, we make a close connection of the results found from this analysis with those obtained from the thermodynamic state space geometry approach. © 2011 American Physical Society.


Dey M.,Saha Institute of Nuclear Physics | Maiti S.K.,Saha Institute of Nuclear Physics | Maiti S.K.,Narasinha Dutt College | Karmakar S.N.,Saha Institute of Nuclear Physics
Organic Electronics: physics, materials, applications | Year: 2011

The effect of dephasing on electron transport through a benzene molecule is carefully examined using a phenomenological model introduced by Büttiker. Within a tight-binding framework all the calculations are performed based on the Green's function formalism. We investigate the influence of dephasing on transmission probability and current-voltage characteristics for three different configurations (ortho, meta and para) of the molecular system depending on the locations of two contacting leads. The presence of dephasing provides a significant change in the spectral properties of the molecule and exhibits several interesting patterns that have so far remain unexplored. © 2011 Elsevier B.V. All rights reserved.


Maiti S.K.,Saha Institute of Nuclear Physics | Maiti S.K.,Narasinha Dutt College
Journal of Computational and Theoretical Nanoscience | Year: 2011

We explore the possibilities of current modulation at nano-scale level using mesoscopic rings. A single mesoscopic ring or an array of such rings is used for current modulation where each ring is threaded by a time varying magnetic flux φ which plays the central role in the modulation action. Within a tight-binding framework, all the calculations are done based on the Green's function formalism. We present numerical results for the two-terminal conductance and current which support the essential features of current modulation. The analysis may be helpful in fabricating mesoscopic or nano-scale electronic devices. Copyright © 2011 American Scientific Publishers.

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