Debnarayan Jana

Bio: Debnarayan Jana is an academic researcher from University of Calcutta. The author has contributed to research in topics: Graphene & Density functional theory. The author has an hindex of 23, co-authored 127 publications receiving 2328 citations. Previous affiliations of Debnarayan Jana include National Taiwan University.

Nonlinear alternating current conduction in polycrystalline manganites

Abstract: The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1−x−yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1−xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc∼Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the differ...

Non-universal finite size scaling of rough surfaces

Abstract: We demonstrate the non-universal behavior of finite size scaling in (1+1) dimension of a nonlinear discrete growth model involving extended particles in generalized point of view. In particular, we show the violation of the universal nature of the scaling function corresponding to the height fluctuation in (1+1) dimension. The 2nd order moment of the height fluctuation shows three distinct crossover regions separated by two crossover time scales namely, tx1 and tx2. Each regime has different scaling property. The overall scaling behavior is postulated with a new scaling relation represented as the linear sum of two scaling functions valid for each scaling regime. Besides, we notice the dependence of the roughness exponents on the finite size of the system. The roughness exponents corresponding to the rough surface is compared with the growth rate or the velocity of the surface.

Dielectric Behavior in B1 and B2 Phases Composed of Unsymmetrical Bent Shaped Liquid Crystal Molecules

Abstract: Detail dielectric measurements were carried out on two different liquid crystalline (LC) samples formed by bent core (BC) molecules, showing B1 and B2 phases in the temperature range 100–150°C. The thermal variation of real part of dielectric permittivity (ϵ′) represents a tiny dip only in the saturated B1 phase which might arising from the dipole orientation disorder due to the inherent phase instability. The experimental data have been used to determine different relaxation parameters. Evidently only one relaxation mode has been detected in the dielectric relaxation spectrum for both phases, which is attributed to the long axis molecular rotation process.

Bose-Einstein condensation in a gas of sodium atoms

Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Intrinsic ripples in graphene

Abstract: The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.