Semonti Bhattacharyya

Alternating current conduction behavior of excimer laser ablated SrBi2Nb2O9 thin films

Bi-layered Aurivillius compounds prove to be efficient candidates of nonvolatile memories.

GROWTH AND CHARACTERIZATION OF SRBI2NB2O9 THIN FILMS BY PULSED-LASER ABLATION

SrBi_2Nb_2O_9

Dielectric relaxation in laser ablated polycrystalline ZrTiO4 thin films

thin films were deposited by excimer laser ablation at low substrate temperature (400°C) followed by an ex situ annealing at 750 °C. The polarization hysteresis behavior was confirmed by variation of polarization with the external applied electric field and also verified with capacitance versus voltage characteristics. The measured values of spontaneous and remnant polarizations were, respectively, 9 and 6

Analysis of leakage current conduction phenomenon in thin SrBi2Ta2O9 films grown by excimer laser ablation

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Bulk-Induced 1/f Noise at the Surface of Three-Dimensional Topological Insulators

C/cm2 with a coercive field of 90 kV/cm. The measured dielectric constant and dissipation factors at 100 kHz were 220 and 0.02, respectively. The frequency analysis of dielectric and ac conduction properties showed a distribution of relaxation times due to the presence of multiple grain boundaries in the films. The values of activation energies from the dissipation factor and grain interior resistance were found to be 0.9 and 1.3 eV, respectively. The deviation in these values was attributed to the energetic conditions of the grain boundaries and bulk grains. The macroscopic relaxation phenomenon is controlled by the higher resistive component in a film, such as grain boundaries at lower temperatures, which was highlighted in the present article in close relation to interior grain relaxation and conduction properties.

Quantized edge modes in atomic-scale point contacts in graphene

Polycrystalline films of SrBi2Nb2O9 were grown using pulsed-laser ablation. The ferroelectric properties were achieved by low-temperature deposition followed by a subsequent annealing process. The lower switching voltage was obtained by lowering the thickness, which did not affect the insulating nature of the films. The hysteresis results showed an excellent square-shaped loop with results (Pr = 6 μC/cm2, Ec = 100 kV/cm) in good agreement with earlier reports. The films also exhibited a dielectric constant of 250 and a dissipation factor of 0.02. The transport studies indicated an ohmic behavior, while higher voltages induced a bulk space charge.

Resistance noise in epitaxial thin films of ferromagnetic topological insulators

Relaxation and conduction mechanisms under small ac fields of laser ablated ZrTiO4 thin films were analyzed in the light of impedance and modulus spectroscopy. The overall dielectric properties were mainly dominated by a Maxwell–Wagner type of relaxation with grains and the grain boundary two distinct parts of the circuit. Each of these parts was found to follow the universal power law of frequency dispersion. The modulus plot confirmed that the capacitive parts were relatively independent of the frequency and temperature, whereas the impedance and ac conduction studies exhibited significant temperature and frequency dependence. The conduction inside the grains was suggestive of a hopping mechanism through various defect sites whereas the interface barrier potential dictated grain boundary conduction.

Bulk-impurity induced noise in large-area epitaxial thin films of topological insulators

The dc conduction behavior of thin films of SrBi2Ta2O9 (SBT) has been investigated on the basis of space-charge limited current theory. The theory was generalized to account for the traps, which were inevitably present in this case. The relative percentage of trapped injected charge and the free injected charge was seen to follow a dynamical equilibrium instead of the true thermal equilibrium as the temperature of the sample was raised during the measurement. The onset voltage of the trap filled region (VTFL) showed a decreasing trend with the increase of temperature. This reduction of VTFL was ascribed to the appearance of some excess charge in the conduction band. It was seen that the thermodynamically stable distribution of charges among the energy levels could not be taken to explain such a situation. A dynamic model was proposed to explain this kind of a nonequilibrium distribution of trapped and free charges.

AC electrical property studies on

Slow intrinsic fluctuations of resistance, also known as the flicker noise or 1/f-noise, in the surface transport of strong topological insulators (TIs) is a poorly understood phenomenon. Here, we have systematically explored the 1/f-noise in field-effect transistors (FET) of mechanically exfoliated Bi1.6Sb0.4Te2Se TI films when transport occurs predominantly via the surface states. We find that the slow kinetics of the charge disorder within the bulk of the TI induces mobility fluctuations at the surface, providing a new source of intrinsic 1/f-noise that is unique to bulk TI systems. At small channel thickness, the noise magnitude can be extremely small, corresponding to the phenomenological Hooge parameter γH as low as ≈10(-4), but it increases rapidly when channel thickness exceeds ∼1 μm. From the temperature (T)-dependence of noise, which displayed sharp peaks at characteristic values of T, we identified generation-recombination processes from interband transitions within the TI bulk as the dominant source of the mobility fluctuations in surface transport. Our experiment not only establishes an intrinsic microscopic origin of noise in TI surface channels, but also reveals a unique spectroscopic information on the impurity bands that can be useful in bulk TI systems in general.

SrBi_2(Ta_{0.5}Nb_{0.5})_2O_9

The zigzag edges of single- or few-layer graphene are perfect one-dimensional conductors owing to a set of gapless states that are topologically protected against backscattering. Direct experimental evidence of these states has been limited so far to their local thermodynamic and magnetic properties, determined by the competing effects of edge topology and electron-electron interaction. However, experimental signatures of edge-bound electrical conduction have remained elusive, primarily due to the lack of graphitic nanostructures with low structural and/or chemical edge disorder. Here, we report the experimental detection of edge-mode electrical transport in suspended atomic-scale constrictions of single and multilayer graphene created during nanomechanical exfoliation of highly oriented pyrolytic graphite. The edge-mode transport leads to the observed quantization of conductance close to multiples of G0 = 2e2/h. At the same time, conductance plateaux at G0/2 and a split zero-bias anomaly in non-equilibrium transport suggest conduction via spin-polarized states in the presence of an electron-electron interaction.