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Papers by Sudeshna Samanta

Research paper thumbnail of Lattice dynamics of the topological Dirac semimetal LaAgSb2 with charge density wave ordering

Research paper thumbnail of Pressure-induced assemblies and structures of graphitic-carbon sheet encapsulated Au nanoparticles

Nanoscale, 2020

A pressure-driven change of the carbon nanostructure encapsulating Au nanoparticles induces a tra... more A pressure-driven change of the carbon nanostructure encapsulating Au nanoparticles induces a transition of the face-centered cubic to two primitive phases in the Au nanoparticles which impacts the electrical conductivity of the Au/C-nanohybrid.

Research paper thumbnail of Redistribution of native defects and photoconductivity in ZnO under pressure

RSC Advances, 2019

The pressure-induced redistribution of native defects and the optoelectronic response in ZnO micr... more The pressure-induced redistribution of native defects and the optoelectronic response in ZnO microstructures might provide new opportunities in promising semiconductors.

Research paper thumbnail of Pressure-induced structural evaluation and insulator-metal transition in the mixed spinel ferrite Zn0.2Mg0.8Fe2O4

Physical Review B, 2017

The effect of pressure on the electronic properties and crystal structure in a mixed spinel ferri... more The effect of pressure on the electronic properties and crystal structure in a mixed spinel ferrite Zn 0.2 Mg 0.8 Fe 2 O 4 was studied for the first time up to 48 GPa at room temperature using x-ray diffraction, Raman spectroscopy, and electrical transport measurements. The sample was cubic (spinel-type F d3m) at ambient pressure and underwent a pressure-induced structural transition to an orthorhombic phase (CaTi 2 O 4 − type Bbmm) at 21 GPa. This structural transformation corresponded to a first-order phase transition that involved 7.5% molar volume shrinkage. The onset of the Mott insulator-metal transition (IMT) around 20 GPa was due to a spin crossover mechanism that led to the Fe 3+ magnetic moment collapse. All the Raman modes disappeared at high pressures, which supported metallization. Analysis of structural and electrical transport measurements showed a simultaneous volume collapse and sharp IMT within a narrow pressure range. The orthorhombic high-pressure phase was found to have a higher conductivity than the cubic phase. The pressure dependence of the conductivity supported the metallic behavior of the high-pressure phase.

Research paper thumbnail of Phase coexistence near the metal-insulator transition in a compressively strainedNdNiO3film grown onLaAlO3: Scanning tunneling, noise, and impedance spectroscopy studies

Physical Review B, 2017

We report an observation of phase coexistence near the metal-insulator transition (MIT) in a film... more We report an observation of phase coexistence near the metal-insulator transition (MIT) in a film of NdNiO 3 grown on crystalline substrate LaAlO 3. This was established through a combination of three techniques, namely, scanning tunneling spectroscopy, 1/f noise spectroscopy, and impedance spectroscopy experiments. The spatially resolved scanning tunneling spectroscopy showed that the two coexisting phases have different types of density of states (DOS) at the Fermi level. One phase showed a depleted DOS close to E F with a small yet finite correlation gap, while the other coexisting phase showed a metal-like DOS that had no depletion. The existence of the phase separation leads to a jump in the resistance fluctuation (as seen through 1/f noise spectroscopy) at the transition, and, notably, the fluctuation becomes non-Gaussian when there is a phase separation even in the metallic phase. This was corroborated by the impedance spectroscopy, which showed a broad hump in capacitance at the transition region as a signature of the existence of two phases that have widely different electrical conductivities. The phase separation starts well within the metallic phase much above the transition temperature and makes the sample electronically "inhomogeneous" in nanoscopic scale close to the transition. We discuss certain scenarios that lead to such a phase separation in the general context of strongly correlated oxides.

Research paper thumbnail of Dynamic phase coexistence and non-Gaussian resistance fluctuations inVO2near the metal-insulator transition

Physical Review B, 2015

We have carried out an extensive investigation on resistance fluctuations (noise) in an epitaxial... more We have carried out an extensive investigation on resistance fluctuations (noise) in an epitaxial thin film of VO2 encompassing the metal-insulator transition (MIT) region to investigate the dynamic phase coexistence of metal and insulating phases. Both flicker noise as well as the Nyquist noise (thermal noise) was measured. The experiments showed that flicker noise that has 1/f spectral power dependence, evolves with temperature in the transition region following the evolution of the phase fractions and is governed by an activated kinetics. Importantly, closer to the insulating end of the transition, when the metallic phase fraction is low, the magnitude of the noise shows an anomaly and a strong non-Gaussian component of noise develops. In this region the local electron temperature (as measured through the Nyquist noise thermometry) shows a deviation from the equilibrium bath temperature. It is proposed that this behavior arises due to current crowding where a substantial amount of current is carried through well separated small metallic islands leading to dynamic correlated current path redistribution and enhanced effective local current density. This leads to non-Gaussian component to the resistance fluctuation and an associated local deviation of electron temperature from the bath. Our experiment establishes that phase coexistence leads to a strong inhomogeneity in the region of MIT that makes the current transport strongly inhomogeneous and correlated.

Research paper thumbnail of Photoresponse of a Single Y-Junction Carbon Nanotube

ACS Applied Materials & Interfaces, 2016

We report investigation of optical response in a single strand of a branched carbon nanotube (CNT... more We report investigation of optical response in a single strand of a branched carbon nanotube (CNT), a Y-junction CNT composed of multiwalled CNTs. The experiment was performed by connecting a pair of branches while grounding the remaining one. Of the three branch combinations, only one combination is optically active which also shows a nonlinear semiconductor-like I−V curve, while the other two branch combinations are optically inactive and show linear ohmic I−V curves. The photoresponse includes a zero-bias photocurrent from the active branch combination. Responsivity of ≈1.6 mA/W has been observed from a single Y-CNT at a moderate bias of 150 mV with an illumination of wavelength 488 nm. The photoresponse experiment allows us to understand the nature of internal connections in the Y-CNT. Analysis of data locates the region of photoactivity at the junction of only two branches and only the combination of these two branches (and not individual branches) exhibits photoresponse upon illumination. A model calculation based on back-to-back Schottky-type junctions at the branch connection explains the I−V data in the dark and shows that under illumination the barriers at the contacts become lowered due to the presence of photogenerated carriers.

Research paper thumbnail of Pressure-induced phase transitions of exposed curved surface nano-TiO2 with high photocatalytic activity

Journal of Applied Physics, 2016

We report a unique phase transition in compressed exposed curved surface nano-TiO2 with high phot... more We report a unique phase transition in compressed exposed curved surface nano-TiO2 with high photocatalytic activity using in situ synchrotron X-ray diffraction and Raman Spectroscopy. High-pressure studies indicate that the anatase phase starts to transform into baddeleyite phase upon compression at 19.4 GPa, and completely transforms into the baddeleyite phase above 24.6 GPa. Upon decompression, the baddeleyite phase was maintained until the pressure was released to 6.4 GPa and then transformed into the α-PbO2 phase at 2.7 GPa. Together with the results of high-resolution transmission electron microscopy and the pressure-volume relationship, this phase transition's characteristics during the compression-decompression cycle demonstrate that the truncated biconic morphology possessed excellent stability. This study may provide an insight to the mechanisms of stability for high photocatalytic activity of nano-TiO2.

Research paper thumbnail of Ni nanowire arXiv

Research paper thumbnail of PhysRevB.85.045127

Research paper thumbnail of Large photoresponse of a single Si nanowire (diameter ∼50nm) Metal-Semiconductor-Metal device

2012 International Conference on Emerging Electronics, 2012

ABSTRACT The photoresponse of a single Si nanowire (50 nm diameter) is reported. The Metal-Semico... more ABSTRACT The photoresponse of a single Si nanowire (50 nm diameter) is reported. The Metal-Semiconductor-Metal device structure is made by focused ion beam assisted Platinum deposited contacts on the single nanowire. Upon illumination with 405 nm light, the nanowires shows a large photoresponse even at zero bias. The dark and illuminated I-V curves have been analyzed using MSM device structure showing that there is lowering of the work function at the junctions on illumination and also a photoconductive component in the response. The response exhibits a rapid turn on/off of the photo-current when the light is turned on/off and can follow the light modulations upto a frequency of 4kHz.

Research paper thumbnail of LSMO single nanowire characterization

Research paper thumbnail of Noise spectroscopy: a sensitive probe to explore hot electron effect in highly correlated systems

Research paper thumbnail of Low-frequency resistance fluctuations in a single nanowire (diameter ≈ 45 nm) of a complex oxide and its relation to magnetic transitions and phase separation

Applied Physics Letters, 2014

We report measurement of low frequency resistance noise spectroscopy in a single strand of a nano... more We report measurement of low frequency resistance noise spectroscopy in a single strand of a nanowire (NW) (diameter ≈ 45 nm) of a complex oxide manganite La0.5Sr0.5MnO3, that showed ferromagnetic transition (TC ≈ 315 K), an antiferromagnetic transition (TN ≈ 210 K) and a phase-separated region below TN. We demonstrated that noise spectroscopy in a single NW can cleanly detect the magnetic transitions including the phase-coexistence that may not be possible to do by magnetic measurements. The normalized noise in the single NW is an order less than that reported in ultralow-noise Si Junction Field Effect Transistor.

Research paper thumbnail of Growth and Physical Property Study of Single Nanowire (Diameter ~45 nm) of Half Doped Manganite

Journal of Nanomaterials, 2013

We report here the growth and characterization of functional oxide nanowire of hole doped mangani... more We report here the growth and characterization of functional oxide nanowire of hole doped manganite of La0.5Sr0.5MnO3(LSMO). We also report four-probe electrical resistance measurement of a single nanowire of LSMO (diameter ~45 nm) using focused ion beam (FIB) fabricated electrodes. The wires are fabricated by hydrothermal method using autoclave at a temperature of 270 °C. The elemental analysis and physical property like electrical resistivity are studied at an individual nanowire level. The quantitative determination of Mn valency and elemental mapping of constituent elements are done by using Electron Energy Loss Spectroscopy (EELS) in the Transmission Electron Microscopy (TEM) mode. We address the important issue of whether as a result of size reduction the nanowires can retain the desired composition, structure, and physical properties. The nanowires used are found to have a ferromagnetic transition (TC) at around 325 K which is very close to the bulk value of around 330 K foun...

Research paper thumbnail of Nyquist noise as probe of hot-electron effects in the ferromagnetic insulating state of manganites

Hole-doped rare-earth manganites (like La1-xCaxMnO3) in the ferromagnetic insulating (FMI) state ... more Hole-doped rare-earth manganites (like La1-xCaxMnO3) in the ferromagnetic insulating (FMI) state show large non-linear conductance. Such non-linear conductance can arise due to hot-electron effect which originates from decoupling of the electron and lattice temperatures at high power level. The non-linear conductance manifests as electro-resistance or current induced resistance change. We report here low frequency temperature dependent noise measurement which allows us to estimate the electronic temperature by measuring Nyquist noise (``white noise'' in contrast to 1/f noise) in La0.8Ca0.2MnO3 single crystals which has a distinct FMI state below 100K. The measurement was performed with low ac biasing current which was mixed with a high current density d.c that leads to electron heating. We observed that in the insulating state, above a certain input d.c power, the Nyquist noise increases by a large extent and this is coupled to the onset of non-linear conduction as signalled...

Research paper thumbnail of Electrical and magnetic transport study on strain driven ferromagnetic insulating thin film of low doped manganite

In this paper we have created a strain driven single crystal like ferromagnetic insulating (FMI) ... more In this paper we have created a strain driven single crystal like ferromagnetic insulating (FMI) state in a PLD grown thin film of low doped LCMO(X = 0.15)on NGO(100) substrate and make a thorough study of strain effects on the electric and magnetic transport of this film. We have studied and compared the FMI state, ferromagnetic transition temperature (TC), ferromagnetic insulating temperature (TFMI) and the resistivity of the film in details with bulk single crystals of X=0.18 to 0.22 doping region. We have found that TFMI and the localisation length of the carriers are increased and there is also a decrease in the Coulomb gap. The magneto transport behavior of the film also differs from the bulk single crystals and the magnetoresistance of the sample is nearly 20 to 75% with the application of the applied field(0 to 10 T) and it falls up to 5 to 40% below a certain temperature and the TC of the film increases to higher temperature with the increasing field. The film also shows an...

Research paper thumbnail of Photoresponse in thin films of WO3 grown by pulsed laser deposition

Applied Physics Letters, 2014

We report, the photoresponse behaviour of Tungsten trioxide (WO3) films of different surface morp... more We report, the photoresponse behaviour of Tungsten trioxide (WO3) films of different surface morphology, grown by using pulsed laser deposition (PLD). The Growth parameters for PLD were changed for two substrates SiO2/Si (SO) and SrTiO3 (STO), such a way which, result nanocrystalline film on SO and needle like structured film on STO. The photoresponse is greatly modified in these two films because of two different surface morphologies. The nanocrystalline film (film on SO) shows distinct photocurrent (PC) ON/OFF states when light was turned on/off, the enhancement of PC is ∼27%. Whereas, the film with needle like structure (film on STO) exhibits significantly enhanced persistent photocurrent even in light off condition, in this case, the enhancement of PC ∼ 50% at room temperature at lowest wavelength (λ = 360 nm) at a nominal bias voltage of 0.1 V.

Research paper thumbnail of Very low frequency resistance fluctuations in thin films ofLa0.67Ca0.33MnO3with quenched disorder

Research paper thumbnail of Non-Gaussian resistance noise in the ferromagnetic insulating state of a hole-doped manganite

Physical Review B, 2012

We report the observation of a large 1/f noise in the ferromagnetic insulating state (FMI) of a h... more We report the observation of a large 1/f noise in the ferromagnetic insulating state (FMI) of a hole doped manganite single crystal of La0.80Ca0.20MnO3 which manifests hopping conductivity in presence of a Coulomb gap. The temperature dependent noise magnitude shows a deep within the FMI state, there is a sharp freeze out of the noise magnitude with temperature on cooling. As the material enters the FMI state, the noise becomes non-Gaussian as seen through probability density function and second spectra. It is proposed to arise from charge fluctuations in a correlated glassy phase of the polaronic carriers which develop in these systems as reported in recent simulation studies.

Research paper thumbnail of Lattice dynamics of the topological Dirac semimetal LaAgSb2 with charge density wave ordering

Research paper thumbnail of Pressure-induced assemblies and structures of graphitic-carbon sheet encapsulated Au nanoparticles

Nanoscale, 2020

A pressure-driven change of the carbon nanostructure encapsulating Au nanoparticles induces a tra... more A pressure-driven change of the carbon nanostructure encapsulating Au nanoparticles induces a transition of the face-centered cubic to two primitive phases in the Au nanoparticles which impacts the electrical conductivity of the Au/C-nanohybrid.

Research paper thumbnail of Redistribution of native defects and photoconductivity in ZnO under pressure

RSC Advances, 2019

The pressure-induced redistribution of native defects and the optoelectronic response in ZnO micr... more The pressure-induced redistribution of native defects and the optoelectronic response in ZnO microstructures might provide new opportunities in promising semiconductors.

Research paper thumbnail of Pressure-induced structural evaluation and insulator-metal transition in the mixed spinel ferrite Zn0.2Mg0.8Fe2O4

Physical Review B, 2017

The effect of pressure on the electronic properties and crystal structure in a mixed spinel ferri... more The effect of pressure on the electronic properties and crystal structure in a mixed spinel ferrite Zn 0.2 Mg 0.8 Fe 2 O 4 was studied for the first time up to 48 GPa at room temperature using x-ray diffraction, Raman spectroscopy, and electrical transport measurements. The sample was cubic (spinel-type F d3m) at ambient pressure and underwent a pressure-induced structural transition to an orthorhombic phase (CaTi 2 O 4 − type Bbmm) at 21 GPa. This structural transformation corresponded to a first-order phase transition that involved 7.5% molar volume shrinkage. The onset of the Mott insulator-metal transition (IMT) around 20 GPa was due to a spin crossover mechanism that led to the Fe 3+ magnetic moment collapse. All the Raman modes disappeared at high pressures, which supported metallization. Analysis of structural and electrical transport measurements showed a simultaneous volume collapse and sharp IMT within a narrow pressure range. The orthorhombic high-pressure phase was found to have a higher conductivity than the cubic phase. The pressure dependence of the conductivity supported the metallic behavior of the high-pressure phase.

Research paper thumbnail of Phase coexistence near the metal-insulator transition in a compressively strainedNdNiO3film grown onLaAlO3: Scanning tunneling, noise, and impedance spectroscopy studies

Physical Review B, 2017

We report an observation of phase coexistence near the metal-insulator transition (MIT) in a film... more We report an observation of phase coexistence near the metal-insulator transition (MIT) in a film of NdNiO 3 grown on crystalline substrate LaAlO 3. This was established through a combination of three techniques, namely, scanning tunneling spectroscopy, 1/f noise spectroscopy, and impedance spectroscopy experiments. The spatially resolved scanning tunneling spectroscopy showed that the two coexisting phases have different types of density of states (DOS) at the Fermi level. One phase showed a depleted DOS close to E F with a small yet finite correlation gap, while the other coexisting phase showed a metal-like DOS that had no depletion. The existence of the phase separation leads to a jump in the resistance fluctuation (as seen through 1/f noise spectroscopy) at the transition, and, notably, the fluctuation becomes non-Gaussian when there is a phase separation even in the metallic phase. This was corroborated by the impedance spectroscopy, which showed a broad hump in capacitance at the transition region as a signature of the existence of two phases that have widely different electrical conductivities. The phase separation starts well within the metallic phase much above the transition temperature and makes the sample electronically "inhomogeneous" in nanoscopic scale close to the transition. We discuss certain scenarios that lead to such a phase separation in the general context of strongly correlated oxides.

Research paper thumbnail of Dynamic phase coexistence and non-Gaussian resistance fluctuations inVO2near the metal-insulator transition

Physical Review B, 2015

We have carried out an extensive investigation on resistance fluctuations (noise) in an epitaxial... more We have carried out an extensive investigation on resistance fluctuations (noise) in an epitaxial thin film of VO2 encompassing the metal-insulator transition (MIT) region to investigate the dynamic phase coexistence of metal and insulating phases. Both flicker noise as well as the Nyquist noise (thermal noise) was measured. The experiments showed that flicker noise that has 1/f spectral power dependence, evolves with temperature in the transition region following the evolution of the phase fractions and is governed by an activated kinetics. Importantly, closer to the insulating end of the transition, when the metallic phase fraction is low, the magnitude of the noise shows an anomaly and a strong non-Gaussian component of noise develops. In this region the local electron temperature (as measured through the Nyquist noise thermometry) shows a deviation from the equilibrium bath temperature. It is proposed that this behavior arises due to current crowding where a substantial amount of current is carried through well separated small metallic islands leading to dynamic correlated current path redistribution and enhanced effective local current density. This leads to non-Gaussian component to the resistance fluctuation and an associated local deviation of electron temperature from the bath. Our experiment establishes that phase coexistence leads to a strong inhomogeneity in the region of MIT that makes the current transport strongly inhomogeneous and correlated.

Research paper thumbnail of Photoresponse of a Single Y-Junction Carbon Nanotube

ACS Applied Materials & Interfaces, 2016

We report investigation of optical response in a single strand of a branched carbon nanotube (CNT... more We report investigation of optical response in a single strand of a branched carbon nanotube (CNT), a Y-junction CNT composed of multiwalled CNTs. The experiment was performed by connecting a pair of branches while grounding the remaining one. Of the three branch combinations, only one combination is optically active which also shows a nonlinear semiconductor-like I−V curve, while the other two branch combinations are optically inactive and show linear ohmic I−V curves. The photoresponse includes a zero-bias photocurrent from the active branch combination. Responsivity of ≈1.6 mA/W has been observed from a single Y-CNT at a moderate bias of 150 mV with an illumination of wavelength 488 nm. The photoresponse experiment allows us to understand the nature of internal connections in the Y-CNT. Analysis of data locates the region of photoactivity at the junction of only two branches and only the combination of these two branches (and not individual branches) exhibits photoresponse upon illumination. A model calculation based on back-to-back Schottky-type junctions at the branch connection explains the I−V data in the dark and shows that under illumination the barriers at the contacts become lowered due to the presence of photogenerated carriers.

Research paper thumbnail of Pressure-induced phase transitions of exposed curved surface nano-TiO2 with high photocatalytic activity

Journal of Applied Physics, 2016

We report a unique phase transition in compressed exposed curved surface nano-TiO2 with high phot... more We report a unique phase transition in compressed exposed curved surface nano-TiO2 with high photocatalytic activity using in situ synchrotron X-ray diffraction and Raman Spectroscopy. High-pressure studies indicate that the anatase phase starts to transform into baddeleyite phase upon compression at 19.4 GPa, and completely transforms into the baddeleyite phase above 24.6 GPa. Upon decompression, the baddeleyite phase was maintained until the pressure was released to 6.4 GPa and then transformed into the α-PbO2 phase at 2.7 GPa. Together with the results of high-resolution transmission electron microscopy and the pressure-volume relationship, this phase transition's characteristics during the compression-decompression cycle demonstrate that the truncated biconic morphology possessed excellent stability. This study may provide an insight to the mechanisms of stability for high photocatalytic activity of nano-TiO2.

Research paper thumbnail of Ni nanowire arXiv

Research paper thumbnail of PhysRevB.85.045127

Research paper thumbnail of Large photoresponse of a single Si nanowire (diameter ∼50nm) Metal-Semiconductor-Metal device

2012 International Conference on Emerging Electronics, 2012

ABSTRACT The photoresponse of a single Si nanowire (50 nm diameter) is reported. The Metal-Semico... more ABSTRACT The photoresponse of a single Si nanowire (50 nm diameter) is reported. The Metal-Semiconductor-Metal device structure is made by focused ion beam assisted Platinum deposited contacts on the single nanowire. Upon illumination with 405 nm light, the nanowires shows a large photoresponse even at zero bias. The dark and illuminated I-V curves have been analyzed using MSM device structure showing that there is lowering of the work function at the junctions on illumination and also a photoconductive component in the response. The response exhibits a rapid turn on/off of the photo-current when the light is turned on/off and can follow the light modulations upto a frequency of 4kHz.

Research paper thumbnail of LSMO single nanowire characterization

Research paper thumbnail of Noise spectroscopy: a sensitive probe to explore hot electron effect in highly correlated systems

Research paper thumbnail of Low-frequency resistance fluctuations in a single nanowire (diameter ≈ 45 nm) of a complex oxide and its relation to magnetic transitions and phase separation

Applied Physics Letters, 2014

We report measurement of low frequency resistance noise spectroscopy in a single strand of a nano... more We report measurement of low frequency resistance noise spectroscopy in a single strand of a nanowire (NW) (diameter ≈ 45 nm) of a complex oxide manganite La0.5Sr0.5MnO3, that showed ferromagnetic transition (TC ≈ 315 K), an antiferromagnetic transition (TN ≈ 210 K) and a phase-separated region below TN. We demonstrated that noise spectroscopy in a single NW can cleanly detect the magnetic transitions including the phase-coexistence that may not be possible to do by magnetic measurements. The normalized noise in the single NW is an order less than that reported in ultralow-noise Si Junction Field Effect Transistor.

Research paper thumbnail of Growth and Physical Property Study of Single Nanowire (Diameter ~45 nm) of Half Doped Manganite

Journal of Nanomaterials, 2013

We report here the growth and characterization of functional oxide nanowire of hole doped mangani... more We report here the growth and characterization of functional oxide nanowire of hole doped manganite of La0.5Sr0.5MnO3(LSMO). We also report four-probe electrical resistance measurement of a single nanowire of LSMO (diameter ~45 nm) using focused ion beam (FIB) fabricated electrodes. The wires are fabricated by hydrothermal method using autoclave at a temperature of 270 °C. The elemental analysis and physical property like electrical resistivity are studied at an individual nanowire level. The quantitative determination of Mn valency and elemental mapping of constituent elements are done by using Electron Energy Loss Spectroscopy (EELS) in the Transmission Electron Microscopy (TEM) mode. We address the important issue of whether as a result of size reduction the nanowires can retain the desired composition, structure, and physical properties. The nanowires used are found to have a ferromagnetic transition (TC) at around 325 K which is very close to the bulk value of around 330 K foun...

Research paper thumbnail of Nyquist noise as probe of hot-electron effects in the ferromagnetic insulating state of manganites

Hole-doped rare-earth manganites (like La1-xCaxMnO3) in the ferromagnetic insulating (FMI) state ... more Hole-doped rare-earth manganites (like La1-xCaxMnO3) in the ferromagnetic insulating (FMI) state show large non-linear conductance. Such non-linear conductance can arise due to hot-electron effect which originates from decoupling of the electron and lattice temperatures at high power level. The non-linear conductance manifests as electro-resistance or current induced resistance change. We report here low frequency temperature dependent noise measurement which allows us to estimate the electronic temperature by measuring Nyquist noise (``white noise'' in contrast to 1/f noise) in La0.8Ca0.2MnO3 single crystals which has a distinct FMI state below 100K. The measurement was performed with low ac biasing current which was mixed with a high current density d.c that leads to electron heating. We observed that in the insulating state, above a certain input d.c power, the Nyquist noise increases by a large extent and this is coupled to the onset of non-linear conduction as signalled...

Research paper thumbnail of Electrical and magnetic transport study on strain driven ferromagnetic insulating thin film of low doped manganite

In this paper we have created a strain driven single crystal like ferromagnetic insulating (FMI) ... more In this paper we have created a strain driven single crystal like ferromagnetic insulating (FMI) state in a PLD grown thin film of low doped LCMO(X = 0.15)on NGO(100) substrate and make a thorough study of strain effects on the electric and magnetic transport of this film. We have studied and compared the FMI state, ferromagnetic transition temperature (TC), ferromagnetic insulating temperature (TFMI) and the resistivity of the film in details with bulk single crystals of X=0.18 to 0.22 doping region. We have found that TFMI and the localisation length of the carriers are increased and there is also a decrease in the Coulomb gap. The magneto transport behavior of the film also differs from the bulk single crystals and the magnetoresistance of the sample is nearly 20 to 75% with the application of the applied field(0 to 10 T) and it falls up to 5 to 40% below a certain temperature and the TC of the film increases to higher temperature with the increasing field. The film also shows an...

Research paper thumbnail of Photoresponse in thin films of WO3 grown by pulsed laser deposition

Applied Physics Letters, 2014

We report, the photoresponse behaviour of Tungsten trioxide (WO3) films of different surface morp... more We report, the photoresponse behaviour of Tungsten trioxide (WO3) films of different surface morphology, grown by using pulsed laser deposition (PLD). The Growth parameters for PLD were changed for two substrates SiO2/Si (SO) and SrTiO3 (STO), such a way which, result nanocrystalline film on SO and needle like structured film on STO. The photoresponse is greatly modified in these two films because of two different surface morphologies. The nanocrystalline film (film on SO) shows distinct photocurrent (PC) ON/OFF states when light was turned on/off, the enhancement of PC is ∼27%. Whereas, the film with needle like structure (film on STO) exhibits significantly enhanced persistent photocurrent even in light off condition, in this case, the enhancement of PC ∼ 50% at room temperature at lowest wavelength (λ = 360 nm) at a nominal bias voltage of 0.1 V.

Research paper thumbnail of Very low frequency resistance fluctuations in thin films ofLa0.67Ca0.33MnO3with quenched disorder

Research paper thumbnail of Non-Gaussian resistance noise in the ferromagnetic insulating state of a hole-doped manganite

Physical Review B, 2012

We report the observation of a large 1/f noise in the ferromagnetic insulating state (FMI) of a h... more We report the observation of a large 1/f noise in the ferromagnetic insulating state (FMI) of a hole doped manganite single crystal of La0.80Ca0.20MnO3 which manifests hopping conductivity in presence of a Coulomb gap. The temperature dependent noise magnitude shows a deep within the FMI state, there is a sharp freeze out of the noise magnitude with temperature on cooling. As the material enters the FMI state, the noise becomes non-Gaussian as seen through probability density function and second spectra. It is proposed to arise from charge fluctuations in a correlated glassy phase of the polaronic carriers which develop in these systems as reported in recent simulation studies.