Rajdeep Adhikari | Indian Institute of Technology Kharagpur (original) (raw)
Papers by Rajdeep Adhikari
Applied Physics Letters, 2021
Heterostructures consisting of alternating GaN/AlN epitaxial layers represent the building blocks... more Heterostructures consisting of alternating GaN/AlN epitaxial layers represent the building blocks of state-of-the-art devices employed for active cooling and energy-saving lightning. Insights into the heat conduction of these structures are essential in the perspective of improving the heat management for prospective applications. Here, the cross-plane (perpendicular to the sample's surface) thermal conductivity of GaN/AlN superlattices as a function of the layers' thickness is established by employing the 3x-method. Moreover, the role of interdiffusion at the interfaces in the phonon scattering is taken into account in the modeling and data treatment. It is found that the cross-plane thermal conductivity of the epitaxial heterostructures can be driven to values as low as 5.9 W/(mÁK) comparable with those reported for amorphous films, thus opening wide perspectives for optimized heat management in III-nitride-based epitaxial multilayers.
F. Mertens, D. Mönkebüscher, E. Coronado, S. Mañas-Valero, C. Boix-Constant, A. Bonanni, M. Matze... more F. Mertens, D. Mönkebüscher, E. Coronado, S. Mañas-Valero, C. Boix-Constant, A. Bonanni, M. Matzer, R. Adhikari, A. M. Kalashnikova, D. Bossini, 1, a) and M. Cinchetti Department of Physics, TU Dortmund University, Otto-Hahn Straße 4, 44227 Dortmund, Germany Instituto de Ciencia Molecular (ICMol) Universidad de Valencia. Catedrático José Beltrán 2 46890, Paterna, Spain Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz, Austria Ioffe Institue, 194021 St. Petersburg, Russia Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457 Konstanz, Germany.
Spintronics XIII, 2020
An interplay of conservation and breaking of local and global symmetries in topological phases of... more An interplay of conservation and breaking of local and global symmetries in topological phases of matter leads to the emergence of topological phenomena including quantum anomalous (QAH) Hall effect, topological superconductivity, and non-Abelian quantum statistics. Among the members of the family of topological materials, magnetically doped topological crystalline insulators (TCI) were foreseen to host topologically protected QAH states generating multiple dissipationless edge and surface conduction channels with Chern number C ≥1. The symmetry protected topological phase of the SnTe class of TCI is characterized by a mirror symmetry resulting in topological surface states. Theoretical and experimental studies demonstrated that four Dirac points are located at the time-reversed-invariant-momentum (TRIM) points for the (111) surface of the SnTe compounds. In this work, via low temperature magnetotransport studies, the opening of the gaps at the TRIMs is demonstrated in ferromagnetic 30 nm thick Sn1-xMnxTe (111) thin epitaxial layers grown onto BaF2(111) substrates by molecular beam epitaxy. While a spin mediated magnetoconductance is observed in layers with 𝑥 ≥ 0.03, the appearance of hysteretic magnetoconductance behaviour and square-like anomalous Hall effect indicate the onset of a hole mediated ferromagnetic ordering in epitaxial Sn1-xMnxTe (111) layers for 𝑥 ≥ 0.06. The anomalous Hall angle, 𝜃AH~0.3 estimated for Sn0.92Mn0.08Te is one of the highest recorded for magnetic topological quantum materials. The tuning of the global band topology by magnetic doping opens wide perspectives for topology driven quantum spintronic technology.
Research on ultrathin quantum materials requires full control of the growth and surface quality o... more Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation show...
Applied Physics A, 2019
We report on the giant junction magnetoresistance observed at low temperature in Fe/p-Si Schottky... more We report on the giant junction magnetoresistance observed at low temperature in Fe/p-Si Schottky heterojunction. The device shows good rectifying characteristics at room temperature and a dual—Schottky as well as magnetic diode—characteristics at low temperature, below 50 K. Formation of a magnetic field-dependent potential barrier due to electrical injection of spin-polarized carriers from the ferromagnetic electrode into the semiconductor is speculated to result in such large junction resistance. The magnetoresistance value is of the order of 10^{4}\%$$104% at 10 K and saturates at \sim 0.5\,\hbox {kOe}$$∼0.5kOe, showing dual functionality—working as a magnetic diode as well as a magnetoresistive element.
Applied Physics Letters, 2016
International Journal of Advanced Applied Physics Research, 2014
Physica B: Condensed Matter, 2012
ABSTRACT We have investigated the mechanical and magneto-transport properties of electron beam ev... more ABSTRACT We have investigated the mechanical and magneto-transport properties of electron beam evaporated Co film on p-Si(1 0 0) substrate. Real time intrinsic stress measurement of the Co film, measured using a cantilever beam technique, shows the evolution of a large tensile stress with the growth of the film on the Si substrate. The analysis of stress reveals a columnar type Volmer–Weber growth which is also confirmed by the atomic force microscopy (AFM) measurements. The Co-film shows high positive (negative) magnetoresistance at all temperatures (below 10 K) on application of out-of-plane (in-plane) magnetic field.
ABSTRACT We report an investigation of the non-linear electrical transport and magnetic transport... more ABSTRACT We report an investigation of the non-linear electrical transport and magnetic transport properties associated with Co/CoO core-shell nanoparticles, over the temperature range 10-300 K. Nanoparticle of size 60-70 nm was synthesized by borohydride reduction technique where the core-shell structure is confirmed by the high resolution Transmission Electron Microscopy. The resistivity was found to vary almost linearly with temperature showing a normal metallic behavior with a residual resistivity of 30μΩ-m. The nonlinear electric transport is observed at temperatures (T) below 300 K and is explained using the Glazman and Matveev model. The nanoparticles showed negative Magnetoresistance (MR), in the range 0.25-2.3% on application of magnetic field parallel and perpendicular to the direction of current flow. This change in magnetoristance is observed to have close relation to the nonlinear electrical transport within the Co/CoO nanoparticles.
Crystal growth & design, Jan 4, 2015
The structural analysis of GaN and Al x Ga1-x N/GaN heterostructures grown by metalorganic vapor ... more The structural analysis of GaN and Al x Ga1-x N/GaN heterostructures grown by metalorganic vapor phase epitaxy in the presence of Mn reveals how Mn affects the growth process and in particular, the incorporation of Al, the morphology of the surface, and the plastic relaxation of Al x Ga1-x N on GaN. Moreover, the doping with Mn promotes the formation of layered Al x Ga1-x N/GaN superlattice-like heterostructures, which opens wide perspectives for controlling the segregation of ternary alloys during the crystal growth and for fostering the self-assembling of functional layered structures.
A tridentate Schiff base ligand (saltrp/saltyr) was synthesized by coupling salicylaldehyde (sal)... more A tridentate Schiff base ligand (saltrp/saltyr) was synthesized by coupling salicylaldehyde (sal) with amino acid-tryptophan (trp) and tyrosine (tyr). Cu(II) Complexes with salicylidene amino acid Schiff base and polypyridyl ligands i.e [Cu(II)(saltrp)(phen)] (1), [Cu(II)(saltrp)(bipy)] (2), [Cu(II)(saltyr)(phen)] (3) and [Cu(II)(saltyr)(bipy)] (4) (where phen = 1,10 phenanthroline and bipy= 2,2' bipyridine) were synthesized, characterized by various techniques and structures were proposed. Complexes display a square pyramidal geometry around Cu(II) with Schiff base coordinating through ONO donor atom and polypyridyl ligands through NN donor atoms. CT-DNA (Calf Thymus) binding studies for complexes (1-4) display an intercalative mode of binding with binding affinity of order 1>2>3>4. Since Small metal complexes that promote hydrolytic cleavage of DNA are useful in molecular biology and drug design, an attempt is made in this article to compare the DNA cleavage abilities of complexes 1-4 reported earlier and to analyze the reasoning for affinity towards DNA cleavage. The hydrolytic DNA cleavage activity of these complexes was studied by gel electrophoresis and DNA cleavage rate constant were determined. Phenanthroline complexes (1, 3) binds and cleaves DNA more effectively as compared to their corresponding bipyridine (2, 4) analogues due to the presence of extended aromatic phenyl ring which might be involved in an additional stacking interaction with DNA bases. Comparison among the amino acid systems revealed that tyrosine schiff base complexes (3, 4) show better DNA cleavage than tryptophan analogues (1, 2) and the DNA cleavage ability follow the order : 3>4>1>2.
Review of Scientific Instruments, 2012
We have designed, fabricated, and made operational an ex situ cantilever beam magnetometer (CBM),... more We have designed, fabricated, and made operational an ex situ cantilever beam magnetometer (CBM), which is versatile in the sense that it can measure most of the magnetic properties of a material in all probable shapes. The working principle of a CBM is discussed considering the magnetic torque into the beam theory. The individual components of the instrument are described in details and experiments were performed on the bulk materials, pellets of nanoparticles, ribbon samples, and thin films, and the magnetization, magnetostriction, and magnetocrystalline anisotropy were studied. This magnetometer is inexpensive, but versatile and would be suitable for the research as well as teaching laboratories.
Physical Review B, 2008
SnO 2 nanoparticles doped with Fe of different concentrations were synthesized by a chemical copr... more SnO 2 nanoparticles doped with Fe of different concentrations were synthesized by a chemical coprecipitation method. After calcination at 600 °C , the samples were characterized using x-ray diffraction (XRD), transmission electron microscope (TEM), and superconducting ...
Journal of Magnetism and Magnetic Materials, 2010
Applied Physics Letters, 2021
Heterostructures consisting of alternating GaN/AlN epitaxial layers represent the building blocks... more Heterostructures consisting of alternating GaN/AlN epitaxial layers represent the building blocks of state-of-the-art devices employed for active cooling and energy-saving lightning. Insights into the heat conduction of these structures are essential in the perspective of improving the heat management for prospective applications. Here, the cross-plane (perpendicular to the sample's surface) thermal conductivity of GaN/AlN superlattices as a function of the layers' thickness is established by employing the 3x-method. Moreover, the role of interdiffusion at the interfaces in the phonon scattering is taken into account in the modeling and data treatment. It is found that the cross-plane thermal conductivity of the epitaxial heterostructures can be driven to values as low as 5.9 W/(mÁK) comparable with those reported for amorphous films, thus opening wide perspectives for optimized heat management in III-nitride-based epitaxial multilayers.
F. Mertens, D. Mönkebüscher, E. Coronado, S. Mañas-Valero, C. Boix-Constant, A. Bonanni, M. Matze... more F. Mertens, D. Mönkebüscher, E. Coronado, S. Mañas-Valero, C. Boix-Constant, A. Bonanni, M. Matzer, R. Adhikari, A. M. Kalashnikova, D. Bossini, 1, a) and M. Cinchetti Department of Physics, TU Dortmund University, Otto-Hahn Straße 4, 44227 Dortmund, Germany Instituto de Ciencia Molecular (ICMol) Universidad de Valencia. Catedrático José Beltrán 2 46890, Paterna, Spain Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz, Austria Ioffe Institue, 194021 St. Petersburg, Russia Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457 Konstanz, Germany.
Spintronics XIII, 2020
An interplay of conservation and breaking of local and global symmetries in topological phases of... more An interplay of conservation and breaking of local and global symmetries in topological phases of matter leads to the emergence of topological phenomena including quantum anomalous (QAH) Hall effect, topological superconductivity, and non-Abelian quantum statistics. Among the members of the family of topological materials, magnetically doped topological crystalline insulators (TCI) were foreseen to host topologically protected QAH states generating multiple dissipationless edge and surface conduction channels with Chern number C ≥1. The symmetry protected topological phase of the SnTe class of TCI is characterized by a mirror symmetry resulting in topological surface states. Theoretical and experimental studies demonstrated that four Dirac points are located at the time-reversed-invariant-momentum (TRIM) points for the (111) surface of the SnTe compounds. In this work, via low temperature magnetotransport studies, the opening of the gaps at the TRIMs is demonstrated in ferromagnetic 30 nm thick Sn1-xMnxTe (111) thin epitaxial layers grown onto BaF2(111) substrates by molecular beam epitaxy. While a spin mediated magnetoconductance is observed in layers with 𝑥 ≥ 0.03, the appearance of hysteretic magnetoconductance behaviour and square-like anomalous Hall effect indicate the onset of a hole mediated ferromagnetic ordering in epitaxial Sn1-xMnxTe (111) layers for 𝑥 ≥ 0.06. The anomalous Hall angle, 𝜃AH~0.3 estimated for Sn0.92Mn0.08Te is one of the highest recorded for magnetic topological quantum materials. The tuning of the global band topology by magnetic doping opens wide perspectives for topology driven quantum spintronic technology.
Research on ultrathin quantum materials requires full control of the growth and surface quality o... more Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation show...
Applied Physics A, 2019
We report on the giant junction magnetoresistance observed at low temperature in Fe/p-Si Schottky... more We report on the giant junction magnetoresistance observed at low temperature in Fe/p-Si Schottky heterojunction. The device shows good rectifying characteristics at room temperature and a dual—Schottky as well as magnetic diode—characteristics at low temperature, below 50 K. Formation of a magnetic field-dependent potential barrier due to electrical injection of spin-polarized carriers from the ferromagnetic electrode into the semiconductor is speculated to result in such large junction resistance. The magnetoresistance value is of the order of 10^{4}\%$$104% at 10 K and saturates at \sim 0.5\,\hbox {kOe}$$∼0.5kOe, showing dual functionality—working as a magnetic diode as well as a magnetoresistive element.
Applied Physics Letters, 2016
International Journal of Advanced Applied Physics Research, 2014
Physica B: Condensed Matter, 2012
ABSTRACT We have investigated the mechanical and magneto-transport properties of electron beam ev... more ABSTRACT We have investigated the mechanical and magneto-transport properties of electron beam evaporated Co film on p-Si(1 0 0) substrate. Real time intrinsic stress measurement of the Co film, measured using a cantilever beam technique, shows the evolution of a large tensile stress with the growth of the film on the Si substrate. The analysis of stress reveals a columnar type Volmer–Weber growth which is also confirmed by the atomic force microscopy (AFM) measurements. The Co-film shows high positive (negative) magnetoresistance at all temperatures (below 10 K) on application of out-of-plane (in-plane) magnetic field.
ABSTRACT We report an investigation of the non-linear electrical transport and magnetic transport... more ABSTRACT We report an investigation of the non-linear electrical transport and magnetic transport properties associated with Co/CoO core-shell nanoparticles, over the temperature range 10-300 K. Nanoparticle of size 60-70 nm was synthesized by borohydride reduction technique where the core-shell structure is confirmed by the high resolution Transmission Electron Microscopy. The resistivity was found to vary almost linearly with temperature showing a normal metallic behavior with a residual resistivity of 30μΩ-m. The nonlinear electric transport is observed at temperatures (T) below 300 K and is explained using the Glazman and Matveev model. The nanoparticles showed negative Magnetoresistance (MR), in the range 0.25-2.3% on application of magnetic field parallel and perpendicular to the direction of current flow. This change in magnetoristance is observed to have close relation to the nonlinear electrical transport within the Co/CoO nanoparticles.
Crystal growth & design, Jan 4, 2015
The structural analysis of GaN and Al x Ga1-x N/GaN heterostructures grown by metalorganic vapor ... more The structural analysis of GaN and Al x Ga1-x N/GaN heterostructures grown by metalorganic vapor phase epitaxy in the presence of Mn reveals how Mn affects the growth process and in particular, the incorporation of Al, the morphology of the surface, and the plastic relaxation of Al x Ga1-x N on GaN. Moreover, the doping with Mn promotes the formation of layered Al x Ga1-x N/GaN superlattice-like heterostructures, which opens wide perspectives for controlling the segregation of ternary alloys during the crystal growth and for fostering the self-assembling of functional layered structures.
A tridentate Schiff base ligand (saltrp/saltyr) was synthesized by coupling salicylaldehyde (sal)... more A tridentate Schiff base ligand (saltrp/saltyr) was synthesized by coupling salicylaldehyde (sal) with amino acid-tryptophan (trp) and tyrosine (tyr). Cu(II) Complexes with salicylidene amino acid Schiff base and polypyridyl ligands i.e [Cu(II)(saltrp)(phen)] (1), [Cu(II)(saltrp)(bipy)] (2), [Cu(II)(saltyr)(phen)] (3) and [Cu(II)(saltyr)(bipy)] (4) (where phen = 1,10 phenanthroline and bipy= 2,2' bipyridine) were synthesized, characterized by various techniques and structures were proposed. Complexes display a square pyramidal geometry around Cu(II) with Schiff base coordinating through ONO donor atom and polypyridyl ligands through NN donor atoms. CT-DNA (Calf Thymus) binding studies for complexes (1-4) display an intercalative mode of binding with binding affinity of order 1>2>3>4. Since Small metal complexes that promote hydrolytic cleavage of DNA are useful in molecular biology and drug design, an attempt is made in this article to compare the DNA cleavage abilities of complexes 1-4 reported earlier and to analyze the reasoning for affinity towards DNA cleavage. The hydrolytic DNA cleavage activity of these complexes was studied by gel electrophoresis and DNA cleavage rate constant were determined. Phenanthroline complexes (1, 3) binds and cleaves DNA more effectively as compared to their corresponding bipyridine (2, 4) analogues due to the presence of extended aromatic phenyl ring which might be involved in an additional stacking interaction with DNA bases. Comparison among the amino acid systems revealed that tyrosine schiff base complexes (3, 4) show better DNA cleavage than tryptophan analogues (1, 2) and the DNA cleavage ability follow the order : 3>4>1>2.
Review of Scientific Instruments, 2012
We have designed, fabricated, and made operational an ex situ cantilever beam magnetometer (CBM),... more We have designed, fabricated, and made operational an ex situ cantilever beam magnetometer (CBM), which is versatile in the sense that it can measure most of the magnetic properties of a material in all probable shapes. The working principle of a CBM is discussed considering the magnetic torque into the beam theory. The individual components of the instrument are described in details and experiments were performed on the bulk materials, pellets of nanoparticles, ribbon samples, and thin films, and the magnetization, magnetostriction, and magnetocrystalline anisotropy were studied. This magnetometer is inexpensive, but versatile and would be suitable for the research as well as teaching laboratories.
Physical Review B, 2008
SnO 2 nanoparticles doped with Fe of different concentrations were synthesized by a chemical copr... more SnO 2 nanoparticles doped with Fe of different concentrations were synthesized by a chemical coprecipitation method. After calcination at 600 °C , the samples were characterized using x-ray diffraction (XRD), transmission electron microscope (TEM), and superconducting ...
Journal of Magnetism and Magnetic Materials, 2010