Research Publications
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Item The tight-binding model study of the role of electron occupancy on the ferromagnetic gap in graphene-on-substrate(2019) Swain R.; Sahu S.; Rout G.C.We propose here a theoretical model for graphene in its ferromagnetic phase. The Hamiltonian describes electron hoppings up-to-third-nearest neighbours for graphene-on-substrate. The sub-lattice coulomb interactions within mean-field approach involve the total electron occupancy and ferromagnetic magnetisations (FMs). The temperature dependent ferromagnetic magnetisation and hence, the ferromagnetic gap are derived from the electron Green�s functions and are solved self-consistently. The result shows that the magnitude of the ferromagnetic gap and the critical coulomb interaction strongly depend on total electron occupancy. The critical coulomb interaction decreases with increase of electron occupancy and the vice-versa. Copyright � 2019 Inderscience Enterprises Ltd.Item Theoretical Model Study of Interplay of Coulomb Interaction and Electron-Phonon Interaction in the Thermal Properties of Monolayer Graphene(2019) Sahu S.; Rout G.C.We propose here a tight-binding (TB) model Hamiltonian for monolayer graphene-on-substrate describing the nearest-neighbor-hopping, on-site Coulomb interaction on the sub-lattices and the electron-phonon interaction under the high-frequency limit of phonon vibration. Applying Lang-Firsov canonical transformation, the electron and phonon systems are decoupled in the atomic Hamiltonian, such that the effective Coulomb interaction and effective nearest-neighbor-hopping integral respectively appear as ?= U? 2 t 1 ? and t~1=t1e?t1??0, where U, t 1 , ? and ? 0 are respectively Coulomb energy, nearest-neighbor-hopping integral, electron-phonon (e-ph) coupling and phonon frequency. The effective Coulomb interaction in the Hamiltonian is considered within mean-field approximation. The Hamiltonian is solved by Zubarev�s Green�s function technique. The temperature-dependent electronic entropy and specific heat are calculated from the free energy of graphene system and are computed numerically. The temperature-dependent electronic specific heat exhibits a charge gap peak at room temperature arising due to the effect of Coulomb interaction and electron-phonon interaction. The evolution of these peaks in specific heat is investigated by varying the model parameters of the system. � 2018, Springer Science+Business Media, LLC, part of Springer Nature.Item Tight-Binding Model Study of Anti-ferromagnetic Order in AA-Stacked Bi-layer Graphene(2018) Sahu S.; Rout G.C.We address here the anti-ferromagnetic order present in AA-stacked bi-layer graphene in a transversely applied electric field. The system is described by kinetic energy with nearest-neighbor electron hopping with same hopping integral t1 for both the layers. Besides this, Coulomb interaction exists at A and B sub-lattices with same Coulomb correlation energy. The electron Green�s functions are calculated by Zubarev�s Green�s technique. The temperature-dependent anti-ferromagnetic magnetization is calculated from the Green�s function and is computed numerically and self-consistently. The strong on-site Coulomb interaction stabilizes the anti-ferromagnetic order in graphene. We assume that the electron spin at A site in the first layer is directed in the opposite direction to that of A site electron in the second layer. Similar spin order is observed for electrons in B site atom in reversed order. It is observed that anti-ferromagnetic (AFM) magnetization in the first layer nearly remains constant up to certain temperature and then increases with temperature, while the AFM magnetization in the second layer remains nearly constant and then rapidly decreases with temperature. The net AFM magnetization in bi-layer graphene remains constant and then rapidly increases with temperature. The evolution of the AFM magnetization is studied by varying transverse electric field, Coulomb energy, and temperature. � 2017, Springer Science+Business Media New York.Item Band gap modulation of graphene by metal substrate: A first principles study(2018) Sahoo M.R.; Sahu S.; Kushwaha A.K.; Nayak S.K.Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion length, graphene guarantees as a completely unique material for devices with various applications. Unaffected 2pz orbitals of carbon atoms in graphene can be highly influenced by substrates and leads to tuning in electronic properties. We report here a density functional calculation of graphene monolayer based on metallic substrate like nickel surfaces. Band-gap of graphene near K points opens due to interactions between 2pz and d-orbitals of nickel atoms and the gap modulation can be done with the increasing number of layers of substrates. � 2018 Author(s).Item Magnetic Susceptibility and Neutron Scattering of Graphene in Antiferromagnetic State: a Tight-Binding Approach(2018) Sahu S.; Panda S.K.; Rout G.C.We address here a tight-binding model study of the frequency-dependent antiferromagnetic spin susceptibility for the graphene systems. The Hamiltonian consists of electron hopping up to the third-nearest-neighbors, substrate and impurity effects in presence of electron-electron interactions at A and B sub-lattices. To calculate susceptibility, we evaluate the two-particle electron Green�s function by using Zubarev�s Green�s function technique. The frequency-dependent antiferromagnetic susceptibility of the system is computed numerically by taking 1000 X 1000 grid points of the electron momentum. The susceptibility displays a sharp peak at the neutron momentum transfer energy at low energies and another higher-energy peak associated with the substrate-induced gap. The evolution of these two peaks are investigated by varying neutron wave vector, Coulomb correlation energy, substrate-induced gap, electron hopping integrals and A- and B-site electron-doping concentrations. � 2017, Springer Science+Business Media, LLC.Item Tight-Binding Theoretical Study of the Tunneling Conductance in Ferromagnetically Ordered Graphene-on-Substrate(2018) Swain R.; Sahu S.; Rout G.C.We report here a tight-binding theoretical study of the tunneling conductance and temperature dependent specific heat of graphene-on-substrate. The Hamiltonian consists of the electron hoppings up to third nearest neighbors in the presence of doping and on-site Coulomb interactions at two sub-lattices of honey-comb lattice. The total Hamiltonian is solved by Zubarev Green�s functions technique. Then, the sub-lattice magnetizations, tunneling conductance, and specific heat are calculated from the Green�s functions and are computed numerically. The effect of impurity, substrate induced gap, and repulsive Coulomb potential on tunneling conductance is discussed. The anomaly in specific heat at low temperatures is described. � 2017, Springer Science+Business Media, LLC, part of Springer Nature.Item Theoretical study of modified electron band dispersion and density of states due to high frequency phonons in graphene-on-substrates(2018) Sahu S.; Rout G.C.We propose here a theoretical model for the study of band gap opening in graphene-on-polarizable substrate taking the effect of electron-electron and electron-phonon (EP) interactions at high frequency phonon vibrations. The Hamiltonian consists of hopping of electrons upto third nearest-neighbors and the effect substrate, where A sublattice site is raised by energy + ? and B sublattice site is suppressed by energy-?, hence producing a band gap energy of 2?. Further, we have considered Hubbard type electron-electron repulsive interactions at A and B sublattices, which are considered within Hartree-Fock meanfield approximation. The electrons in the graphene plane interact with the phonon's present in the polarized substrate in the presence of phonon vibrational energy within harmonic approximation. The temperature-dependent electron occupancies are computed numerically and self-consistently for both spins at both the sublattice sites. By using these electron occupancies, we have calculated the electron band dispersion and density of states (DOS), which are studied for the effects of EP interaction, high phonon frequency, Coulomb energy and substrate induced gap. � 2018 World Scientific Publishing Europe Ltd.Item High-energy-density supercapacitors based on patronite/single-walled carbon nanotubes/reduced graphene oxide hybrids(2016) Ratha S.; Marri S.R.; Behera J.N.; Rout C.S.The facile hydrothermal synthesis of a patronite VS4/single-walled carbon nanotube/reduced graphene oxide hybrid is reported. Detailed electrochemical investigations of the hybrid revealed an exceptionally high energy density of ca. 174 W h/kg. A comparison of this value with those of other supercapacitor electrodes based on metal sulfides and also some with high energy-density values revealed the potential of the patronite hybrid as a fitting candidate for possible application in energy-storage devices. Charge-discharge stability measurements showed the excellent specific capacitance of the hybrid, which has a retention capability of ca. 97 % after 1000 continuous charge-discharge cycles. High-energy-density supercapacitors based on VS4/carbon nanotubes/reduced graphene oxide (VS4/CNTs/RGO) hybrids are synthesized for possible application as energy-storage devices. � 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item On the electric field enhancement and performance of SPR gas sensor based on graphene for visible and near infrared(2015) Maharana P.K.; Jha R.; Padhy P.We propose a high performance surface plasmon resonance (SPR) affinity gas sensor based on graphene on Ag in visible and near infrared. Proposed sensor configuration has been optimized for maximum surface plasmon field at the sensing layer interface. The field intensity enhancement factor at sensing layer interface is found to be higher than that of silicon over layer on Ag thereby increasing the imaging sensitivity by 340%, 120% and 82% and detection accuracy by 440%, 150% and 100% as compared to Si on Ag configuration at ? = 653 nm, ? = 850 nm and ? = 1000 nm respectively. The performance of the sensor is found to be high over a broad refractive index range (1.0000-1.0008) of gaseous analyte with sensor resolution of 8 � 10-5 RIU and 2 � 10-5 RIU at ? = 653 nm and ? = 1000 nm respectively. We believe the proposed SPR based gas sensor configuration will open a new route for efficient gas sensing by riding on the advantage of graphene and latest nanofabrication techniques. � 2014 Elsevier B.V.Item Graphene-Based Conducting Metal Oxide Coated D-Shaped Optical Fiber SPR Sensor(2015) Patnaik A.; Senthilnathan K.; Jha R.We report a graphene-based indium tin oxide coated surface plasmon resonance sensor built on a D-shaped optical fiber for near infrared. Different parameters of the proposed sensor have been optimized to obtain a maximal phase matching between the core guided mode and the plasmon mode using finite element method. Wavelength sensitivity of the proposed structure is as high as 5700 nm/RIU with a maximum resolution of 1.754 � 10-5 RIU. The proposed sensor can also be used for bio layer thickness monitoring with a maximum resolution of 62.5 pm in wavelength interrogation. � 2015 IEEE.