High Field Magneto-Conductivity Analysis of Bi2Se3 Single Crystal. (arXiv:1807.04925v1 [cond-mat.mtrl-sci])

2018-07-16T02:29:17+00:00 July 16th, 2018|Categories: Publications|Tags: |

We report the high field (up to 14Tesla) magneto-conductivity analysis of Bi2Se3 topological insulator grown via the self flux method. The detailed experimental investigations including crystal growth as well as the electrical, thermal and spectroscopic characterizations of the resultant Bi2Se3 single crystal are already reported by some of us. The current letter deals with high field magneto-conductivity analysis in terms of Hikami Larkin Nagaoka (HLN) model, which revealed that the electronic conduction is dominated by both surface states driven weak anti localization (WAL), as well the bulk WL (weak localization) states. Further, by applying the HLN equation we have extracted the fitting parameters i.e., phase coherence length and the pre-factor. The HLN equation exhibited values of [pre factor close to -1.0, indicating both WAL and WL contributions. On the other hand, the extracted phase coherence length is seen to decrease from 11.125 nm to 5.576 nm as the temperature is increased from 5K to 200K respectively. Summarily, the short letter discusses primarily the temperature dependent magneto-conductivity analysis of pristine Bi2Se3 single crystal by the HLN model.

Published in: "arXiv Material Science".

Unusual pressure-induced periodic lattice distortion in SnSe$_2$. (arXiv:1807.04993v1 [cond-mat.mtrl-sci])

2018-07-16T02:29:16+00:00 July 16th, 2018|Categories: Publications|

We performed high pressure x-ray diffraction (XRD), Raman, and transport measurements combined with first-principles calculations to investigate the behavior of tin diselenide (SnSe$_2$) under compression. The obtained single-crystal XRD data indicate the formation of a $(1/3,1/3,1)$-type superlattice above 17 GPa. According to our density functional theory results, the pressure-induced transition to the commensurate periodic lattice distortion (PLD) phase is due to the combined effect of strong Fermi surface nesting and electron-phonon coupling at a momentum wave vector $mathbf{q}=(1/3,1/3,1)$. In contrast, similar PLD transitions associated with charge density wave (CDW) orderings in transition metal dichalcogenides (TMDs) do not involve significant Fermi surface nesting. The discovered pressure-induced PLD is quite remarkable, as pressure usually suppresses CDW phases in related materials. Our findings, therefore, provide new playgrounds to study the intricate mechanisms governing the emergence of PLD in TMD-related materials.

Published in: "arXiv Material Science".

Spin transistor built on 2D van der Waals heterostructures. (arXiv:1807.04898v1 [cond-mat.mes-hall])

2018-07-16T00:30:35+00:00 July 16th, 2018|Categories: Publications|Tags: , , |

Spin transistors (whose on-off operation is achieved by electric-field-controlled spin orientation 1), if realized, can revolutionize modern electronics through the implementation of a faster and a more energy-efficient performance as well as non-volatile data storage 2, 3. The original proposal by Datta and Das 1 that relies on electric-field-controlled spin precession in a semiconductor channel faces significant challenges including inefficient spin injection, spin relaxation and spread of the spin precession angle 4, 5. Recent demonstration of electric-field switching of magnetic order 6-8 and spin filtering 9-12 in two-dimensional magnetic insulator CrI3 has inspired a new operational principle for spin transistors. Here we demonstrate spin field-effect transistors based on dual-gated graphene/CrI3 tunnel junctions. These devices show an ambipolar transistor behavior and tunnel magnetoresistance widely tunable by gating when the CrI3 magnetic tunnel barrier undergoes an antiferromagnetic-ferromagnetic spin-flip transition. Under a constant magnetic bias in the vicinity of the spin-flip transition, the gate voltage can repeatedly alter the device between a high and a low conductance state with a large hysteresis. This new spin transistor concept based on the electric-field-controlled spin-flip transition in the magnetic tunnel barrier is immune to interface imperfections and allows spin injection, control and detection in a single device.

Published : "arXiv Mesoscale and Nanoscale Physics".

Laser-beam patterned topological 1T’-phases on few-layer semiconducting MoS2. (arXiv:1807.04914v1 [cond-mat.mes-hall])

2018-07-16T00:30:34+00:00 July 16th, 2018|Categories: Publications|Tags: |

Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial to the development of voltage-controlled spintronic devices with low power dissipation. However, their experimental observation is rare. Members of the 2D material family of transition metal dichalcogenides (TMDCs) have been recently predicted and experimentally reported as a new class of 2D TI materials. Here, we realize controlled patterning of the 1T’-phase onto thin 2H-semiconducting molybdenum-disulfide (MoS2) only by laser beam irradiation. Integer fractions of the quantum value of resistance are observed for two-different 1T’ patterns, indicating the presence of helical edge spin modes, characteristic of 2D TI state, at the 1T’/2H phase interface. This result is supported by resistance dependence on laser-irradiation time and power, magnetic field, and temperature, scanning tunneling spectroscopy, and theoretical calculations. The present observation opens the door to the controlled patterning of topological phases into non-topological phases of TMDCs and their application to topological quantum computation.

Published : "arXiv Mesoscale and Nanoscale Physics".

Strong exciton regulation of Raman scattering in monolayer dichalcogenides. (arXiv:1807.04929v1 [cond-mat.mes-hall])

2018-07-16T00:30:32+00:00 July 16th, 2018|Categories: Publications|Tags: |

The weakly screened electron-hole interactions in an atomically thin semiconductor not only downshift its excitation spectrum from a quasiparticle one, but also redistribute excitation energies and wavefunction characters with profound effects on diverse modes of material response, including the exciton-phonon scattering processes accessible to resonant Raman measurements. Here we develop a first-principles framework to calculate frequency-dependent resonant Raman intensities that includes excitonic effects and goes beyond the Placzek approximation. We show how excitonic effects in MoS2 strongly regulate Raman scattering amplitudes and thereby explain the puzzling near-absence of resonant Raman response around the A and B excitons (which produce very strong signals in optical absorption), and also the pronounced strength of the resonant Raman response from the C exciton. Furthermore, this efficient perturbative approach reduces the number of GW- BSE calculations from two per Raman mode (in finite displacement) to one for all modes and affords natural extension to higher-order resonant Raman processes.

Published : "arXiv Mesoscale and Nanoscale Physics".

Negative Viscosity and Eddy Flow of Imbalanced Electron-Hole Liquid in Graphene. (arXiv:1807.04770v1 [cond-mat.mes-hall])

2018-07-16T00:30:31+00:00 July 16th, 2018|Categories: Publications|Tags: , |

We present a hydrodynamic theory for electron-hole magnetotransport in graphene incorporating carrier-population imbalance, energy, and momentum relaxation processes. We focus on the electric response and find that the carrier and energy imbalance relaxation strongly modify the shear viscosity so that an effective viscosity can be negative in the vicinity of charge neutrality. We predict an emergent eddy flow phenomenon of swirling currents and explore its manifestation in nonlocal resistivity oscillations in a strip of graphene driven by a source current.

Published : "arXiv Mesoscale and Nanoscale Physics".

Porous Reduced Graphene Oxide {beta}-cyclodextrin Modified Electrode as Enhanced Sensing Platform for the Determination of Dihydrochalcone: Phloretin

2018-07-14T14:31:26+00:00 July 14th, 2018|Categories: Publications|Tags: , |

A facile and sensitive electrochemical sensor based on glassy carbon electrode (GCE) modified with β cyclodextrin (β-CD) functionalized porous reduced graphene oxide (prGO) was fabricated and used for electrochemical determination of dihydrochalcone, phloretin in biological samples. Low temperature solution combustion method was employed to fabricate prGO from graphene oxide. The product so obtained was mixed with β-CD and treated for ultra sonication in order to get β-CD-prGO. Enhanced electrochemical response for phloretin (PHL) was observed at β-CD-prGO modified GCE. The effect of pH, scan rate, accumulation time and amount of modifier on the electrochemical behavior of PHL was studied. The probable electro-oxidation mechanism was proposed based on obtained experimental results. Linearity between the peak current and concentration of PHL was noticed in the range of 0.1–75.2 μM and 0.5–65.25 μM for square wave and differential pulse voltammetric methods, respectively. The developed methods were successfully applied for the determination of PHL in spiked biological samples. Further, prepared β-CD-prGO modified GCE was used to understand the interaction between HSA and PHL.

Published in: "Journal of the Electrochemical Society".

Room temperature in-plane ferroelectricity in van der Waals In2Se3

2018-07-14T02:36:22+00:00 July 14th, 2018|Categories: Publications|Tags: |

Van der Waals (vdW) assembly of layered materials is a promising paradigm for creating electronic and optoelectronic devices with novel properties. Ferroelectricity in vdW layered materials could enable nonvolatile memory and low-power electronic and optoelectronic switches, but to date, few vdW ferroelectrics have been reported, and few in-plane vdW ferroelectrics

Published in: "Science Advances".

Mechanics of spontaneously formed nanoblisters trapped by transferred 2D crystals [Applied Physical Sciences]

2018-07-14T02:31:22+00:00 July 14th, 2018|Categories: Publications|Tags: |

Layered systems of 2D crystals and heterostructures are widely explored for new physics and devices. In many cases, monolayer or few-layer 2D crystals are transferred to a target substrate including other 2D crystals, and nanometer-scale blisters form spontaneously between the 2D crystal and its substrate. Such nanoblisters are often recognized…

Published in: "PNAS (Ahead)".

Chemical intercalation of heavy metal, semimetal, and semiconductor atoms into 2D layered chalcogenides

2018-07-13T16:33:32+00:00 July 13th, 2018|Categories: Publications|Tags: |

A major outstanding challenge in the field of intercalation chemistry has been the insertion of heavy metals into a 2D layered material. Heavy metal intercalation is a promising route towards access of chemically tailored materials or enhancement of novel physics. We present a new series of wet chemical strategies to intercalate atomic heavy metal and semimetal species (Bi, Cr, Ge, Mn, Mo, Ni, Os, Pb, Pd, Pt, Rh, Ru, Sb, and W) into layered chalcogenides. Bismuth selenide, Bi 2 Se 3 , and niobium diselenide, NbSe 2 , are used to demonstrate this chemistry. Atomic intercalation is performed in solution using decomposition of zero-valent coordination compounds at low temperatures (∼50 °C–170 °C) or reduction with tin chloride. This host of chemical routes is non-destructive, general for chalcogens, and can be used to intercalate some lighter elements as well. These intercalation reactions more than double the current number of atomic intercalants and giv…

Published in: "2DMaterials".

Transparency in graphene mediated evaporation

2018-07-13T14:33:49+00:00 July 13th, 2018|Categories: Publications|Tags: |

Droplet evaporation is a ubiquitous phenomenon with numerous applications. It plays a pivotal role in life and industry since it concerns heat transfer in high efficiency to reach a desired temperature. However, to rationally mediate evaporation has always been a significant challenge. Here by studying the interactions of water molecules with graphene-covered substrate, we propose that graphene could effectively affect water evaporation rate by changing the length of contact line. More importantly, evaporation per length of contact line before and after graphene coverage shows negligible change, suggesting graphene is transparent for evaporation (per unit contact length). Molecular dynamics simulations confirm experimental findings and indicate that principal evaporation events take place via single-molecule desorption at the contact line.

Published in: "2DMaterials".

Magnetic properties of single rare-earth atoms on graphene/Ir(111)

2018-07-13T14:33:41+00:00 July 13th, 2018|Categories: Publications|Tags: |

Author(s): Romana Baltic, Fabio Donati, Aparajita Singha, Christian Wäckerlin, Jan Dreiser, Bernard Delley, Marina Pivetta, Stefano Rusponi, and Harald BruneWe employed x-ray absorption spectroscopy and x-ray magnetic circular dichroism to study the magnetic properties of single rare-earth (RE) atoms (Nd, Tb, Dy, Ho, and Er) adsorbed on the graphene/Ir(111) surface. The interaction of RE atoms with graphene results for Tb in a trivalent state with 4fn−1…[Phys. Rev. B 98, 024412] Published Fri Jul 13, 2018

Published in: "Physical Review B".

Superluminal plasmons with resonant gain in population inverted bilayer graphene

2018-07-13T14:33:39+00:00 July 13th, 2018|Categories: Publications|Tags: , |

Author(s): Tony Low, Pai-Yen Chen, and D. N. BasovAB-stacked bilayer graphene with a tunable electronic band gap in excess of the optical phonon energy presents an interesting active medium, and we consider such a theoretical possibility in this Rapid Communication. We argue the possibility of a highly resonant optical gain in the vicinity of the a…[Phys. Rev. B 98, 041403(R)] Published Fri Jul 13, 2018

Published in: "Physical Review B".

Collision-dominated conductance in clean two-dimensional metals

2018-07-13T14:33:38+00:00 July 13th, 2018|Categories: Publications|Tags: |

Author(s): A. Uzair, K. Sabeeh, and Markus MüllerWe study the temperature-dependent corrections to the conductance due to electron-electron (e−e) interactions in clean two-dimensional conductors, such as lightly doped graphene or other Dirac matter. We use semiclassical Boltzmann kinetic theory to solve the problem of collision-dominated transport…[Phys. Rev. B 98, 035421] Published Fri Jul 13, 2018

Published in: "Physical Review B".

Exfoliation energy, quasiparticle band structure, and excitonic properties of selenium and tellurium atomic chains

2018-07-13T14:33:33+00:00 July 13th, 2018|Categories: Publications|Tags: |

Author(s): Eesha Andharia, Thaneshwor P. Kaloni, Gregory J. Salamo, Shui-Qing Yu, Hugh O. H. Churchill, and Salvador Barraza-LopezEffects that are not captured by the generalized-gradient density-functional theory have a prominent effect on the structural binding and on the electronic and optical properties of reduced-dimensional and weakly bound materials. Here, we report the exfoliation energy of selenium and tellurium atomi…[Phys. Rev. B 98, 035420] Published Fri Jul 13, 2018

Published in: "Physical Review B".

Non Noble Metal Catalyst for Oxygen Reduction Reaction and Its Characterization by Simulated Fuel Cell Test

2018-07-13T14:31:35+00:00 July 13th, 2018|Categories: Publications|Tags: , , |

In this work nitrogen doped multi-layer graphene and porous carbon are prepared by the pyrolysis of glycine as precursor. The morphology of the product is controlled by the catalyst used. The nitrogen doped multi-layer graphene exhibits a high onset potentialand four-electron pathway for oxygen reduction reaction (ORR) in alkaline solution as well as much enhanced stability compared with commercial Pt/C catalyst. In a simulated fuel cell test the nitrogen doped multi-layer graphene shows comparable performance with Pt/C catalyst in alkaline environment. The ORR activity of the as-prepared carbon material is found to be related with graphitization degree and graphitic-N.

Published in: "Journal of the Electrochemical Society".

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