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Andreev reflection in ballistic normal metal/graphene/superconductor junctions

2019-10-23T16:33:02+00:00October 23rd, 2019|Categories: Publications|Tags: |

Author(s): P. Pandey, R. Kraft, R. Krupke, D. Beckmann, and R. DanneauWe report the study of ballistic transport in normal metal/graphene/superconductor junctions in edge-contact geometry. While in the normal state, we have observed Fabry-Pérot resonances suggesting that charge carriers travel ballistically, the superconducting state shows that the Andreev reflection …[Phys. Rev. B 100, 165416] Published Wed Oct 23, 2019

Published in: "Physical Review B".

Interacting valley Chern insulator and its topological imprint on moiré superconductors

2019-10-23T16:33:01+00:00October 23rd, 2019|Categories: Publications|Tags: |

Author(s): Xiao-Chuan Wu, Yichen Xu, Chao-Ming Jian, and Cenke XuOne salient feature of systems with moiré superlattice is that the Chern number of “minibands” originating from each valley of the original graphene Brillouin zone becomes a well-defined quantized number because the miniband from each valley can be isolated from the rest of the spectrum due to the m…[Phys. Rev. B 100, 155138] Published Wed Oct 23, 2019

Published in: "Physical Review B".

Diffraction paradox: An unusually broad diffraction background marks high quality graphene

2019-10-23T16:32:58+00:00October 23rd, 2019|Categories: Publications|Tags: |

Author(s): S. Chen, M. Horn von Hoegen, P. A. Thiel, and M. C. TringidesThe realization of the unusual properties of two-dimensional (2D) materials requires the formation of large domains of single-layer thickness, extending over the mesoscale. It is found that the formation of uniform graphene on SiC, contrary to textbook diffraction, is signaled by a strong bell-shape…[Phys. Rev. B 100, 155307] Published Wed Oct 23, 2019

Published in: "Physical Review B".

Exfoliating two-dimensional materials into few layers via optimized environmentally-friendly ternary solvents

2019-10-23T14:32:49+00:00October 23rd, 2019|Categories: Publications|Tags: , , |

Exfoliation of two-dimensional (2D) materials is an issue of concern among scientific researchers. This is because many solvents such as N, N-dimethylformamide and N-methyl-2-pyrrolidone that are capable of better dispersion of 2D materials are relatively toxic and nonvolatile. This work focused on the reasonable design and mixture of two or three less toxic and volatile solvents based on Hansen solubility parameters theory to demonstrate the excellent exfoliation of 2D materials particularly reduced graphene oxide (rGO) and black phosphorus (BP). Polyvinylpyrrolidone (PVP) was introduced as a surfactant to functionalize rGO to help improve its dispersion. Results showed that PVP could effectively functionalize graphene. Few layers of rGO and BP were facilely achieved with 2–3 nm thickness from the use of the designed solvent mixtures, indicating the accomplishment of solvent mixtures in exfoliation/dispersion roles instead of the use of other toxic and nonvolatile solvents.

Published in: "Nanotechnology".

Graphene-TMD van der Waals Heterostucture Plasmonics. (arXiv:1910.09885v1 [cond-mat.mes-hall])

2019-10-23T04:30:54+00:00October 23rd, 2019|Categories: Publications|Tags: , |

The collective excitations of electrons in the bulk or at the surface, namely plasmons, play an important role in the properties of materials, and have generated the field of plasmonics. We report the observation of a highly unusual plasmon mode on the surface of Van der Waals heterostructures of graphene monolayer on 2D transition metal dichalcogenide substrate. Since the exponentially decaying fields of surface plasmon wave propagating along interface is highly sensitive to the ambient refractive index variations, such heterostructures are useful for ultra-sensitive bio-sensing.

Published : "arXiv Mesoscale and Nanoscale Physics".

Berry Curvature Dipole in Strained Graphene: a Fermi Surface Warping Effect. (arXiv:1910.09872v1 [cond-mat.mes-hall])

2019-10-23T04:30:52+00:00October 23rd, 2019|Categories: Publications|Tags: , |

It has been recently established that optoelectronic and non-linear transport experiments can give direct access to the dipole moment of the Berry curvature in non-magnetic and non-centrosymmetric materials. Thus far, non-vanishing Berry curvature dipoles have been shown to exist in materials with substantial spin-orbit coupling where low-energy Dirac quasiparticles form tilted cones. Here, we prove that this topological effect does emerge in two-dimensional Dirac materials even in the complete absence of spin-orbit coupling. In these systems, it is the warping of the Fermi surface that triggers sizeable Berry dipoles. We show indeed that uniaxially strained monolayer and bilayer graphene, with substrate-induced and gate-induced band gaps respectively, are characterized by Berry curvature dipoles comparable in strength to those observed in monolayer and bilayer transition metal dichalcogenides.

Published : "arXiv Mesoscale and Nanoscale Physics".

Origin of the butterfly magnetoresistance in ZrSiS. (arXiv:1910.09852v1 [cond-mat.mes-hall])

2019-10-23T04:30:50+00:00October 23rd, 2019|Categories: Publications|

ZrSiS has been identified as a topological material made from non-toxic and earth-abundant elements. Together with its extremely large and uniquely angle-dependent magnetoresistance this makes it an interesting material for applications. We study the origin of the so-called butterfly magnetoresistance by performing magnetotransport measurements on four different devices made from exfoliated crystalline flakes. We identify near-perfect electron-hole compensation, tuned by the Zeeman effect, as the source of the butterfly magnetoresistance. Furthermore, the observed Shubnikov-de Haas oscillations are carefully analyzed using the Lifshitz-Kosevich equation to determine their Berry phase and thus their topological properties. Although the link between the butterfly magnetoresistance and the Berry phase remains uncertain, the topological nature of ZrSiS is confirmed.

Published : "arXiv Mesoscale and Nanoscale Physics".

Nonmonotonic plasmon dispersion in strongly interacting Coulomb Luttinger liquids. (arXiv:1910.09560v1 [cond-mat.str-el])

2019-10-23T04:30:48+00:00October 23rd, 2019|Categories: Publications|Tags: , |

We demonstrate that the plasmon in one-dimensional Coulomb interacting electron fluids can develop a finite-momentum maxon-roton-like nonmonotonic energy-momentum dispersion. Such an unusual nonmonotonicity arises from the strongly interacting $1/r$ Coulomb potential going beyond the conventional band linearization approximation used in the standard bosonization theories of Luttinger liquids. We provide details for the nonmonotonic plasmon dispersion using both bosonization and RPA theories. We also calculate the specific heat including the nonmonotonicity and discuss possibilities for observing the nonmonotonic plasmon dispersion in various physical systems including semiconductor quantum wires, carbon nanotubes, and the twisted bilayer graphene at sub-degree twist angles, which naturally realize one-dimensional domain-wall states.

Published : "arXiv Mesoscale and Nanoscale Physics".