Understanding Dirac-like fermions has become an imperative in modern condensed matter sciences: All across the research frontier, from graphene to high Tc superconductors to the topological insulators and beyond, various electronic systems exhibit properties that can be well described by the Dirac equation. Such physics is no longer the exclusive domain of quantum field theories and other esoteric mathematical musings; instead, physics of real condensed matter systems is governed by such equations, and important materials science and practical implications hinge on our understanding of Dirac particles in two and three dimensions. Although the physics that gives rise to the massless Dirac fermions in each of the above-mentioned materials is different, the low-energy properties are governed by the same Dirac kinematics. The aim of this article is to review a selected cross-section of this vast field by highlighting the generalities and contrasting the specifics of several physical systems.

http://inspirehep.net/record/1238158/files/arXiv:1306.2272.pdf

Dirac Fermions in Solids: From High-Tc Cuprates and Graphene to Topological Insulators and Weyl Semimetals

High Responsivity, Broadband, and Fast Graphene/Silicon Photodetector in Photoconductor Mode

We study the charge density distribution, the electric field profile, and the resistance of an electrostatically created lateral p-n junction in graphene. We show that the electric field at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles. Accordingly, the junction resistance is lower than estimated in previous literature.

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-005702.pdf

Nonlinear screening and ballistic transport in a graphene p-n junction

Growth of highly dense ZnO nanowires (ZnO NWs) is demonstrated on three-dimensional graphene foam (GF) using resistive thermal evaporation technique. Photoresponse of the as-grown hybrid structure of ZnO NWs on GF (ZnO NWs/GF) is evaluated for ultraviolet (UV) detection. Excellent photoresponse with fast response and recovery times of 9.5 and 38 s with external quantum efficiency of 2490.8% is demonstrated at low illumination power density of 1.3 mW/cm(2). In addition, due to excellent charge carrier transport, mobility of graphene reduces the recombination rate of photogenerated charge carriers, hence the lifetime of photogenerated free charge carriers enhances in the photodetectors.

Highly Dense ZnO Nanowires Grown on Graphene Foam for Ultraviolet Photodetection

A graphene and zinc oxide nanowires (G/ZnO NWs) based ultraviolet (UV) photodetector presents excellent responsivity and photocurrent gain with detectivity. Graphene due to higher charge carrier transport mobility induces faster response to UV illumination at the interface between ZnO and graphene with improved response and decay times as compared to a ZnO NWs device alone. A linear increase is revealed for both the responsivity and photocurrent gain of the G/ZnO NWs device with the applied bias. These results suggest that the G/ZnO NWs device exhibits great promise for highly efficient UV photodetectors.

https://iopscience.iop.org/article/10.1088/0957-4484/26/23/235703/pdf

Few-layer graphene/ZnO nanowires based high performance UV photodetector.

We report a theoretical/experimental study of current-voltage characteristics $(I\text{\ensuremath{-}}V)$ of graphene devices near the Dirac point. The $I\text{\ensuremath{-}}V$ can be described by a power law ($I\ensuremath{\propto}{V}^{\ensuremath{\alpha}}$ with $1l\ensuremath{\alpha}\ensuremath{\le}1.5$). The exponent is higher when the mobility is lower. This superlinear $I\text{\ensuremath{-}}V$ is interpreted in terms of the interplay between Zener-Klein transport, that is tunneling between different energy bands, and defect scattering. Surprisingly, the Zener-Klein tunneling is made visible by the presence of defects.

/pdf/current-voltage-characteristics-of-graphene-devices-4u0qmegz2y.pdf

Current-voltage characteristics of graphene devices: Interplay between Zener-Klein tunneling and defects

The current-voltage curve of metallic carbon nanotubes (CNTs) displays at high bias a sudden increase of the resistivity due to the scattering of electrons with phonons having an anomalously high population (hot phonons). Here, we show that it is possible to improve the electrical performances of metallic CNTs by 13C isotope enrichment. In fact, isotopic disorder creates additional channels for the hot-phonon deexcitation, reduces their population and, thus, the nanotube high-bias differential resistance. This is an extraordinary case where disorder improves the electronic transport.

Niels Vandecasteele

Papers

Current-voltage characteristics of graphene devices: Interplay between Zener-Klein tunneling and defects

Boosting electronic transport in carbon nanotubes by isotopic disorder.