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P. Neugebauer

Publications and source records attributed to P. Neugebauer.

4 recordsLinked to original sources

Towards large-area and defects-free growth of phosphorene on Nickel

Low-dimensional materials synthesis based on phosphorus atoms is under intense study, and it is still one of the big challenges. Phosphorene, a monolayer of black phosphorus, is one of the most promising candidates for transistor and photonics devices at atomistic thickness. However, the lack of large-scale and defects-free growth significantly obstructs its device development. Here, we demonstrate the large-scale and defect-free phosphorene synthesis on Nickel (Ni) substrate. In addition, the effect of substrate orientation on the controllable synthesis of possible allotropes has also been described. We have shown that blue phosphorene can be grown on Ni (111) and Ni (100). While {\gamma}-Phosphorene, named Navy Phosphorene hereafter, can be grown on Ni (110). Furthermore, we found that the synthesis goes through phosphorus pentamers (P5) to phosphorene; P5 is a vital precursor for phosphorene synthesis. Moreover, we confirm the high accuracy of the P-Ni, and P-P potentials and show that the molecular dynamics (M.D.) approach is a powerful tool to simulate the 2D materials synthesis in the vapor phase. This work provides a solid reference to understand and control the synthesis of large-area single-crystalline monolayer phosphorene.

cond-mat.mtrl-sci

3D massless Kane fermions observed in a zinc-blende crystal

Solid state physics and quantum electrodynamics with its ultra-relativistic (massless) particles meet, to their mutual beneit, in the electronic properties of one-dimensional carbon nanotubes as well as two-dimensional graphene or surfaces of topological insulators. However, clear experimental evidence for electronic states with conical dispersion relations in all three dimensions, conceivable in certain bulk materials, is still missing. In the present work, we fabricate and study a zinc-blend crystal, HgCdTe, at the point of the semiconductor-to-semimetal topological transition. Three-dimensional massless electrons with a velocity of about 10$^6$ m/s are observed in this material, as testifed by: (i) the dynamical conductivity which increases linearly with the photon frequency, (ii) in a magnetic field $B$, by a $\sqrt{B}$ dependence of dipole-active inter-Landau-level resonances and (iii) the spin splitting of Landau levels, which follows a $\sqrt{B}$ dependence, typical of ultra-relativistic particles but not really seen in any other electronic system so far.

cond-mat.mes-hall

Cyclotron motion in the vicinity of a Lifshitz transition in graphite

Graphite, a model (semi)metal with trigonally warped bands, is investigated with magneto-absorption experiment and viewed as an electronic system in the vicinity of the Lifshitz transition. A characteristic pattern of up to twenty cyclotron resonance harmonics has been observed. This large number of resonances, their relative strengths and characteristic shapes trace the universal properties of the electronic states near a separatrix in the momentum space. Quantum-mechanical perturbative methods with respect to the trigonal warping term hardly describe the data which are, on the other hand, fairly well reproduced within a quasi-classical approach and conventional band structure model. Trigonal symmetry is preserved in graphite in contrast to a similar system, bilayer graphene.

cond-mat.mes-hall

How perfect can graphene be?

Fabrication of graphene structures has triggered vast research efforts focused on the properties of two-dimensional systems with massless Dirac fermions. Nevertheless, further progress in exploring this quantum electrodynamics system in solid-state laboratories seems to be limited by insufficient electronic quality of manmade structures and the crucial question arises whether existing technologies have reached their limits or major advances are in principle possible. Here we show that graphene in a significantly purer state can be found in nature on the surface of bulk graphite, in form of flakes decoupled from the substrate material. Probing such flakes with Landau level spectroscopy in the THz range at very low magnetic fields, we demonstrate a superior electronic quality of these ultra low density layers (n~3x10^9 cm^-2) expressed by the carrier mobility in excess of 10^7 cm^2/(V.s). This finding represents an important challenge for further improvements of current graphene technologies.

cond-mat.mes-hall