arXiv subjects

Hans-Jürgen Meyer

Publications and source records attributed to Hans-Jürgen Meyer.

3 recordsLinked to original sources

arXiv2026

Intercalation of Alkali Metal into WTe2, the Crystal Structure of A0.5WTe2 and Observation of a Metal-to-Semiconductor Transition

We explore the cationic intercalation of tungsten ditelluride (WTe2) with potassium (K), rubidium (Rb), and cesium (Cs), yielding intercalation compounds of the form A0.5WTe2 (A = K, Rb, Cs). Structural characterization was performed using powder X-ray diffraction (PXRD), while diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and temperature-dependent conductivity measurements were employed to investigate the electronic properties. Density functional theory (DFT) calculations were carried out to support the experimental findings and to provide insight into the intercalation mechanisms and the resulting material characteristics. All synthesized compounds display semiconducting behavior with narrow band gaps, emphasizing the influence of alkali metal intercalation on the electronic structure and transport properties of WTe2. These results advance the fundamental understanding of property modulation in transition-metal dichalcogenides (TMDCs) and highlight their potential for electronic device applications.

cond-mat.mtrl-sci↗

arXiv2026

Structural Evolution during Reversible Halogen Intercalation into WTe2: Commensurate-Incommensurate WTe2I and Multistage WTe2Brx (x = 0.5, 1.0 and 1.25)

Halogen intercalation into the layered material tungsten ditelluride (WTe2) provides a unique pathway to tune its structural and electronic properties. In this study, we detail the synthesis and characterization of the new bromine-intercalated phases WTe2Brx (x = 0.5, 1.0, and 1.25), and reinvestigate the iodine-intercalated analogue, WTe2I. A defining feature of the bromine system is its rapid and reversible "breathing" behavior at room temperature, allowing guest molecules to be absorbed or released from the van der Waals gaps under ambient conditions. Structural analysis shows that the bromine-poor phase WTe2Br0.5 crystallizes in the orthorhombic space group Pmmn, thereby maintaining a uniform stacking sequence. In contrast, the bromine-rich WTe2Br1.25 phase (space group Imm2) adopts an architecture where two distinct types of bromine layers alternate between the host layers. For the iodine system, the compound WTe2I exhibits both incommensurate and commensurate (3+1)D modulated variants in the superspace group P21/m(α0γ)00. In the commensurate polytype, the structural modulation locks into a rational vector, q = (1/2, 0, 1/6), which can be described also as a 3D supercell. Electronic structure calculations show WTe2Br0.5 and commensurately modulated WTe2I to be metals with flat bands at the Fermi energy arising from the intercalation. These findings demonstrate the unusual stability and structural flexibility of anionic intercalation in a transition metal dichalcogenides.

cond-mat.mtrl-sci↗

arXiv2011

Y(9.46 GeV) and the gluon discovery (a critical recollection of PLUTO results)

The hadronic decays of Y(9.46GeV) were first studied by PLUTO experiment at DORIS e+e- storage ring (DESY). To determine the contribution of PLUTO to the discovery of the gluon, as members of the collaboration, we have reconsidered all the material produced by it in 1978 and the first half of 1979. It results clearly that the experiment demonstrated the main decay of the Y resonance to be mediated by 3 gluons hadronizing into 3 jets. Jettiness resulted evident by the with respect to the thrust axis, which was as observed by PLUTO itself at nearby continuum c.m.s. energies for 2-quark jet events. Instead, the average sphericity , more topological variables and the momentum distribution showed a net difference with the same data, results compatible with jettiness only in case of more than 2 jets. Flatness as consequence of a 3-body decay (therefore 3 jets) was indicated by the low , altogether a result independent of models. The charged multiplicity was observed to be larger than in the continuum and in case of MC 3 gluon jets fragmenting like quarks, as expected for gluon jets. In June 1979 PLUTO measured the matrix element of the 3-gluon decay to be quantitatively according QCD (even after hadronization, which does not obscure the perturbative predictions) and demonstrated the spin 1 nature of the gluon by excluding spin 0 and spin 1/2. The gluon hadronization like a quark jet, as in 3-gluon jet MC, was compatible with topological data and multiplicity; this was the first experimental study of (identified) gluon jets. The PLUTO results were confirmed both by other experiments at DORIS and later by more sophisticated detectors. At higher energies at PETRA the existence of gluons of spin 1 was confirmed by PLUTO and by 3 more experiments by measuring the gluon radiation, soft gluons by jet broadening, hard gluons by the emission of (now clearly visible) gluon jets by quarks.

hep-ex↗