Markus Huecker | Searcharxiv

arXiv2023

Growth of bilayer stanene on a magnetic topological insulator aided by a buffer layer

Stanene, a two-dimensional counterpart to graphene, has the potential to exhibit novel quantum phenomena when grown on a magnetic topological insulator (MTI). This work demonstrates the formation of up to bilayer stanene on 30\% Sb-doped MnBi$_{2}$Te$_4$ (MBST), a well known MTI, albeit with a buffer layer (BL) in between. Angle-resolved photoemission spectroscopy (ARPES), when combined with density functional theory (DFT), reveals stanene related bands such as two hole-like bands and an inverted parabolic band around the $\overline{\Gamma}$ point. An outer hole-like band traverses the Fermi level (\ef) and gives rise to a hexagonal Fermi surface, showing that stanene on MBST is metallic. In contrast, a bandgap of 0.8 eV is observed at the $\overline{K}$ point. We find that DFT shows good agreement with ARPES only when the BL and hydrogen passivation of the top Sn layer are considered in the calculation. Scanning tunneling microscopy (STM) establishes the honeycomb buckled structure of stanene. A stanene-related component is also detected in the Sn $d$ core level spectra, in addition to a BL-related component. The BL, which forms because of the chemical bonding between Sn and the top two layers of MBST, has an ordered crystal lattice with random anti-site defects. The composition of the BL is estimated to be Sn:Te:Bi/Sb $\approx$ 2:1:1 from x-ray photoelectron spectroscopy. Low energy electron diffraction shows that the lattice constant of stanene is marginally larger than that of MBST, and the STM result aligns with this. The BL bridges this disparity and provides a platform for stanene growth.

cond-mat.mtrl-sci↗

arXiv2002

The Local Structure of La1.65Eu0.2Sr 0.15CuO4 determined by 63Cu NMR Spectroscopy and Van Vleck Paramagnetism of Eu3+ Ions

We investigate the local symmetry of the tilting of the CuO$_6$ octahedra in La$_{\rm 1.65}$Eu$_{\rm 0.2}$Sr$_{\rm 0.15}$CuO$_{4}$ by means of $^{63}$Cu NMR spectroscopy and the Van Vleck susceptibility of the $\rm Eu^{3+}$ ions. The Cu NMR central line lineshape is sensitive to local structure through the coupling of the $^{63}\rm Cu$ nuclear quadrupole moment to the local electric field gradient.The $\rm Eu^{3+}$ Van Vleck susceptibility, as a single ion effect, locally probes the symmetry of the crystal field at the Eu site. Both techniques independently provide clear evidence for a change of the local tilt symmetry at the first order structural transition from the orthorhombic to the low temperature tetragonal phase, in excellent agreement with the average structure obtained by diffraction techniques. We conclude that the symmetry of the average crystal structure accurately represents the symmetry of the octahedral tilt pattern on a local scale.

cond-mat.str-el↗