Papers by Markus Morgenstern
Surface Science, 2008
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Journal of Electron Spectroscopy and Related Phenomena, Aug 1, 2000
We review our recent work on low temperature scanning tunneling spectroscopy (STS) in magnetic fi... more We review our recent work on low temperature scanning tunneling spectroscopy (STS) in magnetic field on InAs(110). First, we describe the influence of the tip on the sample. It results in band bending at the InAs-surface, more precisely in a so called tip induced quantum dot. STS of the quantum dot states is used to reconstruct the quantum dot potential,
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Physica E-low-dimensional Systems & Nanostructures, 2003
Scanning tunneling spectroscopy performed at T=6K is used to investigate the local density of sta... more Scanning tunneling spectroscopy performed at T=6K is used to investigate the local density of states (LDOS) of electron systems in the bulk conduction band of InAs. In particular, the 3DES of the n-doped material and an adsorbate-induced 2DES located at the surface are investigated at B=0 and 6T. It is found that the 3DES at B=0T can be described by
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Physical Review Letters, Sep 9, 2002
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Review of Scientific Instruments, Nov 1, 2004
We describe the design and development of a scanning tunneling micoscope (STM) working at very lo... more We describe the design and development of a scanning tunneling micoscope (STM) working at very low temperatures in ultra-high vacuum (UHV) and at high magnetic fields. The STM is mounted to the He3 pot of an entirely UHV compatible He3 refrigerator inside a tube which can be baked out to achieve UHV conditions even at room temperature. A base temperature of 315 mK with a hold time of 30 h without any recondensing or refilling of cryogenics is achieved. The STM can be moved from the cryostat into a lower UHV-chamber system where STM-tips and -samples can be exchanged without breaking UHV. The chambers contain standard surface science tools for preparation and characterization of tips and samples in particular for spin-resolved scanning tunneling spectroscopy (STS). Test measurements using either superconducting tips or samples show that the system is adequate for performing STS with both high spatial and high energy resolution. The vertical stability of the tunnel junction is shown to be 5 pmpp and the energy resolution is about 100 μeV.
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Physica Status Solidi B-basic Solid State Physics, Dec 1, 1998
Abstract The in-situ cleaved n-InAs (110) surface is studied by low temperature scanning tunnelin... more Abstract The in-situ cleaved n-InAs (110) surface is studied by low temperature scanning tunneling spectroscopy and microscopy in magnetic fields up to 6 T perpendicular to the surface. The dI/dV (V) curves exhibit characteristic oscillations in magnetic field, which are ...
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Physical Review B
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Bulletin of the American Physical Society, Mar 16, 2021
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Nano Letters, 2022
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arXiv: Mesoscale and Nanoscale Physics, 2012
Graphene flakes are prepared on freshly cleaved mica by exfoliation in different environments and... more Graphene flakes are prepared on freshly cleaved mica by exfoliation in different environments and studied by scanning tunneling microscopy in ultra high vacuum down to the atomic length scale. On the monolayer, we observed an overall roughness of about 60 pm, after heating the sample to 180{\deg}C which is larger than on similarly prepared multilayers (24 pm) and larger than on monolayers which have been mapped recently by atomic force microscopy without heating (24 pm). A slight preference for a distinct wave length ({\lambda}\simeq8 nm) of corrugations could be determined using an autocorrelation analysis. On few-layer graphene, a triangular network of partial dislocations separating ABC stacked and ABA stacked graphene was found similar to the networks occasionally visible on freshly cleaved HOPG. We found differences in the electronic structure of ABC and ABA stacked areas by scanning tunneling spectroscopy, i.e., a pronounced peak at 0.25 eV above the Fermi level exclusively in...
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Advanced Materials, 2021
Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect, which is potentia... more Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect, which is potentially useful for high‐precision metrology, edge channel spintronics, and topological qubits. The stable 2+ state of Mn enables intrinsic magnetic topological insulators. MnBi2Te4 is, however, antiferromagnetic with 25 K Néel temperature and is strongly n‐doped. In this work, p‐type MnSb2Te4, previously considered topologically trivial, is shown to be a ferromagnetic topological insulator for a few percent Mn excess. i) Ferromagnetic hysteresis with record Curie temperature of 45–50 K, ii) out‐of‐plane magnetic anisotropy, iii) a 2D Dirac cone with the Dirac point close to the Fermi level, iv) out‐of‐plane spin polarization as revealed by photoelectron spectroscopy, and v) a magnetically induced bandgap closing at the Curie temperature, demonstrated by scanning tunneling spectroscopy (STS), are shown. Moreover, a critical exponent of the magnetization β ≈ 1 is found, indicating the vicinit...
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Physical Review B, 2016
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Chemistry of Materials, 2017
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physica status solidi (RRL) - Rapid Research Letters, 2015
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Physical Review B - Condensed Matter and Materials Physics, 2012
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Technical Physics Letters, 2008
ABSTRACT Conditions for a transition from the insulator (I) to metal (M) state in the electron sy... more ABSTRACT Conditions for a transition from the insulator (I) to metal (M) state in the electron system of highly oriented pyrolytic graphite (HOPG) have been studied by means of magnetotransport measurements in a broad temperature range (0.3–150 K). In magnetic fields below a certain critical value (B < B c ≈ 0.05 T), HOPG exhibits the classical magnetoresistance, while for B > B c, the temperature dependence of the resistance is determined by the state (insulator versus metal) of the electron system. The M-I transition in HOPG, by analogy with that in heterostructures with two-dimensional electron gas, obeys the power law T c ∞ (B − B c) k (k = 0.25) and is related to the spin-orbit interaction of electron waves. PACS numbers71.30.+h–73.43.Qt
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Physical Review Letters, 2012
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Nano Letters, 2010
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Physical Review Letters, Feb 6, 2003
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2D Materials
Van der Waals layered materials with well-defined twist angles between the crystal lattices of in... more Van der Waals layered materials with well-defined twist angles between the crystal lattices of individual layers have attracted increasing attention due to the emergence of unexpected material properties. As many properties critically depend on the exact twist angle and its spatial homogeneity, there is a need for a fast and non-invasive characterization technique of the local twist angle, to be applied preferably right after stacking. We demonstrate that confocal Raman spectroscopy can be utilized to spatially map the twist angle in stacked bilayer graphene for angles between 6.5∘ and 8∘ when using a green excitation laser. The twist angles can directly be extracted from the moiré superlattice-activated Raman scattering process of the transverse acoustic (TA) phonon mode. Furthermore, we show that the width of the TA Raman peak contains valuable information on spatial twist angle variations on length scales below the laser spot size of ∼500 nm.
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Papers by Markus Morgenstern