CrGeTe
3
(CGT) is a semiconducting vdW ferromagnet shown
to possess magnetism down to a two-layer thick sample. Although CGT
is one of the leading candidates for spintronics devices, a comprehensive
analysis of CGT thickness dependent magnetization is currently lacking.
In this work, we employ scanning SQUID-on-tip (SOT) microscopy to
resolve the magnetic properties of exfoliated CGT flakes at 4.2 K.
Combining transport measurements of CGT/NbSe
2
samples with
SOT images, we present the magnetic texture and hysteretic magnetism
of CGT, thereby matching the global behavior of CGT to the domain
structure extracted from local SOT magnetic imaging. Using this method,
we provide a thickness dependent magnetization state diagram of bare
CGT films. No zero-field magnetic memory was found for films thicker
than 10 nm, and hard ferromagnetism was found below that critical
thickness. Using scanning SOT microscopy, we identify a unique edge
magnetism, contrasting the results attained in the CGT interior.
We study electronic densities of states (DOS) of strongly disordered superconducting thin films of TiN. We find through scanning tunneling microscopy (STM) measurements that the DOS decreases towards the Fermi level in the normal phase obtained by applying magnetic fields. The DOS shows spatial fluctuations whose length scale is related to the energy-dependent decrease in the DOS close to the Fermi level and is similar in normal and superconducting phases. This shows that Coulomb interaction in disordered metals strongly influences the normal DOS and suggests that reduced Coulomb screening leads to spatial variations in the superconducting DOS.
A Scanning Tunneling Microscope (STM) is one of the most important scanning probe tools available to study and manipulate matter at the nanoscale. In a STM, a tip is scanned on top of a surface with a separation of a few Å. Often, the tunneling current between tip and sample is maintained constant by modifying the distance between the tip apex and the surface through a feedback mechanism acting on a piezoelectric transducer. This produces very detailed images of the electronic properties of the surface. The feedback mechanism is nearly always made using a digital processing circuit separate from the user computer. Here we discuss another approach, using a computer and data acquisition through the USB port. We find that it allows succesful ultra low noise studies of surfaces at cryogenic temperatures. We show results on different compounds, a type II Weyl semimetal (WTe 2 ), a quasi two-dimensional dichalcogenide superconductor (2H-NbSe 2 ), a magnetic Weyl semimetal (Co 3 Sn 2 S 2 ) and an iron pnictide superconductor (FeSe).
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