Local Electronic Properties in the Presence of Internal and External Magnetic Fields Studied by Variable-Temperature Scanning Tunneling Spectroscopy

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Abstract
We have developed a new low-temperature ultrahigh vacuum scanning tunneling microscope (UHV-STM) setup combined with a solenoid and a split-pair magnet. The STM can be operated in the 10-11 mbar range, down to 7 K and in a rotatable magnetic field of up to 7 T perpendicular and 2 T parallel to the sample surface. This LT-UHV-STM setup was applied to study the Landau level quantization in n-type InAs(110). In addition to the observation of the Landau level splitting of the conduction band we were able to determine the energy dependence of the effective electron mass due to the nonparabolicity of the conduction band. Furthermore, we have studied the scattering of electron waves at dopant atoms located several nanometers (1–20 nm) below the surface. In a second study we have applied variable-temperature UHV-STM to investigate the temperature-dependent exchange splitting of a d z 2 -like surface state of Gd(0001) thin films. The experimental results indicate that the high spatial localization of the surface state helps to maintain a local exchange splitting even above the Curie temperature but does not result in an enhanced surface Curie temperature. Finally, we have demonstrated spin-polarized vacuum tunneling from a ferromagnetically-coated tip into the exchange-split surface state of Gd(0001).