LOCAL ELECTRONIC-PROPERTIES IN THE PRESENCE OF INTERNAL AND EXTERNAL MAGNETIC-FIELDS STUDIED BY VARIABLE-TEMPERATURE SCANNING TUNNELING SPECTROSCOPY

We have developed a new low-temperature ultrahigh vacuum scanning tunn eling 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 t o 7 K and in a rotatable magnetic field of up to 7T perpendicular and 2T parallel to the sample surface. This LT-UHV-STM setup was applied t o study the Landau level quantization in n-type InAs(110). In addition to the observation of the Landau level splitting of the conduction ba nd we were able to determine the energy dependence of the effective el ectron mass due to the nonparabolicity of the conduction band. Further more, we have studied the scattering of electron waves at dopant atoms located several nanometers (1-20 nm) below the surface. In a second s tudy we have applied variable-temperature UHV-STM to investigate the t emperature-dependent exchange splitting of a d(z)2-like surface state of Gd(0001) thin films. The experimental results indicate that the hig h spatial localization of the surface state helps to maintain a local exchange splitting even above the Curie temperature but does not resul t in an enhanced surface Curie temperature. Finally, we have demonstra ted spin-polarized vacuum tunneling from a ferromagnetically-coated ti p into the exchange-split surface state of Gd(0001).