### Session A3a: STM Manipulation of Single Atoms, Charges, and Spins

 Monday, March 21, 2005 8:00AM - 8:36AM A3a.00001: Single-Atom Spin-Flip Spectroscopy Invited Speaker: Andreas Heinrich The energy levels of a magnetic atom split in an applied magnetic field. We recently built an STM with a base temperature of 0.6K and a maximum magnetic field of 7T. These operating conditions allow the direct measurement of the Zeeman energy with inelastic tunneling spectroscopy [1]. We found that the Mn atoms have to be removed from the metal conduction electrons to suppress strong interactions such as the Kondo effect; we use Al$_{2}$O$_ {3}$ grown on NiAl (110). The tell-tale sign of a vibrational mode in inelastic spectroscopy is the predictable frequency shift with mass. In spin-flip spectroscopy we can continuously tune the Zeeman energy with the applied magnetic field. We observe that the measured Zeeman energy is proportional to the magnetic field which yields a local measure of the 'g-value'. We find g- values in the vicinity of g=2, however the exact value depends on the local environment. When a Mn atom sits near the edge of the oxide film we observe strong coupling with the conduction electrons of the substrate resulting in a Kondo effect with Kondo temperatures of a few Kelvin. In contrast to previous STM work we do not observe the Kondo resonance as a Fano line shape. The logarithmic temperature dependence of the Kondo resonance as well as its splitting in magnetic field corroborates the interpretation as a Kondo effect. [1] A.J. Heinrich, J.A. Gupta, C.P. Lutz, D.M. Eigler, Science 306, 466 (2004). Monday, March 21, 2005 8:36AM - 9:12AM A3a.00002: Localization of Fractionally Charged Quasi-Particles Invited Speaker: Amir Yacoby In this work we address several outstanding questions pertaining to the microscopic properties of the fractional quantum Hall effect: What is the nature of the particles that participate in the localization but do not contribute to transport and can fractionally charged quasi particles localize in space? Using a scanning single electron transistor we image the individual localized states in the fractional quantum Hall regime and determine the charge of the localizing particles. Highlighting the symmetry between filling factors 1/3 and 2/3, our measurements show that fractionally charged quasi particles localize in space to sub-micron dimensions with e*=e/3, where e is the electron charge. In addition, at filling factors 2/3 we follow the behavior of the fractionally charged localized states through the spin phase transition. Monday, March 21, 2005 9:12AM - 9:48AM A3a.00003: Controlling the Dynamics of a Single Atom in Lateral Atom Manipulation Invited Speaker: Joseph A. Stroscio The ability to manipulate single atoms with the scanning tunneling microscope (STM) stirs one's imagination because of the vast opportunities made possible for building atomic scale devices and nanostructures. Understanding the host of interactions in the STM tunnel junction, and their optimization, is required for efficient and reliable atom manipulation. In this talk I will discuss our work on using atom manipulation imaging and the noise characteristics of the tunneling current as probes of the physics of the atom manipulation process [1]. I will first discuss the dynamics of the Co atom in the context of a manipulated atom image, which is obtained by scanning a single Co atom across the surface. When the Co atom is positioned over the hcp site, dynamic behavior is observed both in the manipulated atom image and in the tunnel current. This site dependent noise in the tunneling current is in the audio range and can be heard as the atom is dragged over the surface. This dynamic behavior corresponds to the Co atom switching between the neighboring fcc and hcp sites of the Cu(111) surface. This occurs by the creation of an ideal, tunable, multi-well potential by the tip-adatom interaction. An ideal double well potential is created by positioning the probe tip slightly off center from the hcp site. Two-state transfer rates between the hcp and fcc sites are obtained by measuring the distribution of residence times in each state. The transfer rates show two distinct regimes. A transfer rate independent of tunneling current, voltage and temperature that is ascribed to quantum tunneling between the two wells, followed by a transfer rate with a strong power law dependence on current or voltage, indicative of vibrational heating by inelastic electron scattering. 1. J.A. Stroscio and R. J. Celotta, Science \textbf{306}, 242 (2004).