Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session W8: Scanned Probe Microscopy of Novel Materials and Systems |
Hide Abstracts |
Sponsoring Units: GIMS Chair: Joseph Stroscio, National Institute of Standards and Technology Room: Portland Ballroom 255 |
Thursday, March 18, 2010 11:15AM - 11:51AM |
W8.00001: Quantized spin-momentum transfer in atom-sized magnetic systems Invited Speaker: Our ability to quickly access the vast amounts of information linked in the internet is owed to the miniaturization of magnetic data storage. In modern disk drives the tunnel magnetoresistance effect (TMR) serves as sensitive reading mechanism for the nanoscopic magnetic bits [1]. At its core lies the ability to control the flow of electrons with a material's magnetization. The inverse effect, spin transfer torque (STT), allows one to influence a magnetic layer by high current densities of spin-polarized electrons and carries high hopes for applications in non-volatile magnetic memory [2]. We show that equivalent processes are active in quantum spin systems. We use a scanning tunneling microscope (STM) operating at low temperature and high magnetic field to address individual magnetic structures and probe their spin excitations by inelastic electron tunneling [3]. As model system we investigate transition metal atoms adsorbed to a copper nitride layer grown on a Cu crystal. The magnetic atoms on the surface possess well-defined spin states [4]. Transfer of one magnetic atom to the STM tip's apex creates spin-polarization in the probe tip. The combination of functionalized tip and surface adsorbed atom resembles a TMR structure where the magnetic layers now consist of one magnetic atom each. Spin-polarized current emitted from the probe tip not only senses the magnetic orientation of the atomic spin system, it efficiently transfers spin angular momentum and pumps the quantum spin system between the different spin states. This enables further exploration of the microscopic mechanisms for spin-relaxation and stability of quantum spin systems. \\[4pt] [1] Zhu and Park, Mater. Today 9, 36 (2006).\\[0pt] [2] Huai, AAPPS Bulletin 18, 33 (2008).\\[0pt] [3] Heinrich et al., Science 306, 466 (2004).\\[0pt] [4] Hirjibehedin et al., Science 317, 1199 (2007). [Preview Abstract] |
Thursday, March 18, 2010 11:51AM - 12:27PM |
W8.00002: Scanning Tunneling Microsocpy of Complex Magnetic Order Invited Speaker: |
Thursday, March 18, 2010 12:27PM - 1:03PM |
W8.00003: Scanning Tunneling Microscopy and Spectroscopy of Iron-Based Superconductors Invited Speaker: Two decades after the discovery of high-$T_c$ superconductivity in the cuprates, superconductivity was discovered up to $55\,\mathrm{K}$ in a second family of materials: the iron-pnictides. This recent discovery has generated tremendous excitement for several reasons. First, there is hope that the iron-pnictides will finally provide the foil necessary to understand the enormous yet puzzling body of research on the cuprates. Second, reports of low anisotropy and strong vortex pinning in these new materials have spurred optimism that the iron-pnictides may finally lead to the widespread technological applications which have been elusive for cuprates. In this talk, I will present the first scanning tunneling spectroscopic imaging study of a single crystal iron-pnictide superconductor in high magnetic fields. We study optimally doped BaCo$_{0.2}$Fe$_{1.8}$As$_{2}$ with $T_c = 25.3\,\mathrm{K}$, finding a $\sim6\,\mathrm{meV}$ superconducting gap with nanoscale inhomogeneity, which leads to an average reduced gap of $2\Delta/k_{B}T_{c}\sim5.7$. We further observe a static disordered vortex lattice at $9\,\mathrm{T}$, and demonstrate that vortices are pinned in the bulk of this material, a promising observation for practical application. [Preview Abstract] |
Thursday, March 18, 2010 1:03PM - 1:39PM |
W8.00004: Kondo effect of bulk impurities studied with electron focusing Invited Speaker: By scrutinizing the real-space properties of the single-electron propagator and settling the explicit relation between the Fermi surface shape in k-space and the anisotropic charge oscillations in r-space, we demonstrate a new application of STM: visualization of (i) bulk electron properties of metals and of (ii) embedded single impurities in a metal. Even the very simple Fermi surface of copper causes strongly anisotropic propagation characteristics of bulk electrons that are confined in beamlike paths on the nanoscale, a form of electron focusing. The induced charge density oscillations on the nearby surface can be visualized with a low-temperature scanning tunneling microscope. We have used this focusing effect to study single magnetic impurities. Up to now scanning tunneling spectroscopy has shown that Kondo signatures rapidly vanish with increasing distance from the impurity. Here we report on a hitherto unobserved long range Kondo fingerprint for single magnetic atoms Fe and Co below the surface of copper. [Preview Abstract] |
Thursday, March 18, 2010 1:39PM - 2:15PM |
W8.00005: Charge Measurement of Atoms and Atomic Resolution of Molecules with Noncontact AFM Invited Speaker: Individual gold and silver adatoms [1] and pentacene molecules [2] on ultrathin NaCl films on Cu(111) were investigated using a qPlus tuning fork atomic force microscope (AFM) operated at 5 Kelvin with oscillation amplitudes in the sub-{\AA}ngstrom regime. Charging a gold adatom by one electron charge increased the force on the AFM tip by a few piconewtons. Employing Kelvin probe force microscopy (KPFM) we also measured the local contact potential difference (LCPD). We observed that the LCPD is shifted depending on the sign of the charge and allows the discrimination of positively charged, neutral, and negatively charged atoms. To image pentacene molecules we modified AFM tips by means of vertical manipulation techniques, i.e. deliberately picking up known atoms and molecules, such as Au, Ag, Cl, CO, and pentacene. Using a CO terminated tip we resolved all individual atoms and bonds within a pentacene molecule. Three dimensional force maps showing the site specific distance dependence above the molecule were extracted. We compared our experimental results with density functional theory (DFT) calculations to gain insight on the physical origin of AFM contrast formation. We found that atomic resolution is only obtained due to repulsive force contributions originating from the Pauli exclusion principle. \\[4pt] [1] L. Gross, F. Mohn, P. Liljeroth, J. Repp, F. J. Giessibl, G. Meyer, Science 324, 1428 (2009). \\[0pt] [2] L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 325, 1110 (2009). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700