Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session C3: Experimental Condensed Matter Techniques |
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Chair: Heinz Nakotte, New Mexico State University Room: Macey Center Copper |
Friday, October 26, 2012 1:15PM - 1:39PM |
C3.00001: A superradiant laser with $<1$ intracavity photon Invited Speaker: James K. Thompson We will describe a recently demonstrated laser-cooled Raman laser that operates deep into the superradiant or bad-cavity regime in which the gain medium (i.e. the atoms) acts as the primary reservoir of phase information [1]. The system operates with $<1$ average intracavity photons and with an extremely small effective excited state decay linewidth $<1$~Hz. This model system demonstrates key physics for future active optical clocks (similar to masers) that may achieve frequency linewidths approaching 1~mHz due to 3 to 5 orders of magnitude reduced sensitivity to thermal mirror noise. For scale, a 1~mHz linewidth laser would have a coherence length spanning the distance from the earth to the sun. The measured linewidth of our model system demonstrates that a superradiant laser's frequency linewidth may be below the single atom dephasing and natural linewidths, greatly relaxing experimental requirements on atomic coherence.\\[4pt] [1] Justin G. Bohnet, Zilong Chen, Joshua M. Weiner, Dominic Meiser, Murray J. Holland, and James K. Thompson, ``A steady-state superradiant laser with less than one intracavity photon,'' \textit{Nature} \textbf{484}, pp. 78-81 (2012). [Preview Abstract] |
Friday, October 26, 2012 1:39PM - 1:51PM |
C3.00002: 3D Effect in Determination of Spin Polarization using Andreev Reflection Spectroscopy Jessica Gifford, Charles Snider, Jonny Martinez, Tingyong Chen Andreev Reflection Spectroscopy (ARS) has been utilized to measure spin polarization of many magnetic materials including some half metals, as well as the superconducting gap of superconductors which include the recently discovered Fe superconductors and topological superconductors. The values of spin polarization and superconducting gap are extracted from the ARS data often by a modified Blonder-Tinkham-Klapwijk (BTK) model or the more recent Chen-Tesanovic-Chien (CTC) model. Both consider the ferromagnet/superconductor interface as one dimensional (1D). However, in reality, a tip may have a point angle with three dimensional (3D) effects. In this work, we present both theoretical and experimental studies of the 3D effects in the determination of spin polarization using ARS. We have found that for an ideal interface without interfacial scattering, the 3D ARS spectra are the same as 1D spectra. But for non-ideal interfaces the 3D effect can drastically change the conductance spectra depending on the point angle of the tip. Most importantly, the 3D spectra can be well described by the 1D model with a different interfacial scattering factor and a slightly different inelastic scattering factor. The spin polarization and superconducting gap extracted from the 3D ARS is the same as that extracted using the 1D model, demonstrating that 1D ARS model can be utilized to determine spin polarization as long as interfacial scattering is not of any concern. Finally, we apply the both the 1D and the 3D models to a set of ARS data and show that the extracted spin polarization value is the same for both models. [Preview Abstract] |
Friday, October 26, 2012 1:51PM - 2:03PM |
C3.00003: Andreev Reflection Spectra of $d$-wave Superconductors Charles Snider, Jessica Gifford, Jonathan Martinez, Tingyong Chen At a normal metal/superconductor interface Andreev reflection occurs, which can be utilized to measure spin polarization of the normal metal and also the superconducting gap of the superconductor. An $s$-wave superconductor has an isotropic gap and for an unpolarized current the Andreev reflection spectrum within the gap is twice that of outside the gap. A fully spin polarized current suppresses the Andreev reflection therefore causes zero conductance within the gap. The scenario is quite different in a $d$-wave superconductor because the order parameter has anisotropy and phase. In this work, we calculate Andreev Reelection spectra of an interface between a normal metal and a $d$-wave superconductor for a current with any polarization, based on the recent Chen-Tesanovic-Chien (CTC) model. It is shown that the point angle of the interface can drastically change the Andreev spectra and a zero bias anomaly (ZBA) is observed in the tunneling regime only if the point angle is large. The spin polarization can also drastically affect the spectra and can completely suppress the ZBA. Our calculation shows that one can use both the spin polarization and the point angle to verify the ZBA in unconventional superconductors. [Preview Abstract] |
Friday, October 26, 2012 2:03PM - 2:15PM |
C3.00004: Determination of Spin Polarization of Fe$_{65}$Si$_{35}$ Using Andreev Reflection Spectroscopy Jonathan Martinez, Jessica Gifford, Charles Snider, Tingyong Chen, Julie Karel, Frances Hellman Ferromagnetic Fe$_{\mathrm{x}}$Si$_{\mathrm{1-x}}$ alloys have been proposed as potential spin injectors into silicon with a substantial spin polarization. Experimentally, however, the observed spin polarization of the alloys still remains low. Ideally, spin polarization of a metal is defined as the imbalance of density of states at the Fermi level, but in amorphous alloys it is different since the Fermi level is not well defined. Recently, it has been found that the magnetic properties of the amorphous Fe$_{\mathrm{x}}$Si$_{\mathrm{1-x}}$ alloys are very different from the crystalline phase. In this work, we utilize Andreev Reflection Spectroscopy (ARS) to determine the spin polarization of both amorphous and crystalline Fe$_{65}$Si$_{35}$ alloys. We show that the additional resistance in ARS is quite high because of large resistivity of these alloys and must be taken into account to correctly extract the spin polarization. The obtained spin polarization values are very different: the amorphous phase has a much higher spin polarization than that of the crystalline phase. [Preview Abstract] |
Friday, October 26, 2012 2:15PM - 2:27PM |
C3.00005: Proposed investigation of spin dynamics using time-resolved scanning Kerr microscopy Christopher Finkeldei, Kristen Buchanan Investigation of spin dynamics in thin ferromagnetic structures is currently an area of great interest due in part to applications in magnetic storage devices. The study of spin dynamics in such small samples requires techniques that combine high spatial and temporal resolution. Time-resolved scanning Kerr microscopy is one such technique that employs the magneto-optical Kerr effect to investigate spin dynamics in response to excitations in a sample. The setup and optimization of a time-resolved scanning Kerr microscope will be discussed along with plans for future studies including the investigation of spin dynamics in anti-vortex systems. [Preview Abstract] |
Friday, October 26, 2012 2:27PM - 2:39PM |
C3.00006: Development of a SMOKE Apparatus Susan Stoffer, Karine Chesnel, Luke Pritchett, Kyle Miller Surface Magneto-Optic Kerr Effect (aka SMOKE) is a method for measuring the magnetization of thin films and nano-particles. SMOKE utilizes the optical interaction between linearly-polarized light and a magnetized sample. This interaction causes a rotation in the polarization in the light, as described by the Kerr Effect. SMOKE measures this rotation, which leads to calculation of the magnetization of a sample in the presence of an applied magnetic field. My presentation will discuss the SMOKE method and my progress in developing a SMOKE experimental setup in my lab. Various limitations and advantages of SMOKE will be outlined. Preliminary hysteresis loops measured by the SMOKE will be presented. [Preview Abstract] |
Friday, October 26, 2012 2:39PM - 2:51PM |
C3.00007: Characterization of Surfactant Free Emulsions Ramaninder Brar, Jacob Urquidi There is a pharmacological interest in providing a delivery mechanism for highly hydrophobic drugs through the bloodstream. A typical methodology would be to introduce a surfactant which would serve to bind the hydrophobic molecule to the aqueous environment. Because of the need for the surfactant to be non-toxic this avenue proves problematic and many highly hydrophobic drugs which could prove effective are not useable. We have demonstrated the formation of a stable emulsion of Silicone Oil in degassed water alone. The emulsion droplets were on the order of 50 nm in diameter and stable over a period of 8 hours. Previous studies have shown that the surfactant free emulsions do not lose their stability when the previously removed gasses are reintroduced. The formation of a stable emulsion in the complete absence of a surfactant could provide an alternative approach to a physiologically safe drug carrier. The present work involves the formation of stabilized surfactant free emulsions in a homologous series from pentane through decane. The emulsion's structure and thermodynamic stability were then characterized using small angle x-ray scattering. [Preview Abstract] |
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