Bulletin of the American Physical Society
79th Annual Meeting of the APS Southeastern Section
Volume 57, Number 16
Wednesday–Saturday, November 14–17, 2012; Tallahassee, Florida
Session BC: National High-Field Magnet Laboratory I |
Hide Abstracts |
Chair: James Brooks, Florida State University Room: DoubleTree Adams-Park |
Thursday, November 15, 2012 8:30AM - 8:42AM |
BC.00001: Evolution of the Fermi Surface of Chromium at High Pressure and High Magnetic Fields Ryan Stillwell, David Graf, William Coniglio, Timothy Murphy, Eric Palm, Ju-Hyun Park, Pedro Schlottmann, Jeffrey Whalen, Rafael Vasquez, Theo Siegrist, Stanley Tozer Results on the pressure dependence of the Fermi surface of chromium will be presented. Employing plastic turnbuckle diamond anvil pressure cells in pulsed magnetic fields and metal diamond anvil cells in DC magnetic fields, skin depth measurements of chromium were made at low temperatures which yielded Shubnikov-de Haas oscillations. By performing in situ rotations of the pressure cell we are able to map out the Fermi surfaces as we move towards the quantum critical point at which the antiferromagnetic phase is suppressed. [Preview Abstract] |
Thursday, November 15, 2012 8:42AM - 8:54AM |
BC.00002: High Field Measurements of the Peierls and Spin-Peierls Transition in the Organic Conductor (\textit{Per})$_2$[Pt(\textit{mnt})$_2]$ Using a Tunnel Diode Oscillator Laurel Winter, James Brooks Recently, we have used a tunnel diode oscillator (TDO) to investigate the organic conductor (\textit{Per})$_2$[Pt(\textit{mnt})$_2]$, which undergoes both a Peierls (charge density wave - CDW) and spin-Peierls (SP) transition. Previously performed temperature dependent studies such as resistivity, specific heat, and susceptibility all show a common transition at T$_c\sim$ 6 - 8 K. Since these two transitions appear to occur exactly at the same temperature, the question of coupling between the two chains remains open. In addition, since each method is primarily sensitive to either the CDW transition or the SP transition it is possible some small temperature difference separating the two is not evident from these techniques. In this situation, the TDO technique is ideal to investigate the possible temperature difference between the two transitions, due to its high sensitivity and ability to simultaneously measure both changes in electrical transport and magnetic properties of a material. It is in this context that we will discuss the current TDO developed phase diagram of (\textit{Per})$_2$[Pt(\textit{mnt})$_2]$ at fields up to and above 15 T, as well as discuss what exactly the TDO is measuring since it is a vital part of understanding the results of the study. [Preview Abstract] |
Thursday, November 15, 2012 8:54AM - 9:06AM |
BC.00003: Magnetic Field and Temperature Dependence of Decoherence in a High Mobility Landau Quantized 2DEG Jeremy Curtis, T.T. Tokumoto, J.G. Cherian, X. Wang, Luke McClintock, J.L. Reno, A. Belyanin, J. Kono, S.A. McGill, D.J. Hilton We apply a perpendicular magnetic field to a high mobility ($\mu=3.4\times 10^{6}$ cm$^{2}$ V$^{-1}$ s$^{-1}$) two dimensional electron gas (2DEG) which splits the Fermi surface into a spectrum of Landau levels (LL). The highest filled and lowest unfilled LLs are coherently coupled by an incident THz pulse. The time required for carriers in this superposition state to become out of phase is the decoherence time. The focus of our work is to measure this decoherence time over a wide range of temperatures (0.4 K-100 K) and magnetic fields (1.25 T-17.5 T). Using THz time-domain spectroscopy (TTDS), we map the decoherence as a function of B and T. This talk will review previous work done at 0.4 K and 1.25 T; furthermore, we will discuss current work being done to increase our B dependence to 17.5 T using superconducting magnet 3 at the National High Magnetic Field Lab at Florida State University. This work utilizes a novel \emph{reflection} TTDS system. [Preview Abstract] |
Thursday, November 15, 2012 9:06AM - 9:18AM |
BC.00004: Magneto-transport properties of the ternary topological insulator (Bi$_{0.5}$Sb$_{0.5})_{2}$Te$_{3}$ in the presence of electrostatic gating and magnetic impurity Liuqi Yu, Jorge Barreda, Longqian Hu, P. Xiong, Tong Guan, Xiaoyue He, K. Wu, Y. Li A three-dimensional ternary topological insulator, (Bi$_{0.5}$Sb$_{0.5})_{2}$Te$_{3}$, is used to characterize the unique electronic properties of the spin helical conducting surface state. Epitaxial films are grown via MBE on (111) SrTiO$_{3}$ substrate, which serves as the gate dielectric. Magnetoresistance (MR) and Hall effect measurements have been performed in a broad range of back gate voltages. Ambipolar field effect has been observed, enabling effective tuning of the Fermi level across the band gap and identification of the surface transport in the topological transport regime. Weak antilocalization effect is identified and used to differentiate the surface state. The Hikami-Larkin-Nagaoka (HLN) equation is used to analyze the MR data and the results show the top and bottom surfaces become decoupled when the Fermi level is in the bulk band gap. We also examine the effects of paramagnetic impurity (MI), which introduces time reversal symmetry breaking scattering on the TI surface states. Taking advantage of the unique capability of \textit{in situ} deposition of Cr atoms in a customized dilution refrigerator, MI was incrementally quench-condensed onto the sample surface and transport measurements were performed at each MI density. Pronounced changes in the weak antilocalization effect and the sample carrier density with increasing MI concentration were observed. Possible origins of these observations will be discussed. [Preview Abstract] |
Thursday, November 15, 2012 9:18AM - 9:30AM |
BC.00005: Unusual Hall effect of La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films with percolative phase transition Liuqi Yu, Xiaohang Zhang, S. von Molnar, P. Xiong, Lingfei Wang, W. Wu Detailed transport measurements have been performed on three PLD-grown epitaxial La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) thin films on NdGaO$_{3}$ (NGO) substrate. The films were grown under identical conditions (735$^{\circ}$C substrate temperature and 45 Pa O$_{2}$ pressure) but post-annealed at 780$^{\circ}$C in flowing O$_{2}$ for 1, 10 and 20 hours respectively to produce increasing degrees of strain relaxation which could lead to charge-ordered states.\footnote{Z. Huang et al., JAP 105, 113919(2009)} In all three samples, the Hall resistivity in the paramagnetic phase takes on two distinct slopes: a negative slope at low fields which decreases with increasing temperature, and an almost temperature-independent positive slope at high fields. It is found that the switch in the Hall resistivity slope occurs at the same critical magnetization regardless of both temperature and magnetic field, which we interpret as an indicator of the percolative nature of the phase transitions.\footnote{X. Zhang et al., PRL 103, 106602 (2009)} In the two strain-relaxed samples, pronounced dips in the Hall resistivity are observed near the transition temperature. The apparent correlation of the appearance of the dips with increasing strain relaxation and their suppression by increasing in-plane magnetic field suggests a possible connection of the Hall resistivity dips with the presence of the charge ordered state. Work supported in part by NSF DMR-0908625. [Preview Abstract] |
Thursday, November 15, 2012 9:30AM - 9:42AM |
BC.00006: Mechanical and Physical Measurement Tools and Techniques Related to High Field Magnets Robert Walsh Materials properties are the physical limitation in the achievement of higher magnetic fields and the construction of bigger magnets. High-field magnet designers try to use the newest generation of materials (structural and conductors) and design magnets with factors not acceptable in typical machine design or civil engineering applications. Examples of material property limitations on magnet design are introduced that set the stage for the state-of-the-art facilities necessary for characterizing the materials used in NHMFL magnets. Conventional strain measuring techniques (strain gages are the workhorses) are extended to low temperature tests by using cryogenic compatible materials and low temperature calibrations. For structural materials, strain gage based sensors provide accurate determination of yield strength, ductility, fracture toughness and fatigue life data necessary for efficient/reliable design of the magnets. Superconductors (LTS and HTS) are sensitive materials that often require non-contact strain sensing at cryogenic temperatures. A 3D-Digital Image Correlation system is a non-contact strain measuring system that provides whole-field strain measurement and is currently being extended to cryogenic applications of testing superconductors. Additionally, accurate dimensional characterization of test specimens, before and after testing, is enhanced with a contemporary CNC inspection microscope. [Preview Abstract] |
Thursday, November 15, 2012 9:42AM - 9:54AM |
BC.00007: Enhanced grain connectivity in K-doped ferropnictide Ba-122 bulks and wires with high transport critical current density Jeremy Weiss, Chiara Tarantini, Jianyu Jiang, Fumitake Kametani, Anatolii Polyanskii, David Larbalestier, Eric Hellstrom We present very much improved properties of (Ba$_{0.6}$K$_{0.4})$Fe$_{2}$As$_{2}$ (Ba-122) made as round wires in which transport critical current densities J$_{c}$ (4.2 K, SF) in excess of 0.12 MAcm$^{-2}$, which is approximately 5 times higher than any other ferropnictide wire, have been obtained. Careful low-temperature synthesis was used to eradicate extrinsic current-blocking phases and cracks, which also had the effect of producing fine grain size ($<$200nm) and a high grain boundary density. Very high magnetic field evaluations showed that the upper critical field H$_{c2}$ was well above 50 T and H$_{c2}$ anisotropy was significantly less than 2. This low anisotropy suggests that high vortex stiffness and perhaps less suppression of the grain boundary (GB) order parameter occur in this compound compared to the planar GBs of Co-doped Ba-122 used for bicrystal experiments, which showed weak link behavior that limits critical current across GBs like in other high-temperature superconductors. [Preview Abstract] |
Thursday, November 15, 2012 9:54AM - 10:06AM |
BC.00008: Electron spin resonance measurements using on-chip cavities at low temperature Matt Martens, Kyle Serniak, Sylvain Bertaina, Irinel Chiorescu We describe an Electron Spin Resonance (ESR) measurement technique utilizing a balanced bridge, similar to a ``magic-T,'' in conjunction with a lock-in detector. The setup uses a microstrip line, since this type of approach is highly sensitive and has been gaining more and more interest as of late. We describe the functioning principle and demonstrate that the setup has a high sensitivity, with a low noise baseline. ESR measurements were performed on a s=1/2 DPPH sample at room temperature. Electronic spin excitation of the sample was achieved through use of an ``omega'' shaped microstrip cavity with resonant frequency of 17.4 GHz. Signal detection was done with a homemade heterodyne detector with and without the magic-T bridge and lock-in detector. For comparison, direct measurements were performed using a fast digital acquisition card. [Preview Abstract] |
Thursday, November 15, 2012 10:06AM - 10:18AM |
BC.00009: Spin Configurations in the 2D Frustrated Spin System YBaCo$_{4}$O$_{7}$ Using NMR S. Yuan, M.J.R. Hoch, P.L. Kuhns, T. Besara, J.B. Whalen, T.M. Siegrist, A.P. Reyes, J.S. Brooks, H. Zheng, J.F. Mitchell The system YBaCo$_{4}$O$_{7}$ has frustrated kagome spin planes which are separated by triangular AF spin layers. The configurations of the cobalt spins have been studied by neutron scattering at various temperatures, below \textit{TN}=106 K. In our low temperature NMR experiments on both a powder sample and a single crystal, non-equivalent cobalt sites are associated with distinct peaks in the zero field frequency scan spectra. Information about the internal hyperfine field orientations for both kagome and triangular layers has been obtained in two experiments, (1) rotating the sample with respect to the RF pulse field (zero applied field experiment) and (2) rotating the sample with respect to a small external field (in-field experiment). These approaches can be used to determine the spin configurations. Orthogonal orientations for the kagome hyperfine field and the triangular hyperfine field have been shown in both two experiments. Our low $T $AF spin alignment for the triangular layers is in agreement with the spin configuration in the neutron findings at 5 K, but for spins in kagome layers our orthogonal spin configuration does not agree with the neutron results. [Preview Abstract] |
Thursday, November 15, 2012 10:18AM - 10:30AM |
BC.00010: Low-energy spectroscopy on molecular materials under high pressures K. Thirunavukkuarasu, C.A. Kuntscher, C.C. Beedle, Stephen Winter, K. Kamar\'{a}s, F. Hennrich, A. Kovalev, S. Tozer, R.T. Oakley, S. Hill Low-energy spectroscopy at extreme conditions opens doors to discovery and understanding of novel phenomena in condensed matter physics. In particular, applying hydrostatic pressure is the ideal way to continuously induce structural perturbations such as changes in intermolecular distances, and thereby control the various exchange interactions in novel materials. Among low-energy spectroscopic techniques, infrared and electron spin resonance (ESR) spectroscopy are powerful tools to probe the charge and spin degrees of freedom, respectively, and provide important information on the fundamental energy scales involved in various novel phenomena. However, use of these techniques to investigate materials at high pressures involves a high level of difficulty. In this talk, uncommon combinations of high pressure with IR spectroscopy and multi-frequency ESR spectroscopy, and their application to the study of molecular materials will be discussed. Depending on the availability of time, the strength of these techniques will be illustrated with examples. [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