Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N22: High Magnetic Fields/Electronic and Photonic Devices |
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Sponsoring Units: GIMS Chair: Eric Palm, National High Magnetic Field Lab Room: LACC 409B |
Wednesday, March 23, 2005 8:00AM - 8:12AM |
N22.00001: A new high magnetic field capability at the NHMFL at Los Alamos National Laboratory: 300 tesla Single Turn System Charles Mielke, Joseph Schillig, Jose Ernie Serna, Darryl A. Roybal, Michael Pacheco, James R. Sims, John Singleton We report on the development of a unique system designed to study actinide materials in ultra-high magnetic fields. The energy scales of much of the interesting physics in $f$-electron materials in particular the actinides, demand ultra-high magnetic fields to adequately perturb interactions. We have developed an apparatus to generate magnetic fields approaching 300 tesla; while leaving the hazardous sample intact. The single turn system design is based on a brute force technique to drive a very large electrical current (up to $\sim$3.8 MA) through a simple solenoid before it vaporizes and explodes. Such systems have been pioneered by Herlach and Miura and have proven to be an effective condensed matter research tool. In each shot Lorentz forces and Joule heating destroy the coil, while the sample is untouched, thus allowing for multiple field traces on a single specimen. A distinctive feature of the Los Alamos system is the ability to safely study actinide specimens, this and other design features will be presented as well as experimental data. [Preview Abstract] |
Wednesday, March 23, 2005 8:12AM - 8:24AM |
N22.00002: A photonic bandgap resonator to facilitate GHz frequency conductivity experiments in millisecond duration pulsed magnetic fields. Ross McDonald, Paul Goddard, Neil Harrison, Charles Mielke, John Singleton We report the details of a novel, all-dielectric, microwave resonator measurement system for used in pulsed magnets. In dynamic magnetic field environments, the large rate of change of flux places strict constraints upon the use of metallic components, i.e. avoiding unwanted eddy current heating and destructive magnetic forces and torques. Our solution to this problem is to use dielectric photonic bandgap structures to confine the radiation, producing a high Q-factor resonator. We are thus able to attain sufficient sensitivity to perform a wide range of experiments, such as the measurement of quantum oscillations and electron spin resonance in correlated electron systems. These GHz-frequency techniques are not only an exciting addition to the National High Magnetic Field Laboratory's pulsed field User Program, but also mark an important milestone in the development of instrumentation for dynamic ultra-high $B/T$ environments such as the 300 Tesla single-turn magnet facility currently under construction at the NHMFL in Los Alamos. [Preview Abstract] |
Wednesday, March 23, 2005 8:24AM - 8:36AM |
N22.00003: Contactless Thermal Diffusivity Measurements for Pulsed Magnetic Fields T. Coffey, C.H. Mielke, F.R. Drymiotis, D. Kim, K.-H. Kim, A. Migliori, P. Ruminer Most calorimetric techniques require long time constants. and are limited to DC magnets. We are developing calorimetric measurements on short time scales for pulsed field experiments. Specific heat ($C$) measurements have been performed in high fields (60 T) by Jaime et al.~(Nature, 405 (2000) 160); however, these measurements have been limited to a unique long-pulse magnet. Recently, Kim et al.(to be submitted) have successfully measured thermal conductivity~($\kappa$) in a short pulse magnet; however, the $3-\omega$ technique utilized by Kim et al. requires a time consuming deposition processes. In an effort to bring simple-to-use high field calorimetric measurements to the larger condensed-matter community, we are adapting existing contact-less conductivity techniques to measure the thermal diffusivity ($\frac{C}{\kappa}$) in pulsed magnetic fields. An amplitude modulated rf heater excites surface currents in a sample, which in turn drives small oscillatory variations in the surface temperature and are detected via changes in the sample's skin depth. The amplitude of the surface temperature variations depend upon the thermal diffusivity and the frequency at which the rf heater is modulated. By varying the modulation frequency of the rf heater, the thermal diffusivity can be deduced. As a first step toward performing these measurements in pulsed fields, initial measurements in a dc magnet will be presented. [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 8:48AM |
N22.00004: One Tera Sample-per-Second Single-Shot Digitizer Yan Han, Ozdal Boyraz, Bahram Jalali The ability to digitize wideband electrical waveform is urgently needed in state-of-the-art instruments. The sampling rate of a state-of-the-art system is currently about 20 GSa/s with $\sim $5 ENOB (Effective Number Of Bits). Here, we demonstrate a single-shot digitizer with a record 1 TSa/s sampling rate. This is accomplished by using a photonic time stretch preprocessor which slows down the electrical waveform before it is captured by an electronic digitizer. In the experiment, a 48 GHz tone is digitized in real time at 1 TSa/s. Over a 10 GHz bandwidth centered at 48 GHz, the average SNR within the 1.1 ns time aperture is 22.7 dB corresponding to 3.5 ENOB. Measurements at other input frequencies resulted in up to 4.2 ENOB. While the intrinsic bandwidth of digitizer is 200 GHz, it is presently limited to 80 GHz due to component limitations. To the best of our knowledge, this is by far, the fastest single-shot digitizer ever demonstrated. [Preview Abstract] |
Wednesday, March 23, 2005 8:48AM - 9:00AM |
N22.00005: Non-Gaussian sonar clutter models James Landry, Peter Weichman, Eugene Lavely A new method for interpreting sonar signals in the presence of clutter is presented based on probability distributions following the formalism of the ideal gas. Likelihood detectors, used to evaluate the presence or absence of a desired target, are extremely sensitive to the tails of these distributions. The structure of the tails are highly sensitive to the underlying clutter statistics, implying that detection of a target is extremely sensitive to the underlying physics. We present simulations of non-Gaussian clutter and targets and explore the sensitivity of detection to these physical models and their parameters. [Preview Abstract] |
Wednesday, March 23, 2005 9:00AM - 9:12AM |
N22.00006: Cryogenic RF filters with zero DC resistance Hendrik Bluhm, Kathryn A. Moler We present a design for cryogenic RF filters with zero DC resistance, based on wires with a superconducting core and a resistive sheath. The superconducting core allows low frequency currents to pass with negligible dissipation. Signals above the cutoff frequency are dissipated in the resistive part due to their small skin depth. The filters consist of twisted pairs shielded with copper tape [1]. Above approximately 1 GHz, the attenuation is exponential in $\sqrt{\omega}$, as typical for skin depth based RF filters. This mimics the exponential quantum cutoff above $f = k_BT/h \approx 200 MHz$ in a 10 mK black body spectrum. By using additional capacitors of 10 nF per line, an attenuation of at least 45 dB above 15 MHz, (the timescale relevant for dephasing in metals) can be obtained. Thus one single stage at mixing chamber temperature in a dilution refrigerator is sufficient to attenuate room temperature black body radiation to levels corresponding to 10 mK above about 15 MHz. \\ \\ 1. Lafe Spietz, John Teufel, and R. J. Schoelkopf. Submitted to RSI Sep 20, 2004 [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N22.00007: The nonlinear effect of resistive inhomogeneities on van der Pauw measurements Daniel W. Koon The \textit{resistive weighting function} [D. W. Koon and C. J. Knickerbocker, Rev. Sci. Instrum. 63, 207 (1992)] quantifies the effect of small local inhomogeneities on van der Pauw resistivity measurements, but assumes such effects to be linear. This talk will describe deviations from linearity for a square van der Pauw geometry, modeled using a 5 x 5 grid network of discrete resistors and introducing both positive and negative perturbations to local resistors, covering nearly two orders of magnitude in -$\Delta \rho $/$\rho $ or -$\Delta \sigma $/$\sigma $. While there is a relatively modest quadratic nonlinearity for inhomogeneities of decreasing conductivity, the nonlinear term for inhomogeneities of decreasing resistivity is approximately cubic and can exceed the linear term. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N22.00008: Piezo-electric Sample Rotators optimised for Low Temperature Experiments Kurt Haselwimmer, Sergiy Rozhko, Charlie Farquharson-Roberts The ability to rotate samples at ultra-low temperatures is of great importance to hall effect and quantum oscillation measurements but has traditionally been hampered in millikelvin experiments by friction in and heat leak through mechanical transmission components. Using recent developments in piezo-electric drives we have now been able to develop a range of completely electronically driven rotation devices that make rotation in high field on millikelvin ADR systems significantly easier than previously possible. Measurements to be presented will show that unlike mechanical devices these rotators feature very low backlash and low power dissipation. Together with multiple axis rotation and direct positional readout, these devices are now rugged enough to be made commercially available for the first time as interchangeable cryogenic components. [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N22.00009: Parallel detection of molecular and atomic ions with a delta-doped CCD at the focal plane of a miniature mass spectrometer A. D. Jewell, T. J. Jones, M. Sinha, S. Nikzad A delta-doped back-illuminated charge-coupled device (CCD) was used for the simultaneous detection of low-energy atomic and molecular ions at the focal plane of a miniature mass spectrometer (MMS). MMS is a JPL-developed instrument based on a focal plane double sector mass analyzer (Mattauch-Herzog geometry). Delta-doped, back-illuminated CCD technology enables high efficiency detection of low energy ions and molecules by eliminating the dead layer usually associated with solid-state detectors. The combination of delta-doped CCD and MMS enables high-speed, precision mass spectrometry of ions and molecules. Compounds studied include benzene, toluene, methylene chloride, and iron pentacarbonyl. Spectral images were captured using integration times from 5 to 120 seconds. Results are two-dimensional images of the spectral output for each molecule. Signal intensity and position were compared to NIST spectra and calculated ion trajectories to verify the identification of molecular peaks and mass to charge ratios. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N22.00010: Direct detection of electrons in the 0.1-20 keV energy range using a delta-doped high purity silicon p-i-n diode array Shouleh Nikzad, Thomas J. Cunningham, David Soules, Ron Ruiz, Steve Holland We have demonstrated the direct detection of 0.1-20 keV electrons using a boron delta-doped high purity silicon p-i-n diode array. Full depletion allows the high-gain detection of incident electrons. Delta-doping enables the detection of low-energy electrons with high efficiency, and also allows the determination of device gain as a function of the incident energy over a wide energy range. Using a low-temperature process developed in our laboratory, we formed a thin electrode on the back surface of the pin diode arrays to enable full depletion and transparency to shallow-penetrating ionizing radiation. The electrode consists of a 1.5 nm boron delta layer grown by molecular beam epitaxy. In this talk, we will discuss the device structure, processing, and characterization methods used to demonstrate the direct detection of low-energy electrons. We will also discuss the use of this detector for making more accurate measurements of the silicon quantum yield for low-energy electrons. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N22.00011: Alternate Biased Blocked Impurity Band Detectors S. J. Tschanz, J. C. Garcia, N. M. Haegel Silicon Blocked Impurity Band (BIB) detectors are state-of-the-art devices to detect light in the near to mid IR range (5-40$\mu $m). Extension of BIB wavelength coverage using either Ge or GaAs has been proposed and attempted, but not yet realized due to material growth challenges. BIBs are normally biased to collect free carriers at the blocking layer contact, from a depletion region that begins at the blocking/active layer interface (standard biasing). We propose and describe an alternate bias approach in which the depletion is initiated from the other contact. Numerical simulations, using a finite difference model, will be presented which show electric field, carrier and all current component distributions. The modeling has been applied to GaAs and Ge, as well as Si BIB detectors. Applying the alternate bias in the simulations demonstrates higher signal currents while allowing thicker blocking layers. Alternate biasing avoids significant voltage drop across the blocking layer, which generally limits blocker thickness in conventional BIB devices. The use of thicker blocking layers in alternate bias provides an option for easier fabrication of new far IR BIB detectors. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N22.00012: Propagation properties and mass sensitivity of SAW on an AlN/a-plane Sapphire structure Jianzeng Xu, Qianghua Wang, Guopeng Hu, Hao Ying, Gregory W. Auner AlN thin films were grown on a-plane sapphire substrates by a plasma enhanced RF sputtering system. The x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) techniques were combined studied the structural properties of the films. It is found that high quality (0001)AlN was epitaxially grown on a-plane sapphire. SAW delayline devices operating from 170 MHz up to 1 GHz were fabricated with propagation direction varying in a 15 deg. interval. Besides the excitation of Rayleigh typed SAW (R-SAW) mode at all angles, a shear-horizontal (SH) mode also emerged from the system at particular propagation directions. The measured phase velocities of the SH waves are 6091-6119 m/s, which is very close to the slow shear velocity of a-plane sapphire at about 6100 m/s. This SH mode is most likely the pseudosurface wave with a leaky nature into the sapphire substrate. The phase velocity dispersion with respect to the relative AlN film thickness and azimuth angle is presented. The device electro-mechanical coupling constant was determined to be 0.001-0.003 by the impedance measurements. Mass sensitivity of the two modes was studied by the deposition of highly elastic polymeric overlayers. The measured mass sensitivity is 95 Hz/ng cm-2 and 82 Hz/ng cm-2 for the R-SAW and SH-SAW, respectively. [Preview Abstract] |
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