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High Magnetic Field - Low Temperature Physics Laboratory
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High Magnetic Field - Low Temperature Lab PFLT Lab Homepage More Lab Info Geomorphology Department of Physics Graduate Students About Me |
 Pulsed Field Magnet Lab 
Above: The Pulsed Field Magnet - Low Temperature Lab including the Wall of Capacitors, the Pulsed Field Magnet and the 3He/4He Cryostat. DC Superconducting Magnet Lab 
Above: The DC Superconducting Magnet - Low Temperature Lab and a Organic Superconductor Sample 2008 Clark University GSC Multidisciplinary Conference Poster: Determination of the Pauli Paramagnetic Limit in Quasi 2D Superconductors. Braunen E. Smith, Kyuil Cho, William A. Coniglio and Charles C. Agosta GSC 2008 Poster (PDF) 2008 APS March Meeting Abstracts Abstract: X11.00010: Determination of the Pauli Paramagnetic Limit in Quasi 2D Superconductors. Braunen E. Smith, Kyuil Cho, William A. Coniglio and Charles C. Agosta We have calculated the Pauli paramagnetic limit (Hp) for different quasi 2D superconductors using a semi-empirical method. We then compared the calculated Pauli paramagnetic limits to penetration depth data obtained using a tunnel diode oscillator technique at low temperatures in a swept applied magnetic field. The organic superconductors examined are layered such that their behavior is dependent on their orientation to the applied magnetic field. In order to eliminate the effect of vortex dynamics, we examined data taken with the conducting layers oriented parallel to the applied magnetic field. For one of these materials, κ-(BEDT-TTF)2Cu(NCS)2, we find that eliminating vortex effects leaves us with one remaining feature in the data that may correspond to Hp. We also find that the material β''-(BEDT-TTF)2SF5CH2CF2SO3 exhibits a change in slope for temperature versus upper critical field when the upper critical field exceeds the calculated Hp. In addition, many of the examined quasi 2D superconductors, including the above organic superconductors and CeCoIn5, exhibit upper critical fields that exceed their calculated Hp suggesting some type of non-conventional superconductivity. Abstract: X11.00008: Upper Critical Field and SdH Quantum Oscillation Studies in Organic Superconductor β''-(BEDT-TTF)2SF5CH2CF2SO3. Kyuil Cho, Braunen E. Smith, William A. Coniglio, Laurel Winter, Charles C. Agosta and John A. Schlueter Upper critical fields and SdH quantum oscillations in the organic superconductor β''-(BEDT-TTF)2SF5CH2CF2SO3 have been studied by measuring the in-plane rf penetration depth with a tunnel diode oscillator technique. Previous measurements from other groups, with the applied field parallel to the conducting layers, were inconsistent. We report here that for the applied field parallel to the conducting layers the low temperature upper critical fields exceed the Pauli paramagnetic limit calculated by using a semi-empirical method. We will also discuss SdH quantum oscillation with the applied field perpendicular to the conducting layers, which has been found to have a frequency of 181 T and an effective mass of 1.84 me. The effective mass is consistent with those of other groups, but the oscillation frequency smaller than theirs (~ 196 T). 2007 APS March Meeting Abstract Abstract: N8.00007 : Critical fields, vortex melting and the irreversibility line in quasi 2D organic superconductors. Braunen Smith, Kyuil Cho and Charles Agosta We have measured the critical field and aspects of the vortex structure in anisotropic organic superconductors using pulsed and dc fields up to 50 and 45 T respectively and at temperatures down to 55 mK. In all cases we measured the penetration depth using the tunnel diode oscillator technique. When the sample is oriented with the conducting planes parallel to the applied magnetic field, we have found that the irreversibility line does not extrapolate to the high fields predicted by Mola et. al. [1] based on their measurements and the use of the Tinkham equation. We also find that many signatures of the vortex system, such as jumps, melting and hysteresis are absent in the parallel sample orientation. In addition, when using a pulsed field apparatus we have consistently measured lower critical fields than we find from the use of dc field apparatus. We assume this is due to a time constant associated with the vortices entering and leaving the sample, but not all of our data supports this claim. [1] M.M. Mola, S. Hill, J.S. Brooks, and J.S. Qualls, Phys. Rev. Lett. 86, 2130 (2001). APS 2007 Presentation (PowerPoint) APS 2007 Presentation (PDF) 2007 Clark University GSC Multidisciplinary Conference Poster: Critical fields, vortex melting and the irreversibility line in quasi 2D organic superconductors. Braunen Smith, Kyuil Cho and Charles Agosta GSC 2007 Poster (PDF) Contributors to the work on the page include: Braunen Smith, Kyuil Cho, Andy Coniglio, Mike Viotti and Charles Agosta Contact: Braunen Smith  Department of Physics Clark University Worcester, MA 01610 Phone: (508)793-7680 Last updated February 2, 2008. |