Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S39: Superconductivity: Penetration Depth and Critical Current |
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Sponsoring Units: DCMP Chair: Ken Burch, Boston College Room: 386 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S39.00001: $\mu$SR Investigation of Superconducting PbTaSe$_2$ Murray Wilson, Alannah Hallas, Yipeng Cai, Shengli Guo, Zizhou Gong, Mazhar Ali, Robert Cava, Yasutomo Uemura, Graeme Luke Noncentrosymmetric superconductors are a topic of considerable interest in the condensed matter physics community. These materials have the potential to exhibit exotic superconducting states, particularly in the presence of strong spin orbit coupling. PbTaSe$_2$ is a noncentrosymmetric material which has very strong spin orbit coupling, and is superconducting with a T$_C$ of 3.6~K. Previous studies of this material have identified exotic properties such as Dirac cones gapped by spin-orbit coupling [1], a topological semi-metal state, and possible multi-band superconductivity [2]. To further explore this material, it is of considerable interest to investigate the pairing symmetry of the superconducting state, and determine whether odd-parity superconductivity may exist. In this talk we will present a $\mu$SR investigation of the penetration depth temperature dependece to infer the pairing symmetry. We will also present zero field $\mu$SR measurements which suggest that this material has an even-parity superconducting state. [1] M.N. Ali et al. Physical Review B 69, 020505(R) (2014) [2] C.-L. Zhang et al. Physical Review B 93, 054520 (2016) [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S39.00002: Enhanced charge density wave order in La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4}}$ at high magnetic field. Wei He, Jiajia Wen, Hoyoung Jang, Hiroyuki Nojiri, Satoshi Matsuzawa, Sanghoon Song, Matthieu Chollet, Diling Zhu, Masaki Fujita, Costel R. Rotundu, John P. Sheckelton, Mingde Jiang, Chi-Chang Kao, Jun-Sik Lee, Young S. Lee There has been much recent interest in the charge density wave (CDW) order in the cuprate superconductors. An intriguing form of the density wave occurs in the La$_{\mathrm{2}}$CuO$_{\mathrm{4}}$-based family where both the charge and spin form ``stripes'' near 1/8 doping. Charge order has been reported in La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4}}$ (LSCO) in zero magnetic field near 1/8 doping that was enhanced in moderate DC fields (up to 10 T). In this talk, I will discuss our recent experiment which combines a pulsed magnet with the x-rays from a free electron laser to characterize the CDW in LSCO with x$=$0.115 in fields up to 24 Tesla. In contrast to the YBCO family, which shows field-induced 3D CDW order, the field-enhanced CDW order in LSCO remains two-dimensional up to 24 T. Further results regarding the field-dependence and zero-field behavior of the CDW will be discussed. Our study provides important information on the interplay between CDW order and high-T$_{\mathrm{c}}$ superconductivity. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S39.00003: Campbell penetration depth in single crystals of CaPd$_2$Ge$_2$ superconductor Kyuil Cho, Serafim Teknowijoyo, Makariy A. Tanatar, Vivek K. Anand, David C. Johnston, Ruslan Prozorov, Roland Willa The low-amplitude AC magnetic penetration depth (Campbell length) was measured in a single crystal of CaPd$_2$Ge$_2$ using tunnel diode resonator in a dilution refrigerator down to 100 mK and in the presence of a DC magnetic field. Depending on cooling and warming protocol, hysteretic behavior was found for the most part of the mixed state in fields ranging from 10 Oe to 800 Oe with the strongest irreversibility near H = 300 Oe. The results are analyzed in terms of a recently developed model based on the microscopic theory of strong vortex pinning. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S39.00004: Irradiation-induced enhancement of the Critical Current of YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta }}$ Coated Conductors U. Welp, M. P. Smylie, W. K. Kwok, Y. Zhang, P. M. Niraula, A. Kayani We investigate the enhancement of the critical current density J$_{\mathrm{c}}$ of production-line REBCO coated conductors containing Barium Zirconate (BZO) nanorods due to irradiation with MeV oxygen and copper ions along the c-axis. In magnetic fields exceeding 2 T J$_{\mathrm{c}}$ is substantially enhanced upon irradiation approaching doubling at 6 T \textbar \textbar c and 5 K. In low fields, irradiation causes a suppression of J$_{\mathrm{c}}$. However, we find that off-c-axis irradiation reduces the suppression of Jc at low fields while maintaining enhancements in high fields. Irradiation-induced enhancement of J$_{\mathrm{c}}$ opens an industrially viable approach to address the challenge in HTS conductor development, namely their greatly reduced performance in even modest applied magnetic fields. The major effect of the irradiation-induced defects is the reduction of the in-field suppression of J$_{\mathrm{c}}$, which we attribute to the mixed pinning landscape composed of strong pre-existing pin sites (BZO nanorods) and the finely dispersed irradiation-induced defects. This work was supported as part of the Center for Emergent Superconductivity, an EFRC funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S39.00005: Mean-field Superconductivity in Dirac-cone at high magnetic field Gaurav Chaudhary, Xiao Li, Allan MacDonald Many strategies for realizing topological superconductivity in two dimensions are based on Cooper-pairing of Dirac fermions. Dirac fermions are realized by electrons in graphene and at the surface of three-dimensional topological insulators. In this work we study the influence of Landau-quantization on the superconductivity of Dirac fermions in an external magnetic field. We derive a mean-field theory for the critical temperature of the superconducting instability in such a system, which is valid for both in the weak-field semiclassical limit and in the strong-field extreme quantum limit, demonstrate the presence of topological superconductivity in such a system, and characterize the structure of the emerging vortex lattice states. We find that the present system has important differences compared to the case of two-dimensional electrons with parabolic bands in an external magnetic field. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S39.00006: Non-local effect in superconducting nanowires Rosa Cordoba, Javier Sese, Ricardo Ibarra, Isabel Guillamon, Hermann Suderow, Sebastian Vieira, Jose Maria De Teresa The template-free fabrication of superconducting wires with nanometric control opens fascinating research fields in condensed-matter physics. Ga$^{+}$-based focused ion beam induced deposition (FIBID) technique is utilized for the fabrication of W- based superconducting nanostructures using W(CO)$_{6}$ as the precursor material. This type II superconducting material presents superconducting properties below 5 K and fits correctly to the BCS theory. In this contribution, we report a non-local electrical signal observed in superconducting W- based nanowires (NWs) grown by FIBID. Thus, by applying a bias current in an upper horizontal NW, the generated Lorentz-type force pushes the vortex lattice through a connected vertical NW, and this vortex motion is detected as a non-local voltage in a connected lower horizontal NW, where no current is present. The weak pinning in our material combined with a vortex density determined by the external magnetic field, lead to an efficient driving force of the vortex lattice through the vertical NW. We notice that a non-local signal of 0.42 $\mu $V can be propagated through long distances -above three micrometers- compared to the intervortex distance (only a few nanometers) of the Abrikosov vortex lattice. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S39.00007: The stiffnessometer: a magnetic-field-free superconducting stiffness meter, and its application to the cuprates Itzik Kapon, Amit Keren We developed a new method to measure the stiffness $\rho_{s} $ of a superconductor without applying magnetic field. The method is based on the London equation ${\rm {\bf J}}=-\rho_{s} {\rm {\bf A}}$, where ${\rm {\bf J}}$ is the current density and ${\rm {\bf A}}$ is the vector potential. Using a rotor free ${\rm {\bf A}}$ and a ${\rm {\bf J}}$ measurement we determine $\rho_{s} $. We apply the method to La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4}}$ and find some surprising results. [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S39.00008: Interplay of topological charge density waves and superconductivity in a two-dimensional topological superconductor K. Tanaka, Yuki Nagai, S. L. Goertzen, Evan D. B. Smith We perform microscopic mean-field studies of topological order in a two-dimensional $s$-wave topological superconductor with Rashba spin-orbit coupling and Zeeman field in the Bogoliubov-de Gennes formalism. By solving for the spin-dependent Hartree potential self-consistently along with the superconducting order parameter, we show that topological charge density waves (TCDW) can coexist with topological superconductivity (TSC) at half filling just as in a conventional $s$-wave superconductor. Furthermore, we examine the effects of a nonmagnetic impurity, which tends to create spin-polarised midgap excitation and pin the phase of charge density modulations, on possible interplay of TCDW and TSC. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S39.00009: Hysteretic magneto-transport in superconductor/ferromagnet hybrids with variable domain structure Xavier Palermo, Victor Rouco, Adrian Balan, Constance Moreau-Luchaire, Sophie Collin, William Legrand, Karim Bouzehouane, Jacobo Santamaria, Anke Sander, Vincent Cros, Javier E. Villegas We report magneto-transport experiments in hybrid stacks consisting of an amorphous Mo$_{\mathrm{1-x}}$Si$_{\mathrm{x}}$ superconducting film (S) with a perpendicular magnetic anisotropy ferromagnetic (F) multilayer (either Co/Pt or Ir/Co/Pt) on top. Unlike in plain superconducting films, the magnetoresistance shows a strong hysteresis which is observed during the F layer magnetization reversal and closely follows its dynamics. This effect is strongly dependent of the size and morphology of the domain structure, which results in qualitatively and quantitatively different behavior in Co/Pt and Ir/Co/Pt. The microscopic mechanisms that could explain our results will be reviewed, including domain-wall superconductivity and stray-field to vortex coupling. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S39.00010: Study of RF flux penetration on Nb for SRF Applications Bakhrom Oripov, Steven Anlage Superconducting Radio Frequency (SRF) cavities are being widely used in new generation particle accelerators. Based on the needs of the SRF community to identify defects on Nb surfaces, a novel near-field magnetic field microwave microscope was successfully built using a magnetic writer from a conventional perpendicular magnetic recording hard-disk drive$^{\mathrm{1}}$. Using our probe, we performed microwave measurement of both third P$_{\mathrm{3f\thinspace }}$(P$_{\mathrm{f}}$,T) and fifth P$_{\mathrm{5f}}$ (P$_{\mathrm{f}}$,T) harmonic responses and its dependence on temperature and rf input power by applying a strong and localized RF magnetic field on high quality Nb films. Our preliminary results show significant difference in low-field and high-field harmonic responses. Above a temperature-dependent onset field H$_{\mathrm{1}}$ periodic structures in the harmonic response vs rf field amplitude data emerges. Similar behavior is observed in both bulk Nb and thin film Nb samples. We attribute this periodic response to vortex nonlinearity. Using our microscope, we are able to measure a local lower critical field for vortex formation H$_{\mathrm{c,v}}$ (in arbitrary units), and compare the H$_{\mathrm{c,v}}$'s of samples produced with different techniques and chemical treatments. $^{\mathrm{1}}$Tamin Tai, B. G. Ghamsari, T. Bieler, Steven M. Anlage, ``Nanoscale Nonlinear Radio Frequency Properties of Bulk Nb: Origins of Extrinsic Nonlinear Effects,'' Phys. Rev. B 92, 134513 (2015). [Preview Abstract] |
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