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2Physics Quote:
"Perfect transparency has never been realized in natural transparent solid materials such as glass because of the impedance mismatch with free space or air. As a consequence, there generally exist unwanted reflected waves at the surface of a glass slab. It is well known that non-reflection only occurs at a particular incident angle for a specific polarization, which is known as the Brewster angle effect. Our question is: is it possible to extend the Brewster angle from a particular angle to a wide range of or all angles, so that there is no reflection for any incident angle."
-- Jie Luo, Yuting Yang, Zhongqi Yao, Weixin Lu, Bo Hou, Zhi Hong Hang, Che Ting Chan, Yun Lai

(Read Full Article: "Ultratransparent Media: Towards the Ultimate Transparency"

Sunday, March 10, 2013

Nanostructuring Improves Vortex Pinning in Superconductors at Elevated Temperatures and Magnetic Fields

Photos of all authors -- ordered as the author list below, from top left to bottom right.

R. Córdoba1,2, T. I. Baturina3,4, J. Sesé1,2, A. Yu. Mironov3, J. M. De Teresa2,5, M. R. Ibarra1,2,5, D. A. Nasimov3, A. K. Gutakovskii3, A.V. Latyshev3, I. Guillamón6,7, H. Suderow6, S.Vieira6, M. R. Baklanov8, J. J. Palacios9 & V.M.Vinokur4

1Instituto de Nanociencia de Aragón, Universidad de Zaragoza, Spain
2Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Spain
3A.V. Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, Russia
4Materials Science Division, Argonne National Laboratory, Illinois, USA
5Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, Facultad de Ciencias, Spain
6Laboratorio de Bajas Temperaturas, Departamento de F´ısica de la Materia Condensada, Instituto de Ciencia de Materiales Nicol´as Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
7H.H. Wills Physics Laboratory, University of Bristol, United Kingdom
8IMEC, Leuven, Belgium
9Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain

Corresponding author: Hermann.suderow@uam.es

A recent collaboration of the US, Russian and Spanish researchers finds a new method to improve current carrying capability of superconductors. Usually, superconducting vortices induced by the magnetic field move under the applied current and dissipate the energy degrading thus the ability of superconductors to carry electrical current with zero resistance. To recover superconductivity one has to pin vortices down stopping their motion[1]. However all pinning mechanisms known so far become inefficient at technologically important temperatures and magnetic fields, and this constitutes the major problem restricting applications of superconductivity[2,3,4]. The international team demonstrates the method to immobilize vortices at elevated temperatures and magnetic fields, reversing the deleterious effect of vortex motion as the applied magnetic field is increased[5].

Figure 1: Resistance as a function of the magnetic field in perforated nanostructures.

To achieve this, the authors have carved patterns in superconductors using advanced nanofabrication tools. They have revealed geometrical structures, which impede vortex motion just when it is most harmful for applications, at high magnetic fields and temperatures. The work provides a new avenue for research on blocking vortex motion using nano-patterns[7,8]. The science involved brings new concepts to light: vortices confined on a row dig for themselves a deep potential well which suppresses their capability to move. Being tightly squeezed together vortices join into large clusters so that even the combined action of temperature and current fails to destroy them and move vortices. The result is truly surprising: the resistance drops down when increasing the magnetic field, even if temperature is high and close to the critical one, and remains zero over a broad range. It is exactly opposite to what the conventional wisdom in superconductors would have expected.

Figure 2: Magnetic field dependence of the resistance in a nanowire with a single vortex row.

The to-do list of researchers includes now imaging these immobile clusters and developing a quantitative theory of the effect in order to achieve complete understanding and fully utilize the potential technological promise of their discovery. One of the directions of the future work is the extension of the novel approach to pinning to other materials including high-temperature superconductors[4], where nanopatterning is expected to bring a dramatic improvement of their performance[8]. For example, while many researchers are optimistic about synthesizing the room temperature superconductors, they remain skeptical about their usefulness for applications, since at elevated temperatures mobile vortices would anyway destroy the ability of superconductors to carry current without resistance. The novel approach developed by the team promises to meet this challenge of pinning vortices at high temperatures thus breaking ground for ‘quantum leap’ of superconducting materials into industrial and technological applications.

Figure 3: Perforated superconducting thin film.

[1] P.W. Anderson & Y.B. Kim. "Hard superconductivity-theory of motion of Abrikosov flux lines". Review of Modern Physics, 36, 39-43 (1964). Abstract.
[2] V.V. Moshchalkov, R. Wördenweber and W. Lang, "Nanoscience and engineering in superconductivity" [Springer, ISBN: 9783642151361, 2010].
[3] A.M. Campbell & J.E. Ivetts, "Critical Currents in Superconductors - Monographs on Physics" [Taylor & Francis Ltd., London, 1972].
[4] David Larbalestier, Alex Gurevich, D. Matthew Feldmann & Anatoly Polyanskii. "High-Tc superconducting materials for electric power applications". Nature 414, 368-377 (2001). Abstract.
[5] R. Córdoba, T.I. Baturina, J. Sesé, A. Yu. Mironov, J.M. De Teresa, M.R. Ibarra, D.A. Nasimov, A.K. Gutakovskii, A.V. Latyshev, I. Guillamón, H. Suderow, S. Vieira, M.R. Baklanov, J.J. Palacios and V.M. Vinokur. "Magnetic field-induced dissipation-free state in superconducting nanostructures". Nature Communications, 4, 1437 (2013). Abstract.
[6] M. Baert, V. V. Metlushko, R. Jonckheere, V. V. Moshchalkov, and Y. Bruynseraede. "Composite flux-line lattices stabilized in superconducting films by a regular array of artificial defects". Physical Review Letters, 74, 3269-3272 (1995). Abstract.
[7] J. I. Martín, M. Vélez, A. Hoffmann, Ivan K. Schuller, J. L. Vicent, "Temperature dependence and mechanisms of vortex pinning by periodic arrays of Ni dots in Nb films". Physical Review B, 62, 9110-9116 (2000). Abstract.
[8] A. Llordés, A. Palau, J. Gázquez, M. Coll, R. Vlad, A. Pomar, J. Arbiol, R. Guzmán, S. Ye, V. Rouco, F. Sandiumenge, S. Ricart, T. Puig, M. Varela, D. Chateigner, J. Vanacken, J. Gutiérrez, V. Moshchalkov, G. Deutscher, C. Magen and X. Obradors. "Nanoscale strain‐induced pair suppression as a vortexpinning mechanism in high‐temperature superconductors". Nature Materials, 11, 329 (2012). Abstract.

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