Next Article in Journal
Effects of Symmetry Breaking in Resonance Phenomena
Next Article in Special Issue
Instabilities of the Vortex Lattice and the Peak Effect in Single Crystal YBa2Cu4O8
Previous Article in Journal
Acknowledgement to Reviewers of Condensed Matter in 2017
Previous Article in Special Issue
Single Crystal Growth and Superconducting Properties of Antimony-Substituted NdO0.7F0.3BiS2
Open AccessEditorial

Layered Superconductors

Department of Physics, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji 192-0397, Japan
Condens. Matter 2018, 3(1), 4; https://doi.org/10.3390/condmat3010004
Received: 10 January 2018 / Revised: 30 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
(This article belongs to the Special Issue Layered Superconductors)

Abstract

Since the discovery of cuprates (Cu-oxide superconductors) in 1986 [1–4], layered superconductors have attracted much attention, due to the emergence of high-transition-temperature (high-Tc) and unconventional superconductivity.
Keywords: layered superconductors; high-Tc superocnductors; new superconductors layered superconductors; high-Tc superocnductors; new superconductors

1. Introduction

Since the discovery of cuprates (Cu-oxide superconductors) in 1986 [1,2,3,4], layered superconductors have attracted much attention, due to the emergence of high-transition-temperature (high-Tc) and unconventional superconductivity. The highest record of the cuprates, Tc >130 K, is still the highest among superconductors at ambient pressure. Furthermore, several kinds of new superconductors with exotic mechanisms and properties have been discovered. In 2001, MgB2 with Tc = 39 K was discovered [5]. In 2008, FeAs-based (Fe-based) superconductor LaFeAsO1−xFx was discovered [6] and Tc exceeding 50 K has been recorded [7]. Thus, the discovery of new layered superconductors and increased understanding of superconductivity mechanisms are very important for exploring new high-Tc superconductors. Furthermore, application of layered superconductors is an important and developing field of superconductivity. Therefore, this special issue is aimed to publish review and original papers on various layered superconductors and its application.

2. The Present Issue

This special issue consists of 11 papers, which covers the topics on the physics, chemistry, and application of layered superconductors. The target systems are cuprates, Fe-based superconductors, low-dimensional systems, and newly discovered layered superconductors.
The cuprates and the Fe-based superconductors have been a hot issue in the fields of science and application. In this issue, Adachi et al. give an overview on the novel electronic state and superconductivity in the electron-doped high-Tc T′-superconductors [8]. The superconductivity in the T′ structure is one of the hot topics in the field of high-Tc superconductivity. In this review paper, recent advances on this matter and future prospects for elucidating the mechanisms of the superconductivity in this system have been shown. Miller et al. introduces time-correlated vortex tunneling in layered superconductors [9]. Their model can well explain the experimental observation for measured critical current vs. film thickness of HTS-coated conductors, and the concept proposed in this paper can be applicable to other correlated electron systems. Geahel et al. discuss edge contamination, bulk disorder, flux front roughening, and multiscaling in type II superconducting thin films [10]; they particularly investigate the roughening of magnetic flux fronts penetrating into strongly pinning YBCO (YBa2Cu3O7−d) superconducting films with different degrees of edge and bulk disorder. They also point the similarity to other systems like Fe-based superconductors. Imai, Nabeshima and Maeda give a comparative review on thin film growth of Fe-based superconductors [11]. Since the discovery of the Fe-based superconductors, study on thin films has been actively performed to clarify the mechanisms and to achieve a high performance for superconductivity application. They particularly show the growth of Fe chalcogenide films and their superconducting properties.
According to the experiences of material developments of the cuprates and Fe-based superconductors, several kinds of layered superconductors have been recently discovered. The first example is 122-type pnictides, which have a crystal structure similar to that of FeAs-based Ba1−xKxFe2As2 [12]. Zhang and Zhai review superconductivity in 122-type pnictides without iron [13]. They show the similarity and differences in the structural and physical properties between Fe-based and Fe-free systems. Yajima reviews the properties of titanium pnictide oxide superconductors [14]. The Ti-based system contains Ti2O2Pn (Pn:pnictogen) superconducting layers and various kinds of blocking (spacer) layers; the crystal structure is interesting due to the similarity to high-Tc systems. Similarly, BiS2-based superconductors [15,16], discovered in 2012, also consist of superconducting BiS2 layers and various kinds of blocking layers. Since new superconductors can be designed by replacing the structure of the blocking layers, such a layered superconductor system is a good playground for novel superconductivity with low dimensionality. In the paper by Mizuguchi, review of the discovery of the BiS2-based superconductor and material design concept is introduced [17]. In addition, original work on the single crystal growth and superconducting properties of antimony substituted NdO0.7F0.3BiS2 is reported by Demura et al. [18]
Layered materials have been revisited due to the discovery of topological insulators and related superconductors. In this issue, magnetoresistance, gating and proximity effects in ultrathin NbN-Bi2Se3 bilayers are reported [19]. Furthermore, in a layered conductor, Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase can emerge. Croitoru and Buzdin give a review on the signatures and the underlying theoretical framework for FFLO states in quasi-low dimensional superconductors [20].
To study physics, chemistry, and application of layered superconductors, one of the most important contributions is growth of high quality single crystals. Therefore, we invited Nagao to review crystal growth technique for layered superconductors [21]. For various layered superconductors, the suitable method to grow high quality crystal is introduced.

3. Conclusions

As introduced here, we have published 11 papers related to Layered Superconductors. Although about 30 years have passed since the discovery of the cuprate system, the field of layered superconductors is still developing. One of the ultimate goals of this field may be the discovery of a room-temperature superconductor and its application. Recently, superconductivity with Tc = 203 K under extremely high pressure has been achieved in H3S [22,23]. This fact encourages our field because of the realization of very high Tc exceeding the cuprate record. If we could reproduce the superconducting states of H3S in a layered structure, we will be able to approach room-temperature superconductivity. I hope that this special issue is useful for further development of this field toward the ultimate goal.

Acknowledgments

I express thanks to the authors of the above contributions, and to the journal Condensed Matter and MDPI for their support during this work.

Conflicts of Interest

The author declares no conflict of interest.

References

  1. Bednorz, J.B.; Müller, K. Possible high Tc superconductivity in the Ba−La−Cu−O system. Z. Phys. B Condens. Matter 1986, 64, 189–193. [Google Scholar] [CrossRef]
  2. Wu, M.K.; Ashburn, J.R.; Torng, C.J.; Hor, P.H.; Meng, R.L.; Gao, L.; Huang, Z.J.; Wang, Y.Q.; Chu, C.W. Superconductivity at 93 K in a new mixed-phase Y-Ba-Cu-O compound system at ambient pressure. Phys. Rev. Lett. 1987, 58, 908. [Google Scholar] [CrossRef] [PubMed]
  3. Maeda, H.; Tanaka, Y.; Fukutomi, M.; Asano, T. A New High-Tc Oxide Superconductor without a Rare Earth Element. Jpn. J. Appl. Phys. 1988, 27, L209. [Google Scholar] [CrossRef]
  4. Schilling, A.; Cantoni, M.; Guo, J.D.; Ott, H.R. Superconductivity above 130 K in the Hg–Ba–Ca–Cu–O system. Nature 1993, 363, 56–58. [Google Scholar] [CrossRef]
  5. Nagamatsu, J.; Nakagawa, N.; Muranaka, T.; Zenitani, Y.; Akimitsu, J. Superconductivity at 39 K in magnesium diboride. Nature 2001, 410, 63–64. [Google Scholar] [CrossRef] [PubMed]
  6. Kamihara, Y.; Watanabe, T.; Hirano, M.; Hosono, H. Iron-Based Layered Superconductor La[O1−xFx]FeAs (x = 0.05–0.12) with Tc = 26 K. J. Am. Chem. Soc. 2008, 130, 3296–3297. [Google Scholar] [CrossRef] [PubMed]
  7. Ren, Z.A.; Lu, W.; Yang, J.; Yi, W.; Shen, X.-L.; Zheng, C.; Che, G.-C.; Dong, X.-L.; Sun, L.-L.; Zhou, F.; et al. Superconductivity at 55 K in Iron-Based F-Doped Layered Quaternary Compound Sm[O1−xFx] FeAs. Chin. Phys. Lett. 2008, 25, 2215. [Google Scholar]
  8. Adachi, T.; Kawamata, T.; Koike, Y. Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T′-Superconductors. Condens. Matter 2017, 2, 23. [Google Scholar] [CrossRef]
  9. Miller, J.H., Jr.; Villagrán, M.Y.S. Time-Correlated Vortex Tunneling in Layered Superconductors. Condens. Matter 2017, 2, 21. [Google Scholar] [CrossRef]
  10. Geahel, M.; Jouanny, I.; Gorse-Pomonti, D.; Poirier-Quinot, M.; Briatico, J.; van der Beek, C.J. Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films. Condens. Matter 2017, 2, 27. [Google Scholar] [CrossRef]
  11. Imai, Y.; Nabeshima, F.; Maeda, A. Comparative Review on Thin Film Growth of Iron-Based Superconductors. Condens. Matter 2017, 2, 25. [Google Scholar] [CrossRef]
  12. Rotter, M.; Tegel, M.; Johrendt, D. Superconductivity at 38 K in the Iron Arsenide (Ba1−xKx)Fe2As2. Phys. Rev. Lett. 2008, 101, 107006. [Google Scholar] [CrossRef] [PubMed]
  13. Zhang, P.; Zhai, H.-F. Superconductivity in 122-Type Pnictides without Iron. Condens. Matter 2017, 2, 28. [Google Scholar] [CrossRef]
  14. Yajima, T. Titanium Pnictide Oxide Superconductors. Condens. Matter 2017, 2, 4. [Google Scholar] [CrossRef]
  15. Mizuguchi, Y.; Suzuki, K.; Kuroki, K. Minimal electronic models for superconducting BiS2 layers. Phys. Rev. B 2012, 86, 220510. [Google Scholar] [CrossRef]
  16. Mizuguchi, Y.; Demura, S.; Deguchi, K.; Takano, Y.; Fujihisa, H.; Gotoh, Y.; Izawa, H.; Miura, O. Superconductivity in Novel BiS2-Based Layered Superconductor LaO1−xFxBiS2. J. Phys. Soc. Jpn. 2012, 81, 114725. [Google Scholar] [CrossRef]
  17. Mizuguchi, Y. Discovery of BiS2-Based Superconductor and Material Design Concept. Condens. Matter 2017, 2, 6. [Google Scholar] [CrossRef]
  18. Demura, S.; Otsuki, S.; Fujisawa, Y.; Takano, Y.; Sakata, H. Single crystal growth and superconducting properties of Antimony Substituted NdO0.7F0.3BiS2. Condens. Matter 2017, 3, 1. [Google Scholar] [CrossRef]
  19. Koren, G. Magnetoresistance, Gating and Proximity Effects in Ultrathin NbN-Bi2Se3 Bilayers. Condens. Matter 2017, 2, 14. [Google Scholar] [CrossRef]
  20. Croitoru, M.D.; Buzdin, A.I. In Search of Unambiguous Evidence of the Fulde–Ferrell–Larkin–Ovchinnikov State in Quasi-Low Dimensional Superconductors. Condens. Matter 2017, 2, 30. [Google Scholar] [CrossRef]
  21. Nagao, M. Crystal Growth Techniques for Layered Superconductors. Condens. Matter 2017, 2, 32. [Google Scholar] [CrossRef]
  22. Drozdov, A.P.; Eremets, M.I.; Troyan, I.A.; Ksenofontov, V.; Shylin, S.I. Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system. Nature 2015, 525, 73–76. [Google Scholar] [CrossRef] [PubMed]
  23. Einaga, M.; Sakata, M.; Ishikawa, T.; Shimizu, K.; Eremets, M.I.; Drozdov, A.P.; Troyan, I.A.; Hirao, N.; Ohishi, Y. Crystal structure of the superconducting phase of sulfur hydride. Nat. Phys. 2016, 12, 835–838. [Google Scholar] [CrossRef] [PubMed]
Back to TopTop