celebrating 100 years of superconductivitycms.iopscience.iop.org/alfresco/d/d/workspace/...scene....

ABST

RACT

S FR

OM 25

SELECTED PAPERS CELEBRATING 100 YEARS

SINCE THE DISCOVERY OF SUPERCONDUCTIVITY

iopscience.org/centenary

Celebrating 100 years of superconductivity

100 years ofsuperconductiv

ity

http://iopscience.iop.org/centenary

Reasons to publish with IOP Publishing:

IOP Publishing is a leading scientific publisher that specializes in physics and related subjects. We are an integral part of the Institute of Physics, an international learned society and professional body, whose mission is to promote the advancement and dissemination of physics worldwide.

We want to work with you to help gain recognition for your high-quality work through worldwide visibility and high citations.

The articles in this collection have been selected from five journals which have seen increases in their full-text downloads in recent years, and your next paper could also benefit from this visibility and international reach.

Full-text downloads

0

50000

100000

150000

200000

250000

2007 2008 2009 2010

0

100000

200000

300000

400000

500000

600000

2007 2008 2009 2010

0

500000

1000000

1500000

2000000

2007 2008 2009 2010

0

50000

100000

150000

200000

250000

300000

2007 2008 2009 2010

0

200000

400000

600000

800000

1 000000

2007 2008 2009 2010

Superconductor Science and Technology

EPL

Journal of Physics: Condensed Matter

Physica Scripta

New Journal of Physics


Centen ia l b rochure 3

Dear colleagues,

On the 100th anniversary of the discovery of superconductivity, it is interesting to ask how the field is faring after a century. After all, it was on the fiftieth anniversary, in 1961, when Brian Pippard gave his famous “The Cat and the Cream” speech to an audience at IBM, claiming that (four years after the publication of the BCS theory) the essential fundamental problems in low-temperature physics had been solved. All that remained, he argued, was for the giant industrial laboratories of the day to apply these ideas, lapping up what “cream” remained. If one now examines the list of the best superconductivity papers published by IOP journals, one is confronted with a very different impression: hardly a dying field, superconductivity today is driven by the continuing discoveries of new materials.

These discoveries are still taking place in university departments as well as governmental labs, while industrial labs have almost retired from the scene. Papers on heavy fermions, cuprates, ruthenates, borides fullerides, organics, MgB2 and, most recently, Fe-based materials dominate the publications listed from the last three decades. Moreover, in almost every case the discovery of a new class of superconductors has forced theorists to re-examine cherished theoretical paradigms, many of which are debated in the pages reproduced here. Indeed, Pippard’s speech encouraged Phil Anderson to distill his own ideas as to why emergent quantum phenomena like superconductivity mean “more is different”, and are as “fundamental” to physics as elementary particles.

As the reader browses the stimulating collection of papers assembled by the publishers, I hope he or she will take a moment to reflect upon the diversity of materials represented here, and the remarkably dynamic nature of the superconductivity field a century after Kammerlingh Onnes’ original discovery.

100 years of

superconductiv

ity

Peter Hirschfeld, Editorial Board Member, New Journal of Physics

Image inspired by the crystal structure of superconducting compounds potassium buckide and magnesium diboride.


4 Centen ia l b rochure

Journal of Physics: Condensed Matter publishes experimental, theoretical and simulation studies that cover all areas of condensed matter physics. Papers are published under the following sections: surface, interface and atomic-scale science; liquids, soft matter and biological physics; nanostructures and nanoelectronics; solid structure and lattice dynamics; electronic structure; correlated electrons; superconductors and metals; semiconductors; dielectrics and ferroelectrics; magnetism and magnetic materials.

Authors of timely, novel work can benefit from our fast track communications (FTCs) which offer open access with no publication charge. FTCs report exciting new developments in condensed matter physics and are on average published online within 40 days of receipt. Superconductivity features strongly in our recent FTCs and some of these can be viewed in our special collection which can be found via our homepage http://iopscience.iop.org/jpcm.

Journal of Physics: Condensed Matter

iopscience.org/[email protected]

Superconductor Science and Technology is an international multidisciplinary journal for papers on all aspects of superconductivity. With an Impact Factor of 2.694 (2009 Thomson-Reuters ISI), it is the leading journal specialising in superconductivity. Its coverage includes theories of superconductivity, the basic physics of superconductors, the relation of microstructure and growth to superconducting properties, the theory of novel devices, and the fabrication and properties of thin films and devices. It also encompasses the manufacture and properties of conductors, and their application in the construction of magnets and heavy current machines, together with enabling technology. More details on subject coverage can be found here: http://iopscience.iop.org/0953-2048/page/Scope

We also offer open access to outstanding short articles, called rapid communications, reporting new and timely developments in superconductivity and its applications. They should report very substantial new advances in superconductivity to the readers of Superconductor Science and Technology, but are not expected to meet any requirement of ‘general interest’. These articles will be processed quickly (average receipt to online publication for rapid communications is around 60 days) and are permanently free to read in the electronic journal.

iopscience.org/[email protected]

Superconductor Science and Technology

To celebrate 100 years of superconductivity we have chosen 25 articles selected for their relevance and impact. Their abstracts are shown here in this special collector’s edition brochure.

The selected articles have been chosen from five journals: Superconductor Science and Technology, Journal of Physics: Condensed Matter, New Journal of Physics, EPL and Physica Scripta.

We hope that you will find this collection stimulating and useful throughout this centennial year of superconductivity and beyond.

All articles can be found on our centennial website www.iopscience.org/centenary and are free to read until 31 December 2011.




EPL publishes original, high-quality Letters in all areas of physics, ranging from condensed matter topics and interdisciplinary research to astrophysics, geophysics, plasma and fusion sciences, including those with application potential. Articles must contain sufficient argument and supporting information to satisfy workers in the field, and must also be of interest and relevance to wider sections of the physics community. Four volumes comprising six issues each are published each year.

EPL is published under the scientific policy and control of the European Physical Society by EDP Sciences, IOP Publishing and Società Italiana di Fisica for a partnership of 17 European physical societies (the EPL Association).

[email protected]

EPL

Physica Scripta is an international journal for experimental and theoretical physics comprising strong components of atomic, molecular and optical physics, plasma physics, condensed matter physics and mathematical physics. The journal also publishes Comments in five different sections and maintains a programme of Topical Issues alongside the regular 12 issues of the main journal each year.

Physica Scripta is published by IOP Publishing on behalf of the Royal Swedish Academy of Sciences for the Science Academies and the Physical Societies of the Nordic Countries.

[email protected]

Physica Scripta

New Journal of Physics, co-owned by the Institute of Physics and Deutsche Physikalische Gesellschaft, is an electronic-only, open-access journal publishing original research across the whole of physics, encompassing pure, applied, theoretical and experimental research, as well as interdisciplinary topics where physics forms the central theme.

NJP publishes articles of outstanding scientific quality that merit the attention and interest of the whole physics community. All content is available free to readers around the world and is funded by article publication charges.

[email protected]

New Journal of Physics

ELECTRONIC ONLY

OPEN ACCESS



Contents

page

Superconductivity in the iron-based F-doped layered quaternary compound Nd[O1−x Fx]FeAs 8Zhi-An Ren et al

Sr2RuO4: an electronic analogue of 3He? 8T M Rice and M Sigrist

Near-degeneracy of several pairing channels in multiorbital models for the Fe pnictides 8S Graser et al

Superconductivity at 53.5 K in GdFeAsO1-δ 8Jie Yang et al

Competing orders and spin-density-wave instability in La(O1−xFx)FeAs 9J. Dong et al

Specific heat of MgB2 in a one- and a two-band model from first-principles calculations 9A A Golubov et al

High-temperature macroscopic entanglement 9Vlatko Vedral

Crystallographic phase transition and high-Tc superconductivity in LaFeAsO:F 9T Nomura et al

Observation of Fermi-surface–dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2 10H. Ding et al

Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressures 10Patricia L Alireza et al

Spin susceptibility in superconductors without inversion symmetry 10P A Frigeri et al

Effect of strain, magnetic field and field angle on the critical current density of Y Ba2Cu3O7−δ coated conductors 10D C van der Laan et al

Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO1−δ (Re = rare-earth metal) 11without fluorine doping Zhi-An Ren et al

Pressure-induced superconductivity in CaFe2As2 11Tuson Park et al

Influence of the rare-earth element on the effects of the structural and magnetic phase transitions in CeFeAsO, 11PrFeAsO and NdFeAsO Michael A McGuire et al

DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in 12Co-doped BaFe2As2 epitaxial films Takayoshi Katase et al

http://iopscience.iop.org/0295-5075/82/5/57002


http://iopscience.iop.org/1367-2630/11/2/025016/
















page

• Find relevant content faster• Access more content• Interact and share • Stay up to date • Manage your research information

What makes IOPscience different?

Take an online tour at iopscience.org to discover how IOPscience can help you.

iopscience.org

Discover more with...

Superconductivity at 25 K in hole-doped (La1–xSrx)OFeAs 12Hai-Hu Wen et al

The stripe critical point for cuprates 12A Bianconi et al

Effect of 3d transition metal doping on the superconductivity in quaternary fluoroarsenide CaFeAsF 13Satoru Matsuishi et al

Superconductivity: its role, its success and its setbacks in the Large Hadron Collider of CERN 13Lucio Rossi

Thorium-doping–induced superconductivity up to 56 K in Gd1−xThxFeAsO 14Cao Wang et al

The Fröhlich–Coulomb model of high-temperature superconductivity and charge segregation in the cuprates 14A S Alexandrov and P E Kornilovitch

Topological insulators and superconductors: tenfold way and dimensional hierarchy 15Shinsei Ryu et al

Nanoscale disorder in pure and doped MgB2 thin films 15Y Zhu et al

BCS theory of superconductivity: it is time to question its validity 15J E Hirsc

http://iopscience.iop.org/












Superconductivity in the iron-based F-doped layered quaternary compound Nd[O1−x Fx]FeAsZ Ren, J Yang, W Lu, W Yi, X Shen et al

2008 EPL 82 57002

Abstract Here we report a new quaternary iron-arsenide superconductor Nd[O

1−x Fx]FeAs, with the onset resistivity transition at 51.9 K and Meissner transition at 51 K. This compound has the same crystal structure as LaOFeAs, and becomes the second superconductor after Pr[O

1−x Fx]FeAs that superconducts above 50 K.

Near-degeneracy of several pairing channels in multiorbital models for the Fe pnictidesS Graser, T A Maier, P J Hirschfeld and D J Scalapino

2009 New J. Phys. 11 025016

Abstract Weak-coupling approaches to the pairing problem in the iron pnictide superconductors have predicted a wide variety of superconducting ground states. We argue here that this is due both to the inadequacy of certain approximations to the effective low-energy band structure, and to the natural near degeneracy of different pairing channels in superconductors with many distinct Fermi surface sheets. In particular, we review attempts to construct two-orbital effective band models, the argument for their fundamental inconsistency with the symmetry of these materials, and compare the dynamical susceptibilities of two- and five-orbital tight-binding models. We then present results for the magnetic properties, pairing interactions and pairing instabilities within a five-orbital tight-binding random phase approximation model. We discuss the robustness of these results for different dopings, interaction strengths and variations in

band structures. Within the parameter space explored, an anisotropic, sign-changing s-wave (A

1g) state and a dx2–y2 (B1g) state are nearly degenerate, due to the near nesting of Fermi surface sheets.

Superconductivity at 53.5 K in GdFeAsO1-δJ Yang, Z Li, W Lu, W Yi, X Shen, Z Ren, G Che, X Dong, L Sun et al

2008 Supercond. Sci. Technol. 21 082001

Abstract Here we report the fabrication and superconductivity of the iron-based arsenic oxide GdFeAsO

1−δ compound with oxygen-deficiency, which has an onset resistivity transition temperature at 53.5 K. This material has the same crystal structure as the newly discovered high-T

c ReFeAsO1−δ family (Re = rare earth metal) and a further reduced crystal lattice, while the T

c starts to decrease compared with the SmFeAsO

1−δ system.

Sr2RuO4: an electronic analogue of 3He?T M Rice and M Sigrist

1995 J. Phys.: Condens. Matter 7 L643

Abstract Sr

2RuO4 is a superconductor with a similar structure to a high-Tc cuprate superconductor. Nevertheless, the superconducting state may have different symmetry than that of cuprate superconductors. Strong Hund’s rule coupling favours triplet over singlet pairing, similar to 3He. A strong candidate is the odd-parity pairing state which is the two-dimensional analogue of the Balian–Werthamer state of 3He. Various experimental consequences and tests are analysed.

Figure 2: The temperature dependence of resistivity for the Nd[O0.89F0.11]FeAs superconductor.

Figure 1: The crystal structure of LaOFeAs showing the Fe–As layers with an Fe square lattice (red) and As atoms (yellow) in a pyramidal configuration above and below the Fe plane.

For full-text downloads of the 25 selected articles, plus articles on iron-based superconductors and by Nobel Prize Laureates, please visit iopscience.org/centenary

100 years of

superconductiv

ity








Competing orders and spin-density-wave instability in La(O1−xFx)FeAsJ. Dong, H. J. Zhang, G. Xu, Z. Li, G. Li, W. Z. Hu, D. Wu, G. F. Chen, X. Dai, J. L. Luo, Z. Fang and N. L. Wang

2008 EPL 83 27006

Abstract The interplay between different ordered phases, such as superconducting, charge or spin ordered phases, is of central interest in condensed-matter physics. The very recent discovery of superconductivity with a remarkable T

c=26 K in Fe-based oxypnictide La(O1−xFx)FeAs (see Kamihara Y. et al., J. Am. Chem. Soc., 130 (2008) 3296) is a surprise to the scientific community and has generated tremendous interest. The pure LaOFeAs itself is not superconducting but shows an anomaly near 150 K in both resistivity and dc magnetic susceptibility. Here we provide combined experimental and theoretical evidences showing that a spin-density-wave (SDW) state develops at low temperature, in association with electron Nematic order. The electron-doping by F suppresses the SDW instability and induces the superconductivity. Therefore, the La(O

1−xFx)FeAs offers an exciting new system showing competing orders in layered compounds.

Specific heat of MgB2 in a one- and a two-band model from first-principles calculations A A Golubov, J Kortus, O V Dolgov, O Jepsen, Y Kong, O K Andersen, B J Gibson, K Ahn and R K Kremer

2002 J. Phys.: Condens. Matter 14 1353

Abstract The heat capacity anomaly at the transition to superconductivity of the layered superconductor MgB

2 is compared to first-principles calculations with the Coulomb repulsion, µ*, as the only parameter which is fixed to give the measured T

c. We solve the Eliashberg equations for both an isotropic one-band model and a two-band model with different superconducting gaps on the π-band and σ-band Fermi surfaces. The agreement with

experiments is considerably better for the two-band model than for the one-band model.

Figure 3: Experimental data on the heat capacity difference. The dashed curve is the theoretical result from the one-band model and the thick solid curve corresponds to the two-band model, from the solution of the Eliashberg equations.

shown to be equivalent to calculating multipartite entanglement in totally symmetric states of qubits. It is demonstrated that we can conclusively calculate the relative entropy of entanglement within any subset of qubits in the overall symmetric state. Three main results are then presented. First, the condition for superconductivity, namely existence of the off-diagonal long-range order (ODLRO), is dependent not on two-site entanglement but just classical correlations as the sites become more and more distant. Secondly, the entanglement that does survive in the thermodynamical limit is the entanglement of the total lattice and, at half-filling, it scales with the log of the number of sites. It is this entanglement that will exist at temperatures below the superconducting critical temperature, which can currently be as high as 160 K. Finally, it is proved that a complete mixture of symmetric states does not contain any entanglement in the macroscopic limit. On the other hand, a mixture of symmetric states possesses the same two qubit entanglement features as the pure states involved, in the sense that the mixing does not destroy entanglement for a finite number of qubits, albeit it does decrease it. Furthermore, maximal mixing of symmetric states does not destroy ODLRO and classical correlations. We discuss generalizations to the subsystems of any dimensionality (i.e. higher than spin-half).

High-temperature macroscopic entanglementVlatko Vedral

2004 New J. Phys. 6 102

Abstract In this paper, we intend to show that macroscopic entanglement is possible at high temperatures. We have analysed multipartite entanglement produced by the η-pairing mechanism, which features strongly in the fermionic lattice models of high T

c superconductivity. This problem is

Crystallographic phase transition and high-Tc superconductivity in LaFeAsO:FT Nomura, S W Kim, Y Kamihara, M Hirano, P V Sushko, K Kato, M Takata, A L Shluger, and H Hosono


Abstract Undoped LaFeAsO, the parent compound of the newly found high-T

c superconductor, exhibits a sharp decrease in the temperature-dependent resistivity at ~160 K. The anomaly can be suppressed by F doping with simultaneous appearance of superconductivity appears correspondingly, suggesting a close association of the anomaly with the superconductivity. We examined the crystal structures, magnetic properties and conductivity of undoped (normal conductor) and 14 at.% F-doped LaFeAsO (T

c = 20 K) by synchrotron x-ray diffraction (XRD), DC magnetic measurements, and ab initio calculations demonstrated that the anomaly is associated with a phase transition from tetragonal (P4/nmm) to orthorhombic (Cmma) phases at ~160 K as well as an antiferromagnetic spin ordering transition at ~140 K. These transitions can be explained by spin configuration-dependent potential energy surfaces derived from the ab initio calculations. The suppression of the transitions is ascribed to interrelated effects of geometric and electronic structural changes due to doping by F− ions.

Figure 1: Crystal structure of LaFeAsO. (a) Schematic view of the crystal structure, demonstrating the layered structure. (b) Top view of the crystal structure from the c-direction.







Observation of Fermi-surface–dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2H. Ding, P. Richard, K. Nakayama, K. Sugawara, T. Arakane, Y. Sekiba, A. Takayama, S. Souma et al

2008 EPL 83 47001

Abstract We have performed a high-resolution angle-resolved photoelectron spectroscopy study on the newly discovered superconductor Ba

0.6K0.4Fe2As2 (T

c=37 K). We have observed two superconducting gaps with different values: a large gap (Δ~12 meV) on the two small hole-like and electron-like Fermi surface (FS) sheets, and a small gap (~6 meV) on the large hole-like FS. Both gaps, closing simultaneously at the bulk transition temperature (T

c), are nodeless and nearly isotropic around their respective FS sheets. The isotropic pairing interactions are strongly orbital dependent, as the ratio 2Δ/k

BTc switches from weak to strong coupling on different bands. The same and surprisingly large superconducting gap due to strong pairing on the two small FSs, which are connected by the (π, 0) spin-density-wave vector in the parent compound, strongly suggests that the pairing mechanism originates from the inter-band interactions between these two nested FS sheets.

Figure 4: The superconducting transition temperature and superconducting volume fraction of AFe

2As2 (A Sr, Ba) as a function of pressure.

Figure 2: Finite element analysis-calculated strain profile of the bending spring for the two bending directions

Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressuresP Alireza, Y T Chris Ko, J Gillett, C Petrone, J Cole, G Lonzarich and S Sebastian


Abstract We report the discovery of superconductivity at high pressure in SrFe

2As2 and BaFe

2As2. The superconducting transition temperatures are up to 27 K in SrFe

2As2 and 29 K in BaFe2As2, the highest obtained for materials with pressure-induced superconductivity thus far.

Effect of strain, magnetic field and field angle on the critical current density of Y Ba2Cu3O7−δ coated conductorsD C van der Laan, J W Ekin, J F Douglas, C C Clickner, T C Stauffer and L F Goodrich


Abstract A large, magnetic-field-dependent, reversible reduction in critical current density with axial strain in Y Ba

2Cu3O7−δ coated conductors at 75.9 K has been measured. This effect may have important implications for the performance of Y Ba

2Cu3O7−δ coated conductors in applications where the conductor experiences large stresses in the presence of a magnetic field. Previous studies have been performed only under tensile strain and could provide only a limited understanding of the in-field strain effect. We now have constructed a device for measuring the critical current density as a function of axial compressive and tensile strain and applied magnetic field as well as magnetic field angle, in order to determine the magnitude of this effect and to create a better understanding of its origin. The reversible reduction in critical current density with strain becomes larger with increasing magnetic field at all field angles. At 76 K the critical current density is reduced by about 30% at −0.5% strain when a magnetic field of 5 T is applied parallel to the c-axis of the conductor or 8 T is applied in the ab-plane, compared to a reduction of only 13% in self-field. Differences in the strain response of the critical current density at various magnetic field angles indicate that the pinning mechanisms in Y Ba

2Cu3O7−δ coated conductors are uniquely affected by strain.

Spin susceptibility in superconductors without inversion symmetryP A Frigeri, D F Agterberg and M Sigrist

2004 New J. Phys. 6 115

Abstract In materials without spatial inversion symmetry, the spin degeneracy of the conduction electrons can be lifted by an antisymmetric spin–orbit coupling. We discuss the influence of this spin–orbit coupling on the spin susceptibility of such superconductors, with a particular emphasis on the recently discovered heavy Fermion superconductor CePt

3Si. We find that, for this compound (with tetragonal crystal symmetry) irrespective of the pairing symmetry, the stable superconducting phases would give a very weak change of the spin susceptibility for fields along the c-axis and an intermediate reduction for fields in the basal plane. We also comment on the consequences for the paramagnetic limiting in this material.







Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO1−δ (Re = rare-earth metal) without fluorine dopingZ Ren, G Che, X Dong, J Yang, W Lu, W Yi, X Shen, Z Li, L Sun, F Zhou and Z Zhao

2008 EPL 83 17002

Abstract Here we report a new class of superconductors prepared by high-pressure synthesis in the quaternary family ReFeAsO

1−δ (Re=Sm, Nd, Pr, Ce, La) without fluorine doping. The onset superconducting critical temperature (T

c) in these compounds increases with the reduction of the Re atom size, and

the highest Tc obtained so

far is 55 K in SmFeAsO1−δ.

For the NdFeAsO1−δ

compound with different oxygen concentration a dome-shaped phase diagram was found.

Pressure-induced superconductivity in CaFe2As2T Park, E Park, H Lee, T Klimczuk, E D Bauer, F Ronning and J D Thompson


Abstract We report pressure-induced superconductivity in a single crystal of CaFe

2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature T

c exceeding 10 K. The rate of T

c suppression with applied magnetic field is −0.7 K T−1, giving an extrapolated zero-temperature upper critical field of 10–14 T.

Figure 2: The temperature dependences of resistivity for the nominal ReFeAsO

0.85 samples synthesized by the HP method.

Figure 1: Temperature dependence of the normalized resistance of CaFe2As2. Resistance divided

by its room-temperature value is plotted against temperature for 1 bar (squares) and 0.69 GPa (circles).

Influence of the rare-earth element on the effects of the structural and magnetic phase transitions in CeFeAsO, PrFeAsO and NdFeAsOM McGuire, R Hermann, A Sefat, B Sales, R Jin, D Mandrus, F Grandjean and G Long

2009 New J. Phys. 11 025011

Abstract We present results of transport and magnetic properties and heat capacity measurements on polycrystalline CeFeAsO, PrFeAsO and NdFeAsO. These materials undergo structural phase transitions, spin density wave-like magnetic ordering of small moments on iron and antiferromagnetic ordering of rare-earth moments. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, Hall coefficient and magnetoresistance are reported. The magnetic behavior of the materials have been investigated using Mössbauer spectroscopy and magnetization measurements. Transport and magnetic properties are affected strongly by the structural and magnetic transitions, suggesting significant changes in the band structure and/or carrier mobilities occur, and phonon–phonon scattering is reduced upon transformation to the low-temperature structure. Results are compared with recent reports for LaFeAsO, and systematic variations in properties as the identity of Ln is changed are observed and discussed. As Ln progresses across the rare-earth series from La to Nd, an increase in the hole contributions to the Seebeck coefficient and increases in magnetoresistance and the Hall coefficient are observed in the low-temperature phase. Analysis of hyperfine fields at the iron nuclei

determined from Mössbauer spectra indicates that the moment on Fe in the orthorhombic phase is nearly independent of the identity of Ln, in apparent contrast to reports of powder neutron diffraction refinements.

Figure 5: The lattice thermal conduc-tivity L of CeFeAsO, PrFeAsO and NdFeAsO. Results for LaFeAsO are included for comparison.

Download all the full-text articles within this brochure at:

iopscience.org/centenary

100 years of

superconductiv

ity







Figure 3: Voltage–flux (V) characteristics of the dc-SQUID made using BaFe2As2:Co epitaxial film on a (La, Sr)(Al, Ta)O

3 bicrystal substrate bicrystal substrate measured at 14 K.

Figure 2: The temperature dependence of resistivity of samples (La

1x Srx)OFeAs with the Sr concentration x changing from 0.10 to 0.20. One can see that the onset transition temperaturesmarked here by arrows are quite close to each other, with the highest Tc 25.6K at the doping of 0.13. Beyond x0.20, no superconductiv-ity was observed.

DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2 epitaxial filmsT Katase, Y Ishimaru, A Tsukamoto, H Hiramatsu, T Kamiya, K Tanabe and H Hosono


Abstract DC superconducting quantum interference devices (dc-SQUIDs) were fabricated in Co-doped BaFe

2As2 epitaxial films on (La, Sr)(Al, Ta)O3 bicrystal substrates with 30° misorientation angles. The 18 × 8 µm2 SQUID loop with an estimated inductance of 13 pH contained two 3 µm wide grain boundary junctions. The voltage–flux characteristics clearly exhibited periodic modulations with ΔV = 1.4 µV at 14 K, while the intrinsic flux noise of dc-SQUIDs was 7.8 × 10−5 Φ0 Hz−1/2 above 20 Hz. The rather high flux noise is mainly attributed to the small voltage modulation depth which results from the superconductor–normal-metal–superconductor junction nature of the bicrystal grain boundary.

Superconductivity at 25 K in hole-doped (La1–xSrx)OFeAsH Wen, G Mu, L Fang, H Yang and X Zhu

2008 EPL 82 17009

Abstract By partially substituting the tri-valence element La with di-valence element Sr in LaOFeAs, we introduced holes into the system. For the first time, we successfully synthesized the hole-doped new superconductors (La

1–xSrx)OFeAs. The maximum superconducting transition temperature at about 25 K was observed at a doping level of x0.13. It is evidenced by Hall effect measurements that the conduction in this type of material is dominated by hole-like charge carriers, rather than electron-like ones. Together with the data of the electron-doped system La(O

1–xFx)FeAs, a generic phase diagram is depicted and is revealed to be similar to that of the cuprate superconductors.

Papers by Nobel Laureates

• Magneto oscillations in unconventional superconductors well below Hc2 J R Schrieffer 2002 Physica Scripta

• High-temperature superconductivity–dream or reality? Vitalii L Ginzburg 1976 Soviet Physics Uspekhi

• Effect of high pressure on the superconducting properties of metals N B Brandt and N I Ginzburg 1965 Soviet Physics Uspekhi

• Mixed order parameter symmetries in cuprate superconductors A Bussmann-Holder et al 2007 EPL (Europhysics Letters)

• The search for new high temperature superconductors K A Müller 2006 Superconductor Science and Technology

• Superconductivity due to ferromagnetically ordered localized spins A A Abrikosov 2001 Journal of Physics: Condensed Matter

• Depinning of charge-density-waves by quantum tunneling John Bardeen 1989 Physica Scripta





The stripe critical point for cupratesA Bianconi, G Bianconi, S Caprara, D Di Castro, H Oyanagi and N L Saini


Abstract The experimental determination of the quantum critical point (QCP) that triggers the self-organization of charged striped domains in cuprate perovskites is reported. The phase diagram of doped cuprate superconductors is determined by a first variable, the hole doping δ, and a second variable, the micro-strain ε of the Cu-O bond length, obtained from the Cu K-edge extended x-ray absorption fine structure. For a fixed optimum doping, δc = 0.16, we show the presence of the QCP for the onset of local lattice distortions and stripe formation at the critical micro-strain εc. The critical temperature T

c(ε,δ) reaches its maximum at the quantum critical point (εc,δc) for the formation of bubbles of superconducting stripes. The critical charge, orbital and spin fluctuations near this strain QCP provide the interaction for the pairing.

Figure 6: The superconducting critical temperature Tc plotted as a colour plot (from Tc 0 K,black, to Tc 135 K, through yellow to white) as a function of the micro-strain and doping .

Effect of 3d transition metal doping on the superconductivity in quaternary fluoroarsenide CaFeAsFSatoru Matsuishi, Yasunori Inoue, Takatoshi Nomura, Youichi Kamihara, Masahiro Hirano and Hideo Hosono

2009 New J. Phys. 11 025012

AbstractWe examined the doping effect of 3d transition metal (TM) elements (Cr, Mn, Co, Ni and Cu) at the Fe site of a quaternary fluoroarsenide CaFeAsF, an analogue of 1111-type parent compound LaFeAsO. The anomaly at

~120 K observed in resistivity (ρ) versus temperature (T) plot for the parent compound is suppressed by the doping of each TM element. Furthermore, Co and Ni doping (CaFe

1−xTMxAsF, TM = Co,Ni) induces superconductivity with a transition temperature maximized at the nominal x = 0.10 for Co (22 K) and at x = 0.05 for Ni (12 K). These optimal doping levels may be understood by considering that Ni2+(3d8) adds double electrons to the FeAs layers compared with Co2+ (3d7). Increased x for Co or Ni breaks the superconductivity, while metallic nature dρ/dT > 0 is still kept. These observations indicate that Co and Ni serve as electron donors. In contrast, Cr, Mn and Cu doping does not induce superconductivity, yielding dρ/dT < 0 below the ρ–T anomaly temperature, indicating that these TM

ions act as scattering centers. The two different types of behavior of TM replacing the Fe site are discussed in relation to the changes in the lattice constants with doping.

Superconductivity: its role, its success and its setbacks in the Large Hadron Collider of CERNLucio Rossi


Abstract The Large Hadron Collider (LHC), the particle accelerator at CERN, Geneva, is the largest and probably the most complex scientific instrument ever built. Superconductivity plays a key role because the accelerator is based on the reliable operation of almost 10 000 superconducting magnets cooled by 130 tonnes of helium at 1.9 and 4.2 K and containing a total stored magnetic energy of about 15 000 MJ (including detector magnets). The characteristics of the 1200 tonnes of high quality Nb–Ti cables have met the severe requests in terms of critical currents, magnetization and inter-strand resistance; the magnets are built with an unprecedented uniformity, about 0.01% of variation in field quality among the 1232 main dipoles, which are 15 m in length and 30 tonnes in weight. The results of this 20-year-long enterprise will be discussed together with problems faced during construction and commissioning and their remedies. Particular reference is made to the severe incident which occurred nine days after the spectacular start-up of the machine on 10 September 2008. The status of repair and the plan for the physics programme in 2010 are also presented.

Figure 1: The superconducting magnets in the LHC tunnel.

Get the latest superconductivity research sent straight to you!Sign up for free email alerts at

iopscience.org

http://iopscience.iop.org/






Thorium-doping–induced superconductivity up to 56 K in Gd1−xThxFeAsOC Wang, L Li, S Chi, Z Zhu, Z Ren, Y Li, Y Wang, X Lin, Y Luo et al

2008 EPL 83 67006

Abstract We report a new strategy to induce superconductivity in iron-based oxyarsenide. Instead of F– substitution for O2–, we employed Th4+ doping in GdFeAsO with the consideration of “lattice match” between Gd

2O2 layers and Fe

2As2 ones. As a result, superconductivity with Tconset as high as 56 K

was realized in a Gd0.8Th0.2FeAsO polycrystalline sample. This Tc value is

among the highest ever discovered in the iron-based oxypnictides.

The Fröhlich–Coulomb model of high-temperature superconductivity and charge segregation in the cupratesA S Alexandrov and P E Kornilovitch


Abstract We introduce a generic Fröhlich–Coulomb model of the oxides, which also includes infinite on-site (Hubbard) repulsion, and describe a simple analytical method of solving the multi-polaron problem in complex lattice structures. Two particular lattices, a zigzag ladder and a perovskite layer, are studied. We find that, depending on the relative strength of the Fröhlich and Coulomb interactions, these systems are either polaronic Fermi (or Luttinger) liquids, bipolaronic superconductors, or charge-segregated insulators. In the superconducting phase the carriers are superlight mobile bipolarons. The model describes key features of the cuprates such as their T

c-values, the isotope effects, the normal-state diamagnetism, the pseudogap, and spectral functions measured in tunnelling and photoemission. We argue that a low Fermi energy and strong coupling of carriers with high-frequency phonons is the cause of high critical temperatures in novel superconductors.

Figure 1: Crystal chemistry understanding of the structure of LnFeAsO (Ln =lanthanides). The stacking of fluorite (CaF

2) layers, CsCl-type layers and antifluorite (Li2O) layers along the c-axis forms the LnFeAsO structure. The lattice constant along the stacking direction can be expressed by the formula c 1

–2 aCaF2

1–2 aCsCl 1

–2 aLi2O, which basically satisfies the experimental results.

Note that the lattice match between the Ln2O2 layers and the Fe2As2 layers affects the chemical

stability of LnFeAsO.

Figure 4: Four degenerate bipolaron configurations A, B, C, and D. Some single-polaron hoppings are indicated by arrows.

Topological insulators and superconductors: tenfold way and dimensional hierarchyS Ryu, A Schnyder, A Furusaki and A W W Ludwig

2010 New J. Phys. 12 065010

AbstractIt has recently been shown that in every spatial dimension there exist precisely five distinct classes of topological insulators or superconductors. Within a given class, the different topological sectors can be distinguished, depending on the case, by a Z or a Z

2 topological invariant. This is an exhaustive classification. Here we construct representatives of topological insulators and superconductors for all five classes and in arbitrary spatial dimension d, in terms of Dirac Hamiltonians. Using these representatives we demonstrate how topological insulators (superconductors) in different dimensions and different classes can be related via ‘dimensional reduction’ by compactifying one or more spatial dimensions (in ‘Kaluza–Klein’-like fashion). For Z-topological insulators (superconductors) this proceeds by descending by one dimension at a time into a different class. The Z

2-topological insulators (superconductors), on the other hand, are shown to be lower-dimensional descendants of parent Z-topological insulators in the same class, from which they inherit their topological properties. The eightfold periodicity in dimension d that exists for topological insulators (superconductors) with Hamiltonians satisfying at least one reality condition (arising from time-reversal or charge-conjugation/particle–hole symmetries) is a reflection of the eightfold periodicity of the spinor representations of the orthogonal groups SO(N) (a form of Bott periodicity). Furthermore, we derive for general spatial dimensions a relation between the topological invariant that characterizes topological insulators and superconductors with chiral symmetry (i.e., the winding number) and the Chern–Simons invariant. For lower-dimensional cases, this formula relates the winding number to the electric polarization (d=1 spatial dimensions) or to the magnetoelectric polarizability (d=3 spatial dimensions). Finally, we also discuss topological field theories describing the spacetime theory of linear responses in topological insulators (superconductors) and study how the presence of inversion symmetry modifies the classification of topological insulators (superconductors).

Figure 3: 2D energy spectrum of the surface states of model from Turner, Zang, and Vishwanth (arXiv:0909.3119) with mass m

5 0.5. There are two inequivalent surface modes in agree-ment with the winding number v

3(m5 0.5) 2.






Nanoscale disorder in pure and doped MgB2 thin filmsY Zhu, A V Pogrebnyakov, R Wilke, K Chen, X X Xi, J M Redwing, C G Zhuang et al


AbstractMgB

2 thin films have superior superconducting properties compared to bulk MgB

2 and demonstrate the potential for further improving the performances of MgB

2 wires and tapes. Using transmission electron microscopy, we have characterized the microstructure of pure and C-doped MgB

2 using various carbon sources grown by hybrid physical–chemical vapor deposition (HPCVD), and cold-grown–annealed film deposited by molecular beam epitaxy (MBE). The MgB

2 HPCVD films increase in crystal quality in the order (MeCp)

2Mg-sourced films, CH4-sourced films, B(CH3)3-sourced films, pure films, while the Hc2 values of these films follow the opposite order. The cold-grown–annealed MgB

2 MBE film contains non-epitaxial ≤ 10 nm MgB

2 grains and MgO nanoparticles. The microstructural origins of electron scattering and flux pinning in both films are discussed. We also show the structure and chemistry of the degraded phase in HPCVD films and its effects on superconducting properties.

BCS theory of superconductivity: it is time to question its validityJ E Hirsch

2009 Phys. Scr. 80 035702

Abstract The time-tested Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity is generally accepted to be the correct theory of conventional superconductivity by physicists and, by extension, by the world at large. There are, however, an increasing number of ‘red flags’ that strongly suggest the possibility that BCS theory may be fundamentally flawed. An ever-growing number of superconductors are being classified as ‘unconventional’, not described by the conventional BCS theory and each requiring a different physical mechanism. In addition, I argue that BCS theory is unable to explain the Meissner effect, the most fundamental property of superconductors. There are several other phenomena in superconductors for which BCS theory provides no explanation. Furthermore, BCS theory has proven unable to predict any new superconducting compounds. This paper suggests the possibility that BCS theory itself as the theory of ‘conventional’ superconductivity may require a fundamental overhaul. I outline an alternative to conventional BCS theory proposed to apply to all superconductors, ‘conventional’ as well as ‘unconventional’, that offers an explanation for the Meissner effect as well as for other puzzles and provides clear guidelines in the search for new high temperature superconductors.

Figure 8: Bright field transmission electron microscopic images taken at the [0001] zone-axis from the same area of (a) the as-grown and (b) the degraded pure MgB

2 film.

Sign up online today www.physicsworld.com/signup

Trusted content, expert analysis

Breaking news

In-depth analysis

Online lectures

Exclusive video interviews

Lively blog

Connecting the global physics community



We would like to thank all our authors, referees, board members and supporters across the world for their vital contribution to the work and progress of:

• Superconductor Science and Technology• Journal of Physics: Condensed Matter• New Journal of Physics• EPL • Physica Scripta

IOP PublishingDirac House, Temple Back, Bristol BS1 6BE, UK

Tel: +44 (0)117 929 7481 Fax: +44 (0)117 929 4318Website: iopscience.org/centenary

100 years of

superconductiv

ity


celebrating 100 years of superconductivitycms.iopscience.iop.org/alfresco/d/d/workspace/...scene....

Documents