Showing papers on "High-temperature superconductivity published in 2011"
TL;DR: A detailed review of the superconductivity of FePnictide and chalcogenide (FePn/Ch) superconductors can be found in this paper.
Abstract: Kamihara and coworkers' report of superconductivity at ${T}_{c}=26\text{ }\text{ }\mathrm{K}$ in fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of the superconductivity in this new class of compounds. These iron pnictide and chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface, plus an unusual Fermiology that can change rapidly with doping, which lead to normal and superconducting state properties very different from those in standard electron-phonon coupled ``conventional'' superconductors. Clearly, superconductivity and magnetism or magnetic fluctuations are intimately related in the FePn/Ch, and even coexist in some. Open questions, including the superconducting nodal structure in a number of compounds, abound and are often dependent on improved sample quality for their solution. With ${T}_{c}$ values up to 56 K, the six distinct Fe-containing superconducting structures exhibit complex but often comparable behaviors. The search for correlations and explanations in this fascinating field of research would benefit from an organization of the large, seemingly disparate data set. This review provides an overview, using numerous references, with a focus on the materials and their superconductivity.
1,349 citations
TL;DR: Nuclear magnetic resonance measurements are reported showing that high magnetic fields actually induce charge order, without spin order, in the CuO2 planes of YBa2Cu3Oy, and it is argued that it is most probably the same 4a-periodic modulation as in stripe-ordered copper oxides.
Abstract: Nuclear magnetic resonance measurements of the model high-temperature copper oxide superconductor YBa2Cu3Oy demonstrate that high magnetic fields induce charge order, without spin order, within the material's CuO2 planes. The observed charge order has characteristics similar to those of stripe-ordered copper oxides, in which electronic charges spontaneously organize themselves into 'stripes'. The charge order develops only when superconductivity fades away. This work suggests that stripes are more common objects in the cuprates than was thought. They seem to compete with superconductivity, although the tendency to form stripes may be a necessary ingredient of high temperature superconductivity. Electronic charges introduced in copper-oxide (CuO2) planes generate high-transition-temperature (Tc) superconductivity but, under special circumstances, they can also order into filaments called stripes1. Whether an underlying tendency towards charge order is present in all copper oxides and whether this has any relationship with superconductivity are, however, two highly controversial issues2,3. To uncover underlying electronic order, magnetic fields strong enough to destabilize superconductivity can be used. Such experiments, including quantum oscillations4,5,6 in YBa2Cu3Oy (an extremely clean copper oxide in which charge order has not until now been observed) have suggested that superconductivity competes with spin, rather than charge, order7,8,9. Here we report nuclear magnetic resonance measurements showing that high magnetic fields actually induce charge order, without spin order, in the CuO2 planes of YBa2Cu3Oy. The observed static, unidirectional, modulation of the charge density breaks translational symmetry, thus explaining quantum oscillation results, and we argue that it is most probably the same 4a-periodic modulation as in stripe-ordered copper oxides1. That it develops only when superconductivity fades away and near the same 1/8 hole doping as in La2−xBaxCuO4 (ref. 1) suggests that charge order, although visibly pinned by CuO chains in YBa2Cu3Oy, is an intrinsic propensity of the superconducting planes of high-Tc copper oxides.
639 citations
TL;DR: In this article, the case for magnetically mediated superconductivity was strengthened by the discovery of high-energy magnetic excitations that are not affected by chemical doping levels within several cuprates.
Abstract: In the copper oxide superconductors, spin fluctuations might be involved in the electronic pairing mechanism. The case for such magnetically mediated superconductivity is now strengthened by the discovery of high-energy magnetic excitations that are not affected by chemical doping levels within several cuprates.
333 citations
TL;DR: In this article, molecular beam epitaxy growth of stoichiometric and superconducting FeSe crystalline thin films on double-layer graphene was reported in a well-controlled manner by using Se-rich condition, which allowed to investigate the thickness-dependent superconductivity of FeSe.
Abstract: We report on molecular beam epitaxy growth of stoichiometric and superconducting FeSe crystalline thin films on double-layer graphene. Layer-by-layer growth of high-quality films has been achieved in a well-controlled manner by using Se-rich condition, which allow us to investigate the thickness-dependent superconductivity of FeSe. In situ low-temperature scanning tunneling spectra reveal that the local superconducting gap in the quasiparticle density of states is visible down to two triple layers for the minimum measurement temperature of 2.2 K, and that the transition temperature ${T}_{\mathrm{c}}$ scales inversely with film thickness.
155 citations
TL;DR: In this article, the authors provide sufficient experimental evidence to support the reliability and the consistency of the angle-resolved photoemission spectroscopy measurements over a wide range of material compositions.
Abstract: Angle-resolved photoemission spectroscopy allows direct visualization and experimental determination of the electronic structure of crystals in the momentum space, including the precise characterization of the Fermi surface and the superconducting order parameter. It is thus particularly suited for investigating multi-band systems such as the Fe-based superconductors. In this review, we cover several aspects of these recently discovered materials that have been addressed by this technique, with a special emphasis on their superconducting gap and their Fermi surface topology. We provide sufficient experimental evidence to support the reliability and the consistency of the angle-resolved photoemission spectroscopy measurements over a wide range of material compositions.
150 citations
TL;DR: In this paper, a thermodynamic probe was used to detect quantum oscillations in a copper-oxide superconductor in a magnetic field up to 45'T. Surprisingly, these oscillations lie on a background signal that is consistent with d-wave superconductivity in the vortex state, and were observed in a single-dimensional magnetic field.
Abstract: Quantum oscillations in a copper-oxide superconductor are observed using a thermodynamic probe. Surprisingly, these oscillations lie on a background signal that is consistent with d-wave superconductivity in the vortex state, in a magnetic field up to 45 T.
125 citations
28 Mar 2011
TL;DR: In this article, the authors present an overview of the properties of superconducting field windings and their application in the context of cooling and cooling of high-speed motors, as well as a discussion of the challenges involved in the design of such systems.
Abstract: PREFACE. ACKNOWLEDGEMENTS. Abbreviations. CHAPTER 1 Introduction. CHAPTER 2 HTS Superconductors. 2.1 Introduction. 2.2 HTS Background and Nomenclature. 2.2.1 Background. 2.2.2 Nomenclature. 2.3 BSCCO-2212 Conductors. 2.4 BSCCO-2223 OPIT Wires. 2.4.1 Manufacturing Process. 2.4.2 Characteristics - Electrical and Mechanical. 2.5 YBCO-123 Coated Conductors. 2.6 Magnesium Diboride (MgB2). 2.7 State-of-the-art of Various HTS Conductors. 2.8 Superconducting Magnet Design. 2.9 Summary. References. CHAPTER 3 Cooling and Thermal Insulation Systems. 3.1 Introduction. 3.2 Anatomy of a Cryostat. 3.3 Cryogenic Fluids for Cooling HTS Magnets. 3.4 Direct Cooling with Cryogens. 3.5 Indirect or Conduction Cooling. 3.6 Refrigeration Systems. 3.6.1 Gifford-McMahon (G-M) Cryocoolers. 3.6.2 Stirling Coolers. 3.6.3 Pulse Tube Coolers. 3.7 Open Loop Cooling with Liquid Nitrogen. 3.8 Magnet Materials. 3.9 Current Leads. 3.9.1 Design of Conduction Cooled Leads. 3.10 Example Cryostat Design. 3.10.1 Configuration. 3.10.2 Thermal Load Calculations. 3.10.2.1 Radiation Thermal Load Through MLI. 3.10.3 Current Leads. 3.10.4 Conduction. 3.10.5 Selection of Refrigerator. 3.11 Summary. References. CHAPTER 4 Rotating AC Machines. 4.1 Introduction. 4.2 Topology. 4.3 Analysis and Parameter Calculations. 4.3.1 Magnetic Circuit and Harmonic Components. 4.3.2 Parameter Calculations. 4.3.3 Machine Terminal Parameters. 4.4 Design. 4.4.1 Stator Winding Design Issues. 4.4.2 Field Winding Design Issues. 4.4.3 Electromagnetic (EM) Shield Design Issues. 4.4.4 Loss and Efficiency Calculations. 4.4.5 Example Design. 4.5 Manufacturing Issues. 4.5.1 Superconducting Field Winding and Its Cooling Systems. 4.5.2 Torque Transfer from Col Field Winding to Warm Shaft. 4.5.3 Stator Winding. 4.6 Simulation. 4.7 Generators. 4.7.1 High Speed Generators. 4.7.2 Low Speed Generators. 4.8 Motors. 4.8.1 High Speed Motors. 4.8.2 Low Speed Motors. 4.9 Summary. References. CHAPTER 5 Rotating DC Homoploar Machines. 5.1 Introduction. 5.5 Principle. 5.3 Configuration. 5.4 Design Challenges. 5.5 Prototypes. 5.6 Summary. References. CHAPTER 6 Synchronous AC Homoploar Machines. 6.1 Introduction. 6.2 Principle. 6.3 Design. 6.4 Design Challenges. 6.5 Prototypes. 6.6 Summary. References. CHAPTER 7 Transformers. 7.1 Introduction. 7.2 Configuration. 7.3 Design Analysis. 7.3.1 50MVA Example Design. 7.4 Challenges. 7.5 Manufacturing Issues. 7.6 Prototypes. 7.7 Summary. References. CHAPTER 8 Fault Current Limiters. 8.1 Introduction. 8.2 Principle and Configuration. 8.2.1 Resistive Fault Current Limiters (R-FCL). 8.2.2 Inductive FCL with Shielded Iron Core. 8.2.3 Inductive FCL with Saturated Iron Core. 8.3 Design Analysis. 8.3.1 Example Design - Resistive FCL. 8.3.2 Example Design - Saturated Core FCL. 8.4 Challenges. 8.4.1 Challenges of Resistive FCL. 8.4.2 Challenges of Inductive FCL. 8.5 Manufacturing Issues. 8.6 Prototypes. 8.6.1 AMSC s Fault Current Limiter. 8.6.2 Superpower s Fault Current Limiter. 8.6.3 Zenergy Power s Fault Current Limiter. 8.6.4 Nexans s Fault Current Limiter. 8.7 Summary. References. CHAPTER 9 Power Cables. 9.1 Introduction. 9.2 Configurations. 9.2.1 Resistive Cryogenic Cable. 9.2.2 HTS Cables. 9.3 Design Analysis. 9.3.1 Cryogenic Cable Analysis. 9.3.2 HTS Cable Analysis. 9.3.2.1 HTS Coaxial Cable - High Voltage. 9.3.2.2 HTS Coaxial Cable - Medium Voltage. 9.3.2.3 TriaxTM HTS Cable - Medium Voltage. 9.4 Challenges. 9.4.1 Resistive Cryogenic Cable. 9.4.2 HTS Cable. 9.5 Manufacturing Issues. 9.5.1 Resistive Cryogenic Cable. 9.5.2 HTS Cable. 9.6 Prototypes. 9.6.1 Resistive Cryogenic Cable. 9.6.2 HTS Cable - High Voltage. 9.6.3 HTS Cable - Medium Voltage. 9.6.4 TriaxTM HTS Cable - Medium Voltage. 9.7 Summary. References. CHAPTER 10 Maglev Transport. 10.1 Introduction. 10.2 Configuration. 10.2.1 Electro-dynamic Suspension (EDS). 10.2.2 Electro-magnetic Suspension (EMS) . 10.3 Design Analysis. 10.3.1 Electro-dynamic Suspension Maglev. 10.3.2 Electro-magnetic Suspension Maglev. 10.4 Challenges (Technical/Economic). 10.4.1 EDS System Challenges. 10.4.2 EMS System Challenges. 10.5 Manufacturing Issues. 10.6 Prototypes. 10.6.1 Northrop Grumman Concept. 10.7 Summary. References. CHAPTER 11 Other Applications of HTS. 11.1 Introduction. 11.2 Air-Core Magnets. 11.2.1 High Field Magnets. 11.2.2 Low Field Magnets. 11.3 Iron-Core Magnets. 11.3.1 Beam Bending. 11.3.2 Induction Heating. 11.3.3 Synchrotron. 11.4 Challenges. 11.5 Summary. About the Author. INDEX.
119 citations
TL;DR: In this paper, the authors synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystal, which exhibited a sharp superconducting transition and the onset and zero-resistivity tempera-ture were estimated to be 33 and 31.8 K, respectively.
Abstract: We synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystals. The obtained single crystal exhibited a sharp superconducting transition and the onset and zero-resistivity tempera-ture were estimated to be 33 and 31.8 K, respectively. A high upper critical field of 192 T was obtained. The anisotropy of superconductivity of K0.8Fe2Se2 was ∼3.6. Both the high upper critical field and comparably low anisotropy are advantageous for applications under a high magnetic field.
111 citations
TL;DR: In this paper, a buffered metal template was used to grow a textured FeSe0.5Te 0.5 layer, an approach developed originally for high temperature superconducting coated conductors.
Abstract: The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe0.5Te0.5 layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1 × 104 A/cm2) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.
104 citations
TL;DR: In this paper, the authors review a number of experimental techniques that are beginning to reveal fine details of the bosonic spectrum α2F(Ω) that dominates the interaction between the quasiparticles in high-temperature superconductors.
Abstract: We review a number of experimental techniques that are beginning to reveal fine details of the bosonic spectrum α2F(Ω) that dominates the interaction between the quasiparticles in high-temperature superconductors. Angle-resolved photoemission spectroscopy (ARPES) shows kinks in electronic dispersion curves at characteristic energies that agree with similar structures in the optical conductivity and tunnelling spectra. Each technique has its advantages. ARPES is momentum resolved and offers independent measurements of the real and imaginary part of the contribution of the bosons to the self-energy of the quasiparticles. The optical conductivity can be used on a larger variety of materials and with the use of maximum entropy techniques reveals rich details of the spectra including their evolution with temperature and doping. Scanning tunnelling spectroscopy offers spatial resolution on the unit cell level. We find that together the various spectroscopies, including recent Raman results, are pointing to a unified picture of a broad spectrum of bosonic excitations at high temperatures which evolves, as the temperature is lowered, into a peak in the 30–60 meV region and a featureless high-frequency background in most of the materials studied. This behaviour is consistent with the spectrum of spin fluctuations as measured by magnetic neutron scattering. However, there is evidence for a phonon contribution to the bosonic spectrum as well.
100 citations
TL;DR: In this article, the authors reported electronic and magnetic phase diagram of KxFe2-ySe2 system as a function of Fe valence and found two AFM insulating phases and reveal that the superconducting phase is sandwiched between them.
Abstract: The correlation and competition between antiferromagnetism and superconductivity are one of the most fundamental issues in all of high temperature superconductors. The superconductivity in high temperature cuprate superconductors arises from suppressing an antiferromagnetic (AFM) Mott insulator phase by doping1 while that in iron-pnictide high temperature superconductors arises from AFM semimetals and can coexist with AFM orders2-9. This key difference marked in their phase diagrams has raised many intriguing debates about whether the two materials can be placed in the same category to understand the mechanism of superconductivity. Recently, superconductivity at 32 K has been reported in iron-chalcogenide superconductors AxFe2-ySe2 (A=K, Rb, and Cs)10-12, which have the same structure as that of iron-pnictide AFe2As2 (A=Ba, Sr, Ca and K)13-15. Here, we report electronic and magnetic phase diagram of KxFe2-ySe2 system as a function of Fe valence. We find two AFM insulating phases and reveal that the superconducting phase is sandwiched between them, and give direct evidence that the superconductivity in AxFe2-ySe2 originates from the AFM insulating parent compounds. The two insulating phases are characterized by two distinct superstructures caused by Fe vacancy orders with modulation wave vectors of q1=(1/5, 3/5, 0) and q2=(1/4, 3/4, 0), respectively. These experimental results strongly indicate that iron-based superconductors and cuprates share a common origin and mechanism of superconductivity.
TL;DR: In this article, angle-resolved photoemission spectroscopy (ARPES) evidence of two insulating and one semiconducting phases of KxFe2-ySe2 was presented.
Abstract: While the parent compounds of the cuprate high temperature superconductors (high-Tc's) are Mott insulators, the iron-pnictide high-Tc's are in the vicinity of a metallic spin density wave (SDW) state, which highlights the difference between these two families. However, insulating parent compounds were identified for the newly discovered KxFe2-ySe2. This raises an intriguing question as to whether the iron-based high-Tc's could be viewed as doped Mott insulators like the cuprates. Here we report angle-resolved photoemission spectroscopy (ARPES) evidence of two insulating and one semiconducting phases of KxFe2-ySe2, and the mesoscopic phase separation between the superconducting/semiconducting phase and the insulating phases. The insulating phases are characterized by the depletion of electronic states over a 0.5 eV window below the chemical potential, giving a compelling evidence for the presence of Mott-like physics. The charging effects and the absence of band folding in the superconducting/semiconducting phase further prove that the static magnetic and vacancy orders are not related to the superconductivity. Instead, the electronic structure of the superconducting phase is much closer to the semiconducting phase, indicating the superconductivity is likely developed by doping the semiconducting phase rather than the insulating phases.
TL;DR: A multiple wave vector (Q) reconstruction of the Fermi surface is shown to yield a profoundly different electronic structure to that characteristic of single wave vector reconstruction, despite their proximity in energy.
Abstract: A multiple wave vector (Q) reconstruction of the Fermi surface is shown to yield a profoundly different electronic structure to that characteristic of single wave vector reconstruction, despite their proximity in energy. We consider the specific case in which ordering is generated by Q(x)=[2πa,0] and Q(y)=[0,2πb] (in which a=b=1/4)-similar to those identified in neutron diffraction and scanning tunneling microscopy experiments-and more generally show that an isolated pocket adjacent to the nodal point k(nodal)=[±π/2,±π/2] is a protected feature of such a multiple-Q model, potentially corresponding to the nodal "Fermi arcs" observed in photoemission and the small size of the electronic heat capacity found in high magnetic fields-importantly, containing electron carriers which can yield negative Hall and Seebeck coefficients observed in high magnetic fields.
TL;DR: In this article, the LDA band structure of hole doped high temperature superconductors (Tc ∼ 30 K) KxFe2Se2 and CsxFe 2Se2 was compared with the electronic structure of isostructural FeAs superconductor BaFe2As2.
Abstract: We present LDA band structure of novel hole doped high temperature superconductors (Tc ∼ 30 K) KxFe2Se2 and CsxFe2Se2 and compare it with previously studied electronic structure of isostructural FeAs superconductor BaFe2As2 (Ba122). We show that stoichiometric KFe2Se2 and CsFe2Se2 have rather different Fermi surfaces as compared with Ba122. However at about 60% of hole doping Fermi surfaces of novel materials closely resemble those of Ba122. In between these dopings we observe a number of topological Fermi surface transitions near the Γ point in the Brillouin zone. Superconducting transition temperature Tc of new systems is apparently governed by the value of the total density of states (DOS) at the Fermi level.
TL;DR: The volume pinning force of FeSe1−xTex in this direction is very strong compared with that of Co-doped BaFe2As2, due to a good matching between the interlayer distance in the c direction and the out-ofplane coherence length.
Abstract: Biaxially textured FeSe1−xTex films have been realized on Fe-buffered MgO substrates by pulsed laser deposition. Similar to the Fe/BaFe2As2 bilayers, the crystalline quality of FeSe1−xTex films exhibit a sharp out-of-plane and in-plane texture less than 0.9°. The Fe/FeSe1−xTex bilayers showed high superconducting transition temperatures of over 17 K. The angular-dependent critical current densities exhibit peaks positioned at H ⊥ c similar to other pnictide thin films. The volume pinning force of FeSe1−xTex in this direction is very strong compared with that of Co-doped BaFe2As2, due to a good matching between the interlayer distance in the c direction and the out-of-plane coherence length.
TL;DR: In this article, the authors focus on the recent magnetic oscillation experiments and how they fit into the broader picture of superconductivity in cuprate superconductors and show that many aspects of these experiments can be explained by Fermi liquid theory, and the key issue is the extent to which this is true.
Abstract: High temperature superconductivity in cuprate superconductors remains an unsolved problem in theoretical physics. The same statement can also be made about a number of other superconductors that have been dubbed novel. What makes these superconductors so elusive is an interesting question in itself. This paper focuses on the recent magnetic oscillation experiments and how they fit into the broader picture. Many aspects of these experiments can be explained by Fermi liquid theory; the key issue is the extent to which this is true. If true, the entire paradigm developed over the past three decades must be reexamined. A critical analysis of this issue has necessitated a broader analysis of questions about distinct ground states of matter, which may be useful in understanding other novel superconductors.
TL;DR: In this paper, the differences between the measured and calculated electronic band structures look insignificant but can be crucial for understanding of the mechanism of high temperature superconductivity, focusing on those differences for 111 and 122 compounds.
Abstract: ARPES experiments on iron based superconductors show that the differences between the measured and calculated electronic band structures look insignificant but can be crucial for understanding of the mechanism of high temperature superconductivity. Here we focus on those differences for 111 and 122 compounds and discuss the observed correlation of the experimental band structure with the superconductivity.
TL;DR: In this paper, a model considering the field distribution in superconductor was developed and symmetric and asymmetric magnetization loops of porous and textured Bi1.8Pb0.3Sr1.9Ca2Cu3Ox were fitted.
Abstract: Inhomogeneous distribution of the pinning force in superconductor results in a magnetization asymmetry. A model considering the field distribution in superconductor was developed and symmetric and asymmetric magnetization loops of porous and textured Bi1.8Pb0.3Sr1.9Ca2Cu3Ox were fitted. It is found that the thermal equilibrium magnetization realizes in crystals smaller than some size depending on temperature and magnetic field.
TL;DR: The theory of thermal conductivity of high temperature superconductors (HTS) based on electron and phonon line width (life times) formulation is developed with Quantum dynamical approach of Green's function as mentioned in this paper.
Abstract: The theory of thermal conductivity of high temperature superconductors (HTS) based on electron and phonon line width (life times) formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high T c superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La 1.8 Sr 0.2 CuO 4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high T c superconductors.
TL;DR: In this article, the authors present a brief review on the structural, magnetic and electronic properties of a new superconductor, with an emphasis on the electronic structure and superconducting gap.
Abstract: The latest discovery of a new iron-chalcogenide superconductor AxFe2−ySe2 (A =K, Cs, Rb, and Tl, etc.) has attracted much attention due to a number of its unique characteristics, such as the possible insulating state of the parent compound, the existence of Fe-vacancy and its ordering, a new form of magnetic structure and its interplay with superconductivity, and the peculiar electronic structures that are distinct from other Fe-based superconductors. In this paper, we present a brief review on the structural, magnetic and electronic properties of this new superconductor, with an emphasis on the electronic structure and superconducting gap. Issues and future perspectives are discussed at the end of the paper.
TL;DR: In this article, a review of recent results of quantum oscillation and transport measurements under high magnetic fields in hole-doped cuprates is presented. But it is only in the case of underdoped YBa2Cu3O6.5 that the Fermi surface is observed.
TL;DR: In this article, a brief review on the recent studies of the upper critical field and its anisotropy in a few typical series of the iron-based superconductors (FeSCs) is given.
Abstract: The newly discovered iron-based high temperature superconductors have demonstrated rich physical properties Here we give a brief review on the recent studies of the upper critical field and its anisotropy in a few typical series of the iron-based superconductors (FeSCs) In spite of their characters of a layered crystal structure, all the FeSCs possess an extremely large upper critical field and a weak anisotropy of superconductivity, being unique among the layered superconductors These particular properties indicate potential applications of the FeSCs in the future Based on the experimental facts of the FeSCs, we will discuss the possible mechanisms of pair breaking in high magnetic fields and its restrictions on the theoretical analysis of the superconducting pairing mechanisms
TL;DR: In this article, the fractal scale invariant distribution is found in a cuprate in the proximity to a critical point in the 3D Aeppli-Bianconi phase diagram of cuprates, where T c is a function of both hole doping and superlattice misfit strain.
Abstract: The statistical physics of the 3D ordered oxygen interstitials has been measured in La2CuO4+y
using an advanced tool, scanning x-ray diffraction with focused synchrotron radiation. The observed fractal scale invariant distribution is found in a cuprate in the proximity to a stripes critical point in the 3D Aeppli-Bianconi phase diagram of cuprates, where T
c is function of both hole doping and superlattice misfit strain. Therefore high-temperature superconductivity is favored by complex fractal systems while on the contrary standard low temperature superconductivity is favored in simple periodic crystals. This work shows that the fractal structural distribution in a stack of membranes favors the macroscopic quantum coherent condensate at high temperature. This result opens new perspectives for the understanding the relationship between emergent scale-free distribution in living matter and possible quantum coherent phenomena able to resist to the attacks of temperature decoherence effects.
TL;DR: It is shown from the relationship between the phase and amplitude of the second harmonic with that of the fundamental quantum oscillations that there exists a single carrier Fermi surface pocket, likely located at the nodal region of the Brillouin zone, with the observed multiple frequencies arising from warping, bilayer splitting and magnetic breakdown.
Abstract: It is unclear whether the Fermi surface in the normal state of underdoped cuprates is ambipolar or solely nodal. Here, measuring the second harmonic oscillations in underdoped YBa2Cu3O6+x reveals the origin as an oscillatory chemical potential, based on which a Fermi surface consisting of a nodal pocket is identified.
TL;DR: In the last 25 years, seven distinct families of superconductors with critical temperatures at ambient pressure that equal or surpass the historic 23 K limit for Nb3Ge have been discovered as discussed by the authors.
Abstract: Seven distinct families of superconductors with critical temperatures at ambient pressure that equal or surpass the historic 23 K limit for Nb3Ge have been discovered in the last 25 years. Each family is reviewed briefly and their common chemical features are discussed. High temperature superconductors are distinguished by having a high (≥50%) content of nonmetallic elements and fall into two broad classes. ‘Metal–nonmetal’ superconductors require a specific combination of elements such as Cu–O and Fe–As which give rise to the highest known Tc's, probably through a magnetic pairing mechanism. ‘Nonmetal-bonded’ materials contain covalently bonded nonmetal anion networks and are BCS-like superconductors. Fitting an extreme value function to the distribution of Tc values for the known high-Tc families suggests that the probability of a newly discovered superconductor family having maximum Tc > 100 K is ∼0.1 to 1%, decreasing to ∼0.02 to 0.2% for room temperature superconductivity.
TL;DR: In this article, the influence of thermomagnetic prehistory on the behavior of a resistive transition R(T) in external magnetic fields of polycrystalline YBa2Cu3O7 and Bi1.8Pb0.3Sr1.
Abstract: The influence of thermomagnetic prehistory on the behavior of a resistive transition R(T) in external magnetic fields of polycrystalline YBa2Cu3O7 and Bi1.8Pb0.3Sr1.9Ca2Cu3Ox high-temperature supercon-ductors and the Bi1.8Pb0.3Sr1.9Ca2Cu3Ox + Ag texture has been investigated. It has been found that, for YBa2Cu3O7, the thermomagnetic prehistory exerts a substantial influence on the dissipation in the subsystem of grain boundaries in magnetic fields up to ∼103 Oe, and this effect becomes insignificant in fields higher than ∼104 Oe. This behavior has been explained by the influence of magnetic moments of high-temperature superconductor grains on the effective magnetic field in the intergranular medium. For bismuth high-temperature superconductors, no influence of thermomagnetic prehistory on the resistive transition has been observed; however, this effect manifests itself in current-voltage characteristics at high transport current densities. There is also a radical difference in the behavior of isotherms of the magnetoresistance R(H) for the yttrium and bismuth systems. For YBa2Cu3O7, there is a clear separation between the dissipation regimes in the intergranular medium and in grains, which manifests itself even at low transport current densities as a change of sign in the curvature of the dependence R(H). For a texture based on the bismuth high-temperature superconductor, this feature has been observed only at high current densities (comparable to the critical current density at H = 0). This difference in the behavior of magnetoresistive properties of the classical high-temperature superconductor systems under investigation has been explained by relatively low irreversibility fields of the bismuth high-temperature superconductors. In these materials, simultaneous processes of dissipation can occur in an external magnetic field both in the subsystem of grain boundaries between crystallites and in the crystallites themselves.
TL;DR: The planar oxygen isotope effect coefficient measured as a function of hole doping in the Pr-and La-doped YBa2Cu3O7 (YBCO) and Ni-Doped La1.85Sr0.15CuO4 (LSCO) superconductors quantitatively and qualitatively follows the form originally proposed by Kresin and Wolf [Phys. Rev. 49, 3652 (1994) as discussed by the authors.
Abstract: The planar oxygen isotope effect coefficient measured as a function of hole doping in the Pr- and La-doped YBa2Cu3O7 (YBCO) and the Ni-doped La1.85Sr0.15CuO4 (LSCO) superconductors quantitatively and qualitatively follows the form originally proposed by Kresin and Wolf [Phys. Rev. B 49, 3652 (1994)], which was derived for polarons perpendicular to the superconducting planes. Interestingly, the inverse oxygen isotope effect coefficient at the pseudogap temperature also obeys the same formula. These findings allow the conclusion that the superconductivity in YBCO and LSCO results from polarons or rather bipolarons in the CuO2 plane. The original formula, proposed for the perpendicular direction only, is obviously more generally valid and accounts for the superconductivity in the CuO2 planes.
TL;DR: In this paper, the authors present a summary of the results on single crystal growth of two types of iron-chalcogenide superconductors, Fe(1+y)Te(1-x)Se(x) (11), and A(x,Fe(2-y)Se (2) (2), using Bridgman, zone-melting, vapor selftransport, and flux techniques.
Abstract: In this review, we present a summary of the results on single crystal growth of two types of iron-chalcogenide superconductors, Fe(1+y)Te(1-x)Se(x) (11), and A(x)Fe(2-y)Se(2) (A= K, Rb, Cs, Tl, Tl/K, Tl/Rb), using Bridgman, zone-melting, vapor self-transport, and flux techniques. The superconducting and magnetic properties (the latter gained mainly from neutron scattering measurements) of these materials are reviewed to demonstrate the connection between magnetism and superconductivity. It will be shown that for the 11 system, while static magnetic order around the reciprocal lattice position (0.5, 0) competes with superconductivity, spin excitations centered around (0.5, 0.5) are closely coupled to the materials' superconductivity; this is made evident by the strong correlation between the spectral weight around (0.5, 0.5) and the superconducting volume fraction. The observation of a spin resonance below the superconducting temperature, Tc, and the magnetic-field dependence of the resonance, emphasize the important role spin excitations play in the superconductivity. Generally, these results illustrate the similarities between the iron-based and cuprate superconductors. In A(x)Fe(2-y)Se(2), superconductivity with Tc ~ 30 K borders an antiferromagnetic insulating phase; this is closer to the behavior observed in the cuprates but differs from that in other iron-based superconductors.
TL;DR: In this article, the authors have successfully grown epitaxial, superconducting films of Ba(Fe1-xCox)2As2 (Ba-122) with x ~ 0.1.
Abstract: We have successfully grown epitaxial, superconducting films of Ba(Fe1-xCox)2As2 (Ba-122)with x ~ 0.1. The films grow without observable correlated defects parallel to the c-axis, as confirmed by TEM. This is also reflected in the absence of a c-axis peak in Jc(θ). In contrast to cuprate high-Tc superconductors such as YBa2Cu3O7-δ or even Bi2Sr2Ca2Cu3O10-δ, the pnictides show a rather low anisotropic behavior in their Jc(θ) behavior as well as in their upper critical fields, Hc2. As a multiband superconductor, Ba-122 exhibits a temperature dependent electronic mass anisotropy.
TL;DR: In this paper, the shape resonance in the superconducting gaps of a two-band superconductor was investigated by tuning the chemical potential at a Lifshitz transition for Fermi surface neck collapsing and for spot appearing.
Abstract: We discuss the shape resonance in the superconducting gaps of a two-band superconductor by tuning the chemical potential at a Lifshitz transition for Fermi surface neck collapsing and for spot appearing. The high temperature superconducting scenario for complex matter shows the coexistence of a first BCS condensate made of Cooper pairs in the first band and a second boson-like condensate made of bosons like bipolarons, in the second band where the chemical potential is tuned near a Lifshitz transition. The interband coupling controls the shape resonance in the pair exchange between the two condensates. We discuss the particular BCS–Bose crossover that occurs at the shape resonance tuning the Lifshitz parameter (the energy difference between the chemical potential and the Lifshitz topological transition) like tuning the external magnetic field for the Feshbach resonances in ultracold gases. This superconducting phase provides a particular case of topological superconductivity with multiple condensates of different winding numbers.