Magnetic and electronic properties of iron-based superconducting systems

Creep Model ◽

Hole Doping ◽

Magnetic Impurities ◽

Superconducting Layer ◽

Fluctuation Conductivity ◽

Strong Localization

<p>This thesis is motivated by the large variety of high-temperature superconductors that contain iron in the superconducting layer. This number has grown rapidly since the discovery in 2008 of the iron-pnictides (and chalcogenides), where iron and arsenic form the superconducting layer. Also of interest are the iron-cuprate hybrid materials, where one out of three copper atoms is replaced by iron. The aim is to understand the superconducting, magnetic and electronic properties of these materials in respect to their iron content. This thesis describes some of these properties for the iron-pnictide compounds of CeFeAsO₁₋xFx and AFe₂As₂ (A=Ba, Sr), and for the ironcuprate hybrids of FeSr₂YCu₂O₆₊y and FeSr₂Y₂₋xCexCu₂O₁₀₋y. Here it has been found that CeFeAsO₁₋xFx follows a 3D fluctuation conductivity above the superconducting transition and the thermal activation energy is correlated to the critical current density within a two fluid-flux creep model below the superconducting transition. NMR measurements show that there is considerable charge disorder within the superconducting doping region. The AFe₂As₂ show a positive magnetoresistance, which could be interpreted through three-carrier transport. Superconducting samples of SrFe₂As₂ display a large enhancement in the magnetoresistance below the superconducting transition up to 1600 %, which is due to three-carrier transport through metallic and superconducting regions in an inhomogeneous state. The superconducting properties of the iron-cuprate FeSr₂YCu₂O₆₊y in respect to the location of iron was studied under the influence of electron and hole doping and with additional magnetic impurities. FeSr₂Y₂₋xCexCu₂O₁₀₋y shows a disorder induced spin-glass state and strong localization depending on the doping.</p>

Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder

Materials ◽

10.3390/ma13245830 ◽

2020 ◽

Vol 13 (24) ◽

pp. 5830

Author(s):

Andrzej Ślebarski ◽

Maciej M. Maśka

Keyword(s):

High Temperature ◽

Transition Temperature ◽

Superconducting Phase ◽

Length Scale ◽

Atomic Disorder ◽

Strong Inhomogeneity ◽

Related Compounds

We investigated the effect of enhancement of superconducting transition temperature Tc by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La3M4Sn13, Ca3Rh4Sn13, Y5Rh6Sn18, Lu5Rh6Sn18; M= Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale ξ in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with Tc⋆>Tc (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of Tc⋆∼2Tc (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase Tc⋆ in respect to the bulk Tc one and proposed a model that explains the Tc⋆>Tc behavior in the series of nonmagnetic skutterudite-related compounds.

Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1704505114 ◽

2017 ◽

Vol 114 (27) ◽

pp. 6990-6995 ◽

Cited By ~ 214

Author(s):

Hanyu Liu ◽

Ivan I. Naumov ◽

Roald Hoffmann ◽

N. W. Ashcroft ◽

Russell J. Hemley

Keyword(s):

Group Structure ◽

Face Centered Cubic ◽

High Tc ◽

Structure Search ◽

Systematic Structure ◽

Face Centered ◽

Fcc Structure ◽

Very High

A systematic structure search in the La–H and Y–H systems under pressure reveals some hydrogen-rich structures with intriguing electronic properties. For example, LaH10 is found to adopt a sodalite-like face-centered cubic (fcc) structure, stable above 200 GPa, and LaH8 a C2/m space group structure. Phonon calculations indicate both are dynamically stable; electron phonon calculations coupled to Bardeen–Cooper–Schrieffer (BCS) arguments indicate they might be high-Tc superconductors. In particular, the superconducting transition temperature Tc calculated for LaH10 is 274–286 K at 210 GPa. Similar calculations for the Y–H system predict stability of the sodalite-like fcc YH10 and a Tc above room temperature, reaching 305–326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very high-temperature superconductors.

Evolution of atomic ordering in fine-grained YBa2Cu3O y high-temperature superconductors and its effect on superconducting transition temperature

Bulletin of the Russian Academy of Sciences Physics ◽

10.3103/s1062873813030258 ◽

2013 ◽

Vol 77 (3) ◽

pp. 242-245 ◽

Cited By ~ 1

Author(s):

L. G. Mamsurova ◽

K. S. Pigalskiy ◽

A. A. Vishnev

Keyword(s):

High Temperature ◽

Transition Temperature ◽

Atomic Ordering ◽

Fine Grained

Crystal Growth of High Temperature Superconductors

MRS Bulletin ◽

10.1557/s0883769400064204 ◽

1988 ◽

Vol 13 (10) ◽

pp. 56-61 ◽

Cited By ~ 31

Author(s):

H.J. Scheel ◽

F. Licci

Keyword(s):

High Temperature ◽

Critical Current Density ◽

Single Crystals ◽

Critical Current ◽

Current Density ◽

Large Scale ◽

High Temperature Superconductivity ◽

Theoretical Understanding

The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.

Carrier-mediated ferromagnetism in two-dimensional PtS2

RSC Advances ◽

10.1039/c9ra09756b ◽

2020 ◽

Vol 10 (2) ◽

pp. 952-957 ◽

Cited By ~ 3

Author(s):

Konstantina Iordanidou ◽

Michel Houssa ◽

Clas Persson

Keyword(s):

Density Functional Theory ◽

Electronic Properties ◽

First Principles ◽

Density Functional ◽

Hole Doping ◽

Two Dimensional ◽

First Principles Calculations ◽

Functional Theory ◽

The Impact

Using first principles calculations based on density functional theory the impact of hole doping on the magnetic and electronic properties of two dimensional PtS2 is studied.

Energy Scale of the Charge Density Wave in Cuprate Superconductors

Proceedings ◽

10.3390/proceedings2019026020 ◽

2019 ◽

Vol 26 (1) ◽

pp. 20

Author(s):

Sacuto ◽

Loret ◽

Auvray ◽

Civelli ◽

Indranil ◽

...

Keyword(s):

High Temperature ◽

Charge Density ◽

Charge Density Wave ◽

Cuprate Superconductors ◽

Density Wave ◽

Energy Scale ◽

Hole Doping ◽

Wide Range

The cuprate high temperature superconductors develop spontaneous charge density wave(CDW) order below a temperature TCDW and over a wide range of hole doping (p). [...]

Higher superconducting transition temperature by breaking the universal pressure relation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1819512116 ◽

2019 ◽

Vol 116 (6) ◽

pp. 2004-2008 ◽

Cited By ~ 9

Author(s):

Liangzi Deng ◽

Yongping Zheng ◽

Zheng Wu ◽

Shuyuan Huyan ◽

Hung-Cheng Wu ◽

...

Keyword(s):

Density Functional Theory ◽

High Temperature ◽

Transition Temperature ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Universal Relation ◽

Functional Theory ◽

A Charge

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+δ(Bi2201) and bilayer Bi2Sr2CaCu2O8+δ(Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tcand doping (p) or pressure (P) at higher pressures. The Tcof underdoped Bi2201 initially increases from 9.6 K at ambient to a peak at 23 K at 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above 40 GPa, Tcrises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the Tcfor the slightly overdoped Bi2212 increases after passing a broad valley between 20 and 36 GPa and reaches 90 K without any sign of saturation at 56 GPa. We have, therefore, attributed this Tcresurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3dx2−y2and the O 2pbands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+δ(Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.

Distinct superconducting properties and hydrostatic pressure effects in 2D α- and β-Mo2C crystal sheets

NPG Asia Materials ◽

10.1038/s41427-020-00242-3 ◽

2020 ◽

Vol 12 (1) ◽

Author(s):

Yunjie Fan ◽

Chuan Xu ◽

Xiang Liu ◽

Chao Ma ◽

Yuewei Yin ◽

...

Keyword(s):

Transition Temperature ◽

Hydrostatic Pressure ◽

Electronic Properties ◽

Important Influence ◽

Pressure Effects ◽

Superconducting Properties ◽

Disordered Carbon

Abstract Recently, 2D Mo2C, a new member of the MXene family, has attracted much attention due to the exotic superconducting properties discovered in 2D α-Mo2C. Here, not only 2D α-Mo2C but also 2D β-Mo2C crystal sheets with distinct disordered carbon distributions were successfully grown. 2D β-Mo2C shows a much stronger superconductivity than 2D α-Mo2C, and their superconductivities have different hydrostatic pressure responses. The superconducting transition temperature Tc of 2D α-Mo2C shows a dome-shaped profile under pressure, implying the existence of two competing effects arising from phononic and electronic properties, while for 2D β-Mo2C, Tc decreases monotonically with increasing pressure, possibly due to phonon stiffening. These results indicate that the electronic properties have a more important influence on the superconductivity in 2D α-Mo2C compared to 2D β-Mo2C. The ordered and disordered carbon distributions in 2D α-Mo2C and β-Mo2C, respectively, may be the underlying origin for their different electronic and superconducting properties.

Two-dimensional stoichiometric boron carbides with unexpected chemical bonding and promising electronic properties

Journal of Materials Chemistry C ◽

10.1039/c7tc04505k ◽

2018 ◽

Vol 6 (7) ◽

pp. 1651-1658 ◽

Cited By ~ 17

Author(s):

Dong Fan ◽

Shaohua Lu ◽

Yundong Guo ◽

Xiaojun Hu

Keyword(s):

Transition Temperature ◽

Electronic Properties ◽

Young’S Modulus ◽

Chemical Bonding ◽

Young's Modulus ◽

Two Dimensional ◽

Pyramidal Geometry ◽

Bonding Patterns

We identify two B–C bonding patterns: pyramidal-geometry tetra-coordinated and hexa-coordinated sp2carbon moiety; B4C3has an ultrahigh Young's modulus that can even outperform graphene; the B2C sheet is metallic with a relatively high superconducting transition temperature (Tc≈ 21.20 K).