scholarly journals Energy gap evolution across the superconductivity dome in single crystals of (Ba1−xKx)Fe2As2

2016 ◽  
Vol 2 (9) ◽  
pp. e1600807 ◽  
Author(s):  
Kyuil Cho ◽  
Marcin Kończykowski ◽  
Serafim Teknowijoyo ◽  
Makariy A. Tanatar ◽  
Yong Liu ◽  
...  
Keyword(s):  
Single Crystals ◽  
Abrupt Change ◽  
Energy Gap ◽  
Superconducting Transition ◽  
London Penetration Depth ◽  
Wave State ◽  
Iron Based Superconductors ◽  
Optimal Doping ◽  
Gap Anisotropy ◽  
Materials Research

The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba1−xKx)Fe2As2has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping (x≈ 0.4) to becoming nodal atx> 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We conducted a systematic study of the London penetration depth, λ(T), across the full phase diagram for different concentrations of point-like defects introduced by 2.5-MeV electron irradiation. Fitting the low-temperature variation with the power law, Δλ ~Tn, we find that the exponentnis the highest and theTcsuppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change aroundx≃ 0.8, indicating the onset of nodal behavior. Our analysis using a self-consistentt-matrix approach suggests the ubiquitous and robust nature ofs±pairing in IBSs and argues against a previously suggested transition to ad-wave state nearx= 1 in this system.

Doping Induced Gap Anisotropy in Iron-Based Superconductors: a Point-Contact Andreev Reflection Study of BaFe 2−x Ni x As 2 Single Crystals

2015 ◽  
Vol 32 (7) ◽  
pp. 077401 ◽  
Author(s):  
Jun Zhu ◽  
Zhao-Sheng Wang ◽  
Zhen-Yu Wang ◽  
Xing-Yuan Hou ◽  
Hui-Qian Luo ◽  
...  
Keyword(s):  
Single Crystals ◽  
Andreev Reflection ◽  
Point Contact ◽  
Iron Based Superconductors ◽  
Gap Anisotropy ◽  
Iron Based

scholarly journals Superconductivity mediated by polar modes in ferroelectric metals

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
C. Enderlein ◽  
J. Ferreira de Oliveira ◽  
D. A. Tompsett ◽  
E. Baggio Saitovitch ◽  
S. S. Saxena ◽  
...  
Keyword(s):  
Critical Point ◽  
Energy Gap ◽  
Quantum Critical Point ◽  
Quantitative Model ◽  
Superconducting Transition ◽  
Pairing Interaction ◽  
Optimal Doping ◽  
Occurrence Of Superconductivity ◽  
Quantum Critical ◽  
Dynamical Screening

Abstract The occurrence of superconductivity in doped SrTiO3 at low carrier densities points to the presence of an unusually strong pairing interaction that has eluded understanding for several decades. We report experimental results showing the pressure dependence of the superconducting transition temperature, Tc, near to optimal doping that sheds light on the nature of this interaction. We find that Tc increases dramatically when the energy gap of the ferroelectric critical modes is suppressed, i.e., as the ferroelectric quantum critical point is approached in a way reminiscent to behaviour observed in magnetic counterparts. However, in contrast to the latter, the coupling of the carriers to the critical modes in ferroelectrics is predicted to be small. We present a quantitative model involving the dynamical screening of the Coulomb interaction and show that an enhancement of Tc near to a ferroelectric quantum critical point can arise due to the virtual exchange of longitudinal hybrid-polar-modes, even in the absence of a strong coupling to the transverse critical modes.

Phonon Anomaly at Tc In (Y/Er)Ba2Cu3O7–δ

1989 ◽  
Vol 169 ◽  
Author(s):  
Rajeshwar P. Sharma ◽  
L. E. Rehn ◽  
P. Baldo ◽  
J. Z. Liu
Keyword(s):  
Transition Temperature ◽  
Single Crystals ◽  
Superconducting Transition Temperature ◽  
Structural Changes ◽  
Abrupt Change ◽  
Superconducting Transition ◽  
Ion Channeling ◽  
Atomic Displacements ◽  
Induced Changes ◽  
Phonon Anomaly

AbstractIon channeling in single crystals of (Y/Er)Ba2Cu3O7–δ reveal an abrupt change (~0.01Å) at the superconducting transition temperature (Tc) in displacements of the Cu and O atoms perpendicular to the [001] direction. This anomalous change in atomic displacements shifts directly with stoichiometry-induced changes in Tc. Blocking patterns indicate no large structural changes across Tc.

On the energy gap in superconducting tin

1962 ◽  
Vol 268 (1333) ◽  
pp. 276-289 ◽  
Keyword(s):  
Single Crystal ◽  
Absorption Edge ◽  
Surface Resistance ◽  
Energy Gap ◽  
Superconducting Transition ◽  
Isotropic Energy ◽  
A Value ◽  
Indium Alloys ◽  
Polycrystalline Alloy ◽  
Gap Anisotropy

The surface resistance of specimens of superconducting tin and of tin-indium alloys has been measured at a frequency of 140 kmc/s and at temperatures near to the superconducting transition. In both single crystal and polycrystalline alloy specimens, the onset of quantum absorption was well defined and corresponded to an isotropic energy gap with a value at absolute zero of about 3·6 kT c . With pure tin, however, the absorption edge was not well defined in specimens oriented away from the tetrad axis; but near to the tetrad axis, there seems to be a considerable region in which the gap varies com paratively slowly, taking a value of about 3·6 kT c . Assuming that the absence of a clearly defined absorption edge for other orientations is the result of gap anisotropy, it is shown that regions in which the gap takes values very different from 3·6 kT c must lie well away from the tetrad axis. The analysis also shows that such regions are comparatively unimportant, and that the 3·6 kT c gap predominates strongly.

scholarly journals p-wave superconductivity in iron-based superconductors

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
E. F. Talantsev ◽  
K. Iida ◽  
T. Ohmura ◽  
T. Matsumoto ◽  
W. P. Crump ◽  
...  
Keyword(s):  
Energy Gap ◽  
Atomic Layer ◽  
P Wave ◽  
Physical Parameters ◽  
Superconducting Transition ◽  
Iron Based Superconductors ◽  
Wave Pairing ◽  
Superconducting Energy Gap ◽  
Wave States ◽  
Iron Based

Abstract The possibility of p-wave pairing in superconductors has been proposed more than five decades ago, but has not yet been convincingly demonstrated. One difficulty is that some p-wave states are thermodynamically indistinguishable from s-wave, while others are very similar to d-wave states. Here we studied the self-field critical current of NdFeAs(O,F) thin films in order to extract absolute values of the London penetration depth, the superconducting energy gap, and the relative jump in specific heat at the superconducting transition temperature, and find that all the deduced physical parameters strongly indicate that NdFeAs(O,F) is a bulk p-wave superconductor. Further investigation revealed that single atomic layer FeSe also shows p-wave pairing. In an attempt to generalize these findings, we re-examined the whole inventory of superfluid density measurements in iron-based superconductors and show quite generally that single-band weak-coupling p-wave superconductivity is exhibited in iron-based superconductors.

Magnetic Flux Penetration into MgB2

2003 ◽  
Vol 17 (10n12) ◽  
pp. 675-689 ◽  
Author(s):  
P. Mikheenko ◽  
R. Chakalov ◽  
R. I. Chakalova ◽  
M. S. Colclough ◽  
C. M. Muirhead
Keyword(s):  
Thin Films ◽  
Single Crystals ◽  
Magnetic Moments ◽  
Superconducting Transition ◽  
London Penetration Depth ◽  
Normal State Resistivity ◽  
Resistivity Ratio ◽  
The Moment ◽  
Magnetization Behavior ◽  
Anisotropic Magnetization

We report magnetization and transport measurements on MgB2 in the form of powder, bulk ceramic, wire made by diffusion of Mg into B, and pulsed laser deposited thin films. Ceramic and wire forms show strong intergranular links, and we compare their properties with those of single crystals. The powder shows a magnetic moment versus temperature curve that scales with the moment at the lowest temperature, consistent with a distribution of grain sizes, on the scale of the London penetration depth. The ceramics shows anisotropic magnetization behavior, which is probably a consequence of the anisotropic compressional forces used in its manufacture. In both powder and ceramic, we have observed intriguing negative magnetic moments and steps therein upon changing temperature, well above the obvious superconducting transition. These could indicate small amounts of some higher Tc superconducting phases. However, magnetization loops measured in this regime show ferromagnetism, which we suggest is the origin of the magnetic properties above Tc. The wire shows a linear diamagnetic response up to an Hc1 of 236 Oe, has a normal state resistivity of 2.6 × 10-6 Ω·cm just above the transition and a resistivity ratio of 21, which is also similar to those of single crystals. The thin films are composed of large crystalline platelets, have a Tc of 35 K, and are diamagnetic.

scholarly journals Importance of $${{d}}_{{{xy}}}$$ orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tsuyoshi Kawashima ◽  
Shigeki Miyasaka ◽  
Hirokazu Tsuji ◽  
Takahiro Yamamoto ◽  
Masahiro Uekubo ◽  
...  
Keyword(s):  
Electron Correlation ◽  
Weak Coupling ◽  
Structural Parameters ◽  
Structural Flexibility ◽  
Superconducting Transition ◽  
Iron Based Superconductors ◽  
Wide Range ◽  
Band Filling ◽  
Iron Based ◽  
Correlation Strength

AbstractThe structural flexibility at three substitution sites in LaFeAsO enabled investigation of the relation between superconductivity and structural parameters over a wide range of crystal compositions. Substitutions of Nd for La, Sb or P for As, and F or H for O were performed. All these substitutions modify the local structural parameters, while the F/H-substitution also changes band filling. It was found that the superconducting transition temperature $$T_{\text{c}}$$ T c is strongly affected by the pnictogen height $$h_{Pn}$$ h Pn from the Fe-plane that controls the electron correlation strength and the size of the $$d_{xy}$$ d xy hole Fermi surface (FS). With increasing $$h_{Pn}$$ h Pn , weak coupling BCS superconductivity switches to the strong coupling non-BCS one where electron correlations and the $$d_{xy}$$ d xy hole FS may be important.

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