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.

scholarly journals The 3-Dimensional Fermi Liquid Description for the Iron-Based Superconductors

2017 ◽  
Vol 190 (1-2) ◽  
pp. 45-66 ◽  
Author(s):  
Setsuo Misawa
Keyword(s):  
Fermi Liquid ◽  
Fermi Liquids ◽  
Electronic Specific Heat ◽  
Superconducting Transition ◽  
Iron Based Superconductors ◽  
Fermi Surfaces ◽  
3 Dimensional ◽  
Quasiparticle Energy ◽  
Iron Based ◽  
Specific Heat Coefficient

Abstract The quasiparticles in the normal state of iron-based superconductors have been shown to behave universally as a 3-dimensional Fermi liquid. Because of interactions and the presence of sharp Fermi surfaces, the quasiparticle energy contains, as a function of the momentum $$\varvec{p}$$ p , a term of the form $$( p - p_0)^3 \ln {( |p-p_0|/p_0)} $$ ( p - p 0 ) 3 ln ( | p - p 0 | / p 0 ) , where $$p = | \varvec{p} |$$ p = | p | and $$p_0$$ p 0 is the Fermi momentum. The electronic specific heat coefficient, magnetic susceptibility (Knight shift), electrical resistivity, Hall coefficient and thermoelectric power divided by temperature follow, as functions of temperature T, the logarithmic formula $$a-b T^2 \ln {(T/T^*)}$$ a - b T 2 ln ( T / T ∗ ) , $$a, \, b$$ a , b and $$T^*$$ T ∗ being constant; these formulae have been shown to explain the observed data for all iron-based superconductors. It is shown that the concept of non-Fermi liquids or anomalous metals which appears in the literature is not needed for descriptions of the present systems. When the superconducting transition temperature $$T_{\mathrm {C}}$$ T C and the b / a value for the resistivity are plotted as functions of the doping content x, there appear various characteristic diagrams in which regions of positive correlation and those of negative correlation between $$T_{\mathrm {C}}$$ T C and b / a are interconnected; from these diagrams, we may make speculations about the types of superconductivity and the crossover between them.

ANOMALOUS ELASTIC BEHAVIOR AND ITS CORRELATION WITH SUPERCONDUCTIVITY IN IRON-BASED SUPERCONDUCTOR Ba(Fe1-xCox)2As2

2012 ◽  
Vol 26 (19) ◽  
pp. 1230011 ◽  
Author(s):  
MASAHITO YOSHIZAWA ◽  
SHALAMUJIANG SIMAYI
Keyword(s):  
Elastic Behavior ◽  
Clear Correlation ◽  
Superconducting Transition ◽  
Strong Electron ◽  
Iron Based Superconductors ◽  
Unconventional Superconductors ◽  
Structural Fluctuation ◽  
Iron Based ◽  
Lattice Coupling ◽  
Quantum Critical Behavior

Elastic properties of iron-based superconductor Ba ( Fe 1-x Co x)2 As 2 with various Co concentrations x were reviewed. Among all elastic constants, C66 shows remarkable softening associated with the structural transition from tetragonal to orthorhombic. The amount of anomaly in C66 is 90% for the underdoped samples of x < 0.07 For the overdoped samples, the anomalies in C66 gradually disappear with the increasing of Co concentration. The elastic compliance S66 (= 1/C66) shows a quantum critical behavior, which behaves just like the magnetic susceptibility of unconventional superconductors. There exists a clear correlation between the superconducting transition temperature and the amount of anomaly in S66. It was suggested that the structural fluctuation, which is measured by S66, plays an important role in the emergence of superconductivity. The elastic anomaly of Ba ( Fe 1-x Co x)2 As 2 is characterized by a strong electron–lattice coupling, which would be originated from the 3d orbitals of iron. This might be a universal phenomenon not only in iron-based superconductors but also d-electron based superconductors. The results on Ba ( Fe 1-x Co x)2 As 2 would reveal relevant roles of the structural fluctuations due to the orbitals, which should be taken into account for the understanding of a whole picture of the superconductivity in iron-based superconductors and related materials.

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.

scholarly journals High Pressure Low Temperature Studies on 1-2-2 Iron-based Superconductors Using Designer Diamond Cells

2013 ◽  
Vol 1582 ◽  
Author(s):  
Walter O. Uhoya ◽  
Georgiy M. Tsoi ◽  
Yogesh K. Vohra ◽  
Jonathan, E. Mitchell ◽  
Athena Safa-Sefat ◽  
...  
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
High Pressures ◽  
Density Wave ◽  
Spin Density Wave ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
Iron Based Superconductors ◽  
Diamond Anvil ◽  
Iron Based

ABSTRACTHigh pressure low temperature electrical resistance measurements were carried out on a series of 122 iron-based superconductors using a designer diamond anvil cell. These studies were complemented by image plate x-ray diffraction measurements under high pressures and low temperatures at beamline 16-BM-D, HPCAT, Advanced Photon Source. A common feature of the 1-2-2 iron-based materials is the observation of anomalous compressibility effects under pressure and a Tetragonal (T) to Collapsed Tetragonal (CT) phase transition under high pressures. Specific studies on antiferromagnetic spin-density-wave Ba0.5Sr0.5Fe2As2 and Ba(Fe0.9Ru0.1)2As2 samples are presented to 10 K and 41 GPa. The collapsed tetragonal phase was observed at a pressure of 14 GPa in Ba0.5Sr0.5Fe2As2 at ambient temperature. The highest superconducting transition temperature in Ba0.5Sr0.5Fe2As2 was observed to be at 32 K at a pressure of 4.7 GPa. The superconductivity was observed to be suppressed on transformation to the CT phase in 122 materials.

EFFECT OF ZINC IMPURITY AND ITS IMPLICATION TO THE PAIRING SYMMETRY IN IRON-BASED SUPERCONDUCTORS

2012 ◽  
Vol 26 (20) ◽  
pp. 1230012 ◽  
Author(s):  
ZHU-AN XU ◽  
GUANGHAN CAO ◽  
YUKE LI
Keyword(s):  
Parent Compound ◽  
Pairing Symmetry ◽  
Impurity Effect ◽  
Superconducting Transition ◽  
S Wave ◽  
Iron Based Superconductors ◽  
Co Doping ◽  
Wave States ◽  
Iron Based ◽  
Carrier Doping

The effect of nonmagnetic Zn impurity on superconductivity in iron-based superconductors is reviewed. Zn impurity can severely suppress the antiferromagnetic (AFM) order of Fe ions in the parent compound LaFeAsO . In the 1111 type F-doped LaFeAs ( O , F ) system, the superconducting transition temperature (Tc) increases in the underdoped regime, remains unchanged in the optimally-doped regime, and is severely suppressed in the overdoped regime in the presence of Zn impurity. The results suggest a switch of the symmetry of the superconducting order parameters from a s-wave to s±- or d-wave states as the charge carrier doping increases in this system. To our surprise, Zn impurity strongly suppresses Tc in the Co -doped LaFeAsO and BaFe 2 As 2 systems despite of the Co doping level. The absence of universal Zn impurity effect implies that the pairing symmetry of the iron-based superconductors may be dependent on the details of the electronic structure.

scholarly journals Photoinduced possible superconducting state with long-lived disproportionate band filling in FeSe

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Takeshi Suzuki ◽  
Takashi Someya ◽  
Takahiro Hashimoto ◽  
Shoya Michimae ◽  
Mari Watanabe ◽  
...  
Keyword(s):  
Superconducting State ◽  
Degrees Of Freedom ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Photoemission Spectroscopy ◽  
Iron Based Superconductors ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Dynamical Behaviors ◽  
Band Filling ◽  
Iron Based

Abstract Photoexcitation is a very powerful way to instantaneously drive a material into a novel quantum state without any fabrication, and variable ultrafast techniques have been developed to observe how electron, lattice, and spin degrees of freedom change. One of the most spectacular phenomena is photoinduced superconductivity, and it has been suggested in cuprates that the transition temperature Tc can be enhanced from the original Tc with significant lattice modulations. Here, we show a possibility for another photoinduced high-Tc superconducting state in the iron-based superconductor FeSe. The transient electronic state over the entire Brillouin zone is directly observed by time- and angle-resolved photoemission spectroscopy using extreme ultraviolet pulses obtained from high harmonic generation. Our results of dynamical behaviors from 50 fs to 800 ps consistently support the favourable superconducting state after photoexcitation well above Tc. This finding demonstrates that multiband iron-based superconductors emerge as an alternative candidate for photoinduced superconductors.

scholarly journals Iron-based high transition temperature superconductors

2014 ◽  
Vol 1 (3) ◽  
pp. 371-395 ◽  
Author(s):  
Xianhui Chen ◽  
Pengcheng Dai ◽  
Donglai Feng ◽  
Tao Xiang ◽  
Fu-Chun Zhang
Keyword(s):  
Transition Temperature ◽  
Point Of View ◽  
Scanning Tunneling ◽  
Electric Transport ◽  
Superconducting Transition ◽  
Tunneling Microscopy ◽  
Iron Based Superconductors ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Iron Based ◽  
Coupling Point

Abstract In a superconductor electrons form pairs and electric transport becomes dissipation-less at low temperatures. Recently discovered iron-based superconductors have the highest superconducting transition temperature next to copper oxides. In this article, we review material aspects and physical properties of iron-based superconductors. We discuss the dependence of transition temperature on the crystal structure, the interplay between antiferromagnetism and superconductivity by examining neutron scattering experiments, and the electronic properties of these compounds obtained by angle-resolved photoemission spectroscopy in link with some results from scanning tunneling microscopy/spectroscopy measurements. Possible microscopic model for this class of compounds is discussed from a strong coupling point of view.

scholarly journals Superconductivity in K- and Na-doped BaFe2As2: What can we learn from heat capacity and pressure dependence of Tc

2015 ◽  
Vol 29 (02) ◽  
pp. 1430019 ◽  
Author(s):  
Sergey L. Bud'ko
Keyword(s):  
Heat Capacity ◽  
Transition Temperature ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Pressure Dependence ◽  
Superconducting Transition ◽  
Phase Boundaries ◽  
Iron Based Superconductors ◽  
Heat Capacity Jump ◽  
Iron Based

A brief overview of changes in the superconducting transition temperature under pressure and evolution of specific heat capacity jump at Tc for two related families of iron-based superconductors, Ba 1-x K x Fe 2 As 2 (0.2 ≤ x ≤ 1.0) and Ba 1-x Na x Fe 2 As 2 (0.2 ≤ x ≤ 0.9) will be given. For Ba 1-x K x Fe 2 As 2 the specific heat capacity jump at Tc measured over the whole extent of the superconducting dome shows clear deviation from the empirical, [Formula: see text], scaling (known as the BNC scaling) for x > 0.7. At the same concentrations range apparent equivalence of effects of pressure and K -substitution on Tc fails. These observations suggests a significant change of the superconducting state for x > 0.7. In contrast, the data for the large portion of Ba 1-x Na x Fe 2 As 2 (0.2 ≤ x ≤ 0.9) series follow the BNC scaling. However, the pressure dependence of Tc (measured up to ~12 kbar) have clear nonlinearities for Na concentration in 0.2–0.25 region, that may be consistent with Tc crossing the phase boundaries of the emergent, narrow, antiferromagnetic/tetragonal phase. Results will be discussed in context other studies of these two related families of iron-based superconductors.

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