Magnetic imaging of antiferromagnetic and superconducting phases in RbxFe2−ySe2 crystals (original) (raw)

TOPICAL REVIEW: Magnetism in Fe-based superconductors

J Phys Condens Matter, 2010

In this review, we present a summary of experimental studies of magnetism in Fe-based superconductors. The doping dependent phase diagram shows strong similarities to the generic phase diagram of the cuprates. Parent compounds exhibit magnetic order together with a structural phase transition both of which are progressively suppressed with doping allowing superconductivity to emerge. The stripe-like spin arrangement of Fe moments in the magnetically ordered state shows the identical in-plane structure for the RFeAsO (R=rare earth) and AFe 2 As 2 (A=Sr, Ca, Ba, Eu and K) parent compounds, notably different than the spin configuration of the cuprates. Interestingly, Fe 1+y Te orders with a different spin order despite very similar Fermi surface topology. Studies of the spin dynamics in the parent compounds shows that the interactions are best characterized as anisotropic three-dimensional (3D) interactions. Despite the room temperature tetragonal structure, analysis of the low temperature spin waves under the assumption of a Heisenberg Hamiltonian indicates strong in-plane anisotropy with a significant next-near neighbor interaction. In the superconducting state, a resonance, localized in both wavevector and energy is observed in the spin excitation spectrum as in the cuprates. This resonance is observed at a wavevector compatible with a Fermi surface nesting instability independent of the magnetic ordering of the relevant parent compound. The resonance energy (E r) scales with superconducting transition temperature (T C) as E r ∼4.9 k B T C consistent with the canonical value of ∼5 k B T C observed in the cuprates. Moreover, the relationship between the resonance energy and the superconducting gap, ∆, is similar to that observed in many unconventional superconductors (E r /2∆ ∼ 0.64). Material Max. T C (K) LaFeAsO 1−x F x [1] 26 NdFeAsO 1−x F x [2] 52 PrFeAsO 1−x F x [3] 52 SmFeAsO 1−x F x [4] 55 CeFeAsO 1−x F x [5] 41 GdFeAsO 1−x F x [7] 50 TbFeAsO 1−x F x [9] 46 DyFeAsO 1−x F x [9] 45 Gd 1−x Th x FeAsO [10] 56 LaFeAsO 1−y [11, 12] 28 NdFeAsO 1−y [11, 12, 13] 53 PrFeAsO 1−y [11, 12] 48 SmFeAsO 1−y [11] 55 GdFeAsO 1−y [14, 12] 53 TbFeAsO 1−y [12] 52 DyFeAsO 1−y [12] 52 LaFe 1−x Co x AsO [17] 14 SmFe 1−x Ni x AsO [26] 10 SmFe 1−x Co x AsO [27] 15 LaFe 1−x Ir x AsO [28] 12 Material Max. T C (K) Ba 1−x K x Fe 2 As 2 [16] 38 Ba 1−x Rb x Fe 2 As 2 [29] 23 K 1−x Sr x Fe 2 As 2 [30] 36 Cs 1−x Sr x Fe 2 As 2 [30] 37 Ca 1−x Na x Fe 2 As 2 [31] 20 Eu 1−x K x Fe 2 As 2 [32] 32 Eu 1−x Na x Fe 2 As 2 [33] 35 Ba(Fe 1−x Co x) 2 As 2 [18, 34] 22-24 Ba(Fe 1−x Ni x) 2 As 2 [19] 20 Sr(Fe 1−x Ni x) 2 As 2 [35] 10 Ca(Fe 1−x Co x) 2 As 2 [36] 17 Ba(Fe 1−x Rh x) 2 As 2 [20] 24 Ba(Fe 1−x Pd x) 2 As 2 [20] 19 Sr(Fe 1−x Rh x) 2 As 2 [21] 22 Sr(Fe 1−x Ir x) 2 As 2 [21] 22 Sr(Fe 1−x Pd x) 2 As 2 [21] 9 Ba(Fe 1−x Ru x) 2 As 2 [22] 21 Sr(Fe 1−x Ru x) 2 As 2 [23] 13.5 LiFeAs [37, 38, 39] 18 Na 1−x FeAs [40] 25 Fe 1+y Se x Te 1−x [41] 15

Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article

Angle resolved photoemission spectroscopy (ARPES) reveals the features of the electronic structure of quasi-two-dimensional crystals which are crucial for spin and charge ordering and determine the mechanisms of electron-electron interactions, including superconducting pairing. The newly discovered iron-based superconductors (FeSC) promise interesting physics stemming, on one hand, from a coexistence of superconductivity and magnetism and, on the other, from a complex multi-band electronic structure.

Magnetism in Fe-based superconductors

Journal of Physics: Condensed Matter, 2010

In this review, we present a summary of experimental studies of magnetism in Fe-based superconductors. The doping dependent phase diagram shows strong similarities to the generic phase diagram of the cuprates. Parent compounds exhibit magnetic order together with a structural phase transition both of which are progressively suppressed with doping allowing superconductivity to emerge. The stripe-like spin arrangement of Fe moments in the magnetically ordered state shows the identical in-plane structure for the RFeAsO (R=rare earth) and AFe 2 As 2 (A=Sr, Ca, Ba, Eu and K) parent compounds, notably different than the spin configuration of the cuprates. Interestingly, Fe 1+y Te orders with a different spin order despite very similar Fermi surface topology. Studies of the spin dynamics in the parent compounds shows that the interactions are best characterized as anisotropic three-dimensional (3D) interactions. Despite the room temperature tetragonal structure, analysis of the low temperature spin waves under the assumption of a Heisenberg Hamiltonian indicates strong in-plane anisotropy with a significant next-near neighbor interaction. In the superconducting state, a resonance, localized in both wavevector and energy is observed in the spin excitation spectrum as in the cuprates. This resonance is observed at a wavevector compatible with a Fermi surface nesting instability independent of the magnetic ordering of the relevant parent compound. The resonance energy (E r) scales with superconducting transition temperature (T C) as E r ∼4.9 k B T C consistent with the canonical value of ∼5 k B T C observed in the cuprates. Moreover, the relationship between the resonance energy and the superconducting gap, ∆, is similar to that observed in many unconventional superconductors (E r /2∆ ∼ 0.64). Material Max. T C (K) LaFeAsO 1−x F x [1] 26 NdFeAsO 1−x F x [2] 52 PrFeAsO 1−x F x [3] 52 SmFeAsO 1−x F x [4] 55 CeFeAsO 1−x F x [5] 41 GdFeAsO 1−x F x [7] 50 TbFeAsO 1−x F x [9] 46 DyFeAsO 1−x F x [9] 45 Gd 1−x Th x FeAsO [10] 56 LaFeAsO 1−y [11, 12] 28 NdFeAsO 1−y [11, 12, 13] 53 PrFeAsO 1−y [11, 12] 48 SmFeAsO 1−y [11] 55 GdFeAsO 1−y [14, 12] 53 TbFeAsO 1−y [12] 52 DyFeAsO 1−y [12] 52 LaFe 1−x Co x AsO [17] 14 SmFe 1−x Ni x AsO [26] 10 SmFe 1−x Co x AsO [27] 15 LaFe 1−x Ir x AsO [28] 12 Material Max. T C (K) Ba 1−x K x Fe 2 As 2 [16] 38 Ba 1−x Rb x Fe 2 As 2 [29] 23 K 1−x Sr x Fe 2 As 2 [30] 36 Cs 1−x Sr x Fe 2 As 2 [30] 37 Ca 1−x Na x Fe 2 As 2 [31] 20 Eu 1−x K x Fe 2 As 2 [32] 32 Eu 1−x Na x Fe 2 As 2 [33] 35 Ba(Fe 1−x Co x) 2 As 2 [18, 34] 22-24 Ba(Fe 1−x Ni x) 2 As 2 [19] 20 Sr(Fe 1−x Ni x) 2 As 2 [35] 10 Ca(Fe 1−x Co x) 2 As 2 [36] 17 Ba(Fe 1−x Rh x) 2 As 2 [20] 24 Ba(Fe 1−x Pd x) 2 As 2 [20] 19 Sr(Fe 1−x Rh x) 2 As 2 [21] 22 Sr(Fe 1−x Ir x) 2 As 2 [21] 22 Sr(Fe 1−x Pd x) 2 As 2 [21] 9 Ba(Fe 1−x Ru x) 2 As 2 [22] 21 Sr(Fe 1−x Ru x) 2 As 2 [23] 13.5 LiFeAs [37, 38, 39] 18 Na 1−x FeAs [40] 25 Fe 1+y Se x Te 1−x [41] 15

Evidence for the microscopic coexistence of superconductivity and ferromagnetism in -NMR/NQR study

Physica B: Condensed Matter, 2005

We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of Ba(Fe1−xRux)2As2 (x = 0.23). We find two phase transitions, to antiferromagnetism at TN ≈ 60 K and to superconductivity at TC ≈ 15 K. Below TN , our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4 µB/Fe. The spin-lattice relaxation rate 1/ 75 T1 is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below TC, 1/ 75 T1 on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity.

Microstructural magnetic phases in superconducting FeTe 0.65 Se 0.35

Superconductor Science and Technology, 2012

In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogenities in the iron chalcogenide system FeTe 1-x Se x and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe 0.65 Se 0.35 studied with transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate a presence of nanometre scale hexagonal regions coexisting with tetragonal host lattice, a chemical disorder demonstrating non homogeneous distribution of host atoms in the crystal lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe 3 O 4 inclusions and to hexagonal symmetry nanometre scale regions with structure of Fe 7 Se 8 type. Our results suggest that nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that faster grown crystal of inferior crystallographic properties is a better superconductor.

Segregation of antiferromagnetism and high-temperature superconductivity in Ca1−xLaxFe2As2

Physical Review B, 2014

We report the effect of applied pressures on magnetic and superconducting order in single crystals of the aliovalent La-doped iron pnictide material Ca1−xLaxFe2As2. Using electrical transport, elastic neutron scattering and resonant tunnel diode oscillator measurements on samples under both quasihydrostatic and hydrostatic pressure conditions, we report a series of phase diagrams spanning the range of substitution concentrations for both antiferromagnetic and superconducting ground states that include pressure-tuning through the antiferromagnetic (AFM) quantum critical point. Our results indicate that the observed superconducting phase with maximum transition temperature of Tc=47 K is intrinsic to these materials, appearing only upon suppression of magnetic order by pressure tuning through the AFM critical point. In contrast to all other intermetallic ironpnictide superconductors with the ThCr2Si2 structure, this superconducting phase appears to exist only exclusively from the antiferromagnetic phase in a manner similar to the oxygen-and fluorinebased iron-pnictide superconductors with the highest transition temperatures reported to date. The unusual dichotomy between lower-Tc systems with coexistent superconductivity and magnetism and the tendency for the highest-Tc systems to show non-coexistence provides an important insight into the distinct transition temperature limits in different members of the iron-based superconductor family.

Phase transitions and superconductivity of iron-based superconductors from first-principles

Physics Letters A, 2020

First-principles calculations were performed to explore the atomic, electronic and superconductivity properties of the Ba 1−x (K, Na) x Fe 2 As 2 , LaFeAsO 1−x F x and Ca 1−x La x FeAsH iron-based superconductors. The calculations show that the iron-based superconductors undergo structural and magnetic phase transitions from an orthorhombic antiferromagnetic (AFM) structure to a tetragonal structure when the impurity (K/Na/F/La) concentration increases, indicating that the impurity can suppress the AFM of the BaFe 2 As 2 , LaFeAsO and CaFeAsH compounds and then induce superconductivity under the K/Na/F/La-rich conditions, in agreement with experimental observations. In addition, the electronic band structures of the tetragonal iron-based superconductors show flat bands near the Fermi levels, and the superconductive transition temperature scales with the length of the flat band segment, consistent with the previous study on the cuprate superconductors. The mechanism of the iron-based superconductors is further understood with string theory.