Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2

Moll, Philip J. W.; Zhu, Xiyu; Cheng, Peng; Wen, Hao; Batlogg, B.

doi:10.1038/nphys3034

Cited by 46 publications

(32 citation statements)

References 32 publications

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“…We explain the appearance of the hysteresis in Ca 10 (FeAs) 10 (Pt 4 As 8 ) by the weaker interlayer coupling caused by the increased distance (10.46 Å) between the superconducting FeAs planes in comparison with the previously studied LaO 1− x F x FeAs materials (8.7 Å). Similar measurements on PrFeAsO 0.7 and on (V 2 Sr 4 O 6 )Fe 2 As 2 were published earlier, confirming the increase of anisotropy with increased distance between the FeAs sheets in the crystal.…”

Section: Resultssupporting

confidence: 88%

C‐axis transport of pnictide superconductors

Müller

Koval

Lazareva

et al. 2016

Physica Status Solidi (b)

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The generic structure of most high Tc superconductors is a stacking sequence of superconducting planes separated by so‐called charge reservoir layers. It is well known that carrier doping of these materials is achieved either by substitution of atoms or by nonstoichiometry in the charge reservoir layer. The alternating type of stacking causes yet another two important consequences. First, the transport anisotropy of these materials can be so high, that in the superconducting state the c‐axis transport is governed by the intrinsic Josephson effect. Whereas the anisotropy of our investigated LaO1–xFxFeAs samples was not sufficient, optimum‐doped Ca10(FeAs)10Pt4As8 showed hysteretic c‐axis current–voltage characteristics. Together with the Ambegaokar–Baratoff like temperature dependence of the critical current, this is a strong indication of intrinsic Josephson effects. Second, it is possible to deposit in the charge reservoir layers a substantial amount of charge only by injecting large c‐axis currents. By charge compensation, this decreases the concentration of mobile electrons in the conducting layers of electron‐doped materials. We were able to verify this in all details by c‐axis transport measurements of LaO1−xFxFeAs single crystals and pure and Pt doped (CaFe1–xPtxAs)10Pt4As8 single crystals. After current injection, we observed a decrease of Tc for doping levels at or below the Tc maximum, and a Tc increase for doping levels beyond the maximum. In all cases, the resistivity of the samples increased significantly. In both material classes, heavily overdoped samples showed a spectacular Tc increase by more than 10 K only accomplished by carrier injection. Generic stacking sequence of layered superconductors and crystal structure of the pnictide LaOFeAs.

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Section: Resultssupporting

confidence: 88%

C‐axis transport of pnictide superconductors

Müller

Koval

Lazareva

et al. 2016

Physica Status Solidi (b)

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“…ref. [29][30][31][32][33] , to study meso-and microscopic transport phenomena such as the Weyl-orbit quantum oscillations presented in this study. In this process, the microstructures are carved out of macroscopic crystals using the FIB.…”

Section: Methodsmentioning

confidence: 99%

Transport evidence for Fermi-arc-mediated chirality transfer in the Dirac semimetal Cd3As2

Moll

Nair

Helm

et al. 2016

Nature

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356

310

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The dispersion of charge carriers in a metal is distinctly different from that of free electrons due to their interactions with the crystal lattice. These interactions may lead to quasiparticles mimicking the massless relativistic dynamics of high-energy particle physics 1-3 , and they can twist the quantum phase of electrons into topologically nontrivial knots -producing protected surface states with anomalous electromagnetic properties 4-9 . In contrast to conventional cyclotron orbits, this motion is driven by the transfer of chirality from one Weyl node to another, rather than momentum transfer of the Lorentz force. Our observations provide evidence for direct access to the topological properties of charge in a transport experiment, a first step towards their potential application. These effects intertwine in materials known asThe bulk electrons in topological semimetals are described by an ultra-relativistic dispersion relation, E(k)=±ħv F σ*k, resembling the Weyl equation for massless spin-1/2 particles. Here σ is a pseudo-spin-1/2 degree of freedom that is energetically locked parallel or anti-parallel to the momentum, k, of the electron, giving electrons definite chirality k ±σ. Applying electromagnetic fields to Weyl or Dirac semimetals induces a pumping of electric charge between Weyl nodes with opposite chirality, a phenomena known in high energy physics as the chiral anomaly [13][14][15] . At the surface of these materials, this anomalous chirality transfer is facilitated by topologically protected surface arcs, the so-called "Fermi arc" surface states, which act as a pipeline connecting opposite chirality Weyl points 11,16 (Fig.1) weaves together the chiral states in the bulk with the topological Fermi-arc states on opposite surfaces into a closed orbit. Its quantization produces a distinctive contribution to the quantum oscillation spectrum that provides an observable signature of the chiral and topological character of these materials. This closed orbit is strikingly different from typical electrons orbiting around a Fermi surface in a metal as the quasiparticle experiences zero Lorentz force on the chiral path segments traversing the bulk.The main result of this study is an additional quantum oscillation frequency observed in microstructures smaller than the mean-free-path that exhibits characteristics of both surface-like and bulk-like states, as naturally expected for Weyl orbits. The microstructures were prepared from Cd 3 As 2 single crystals by FIB etching (Fig.1, see Methods). Down to the smallest thickness of L=150nm, the magnetoresistance at temperatures below 100K shows pronounced Shubnikovde Haas oscillations signaling the low effective mass of the charge carriers and the high crystal quality of the devices (Fig.1b). Quantum oscillations on bulk crystals have reported one single frequency 19,26 , arising from an essentially spherical 3D Fermi surface in agreement with ARPES and STM experiments. This single bulk frequency (F B ) is also consistently observed in all of the studied parent ...

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“…By proper design of the microstructure, these issues can be avoided and high quality data obtained from a metal regardless of its resistivity. This approach has proven to be a reliable method to fabricate crystalline samples for transport measurements in high magnetic fields in a large variety of different compounds [22,23]. In addition, the microstructuring also allows to specifically probe the most pristine region of the crystal and to exclude damaged regions from influencing the measurement.…”

Section: Device Fabricationmentioning

confidence: 99%

Quantum oscillations in the type-II Dirac semi-metal candidate PtSe₂

et al. 2018

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Three-dimensional topological semi-metals carry quasiparticle states that mimic massless relativistic Dirac fermions, elusive particles that have never been observed in nature. As they appear in the solid body, they are not bound to the usual symmetries of space-time and thus new types of fermionic excitations that explicitly violate Lorentz-invariance have been proposed, the so-called type-II Dirac fermions. We investigate the electronic spectrum of the transition-metal dichalcogenide PtSe 2 by means of quantum oscillation measurements in fields up to 65 T. The observed Fermi surfaces agree well with the expectations from band structure calculations, that recently predicted a type-II Dirac node to occur in this material. A hole-and an electron-like Fermi surface dominate the semi-metal at the Fermi level. The quasiparticle mass is significantly enhanced over the bare band mass value, likely by phonon renormalization. Our work is consistent with the existence of type-II Dirac nodes in PtSe 2 , yet the Dirac node is too far below the Fermi level to support free Dirac-fermion excitations.

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Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2

Cited by 46 publications

References 32 publications

C‐axis transport of pnictide superconductors

C‐axis transport of pnictide superconductors

Transport evidence for Fermi-arc-mediated chirality transfer in the Dirac semimetal Cd3As2

Quantum oscillations in the type-II Dirac semi-metal candidate PtSe₂

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Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2

Cited by 46 publications

References 32 publications

C‐axis transport of pnictide superconductors

C‐axis transport of pnictide superconductors

Transport evidence for Fermi-arc-mediated chirality transfer in the Dirac semimetal Cd3As2

Quantum oscillations in the type-II Dirac semi-metal candidate PtSe2

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Quantum oscillations in the type-II Dirac semi-metal candidate PtSe₂