Effects of magnetic impurities on upper critical fields in the high-Tcsuperconductor La-doped CaFe2As2

Jung, Soon‐Gil; Shin, Soohyeon; Jang, Hye Min; Mikheenko, P.; Johansen, T. H.; Park, Tuson

doi:10.1088/1361-6668/aa766c

Cited by 7 publications

(6 citation statements)

References 37 publications

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“…2F). A similar feature has been reported in some other quasi-2D superconductors (30)(31)(32), but its nature, and the role of disorder, remain unresolved.…”

Section: Supplementary Materials)supporting

confidence: 69%

Gate-induced superconductivity in a monolayer topological insulator

Sajadi

Palomaki

Fei

et al. 2018

Science

356

298

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The layered semimetal WTe2 has recently been found to be a two-dimensional topological insulator (2D TI) when thinned down to a single monolayer, with conducting helical edge channels. We report here that intrinsic superconductivity can be induced in this monolayer 2D TI by mild electrostatic doping, at temperatures below 1 K. The 2D TI-superconductor transition can be easily driven by applying a just a small gate voltage. This discovery offers new possibilities for gatecontrolled devices combining superconductivity and topology, and could provide a basis for quantum information schemes based on topological protection. Main text:Many of the most important, and fascinating, phenomena in condensed matter emerge from the quantum mechanics of electrons in a lattice. The periodic potential of the lattice gives rise to Bloch energy bands, and so to the physics of semiconductors that underlies all modern-day electronics. On the more exotic side, electrons in a lattice can pair up to act as bosons and condense into a macroscopic quantum state conducting electricity with zero resistance. More recently, it was realized that Bloch wavefunctions can have a non-trivial topology, incorporating twists analogous to a Möbius strip. This led to the discovery of topological insulators-materials that are electrically insulating in their interior but have conducting boundary modes that result from the topological discontinuity between inside and outside(1). The first of these to be studied was the so-called 2D topological insulator (2D TI), in which the one-dimensional helical edge modes (spin locked to momentum) give rise to the quantum spin Hall effect(2-4).Materials that combine non-trivial topology with superconductivity have been the subject of active investigation in recent years. For example, hybrid structures that couple an s-wave superconductor to a 2D TI have also been proposed as platform for Majorana modes(5), whose non-abelian exchange properties might be harnessed for qubits(6) with coherence times far longer than those built on conventional platforms. There are also topological superconductors, in which vortices or boundaries can host Majorana modes(7).Here we report the remarkable finding that monolayer WTe2, recently shown(8-13) to be an intrinsic 2D TI, itself turns superconducting under moderate electrostatic gating. Several other non-topological layered materials superconduct in the monolayer limit, either intrinsically or under heavy doping using ionic liquid gates(14-22). However, the present case constitutes the first instance of a phase transition from a 2D topological insulator to a superconductor, which moreover is readily controlled by a gate voltage. The discovery creates new opportunities for gateable superconducting circuitry, and offers the potential to develop topological superconducting devices in a single material, as opposed to the hybrid constructions currently required.

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“…2F). A similar feature has been reported in some other quasi-2D superconductors (30)(31)(32), but its nature, and the role of disorder, remain unresolved.…”

Section: Supplementary Materials)supporting

confidence: 69%

Gate-induced superconductivity in a monolayer topological insulator

Sajadi

Palomaki

Fei

et al. 2018

Science

356

298

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“…Arguments for this scenario can also be seen in figure 2(c), where a double transition, characteristic for inhomogeneous superconductors [47] and suggesting the presence of microscopic segregation, can be seen. Other explanations of the shape of H c2 (T) are related to the presence of magnetic impurities [48][49][50], strong quantization of Landau orbits [51,52], inhomogeneity-induced reduction of the diamagnetic pair-breaking [53] or singularities in the DOSs [54].…”

Section: Resultsmentioning

confidence: 99%

The effective increase in atomic scale disorder by doping and superconductivity in Ca₃Rh₄Sn₁₃

et al. 2018

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A comprehensive study of the electronic structure, thermodynamic and electrical transport properties reveals the existence of inhomogeneous superconductivity due to structural disorder in Ca 3 Rh 4 Sn 13 doped with La (Ca 3−x La x Rh 4 Sn 13 ) or Ce (Ca 3−x Ce x Rh 4 Sn 13 ) with superconducting critical temperatures T c  higher than those (T c ) observed in the parent compounds. The T−x diagrams and the entropy S(x) T isotherms document well the relation between the degree of atomic disorder and separation of the high-temperature T c  and T c -bulk phases. In these dirty superconductors, with the mean free path much smaller than the coherence length, the Werthamer-Helfand-Hohenber theoretical model does not fit well the H c2 (T) data. We demonstrate that this discrepancy can result from the presence of strong inhomogeneity or from two-band superconductivity in these systems. Both the approaches very well describe the H−T dependencies, but the present results as well as our previous studies give stronger arguments for the scenario based on the presence of nanoscopic inhomogeneity of the superconducting state. A comparative study of La-doped and Ce-doped Ca 3 Rh 4 Sn 13 showed that in the disordered Ca 3−x Ce x Rh 4 Sn 13 alloys the presence of spin-glass effects is the cause of the additional increase of T c  in respect to the critical temperatures of disordered Ca 3−x La x Rh 4 Sn 13 . We also revisited the nature of structural phase transition at T 130 170 ~¸K and documented that there might be another precursor transition at higher temperatures. Raman spectroscopy and thermodynamic properties suggest that this structural transition may be associated with a CDW-type instability.

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“…Vortex physics in iron-pnictide superconductors is of a great importance for many future technological advancements [1] as well as for the understanding of various exciting phases of vortex matter [2]. Among the various interesting phenomenon the crystal ab-plane [7] (and references therein), its occurrence has not been observed in some pnictide crystals even with H ∥ c-axis, as for instance in overdoped Ba-KFe 2 As 2 [8], in (Li-Fe)OHFeSe [9], in La-doped CaFe 2 As 2 [10] and in La 0.34 Na 0.66 Fe 2 As 2 [11]. The importance of the SMP appearing on isothermal magnetization curves relies on its direct association with the peak effect appearing in the magnetic field dependence of critical current density, J c (H) [12], which is of technological importance.…”

Section: Introductionmentioning

confidence: 99%

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca_0.82La_0.18Fe_0.96Ni_0.04As₂

Llovo

Sóñora

Mosqueira

et al. 2021

Supercond. Sci. Technol.

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We report the studies of detailed magnetic relaxation and isothermal magnetization measurements in the vortex state of the 112-type iron-pnictide Ca0.82La0.18Fe0.96Ni0.04As2 superconductor with 22 K. In the isothermal M(H), a well defined second magnetization peak (SMP) feature is observed in the entire temperature range below T c for measurements with -axis. However, for -planes, the SMP feature is suppressed at low temperatures, which might be due to 2D Josephson vortices forming at low temperatures and high magnetic fields in such an anisotropic system. A rigorous analysis considering the magnetic relaxation data for -axis suggests an elastic to plastic pinning crossover across H p , which also seems accompanied with a possible phase transition in vortex lattice near . Moreover, point disorder and surface defects are likely to be the dominant sources of pinning, which contribute to the -type of pinning in the sample. A high J c , in access of 105 A cm−2 observed could potentially make this material technologically important.

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Effects of magnetic impurities on upper critical fields in the high-T_csuperconductor La-doped CaFe₂As₂

Cited by 7 publications

References 37 publications

Gate-induced superconductivity in a monolayer topological insulator

Gate-induced superconductivity in a monolayer topological insulator

The effective increase in atomic scale disorder by doping and superconductivity in Ca₃Rh₄Sn₁₃

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca_0.82La_0.18Fe_0.96Ni_0.04As₂

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Effects of magnetic impurities on upper critical fields in the high-Tcsuperconductor La-doped CaFe2As2

Cited by 7 publications

References 37 publications

Gate-induced superconductivity in a monolayer topological insulator

Gate-induced superconductivity in a monolayer topological insulator

The effective increase in atomic scale disorder by doping and superconductivity in Ca3Rh4Sn13

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca0.82La0.18Fe0.96Ni0.04As2

Contact Info

Product

Resources

About

Effects of magnetic impurities on upper critical fields in the high-T_csuperconductor La-doped CaFe₂As₂

The effective increase in atomic scale disorder by doping and superconductivity in Ca₃Rh₄Sn₁₃

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca_0.82La_0.18Fe_0.96Ni_0.04As₂