Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors

Weickert, Franziska; Schnelle, Walter; Wosnitza, J.; Leithe‐Jasper, Andreas; Rösner, H.

doi:10.1063/1.3665700

Cited by 7 publications

(7 citation statements)

References 28 publications

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“…The magnetic field dependence of ρ ab (P , T ) for all studied single crystals around the OPD region is exemplified by the x = 0.11 sample in figure 2(d). The small suppression of the SC transition as a function of field up to 9 T is consistent with the high critical fields observed in these compounds [4][5][6][7][8][9][10][11][12][13]32]. Interestingly, the resistivity in the normal state of BaFe 1.89 Cu 0.11 As 2 shows a small positive magnetoresistance (MR) for all applied pressures (see figure 2(e)).…”

Section: Resultssupporting

confidence: 84%

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Piva

Besser

Mydeen

et al. 2015

J. Phys.: Condens. Matter

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We report a combined study of external pressure and Cu-substitution on BaFe 2 As 2 single crystals grown by the in-flux technique. At ambient pressure, the Cu-substitution is known to suppress the spin density wave (SDW) phase in pure BaFe 2 As 2 (T SDW ≈ 140 K) and to induce a superconducting (SC) dome with a maximum transition temperature T max c 4.2 K. This T max c is much lower than the T c ∼ 15-28 K achieved in the case of Ru, Ni and Co substitutions. Such a lower T c is attributed to a Cu 2+ magnetic pair-breaking effect. The latter is strongly suppressed by applied pressure, as shown herein, T c can be significantly enhanced by applying high pressures. In this work, we investigated the pressure effects on Cu 2+ magnetic pair-breaking in the BaFe 2−x Cu x As 2 series. Around the optimal concentration (x opd = 0.11), all samples showed a substantial increase of T c as a function of pressure. Yet for those samples with a slightly higher doping level (over-doped regime), T c presented a dome-like shape with maximum T c 8 K. Remarkably interesting, the under-doped samples, e.g. x = 0.02 display a maximum pressure induced T c 30 K which is comparable to the maximum T c 's found for the pure compound under external pressures. Furthermore, the magnetoresistance effect as a function of pressure in the normal state of the x = 0.02 sample also presented an evolution consistent with the screening of the Cu 2+ local moments. These findings demonstrate that the Cu 2+ magnetic pair-breaking effect is completely suppressed by applying pressure in the low concentration regime of Cu 2+ substituted BaFe 2 As 2 .

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Section: Resultssupporting

confidence: 84%

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Piva

Besser

Mydeen

et al. 2015

J. Phys.: Condens. Matter

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“…We note that the transition slightly broadens upon increasing the magnetic field. This is expected in a polycrystalline material possessing an anisotropic H c2 (T ) as anticipated for a quasi-two dimensional electronic structure [26]. The H c2 (T ) curves obtained from T onset c,ρ , T mid c,ρ , and T final c,ρ are displayed in…”

Section: Introductionmentioning

confidence: 62%

“…While pressure‐induced superconductivity in stoichiometric

{SrFe}_{2} {As}_{2}

as well as superconductivity on electron‐ and hole‐doping has been studied extensively , only one combined pressure–hole‐doping study has been reported in

{Sr}_{1 - x} K_{x} {Fe}_{2} {As}_{2}

, but no pressure–electron‐doping investigation. Substituting Fe by Co in

{SrFe}_{2 - x} {Co}_{x} {As}_{2}

corresponds to an electron doping directly inside the iron‐arsenide layers.…”

Section: Introductionmentioning

confidence: 99%

Effect of Co doping and hydrostatic pressure on SrFe₂ As₂

Lengyel

Kumar

Schnelle

et al. 2016

Physica Status Solidi (b)

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We report a pressure study on electron doped SrFe$_{2-x}$Co$_x$As$_2$ by electrical-resistivity ($\rho$) and magnetic-susceptibility ($\chi$) experiments. Application of either external pressure or Co substitution rapidly suppresses the spin-density wave ordering of the Fe moments and induces superconductivity in SrFe$_2$As$_2$. At $x=0.2$ the broad superconducting (SC) dome in the $T-p$ phase diagram exhibits its maximum $T_{c,{\rm max}}=20$ K at a pressure of only $p_{\rm max}\approx 0.75$ GPa. In SrFe$_{1.5}$Co$_{0.5}$As$_2$ no superconductivity is observed anymore up to 2.8 GPa. Upon increasing the Co concentration the maximum of the SC dome shifts toward lower pressure accompanied by a decrease in the value of $T_{c,{\rm max}}$. Even though, superconductivity is induced by both tuning methods, Co substitution leads to a much more robust SC state. Our study evidences that in SrFe$_{2-x}$Co$_x$As$_2$ both, the effect of pressure and Co-substitution, have to be considered in order to understand the SC phase-diagram and further attests the close relationship of SrFe$_2$As$_2$ and its sister compound BaFe$_2$As$_2$.Comment: 6 pages, 6 figure

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“…This is justified by the low residual resistivity ratio (as low as 4) [19], the low superconducting volume fraction (<20%) of the parent compound [10], and the tendency of pnictide superconductors to have a small l due to the low Fermi velocities [35] and high scattering rates [30,36]. A comparison of the mean free path as estimated 3 from published resistivity data [37], and the coherence length as calculated later in this paper, gives values for l that are less than ξ at all dopings, but of similar order of magnitude.…”

Section: Discussionmentioning

confidence: 99%

Upper critical field ofNaFe1−xCoxAs superconductors

et al. 2014

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The upper critical field of NaFe 1−x Co x As was measured from x = 0 to x = 0.08, with the magnetic field applied parallel (H c2 ) and normal (H ⊥ c2 ) to the planes. The data were fitted using one-band and two-band models. The orbital and paramagnetic components of the upper critical field were extracted for H c2 , which we find to be strongly dominated by paramagnetic pair breaking. In the parent compound the paramagnetic limit is equal to the value expected by BCS theory. However, substitution of Fe by Co leads to an enhancement above the BCS limit by a factor of approximately 1.6. In the overdoped region, we observe a significant convex curvature in H ⊥ c2 at low temperatures, which we attribute to the two-band nature of the superconductivity and the asymmetry between the two bands. Additionally, we discuss the behavior of critical field anisotropy, coherence length ξ , and the penetration depth λ.

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Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors

Cited by 7 publications

References 28 publications

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Effect of Co doping and hydrostatic pressure on SrFe₂ As₂

Upper critical field ofNaFe1−xCoxAs superconductors

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Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors

Cited by 7 publications

References 28 publications

Combined external pressure and Cu-substitution studies on BaFe2As2single crystals

Combined external pressure and Cu-substitution studies on BaFe2As2single crystals

Effect of Co doping and hydrostatic pressure on SrFe2 As2

Upper critical field ofNaFe1−xCoxAs superconductors

Contact Info

Product

Resources

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Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Effect of Co doping and hydrostatic pressure on SrFe₂ As₂