Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

Teknowijoyo, Serafim; Cho, Kyuil; Tanatar, M. A.; Gonzales, Jesus; Böhmer, Anna E.; Cavani, Olivier; Mishra, Vivek; Hirschfeld, P. J.; Bud’ko, Sergey L.; Canfield, Paul C.; Prozorov, Ruslan

doi:10.1103/physrevb.94.064521

Cited by 62 publications

(73 citation statements)

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“…Such an effect is indeed observed in YBa 2 Cu 3 O 7−δ thin films [50] and in similar compounds FeTe 1−x Se x [51]. However, the electron irradiation has already been reported not to suppress the T c of FeSe, and instead an unexpected small enhancement of T c was observed [52]. Hence, the large T c suppression observed here cannot be explained by the effect of the secondary electron irradiation.…”

Section: Methodssupporting

confidence: 71%

Effects of heavy-ion irradiation on FeSe

et al. 2017

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We report the effects of heavy-ion irradiation on FeSe single crystals by irradiating Uranium up to a dose equivalent matching field of B φ = 16 T. Almost continuous columnar defects along the c-axis with a diameter ∼10 nm are confirmed by high-resolution transmission electron microscopy. Tc is found to be suppressed by introducing columnar defects at a rate of dTc/dB φ ∼ -0.29KT −1 , which is much larger than those observed in iron pnictides. This unexpected large suppression of Tc in FeSe is discussed in relation to the large diameter of the columnar defects as well as its unique band structure with a remarkably small Fermi energy. The critical current density is first dramatically enhanced with irradiation reaching a value over ∼2×10 5 A/cm 2 (∼5 times larger than that of the pristine sample) at 2 K (self-field) with B φ = 2 T, then gradually suppressed with increasing B φ . The δl-pinning associated with charge-carrier mean free path fluctuations, and the δTc-pinning associated with spatial fluctuations of the transition temperature are found to coexist in the pristine FeSe, while the irradiation increases the contribution from δl-pinning, and makes it dominant over B φ = 4 T.

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Section: Methodssupporting

confidence: 71%

Effects of heavy-ion irradiation on FeSe

et al. 2017

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“…Recently, it was shown that a dose of 2.5 MeV electron irradiation producing approximately ∼ 0.1% Frenkel pairs per formula unit, decreases T s by 0.9 K and increases T c by 0.4 K (Ref. 28), similarly to the effects of pressure and Te or S substitution, but different from the sample-to-sample variation observed here. This indicates that origin of the variation of RRR, T s and T c in our samples is more complex than simple vacancy/interstitial-type defects, suggesting instead more extended defects such as dislocation lines.…”

Section: Resistance: Results and Discussionmentioning

confidence: 45%

Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

et al. 2016

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The study of the iron-based superconductor FeSe has blossomed with the availability of highquality single crystals, obtained through flux/vapor-transport growth techniques below the structural transformation temperature of its tetragonal phase, T ≈ 450• C. Here, we report on the variation of sample morphology and properties due to small modifications in the growth conditions. A considerable variation of the superconducting transition temperature Tc, from 8.8 K to 3 K, which cannot be correlated with the sample composition, is observed. Instead, we point out a clear correlation between Tc and disorder, as measured by the residual resistivity ratio. Notably, the tetragonal-to-orthorhombic structural transition is also found to be quite strongly disorder dependent (Ts ≈ 72 − 90 K), and linearly correlated with Tc.

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“…F, Calculated N(E) using the band-structure and a gap structure model which will be discussed in chapter 7. with gap minima ∆ min 150µeV. Indeed, evidence for a nodeless gap structure for FeSe has been detected by a wide variety of different techniques [64][65][66][67][68]. As a last remark, we note that since our samples are not detwinned and our field of view limited to ∼ 200 x 200 nm 2 we cannot exclude that the existence of nodes in the gap structure is affected by long-range effects of twin boundaries [63,65].…”

Section: Fermi Surface and Gap Structure From Bqpimentioning

confidence: 99%

“…1.15A) was interpreted as indicative of a nodal gap structure [53]. The existence of nodes in the gap structure of FeSe has since then come under scrutiny, and contradictory studies for [62,63] and against nodes [64][65][66][67][68] have since then be published. Figure 1.16 presents microwave and thermal conductivity measurements that both find results consistent with nodeless superconductivity [65,66].…”

Section: -Symmetric Superconductivitymentioning

confidence: 99%

Discovery of orbital-selective Cooper pairing in FeSe

Sprau

Kostin

Kreisel

et al. 2017

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FeSe is the focus of intense research interest because of its unusual non-magnetic nematic state and because it forms the basis for achieving the highest critical temperatures of any iron-based superconductor. However, its Cooper pairing mechanism has not been determined because an accurate knowledge of the momentum-space structure of superconducting energy gaps ∆ i ( k) on the different electron-bands E i ( k) does not exist. Here we use Bogoliubov quasiparticle interference (BQPI) imaging to determine the coherent Fermi surface geometry of the α-and ε-bands surrounding the Γ = (0, 0) and X = (π/a Fe , 0) points of FeSe, and to measure their superconducting energy gaps ∆ α ( k) and ∆ ε ( k).We show directly that both gaps are extremely anisotropic but nodeless, and are aligned along orthogonal crystal axes. Moreover, by implementing a novel technique we demonstrate the sign change between ∆ α ( k) and ∆ ε ( k). This complex configuration of ∆ α ( k) and ∆ ε ( k), which was unanticipated within pairing theories for FeSe, reveals a unique form of superconductivity based on orbital selective Cooper pairing of electrons from the d yz orbitals of iron atoms. This new paradigm of orbital selectivity may be pivotal to understanding the microscopic interplay of quantum paramagnetism, nematicity and high temperature superconductivity. BIOGRAPHICAL SKETCHPeter Oliver Sprau was born on June 13th 1986 in the small town of Kirchheimbolanden, Germany, where he completed both his primary and secondary education. Long before he was a physicist, Peter was an active member of the track and field team in his school and a local club, even going on to compete in the dash and relay event on the state and federal youth level. Upon finishing school, he fulfilled his civic duty and carried out his alternative civilian service in the hospital in Kirchheimbolanden. While Peter's academic interests were diverse, including not just science but also Latin and history, his natural curiosity about the world finally urged him to pursue a higher education in physics. Mistakes. Make glorious, amazing mistakes. Make mistakes nobody's ever made before. Don't freeze, don't stop, don't worry that it isn't good enough, or it isn't perfect, whatever it is: art, or love, or work or family or life.Whatever it is you're scared of doing, Do it. Make your mistakes, next year and forever." I also want to acknowledge in no specific order the following people for useful discussions throughout my PhD:

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Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

Cited by 62 publications

References 70 publications

Effects of heavy-ion irradiation on FeSe

Effects of heavy-ion irradiation on FeSe

Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

Discovery of orbital-selective Cooper pairing in FeSe

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