Specific heat and gap structure of a nematic superconductor: Application to FeSe

Islam, Kazi Ranjibul; Böker, Jakob; Eremin, I.; Chubukov, Andrey V.

doi:10.1103/physrevb.104.094522

Cited by 10 publications

(8 citation statements)

References 59 publications

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“…Thus we consider the possibility of a second superconducting transition in this Cr 3 Ru with A15 structure. According to the theoretical study [45], a hidden transition from an s + d state to an s + e iη d state may occur leading to a second jump of specific heat far below T c . Due to the magnetic nature of the Cr atoms and the correlation effect, together with the extra amount of Cr beyond the stoichiometry, the system may be noncentrosymmetric, which leads to the existence of, or partially the chiral superconductivity.…”

Section: Discussionmentioning

confidence: 99%

Comparative studies on unconventional superconductivity in Cr$_3$Ru compounds with bcc and A15 structures

Zhu¹,

Zhang²,

Li³

et al. 2022

Preprint

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Chromium (Cr) is a transition metal element with 3d orbital electrons. In most compounds containing Cr, due to the correlation effect, twofold features of localization and itinerancy are expected. The localization gives rise to a magnetic moment, while the latter exhibits as the effective coherent weight for conductivity. Here we report the physical properties of Cr3Ru compounds with bcc or A15 structures by using multiple experimental tools. The resistivity measurements show sharp superconducting transitions at Tc = 2.77 K and Tc = 3.37 K for the bcc and A15 structures, respectively. A high residual resistivity exists for both samples with the mean-free-path in the scale of about 2 nm. Magnetization measurements also show rather narrow transitions, with a clear hump structure at high temperatures (Tc ≤ T ≤ 300 K), which may be ascribed to the remaining antiferromagnetic spin fluctuations. A pronounced second peak effect has been observed in magnetization hysteresis loops in the superconducting state only for samples with bcc structure. The specific heat coefficient reveals a clear jump at Tc. We find that s-wave gaps can be adopted to fit the low temperature specific heat data of both samples yielding ratios of about 2∆/kBTc ≈ 3.6, indicating a moderate pairing strength. Interestingly, the Wilson ratios RW = Aχ0/γn are 3.81 and 3.62 for the bcc and A15 phases, suggesting a moderate correlation effect of conducting electron in the normal state. Besides, for samples with A15 structure, another specific heat anomaly occurs at about 0.85 K and is sensitive to magnetic fields. By applying high pressures, both system will exhibit an enhancement of Tc with a rate of about 0.019 K/GPa and 0.013 K/GPa for the bcc and A15 phases, respectively. We also conduct tunneling spectrum measurements on these samples, and found that the coherence peaks are strongly smeared out with a gap in the scale of about 0.3 ∼ 0.5 meV. The strong suppression to the coherence peaks may be ascribed to the strong scattering seen from the resistivity measurements. Our combinatory results point to an unconventional superconductivity in these Cr based compounds.

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Section: Discussionmentioning

confidence: 99%

Comparative studies on unconventional superconductivity in Cr$_3$Ru compounds with bcc and A15 structures

Zhu¹,

Zhang²,

Li³

et al. 2022

Preprint

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“…In order to explain the nematic order and strong anisotropic gap in FeSe, the mixed s + d wave scenario has been invoked [24][25][26]. In addition, a transition to an s + e iα d pairing that breaks the time-reversal symmetry below T c has been also proposed [27,28].…”

Section: Introductionmentioning

confidence: 99%

Atomic scale imaging of sign-changing order parameter in superconducting FeSe with Tunneling Andreev Reflection

Ko¹,

Song²,

Yan³

et al. 2023

Preprint

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The pairing symmetry of the superconducting order parameter in iron-based superconductors has been a subject of debate, with various models proposing s-wave, d-wave, and mixed combinations as possible candidates. Here we probe the pairing symmetry of FeSe utilizing the new methodology of Tunneling Andreev Reflection (TAR). TAR directly exploits the transparency-dependence of tunneling current to disentangle contributions of single-particle current and Andreev reflection. These measurements provided new direct evidence in favor of the sign-changing nature of the superconducting order in FeSe, in a distinctly complementary approach to nanoscale imaging of quasiparticle interference. Crucially TAR can also probe higher-order contributions to Andreev reflection. Quantitative comparison of the experimental signatures of higher-order Andreev reflections with those in concomitant tight-binding simulations revealed new evidence in support of the nodal gap structure of superconductivity in FeSe. Finally, the effect of structural topological defects can be directly probed with TAR owing to its atomic spatial resolution. In particular, we find that superconductivity is completely suppressed along the twin boundary while its electronic structure is characterized by a V-shaped signature of a pseudogap state. Our findings provide new insight into the pairing symmetry of an unconventional superconductor, demonstrating the potential of differential tunneling Andreev reflection to reveal microscopic properties of emerging quantum materials.

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“…One approach to explain these experimental data and to suppress modelled contributions associated with this pocket, is to include orbital-selective quasiparticle weights [26,44,54,55]. More recently an alternative scenario has been proposed [56][57][58][59], where an additional non-local nematic order parameter accounting for the splitting of the xy occupancy in the two electron pockets [56][57][58] plays a crucial role. An important consequence of this scenario is a resulting occurrence of a Lifshitz transition at the M-point leaving only one electron pocket at the Fermi level.…”

Section: Introductionmentioning

confidence: 99%

Feedback of Non-Local dxy Nematicity on the Magnetic Anisotropy in FeSe

Bötzel

Eremin²

2022

Front. Phys.

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We analyze theoretically the magnetic anisotropy in the nematic phase of FeSe by computing the spin and the orbital susceptibilities from the microscopic multiorbital model. In particular, we take into account both the xz/yz and the recently proposed non-local xy nematic ordering and show that the latter one could play a crucial role in reproducing the experimentally-measured temperature dependence of the magnetic anisotropy. This provides a direct fingerprint of the different nematic scenarios on the magnetic properties of FeSe.

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Specific heat and gap structure of a nematic superconductor: Application to FeSe

Cited by 10 publications

References 59 publications

Comparative studies on unconventional superconductivity in Cr$_3$Ru compounds with bcc and A15 structures

Comparative studies on unconventional superconductivity in Cr$_3$Ru compounds with bcc and A15 structures

Atomic scale imaging of sign-changing order parameter in superconducting FeSe with Tunneling Andreev Reflection

Feedback of Non-Local dxy Nematicity on the Magnetic Anisotropy in FeSe

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