Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr0.1Bi2Se3

Wang, Jinghui; Ran, Kejing; Li, Shichao; Ma, Zhen; Bao, Song; Cai, Zhengwei; Zhang, Youtian; Nakajima, Kenji; Ohira‐Kawamura, Seiko; Čermák, P.; Schneidewind, A.; Savrasov, S. Y.; Wan, Xiangang; Wen, Jinsheng

doi:10.1038/s41467-019-10942-2

Cited by 29 publications

(22 citation statements)

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“…This observation agrees well with recently confirmed low-kz-phonon mediated pairing mechanism [26]. Indeed, Sr, presumably hosting the Van der Waals gaps [16,17,28] provides some inter-layer bonds.…”

Section: Discussionsupporting

confidence: 92%

“…Correspondingly, there are two options. Either the pairing mechanism is unusual (that was suggested in [26]), or density of states weakly depends on the Fermi level. The latter case corresponds to quasi-two-dimensional, cylinder-like Fermi surface.…”

Section: Discussionmentioning

confidence: 99%

“…This structural supremacy allowed the discovery of new physics: in particular, resistive nematicity [20,21,22], the Dirac-like character of surface superconducting states [23] and nematic effects above critical temperature [24,25]. Inelastic neutron scattering experiments [26] recently confirmed the p -wave low-momentum phonon pairing mechanism in these crystals.…”

Section: Introductionmentioning

confidence: 99%

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Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals

et al. 2019

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In this study, we grew Cu co-doped single crystals of a topological superconductor candidate SrxBi2Se3, and studied their structural and transport properties. We reveal that the addition of even as small an amount of Cu co-dopant as 0.6 atomic %, completely suppresses superconductivity in SrxBi2Se3. Critical temperature (∼2.7 K) is rather robust with respect to co-doping. We show that Cu systematically increases the electron density and lattice parameters a and c. Our results demonstrate that superconductivity in SrxBi2Se3-based materials is induced by significantly lower Sr doping level x<0.02 than commonly accepted x∼0.06, and it strongly depends on the specific arrangement of Sr atoms in the host matrix. The critical temperature in superconductive Sr-doped Bi2Se3 is shown to be insensitive to carrier density.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals

et al. 2019

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“…Such model should also explain the observed weak sensitivity of T c on ε x x . For example, a proposed odd-parity fluctuation model making use of phonons dispersing along the k z direction 37 – 40 can be compatible with our observation, since such k z phonons should be less sensitive to the in-plane distortions.…”

Section: Discussionsupporting

confidence: 83%

Uniaxial-strain control of nematic superconductivity in SrxBi2Se3

et al. 2020

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Nematic states are characterized by rotational symmetry breaking without translational ordering. Recently, nematic superconductivity, in which the superconducting gap spontaneously lifts the rotational symmetry of the lattice, has been discovered. In nematic superconductivity, multiple superconducting domains with different nematic orientations can exist, and these domains can be controlled by a conjugate external stimulus. Domain engineering is quite common in magnets but has not been achieved in superconductors. Here, we report control of the nematic superconductivity and their domains of Sr x Bi 2 Se 3 , through externallyapplied uniaxial stress. The suppression of subdomains indicates that it is the Δ 4y state that is most favoured under compression along the basal Bi-Bi bonds. This fact allows us to determine the coupling parameter between the nematicity and lattice distortion. These results provide an inevitable step towards microscopic understanding and future utilization of the unique topological nematic superconductivity.

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“…Theoretically, Wan and Savrasov showed the phonon dispersions of electron-doped Bi 2 Se 3 has an unusual large linewidth for both highest optical and acoustic phonons along Γ-Z direction [27]. In the antiadiabatic limit, the enhanced e-p interaction by optical phonons may be crucial generating the unusual 'high T c ' for Cu 0.09 Bi 2 Se 3 although the acoustic phonon-mediated exotic superconductivity cannot be fully ruled out [73]. In this context, further experimental and theoretical efforts shall be made to clarify the unusual 'high T c ' for Bi 2 Se 3 -based superconductors.…”

Section: Discussionmentioning

confidence: 99%

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport

Fang

You

2020

New J. Phys.

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Although the Cu doped Bi 2 Se 3 topological insulator was discovered and intensively studied for almost a decade, its electrical and magnetic properties in normal state, and the mechanism of 'high-T c ' superconductivity regarding the relatively low-carrier density are still not addressed yet. In this work, we report a systematic investigation of magnetic susceptibility, critical fields, and electrical transport on the nominal Cu 0.20 Bi 2 Se 3 single crystals with T onset c = 4.18 K, the highest so far. The composition analysis yields the Cu stoichiometry of x = 0.09(1). The magnetic susceptibility shows considerable anisotropy and an obvious kink at around 96 K was observed in the magnetic susceptibility for H c, which indicates a charge density anomaly. The electrical transport measurements indicate the two-dimensional (2D) Fermi liquid behavior at low temperatures with a high Kadowaki-Woods ratio, A/γ 2 = 30.3a 0 . The lower critical field at 0 K limit was extracted to be 6.0 Oe for H ab. In the clean limit, the ratio of energy gap to T c was determined to be Δ 0 /k B T c = 2.029 ± 0.124 exceeding the standard BCS value 1.764, suggesting Cu 0.09 Bi 2 Se 3 is a strong-coupling superconductor. The in-plane penetration depth at 0 K was calculated to be 1541.57 nm, resulting in an unprecedented high ratio of T c /λ −2 (0) ∼ = 9.86. Moreover, the ratio of T c to Fermi temperature is estimated to be T c /T 2D F = 0.034. Both ratios fall into the region of unconventional superconductivity according to Uemura's regime, supporting the unconventional superconducting mechanism in Cu x Bi 2 Se 3 . Finally, the enhanced T c value higher than 4 K is proposed to arise from the increased density of states at Fermi energy and strong electron-phonon interaction induced by the charge density instability. 1 K, such as SrTiO 3 (T c ∼ 0.05-0.29 K, n e = 0.65 to 42.4 × 10 20 cm −3 ) [3,4], GeTe (T c ∼ 0.07-0.3 K, n e = 8.6 to 15.2 × 10 20 cm −3 ) [5], and SnTe (T c ∼ 0.034-0.214 K, n p = 7.5 to 20.0 × 10 20 cm −3 ) [6]. To compare with these systems, the T c value of Cu x Bi 2 Se 3 is relatively 'high' given it is a highly doped narrow semiconductor with lower carrier density. However, the mechanism of such anomalous enhanced T c phenomenon remains unclear despite nearly a decade of extensive research. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft New J. Phys. 22 (2020) 053026 Y Fang et alThe emergence and enhancement of superconductivity may occur in various cases by tailoring the ground states of quantum materials. For example, suppression of charge density wave (CDW) by chemical doping or pressure is observed in many systems [7-10], including low dimensional layered Cu x TiSe 2 and three dimensional (3D) alloys Lu(Pt 1−x Pd x ) 2 In and (Sr, Ca) 3 Ir 4 Sn 13 , 3D oxides Ba 1−x K x BiO 3 . Similarly, the magnetic ordering or spin density wave (SDW) have also been suppressed in strongly correlated heavy fermions materials, high-T c cuprates and i...

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Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr0.1Bi2Se3

Cited by 29 publications

References 50 publications

Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals

Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals

Uniaxial-strain control of nematic superconductivity in SrxBi2Se3

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport

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Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr0.1Bi2Se3

Cited by 29 publications

References 50 publications

Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals

Superconductivity in Cu Co-Doped SrxBi2Se3 Single Crystals

Uniaxial-strain control of nematic superconductivity in SrxBi2Se3

Unconventional superconductivity in CuxBi2Se3 from magnetic susceptibility and electrical transport

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Product

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Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport