Superconductivity near a Ferroelectric Quantum Critical Point in Ultralow-Density Dirac Materials

Kozii, Vladyslav; Bi, Zhen; Ruhman, Jonathan

doi:10.1103/physrevx.9.031046

Cited by 41 publications

(61 citation statements)

References 66 publications

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“…In particular, doped topological materials are characterized by small electronic density and small density of states. As a result, the pairing interaction must be more singular [69]. Such an interaction is expected to be sensitive to the presence of disorder [75].…”

Section: Discussionmentioning

confidence: 99%

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Effect of interorbital scattering on superconductivity in doped Dirac semimetals

Dentelski

Kozii

Ruhman

2020

Phys. Rev. Research

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Unconventional superconductivity has been discovered in a variety of doped quantum materials, including topological insulators and semimetals. A unifying property of these systems is strong orbital hybridization, which leads to pairing of states with nontrivial Bloch wave functions. In contrast to naive expectation, however, many of these superconductors are relatively resilient to disorder. Here we study the interplay of superconductivity and disorder in doped three-dimensional Dirac systems, which serve as a paradigmatic dispersion in quantum materials, using Abrikosov-Gor'kov theory. In this way, the role of disorder is captured by a single parameter , the pair scattering rate. In contrast to previous studies, we argue that interorbital scattering cannot be neglected due to the strong orbital hybridization in Dirac systems. We find that the robustness of different pairing states highly depends on the relative strength of the different interorbital scattering channels. In particular, we find that the "nematic" superconducting state, which is argued to be the ground state in many Bi 2 Se 3-related compounds, is not protected from disorder in any way. The pair scattering rate in this case is at best smaller by a factor of 3 compared to systems without spin-orbit coupling. We also find that the odd-parity pairing state with total angular momentum zero (the B phase of superfluid 3 He) is protected against certain types of disorder, which include a family of time-reversal odd (magnetic) impurities. Namely, this odd-parity state is a singlet of partners under CT symmetry (rather than T symmetry in the standard Anderson's theory), where C and T are chiral and time-reversal symmetries, respectively. As a result, it is protected against any disorder potential that respects CT symmetry. Our procedure is very general and can be readily applied to different band structures and disorder configurations.

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Section: Discussionmentioning

confidence: 99%

“…The action in Eq. (1) can be conveniently diagonalized in the manifestly covariant Bloch basis (MCBB), in which the electron spinor transforms as an ordinary SU(2) spin-1/2 [40,49,68,69]…”

Section: The Modelmentioning

confidence: 99%

Effect of interorbital scattering on superconductivity in doped Dirac semimetals

Dentelski

Kozii

Ruhman

2020

Phys. Rev. Research

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“…For example, Raman scattering found that the hardening of the FE soft mode in the dilute metal is indistinguishably similar to what is seen in the insulator [21]. The anomaly in resistivity was found to terminate at a threshold carrier density (n * ), near which the superconducting transition temperature was enhanced [21] providing evidence for a link between superconducting pairing and ferroelectricity, a subject of present attention [22][23][24][25][26][27][28][29][30][31][32].…”

Section: Introductionmentioning

confidence: 98%

Charge transport in a polar metal

et al. 2019

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The fate of electric dipoles inside a Fermi sea is an old issue, yet poorly-explored. Sr1−xCaxTiO3 hosts a robust but dilute ferroelectricity in a narrow (0.002 < x < 0.02) window of substitution. This insulator becomes metallic by removal of a tiny fraction of its oxygen atoms. Here, we present a detailed study of low-temperature charge transport in Sr1−xCaxTiO 3−δ , documenting the evolution of resistivity with increasing carrier concentration (n). Below a threshold carrier concentration, n * (x), the polar structural phase transition has a clear signature in resistivity and Ca substitution significantly reduces the 2 K mobility at a given carrier density. For three different Ca concentrations, we find that the phase transition fades away when one mobile electron is introduced for about 7.9±0.6 dipoles. This threshold corresponds to the expected peak in anti-ferroelectric coupling mediated by a diplolar counterpart of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Our results imply that the transition is driven by dipole-dipole interaction, even in presence of a dilute Fermi sea. At higher carrier concentrations, our data resolves slight upturns in low-temperature resistivity in both Ca-free and Ca-substituted samples, reminiscent of Kondo effect and most probably due to oxygen vacancies.arXiv:1909.04278v1 [cond-mat.supr-con]

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“…Before applying the BCS theory to further discuss the unusual 'high T c ' for Cu 0.09 Bi 2 Se 3 , we have examined if the adiabatic limit satisfies or not in Cu x Bi 2 Se 3 . The BCS solution is only a good description for the systems in the adiabatic limit [68,69], which requires the phonon energy ω must be much smaller than the carrier relaxation rate /τ , namely, ωτ 1. To make such an estimation, taking the highest phonon frequency A 2 1g mode 175.4 cm −1 at 3 K for Bi 2 Se 3 [70] and the scattering time τ = 5.2 × 10 −14 s for Cu 0.25 Bi 2 Se 3 [2], we obtain ωτ = 0.27 as an upper bound.…”

Section: Discussionmentioning

confidence: 99%

“…Nevertheless, according to our calculation of E F for Cu x Bi 2 Se 3 in the following, the Debye frequency (ω D ) [43] is actually comparable with the order of the E F , suggesting the antiadiabatic effect needs to be considered. If the optical phonons are at play in mediating superconductivity in Cu x Bi 2 Se 3 , the standard BCS theory has to be modified by including the antiadiabatic effect [68,71,72]. 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].…”

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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Superconductivity near a Ferroelectric Quantum Critical Point in Ultralow-Density Dirac Materials

Cited by 41 publications

References 66 publications

Effect of interorbital scattering on superconductivity in doped Dirac semimetals

Effect of interorbital scattering on superconductivity in doped Dirac semimetals

Charge transport in a polar metal

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport

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Superconductivity near a Ferroelectric Quantum Critical Point in Ultralow-Density Dirac Materials

Cited by 41 publications

References 66 publications

Effect of interorbital scattering on superconductivity in doped Dirac semimetals

Effect of interorbital scattering on superconductivity in doped Dirac semimetals

Charge transport in a polar metal

Unconventional superconductivity in CuxBi2Se3 from magnetic susceptibility and electrical transport

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Product

Resources

About

Unconventional superconductivity in Cu_xBi₂Se₃ from magnetic susceptibility and electrical transport