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Cited by 1,028Topological Materials and PhenomenaPhysics of Superconductivity and Magnetism2D Materials and Applications

Superconductivity in Cu x Bi 2 Se 3 and its Implications for Pairing in the Undoped Topological Insulator

Open access
Hor, Y. S., Williams, A. J., Checkelsky, J. G., Roushan, P., Seo, J., Xu, Q., Zandbergen, H. W., Yazdani, A. +2 more·2010·Physical Review Letters
DOI 10.1103/physrevlett.104.057001
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Abstract

${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ is one of a handful of known topological insulators. Here we show that copper intercalation in the van der Waals gaps between the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ layers, yielding an electron concentration of $\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$, results in superconductivity at 3.8 K in ${\mathrm{Cu}}_{x}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ for $0.12\ensuremath{\le}x\ensuremath{\le}0.15$. This demonstrates that Cooper pairing is possible in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ at accessible temperatures, with implications for studying the physics of topological insulators and potential devices.

AI snapshot

Written from the paper’s full text.

TL;DR

Cu intercalation into the van der Waals gaps of the topological insulator Bi₂Se₃ produces n-type CuₓBi₂Se₃ with superconductivity at ~3.8 K. This shows Cooper pairing is possible in Bi₂Se₃ at accessible temperatures, with implications for proximity-effect studies of topological surface states.

Key findings

  • Superconductivity occurs in CuₓBi₂Se₃ at ~3.8 K, with optimal single-crystal compositions between x = 0.12 and x = 0.15; the abstract states 0.12 ≤ x ≤ 0.15, while the text also reports an observed window of 0.1 ≤ x ≤ 0.3.
  • The superconducting crystals are n type with a temperature-independent carrier density of ~2 × 10²⁰ cm⁻³; resistivity is weakly metallic, dropping from ~0.5 mΩ cm to 0.27 mΩ cm on cooling to 4 K.
  • At 0.3 K, the upper critical field Hc₂ is 1.7 T for H ∥ c and 4.6 T for H ∥ ab; the material is a strongly type II superconductor with Ginzburg-Landau parameter ~50 and coherence lengths ξc = 52 Å and ξab = 140 Å.
  • Superconductivity is absent for x < 0.1 and x > 0.3, in Bi₂₋yCuySe₃, and in Cu₂Se, CuBi₃Se₅, BiCuSe₂, and BiCu₃Se₃ above 1.8 K; STM on Cu₀.₁₅Bi₂Se₃ at 4.2 K identifies Cu clusters on the cleaved surface and intercalated Cu in subsurface van der Waals layers.

Methods

  • Single crystals of CuₓBi₂Se₃ were grown by melting stoichiometric mixtures of Bi, Cu, and Se at 850 °C overnight in sealed evacuated quartz tubes, slow cooling from 850 to 620 °C, then quenching in cold water; Bi₂₋yCuySe₃ crystals were grown by the same technique.
  • Structural characterization used X-ray powder diffraction, transmission electron microscopy, electron diffraction, and high-resolution electron microscopy; scanning tunneling microscopy was performed at 4.2 K in ultrahigh vacuum on in situ cleaved surfaces.
  • Resistivity and AC magnetization were measured in a PPMS using standard four-probe contacts with current in the ab plane; Hall effect was measured in a home-built apparatus at 0.3 and 15 K; DC magnetization used a SQUID at 10 Oe, and AC susceptibility used the PPMS at 5 Oe amplitude.

Limitations

  • The paper states that the ZFC magnetization at the lowest temperature is about 20% of full diamagnetism, but this is a lower limit because temperatures substantially below the transition were not accessible and the transition was not complete at the temperature where the field was applied.
  • The paper states that resistivity does not drop to zero below Tc, indicating no continuous superconducting path; this is attributed to sensitivity of the superconducting phase to processing and stoichiometry. For nominal x > 0.15, pure single crystals were not obtained, with minor impurity phases Cu₂Se and CuBi₃Se₅.
  • The paper states that the precise distribution of Cu between intercalated and substituted sites is expected to be strongly processing dependent, and that unambiguous identification of the STM type-3 feature requires further study. Evident from the text: the narrow composition window and processing sensitivity limit reproducibility and generalization, and the lack of zero resistance complicates transport-based confirmation of bulk superconductivity.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1103/physrevlett.104.057001

Cites

24 of 24 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 30 cited sources checked · 0 supported · 0 flagged

  • Findingnone given
    § Abstract · p. 1

    Copper intercalation in the van der Waals gaps between Bi2Se3 layers yields an electron concentration of ~2 x 10^20 cm^-3 in CuxBi2Se3.

    “copper intercalation in the van der Waals gaps between the Bi 2 Se3 layers, yielding an electron concentration of ~ 2 x 10 20 cm -3”
    Quote in the paperSubstantial claim
  • Findingnone given
    § Abstract · p. 3

    Small deviations of Se stoichiometry from 3.00 per formula unit suppress superconductivity in CuxBi2Se3.

    “Small deviations of Se stoichiometry from 3.00/formula unit suppress the superconductivity.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Abstract · p. 4

    The resistivity of Cu0.12Bi2Se3 is weakly metallic, dropping from approximately 0.5 mΩ cm to 0.27 mΩ cm on cooling to 4 K.

    “The resistivity is weakly metallic, dropping from approximately 0.5 m Ω cm to 0.27 m Ω cm on cooling to 4 K.”
    Quote in the paperNot a substantial claim
  • Findingnone given
    § Abstract · p. 3

    Single crystals of Bi2-xCuxSe3 prepared for x = 0 to 0.15 were never superconducting.

    “Single crystals of Bi 2-x CuxSe3 prepared for x = 0 to 0.15 were never superconducting.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Abstract · p. 3

    Superconductivity in CuxBi2Se3 occurs only in a narrow window of x, for 0.1 ≤ x ≤ 0.3.

    “Superconductivity was observed only in a narrow window of x in CuxBi2Se3 , for 0.1 ≤ x ≤ 0.3”
    • Also stated in: § Abstract · p. 3 · plain
      “Superconductivity is not found for x &lt; 0.1 and x &gt; 0.3”
    Quote in the paperSubstantial claim
  • May combine two claims. 12
  • Classified as probably not a substantial claim. 4
  • The quote only partly states this claim. 2

  • May combine two claims.

    Findingown data
    § Abstract · p. 4

    The resistivity of Cu0.12Bi2Se3 does not drop to zero below Tc, indicating there is not a continuous superconducting path in the crystal.

    “The resistivity does not drop to zero below T c however, indicating that there is not a continuous superconducting path in the crystal.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Abstract · p. 3

    At 0.3 K, the upper critical field Hc2 of Cu0.12Bi2Se3 is 1.7 T for field parallel to the c-axis and 4.6 T for field parallel to the ab-plane.

    “At 0.3 K, H c2 is 1.7 T and 4.6 T for the field parallel to the c -axis, H // c , and parallel to the ab ('basal') plane, H // ab , respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning
    § Abstract · p. 3

    The magnetization at the lowest temperature of the ZFC measurement on Cu0.12Bi2Se3 is about 20% of that expected for full diamagnetism, representing a lower limit.

    “The magnetization observed at the lowest temperature of the zero field cooled (ZFC) measurement on the single crystal is about 20 % of that expected for full diamagnetism, but that estimate represents a lower limit”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingcitation
    § Abstract · p. 4

    The carrier concentration of Cu0.12Bi2Se3 is one order of magnitude higher than native Bi2Se3 and two orders of magnitude higher than Ca-doped Bi2Se3.

    “This carrier concentration is one order of magnitude higher than is found in native Bi2 Se3 24,25 , and two orders of magnitude higher than is found for crystals with chemical potentials tuned by Ca doping 28,29 .”
    Quote in the paperNot a substantial claim0 of 4 sources checked
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  • May combine two claims.

    Findingown data
    § Abstract · p. 3

    Bi2-yCuySe3, Cu2Se, CuBi3Se5, BiCuSe2, and BiCu3Se3 are not superconducting above 1.8 K.

    “Samples of these phases, and other reported phases in the Cu-Bi-Se system, CuBiSe 2 23 and BiCu3Se3 27 as well as any compositions deviating from the stoichiometry Cu x Bi2 Se3 for 0.1 ≤ x ≤ 0.30 were not superconducting above 1.8 K”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [23]

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  • May combine two claims.

    Findingown data
    § Abstract · p. 3

    For nominal x > 0.15 in CuxBi2Se3 melts, pure single crystals were not obtained; melts included minor impurity phases Cu2Se and CuBi3Se5.

    “For nominal x greater than 0.15 in Cu x Bi2 Se3 melts, pure single crystals were not obtained - the melts included minor amounts of impurity phases. These minor extra phases were Cu 2 Se and CuBi3Se5”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation
    § Abstract · p. 1

    Bi2Se3 is a layered compound made of weakly van der Waals bonded Se-Bi-Se-Bi-Se five-layer sandwiches, yielding excellent basal plane cleavage and high-quality layered crystals.

    “The resulting Se-Bi-Se-Bi-Se five layer sandwich is only weakly van der Waals bonded to the next sandwich, through the outer Se layers, yielding a material with excellent basal plane cleavage and excellent quality layered crystals both in the bulk and in thin films 19-21 .”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [19]

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  • May combine two claims.

    Premisecitation
    § Abstract · p. 1

    Cu can either intercalate between the Se layers in CuxBi2Se3 or randomly substitute for Bi within the host structure.

    “The dopant employed here, Cu, may either intercalate between the Se layers, as it does in Cu x TiSe2 22 , or randomly substitute for Bi within the host structure, as has been reported for the NaCl structure compound CuBiSe2 23 .”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [22]

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  • The quote only partly states this claim.

    Interpretationreasoning
    § Abstract · p. 4

    STM type 2 features (bright triangular areas of lateral dimension ~20 Å) are intercalated Cu in sub-surface van der Waals gap layers of Cu0.15Bi2Se3.

    “We associate these features with intercalated Cu in sub-surface van der Waals gap layers.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation
    § Abstract · p. 5

    Previous experimental and theoretical work suggests Bi2Se3 may be the most interesting of the bulk topological insulators known to date because it can be made resistive in the bulk through doping and only topological surface states are present.

    “Previous experimental and theoretical work on Bi 2 Se3 suggests that it may be the most interesting of the bulk topological insulators known to date because it can in fact be made resistive in the bulk through doping and also because only topological surface states are present 28-31 .”
    Quote in the paperSubstantial claim0 of 4 sources checked
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  • The quote only partly states this claim.

    Interpretationown data
    § Abstract · p. 4

    STM type 1 features (apparent height ~2 to 3 Å) are clusters of intercalated Cu atoms located on the cleaved surface of Cu0.15Bi2Se3.

    “From the height of these features and their shapes, we conclude that they are located on the cleaved surface and are clusters of intercalated Cu atoms.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation
    § Abstract · p. 4

    STM type 1 and type 2 features are absent in native or Ca-doped Bi2Se3 and thus are associated with Cu intercalation.

    “Neither of these features is present in native or Ca-doped Bi 2 Se3 [28] and thus they are clearly associated with the Cu intercalation.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [28]

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data
    § Abstract · p. 4

    There is no evidence of Cu cluster formation within the van der Waals layers below the exposed surface of Cu0.15Bi2Se3, suggesting that the clusters of Cu atoms on the surface have formed by surface diffusion.

    “Hence there is no evidence of Cu cluster formation within the van der Waals layers below the exposed surface, suggesting that the clusters of Cu atoms on the surface have formed by surface diffusion.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationreasoning
    § Abstract · p. 5

    CuxBi2Se3 and Bi2Se3 are chemically closely similar, so supercurrents should readily tunnel between them.

    “As Cu x Bi2 Se3 and Bi2 Se3 are chemically closely similar, supercurrents should readily tunnel between them.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation
    § Abstract · p. 5

    Most proposals to manipulate the topological surface states in Bi2Se3 rely on the opening of a superconducting gap by proximity to a superconductor.

    “Most proposals to manipulate the topological surface states in Bi 2 Se3 rely on the opening of a superconducting gap by proximity to a superconductor.”
    Quote in the paperSubstantial claim0 of 8 sources checked
    • cites [11] source

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15 of 15

  • The paper relies on this without support.

    Cooper pairing of electrons at accessible temperatures in a topological insulator has never been reported.

    “However, Cooper pairing of electrons at accessible temperatures in a topological insulator has never been reported.”
1 of 1

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • LuPtBi, YPtBi and LaPtBi possess the most stable inverted Z2=-1 type bulk band structures.

    “LuPtBi, YPtBi and LaPtBi possess the most stable inverted Z 2 =-1 type bulk band structures.”

    From Three-Dimensional Topological Insulators (2011) · cites this paper as [35]

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Stated superconducting range excludes a demonstrated composition

    Minor

    The conclusion gives a strict lower bound of x > 0.12, but the paper repeatedly identifies Cu0.12Bi2Se3 as superconducting, with a transition near 3.8 K.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 3

  1. V. P. Zhuse, 1958, Sov. Phys. Tech. Phys., 3, 1925
  2. B. Liautard, 1990, Eur. J. Solid State Inorg. Chem., 27, 819
  3. M. I. Golovej, 1985, Izv. Vyss. Uch. Zaved., Khym I Khym. Tekh., 28, 7

Cited by

Sorted by citations

Authors
Hor, Y. S., Williams, A. J., Checkelsky, J. G., Roushan, P., Seo, J., Xu, Q., Zandbergen, H. W., Yazdani, A., Ong, N. P., & Cava, R. J.
Affiliations
  • Princeton University (US)
  • Delft University of Technology (NL)
ORCID
Venue
Physical Review Letters
Publisher
American Physical Society (APS)
Published
2010-02-01
Volume
104
Issue
5
Pages
057001-057001
ISSN
  • 0031-9007 (ISSN-L)
  • 1079-7114
DOI
10.1103/physrevlett.104.057001
OpenAlex
W1990827612
Semantic Scholar
f96dce83daf5cddb36974054512620df4aefae8a
Cited by
1,028
References
24
Citations by year
2026: 16 · 2025: 33 · 2024: 40 · 2023: 52 · 2022: 79 · 2021: 74 · 2020: 81 · 2019: 80 · 2018: 86 · 2017: 74 · 2016: 87 · 2015: 74 · 2014: 64 · 2013: 70 · 2012: 61
FWCI
32.18
Type
journal article
Language
en
Open access
Licence
link.aps.org/licenses/aps-default-license (vor)
Locations
  • Physical Review Letters (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • Research Repository (Delft University of Technology) (submittedVersion)
  • Data Archiving and Networked Services (DANS) (submittedVersion, other-oa)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Topological Materials and Phenomena
  • Physical Sciences › Physics and Astronomy › Condensed Matter Physics › Physics of Superconductivity and Magnetism
  • Physical Sciences › Materials Science › Materials Chemistry › 2D Materials and Applications
Keywords
superconductivity, Bi2Se3, topological insulators, copper intercalation, Cooper pairing, van der Waals heterostructures, electron density

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