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Scientists Detect Cooper‑Pair Emission in a Cuprate Superconductor with Two‑Electron Photoemission

November 10, 2026arXiv: 2611.09857v1

A team of physicists has, for the first time, captured a clear signature of Cooper pairs—pairs of electrons bound together in a superconducting state—using two‑electron angle‑resolved photoemission (2e‑ARPES). By measuring the joint‑energy distribution of two photoelectrons emitted from an optimally doped Bi‑2212 crystal, the experiment revealed a sharp peak at zero pair binding energy and zero pair momentum that appears only below the superconducting transition temperature (≈8.5 K) and disappears at 200 K. The peak’s presence at 8.5 K and absence at 200 K confirms that the observed signal is directly tied to Cooper‑pair formation.

Figure 3 shows two panels, one at 8.5 K and one at 200 K, each displaying a two‑dimensional map of joint‑energy correlations. In the 8.5 K map a bright spot appears at zero pair binding energy and momentum, while the 200 K map lacks this feature.
Figure 3. Joint‑energy maps at 8.5 K and 200 K show a sharp zero‑binding‑energy peak only below Tc.Amir, Henry, Zwettler, Jack, Wong, Ka Ho, Gu, Genda, Fernandes, Rafael M., Noronha, Jorge et al. · arXiv:2611.09857v1 · Figure 3: ·
CC BY 4.0

The technique employs a high‑flux 525 kHz extreme‑ultraviolet (XUV) light source tuned to 22.8 eV photon energy. Two time‑of‑flight analyzers detect coincident electrons emitted near the antinodal Fermi surface, enabling momentum‑resolved pair‑emission measurements. The analysis uses a normalized correlation measure that subtracts background events from different laser pulses, isolating true coincidences.

Temperature‑dependent scans of the 2e‑ARPES signal show that the width of the joint‑energy distribution along the relative‑energy (anti‑diagonal) direction broadens from roughly 12 meV at 70 K to about 23 meV at 8.5 K, while the width along the total‑energy (diagonal) direction remains nearly constant. This contrasting temperature dependence cannot be explained by instrumental resolution, static disorder, or ordinary thermal broadening, suggesting that interactions with collective excitations inside the superconductor broaden the relative‑energy width as superconductivity strengthens.

Figure 4 displays contour plots of the joint‑energy distribution at 8.5 K, 30 K, and 70 K, with accompanying Lorentzian fits. A plot of full width at half maximum shows the anti‑diagonal width growing with lower temperature while the diagonal width remains stable.
Figure 4. Temperature dependence of the width along the anti‑diagonal increases from ≈12 meV at 70 K to ≈23 meV at 8.5 K; the diagonal width stays constant.Amir, Henry, Zwettler, Jack, Wong, Ka Ho, Gu, Genda, Fernandes, Rafael M., Noronha, Jorge et al. · arXiv:2611.09857v1 · Figure 4: · CC BY 4.0

These observations provide the first momentum‑ and energy‑resolved evidence of Cooper‑pair emission from a superconductor and open a new avenue for probing the internal dynamics of superconducting states with electron‑pair spectroscopy.

Source paper

Energy- and momentum-resolved Cooper-pair emission from a cuprate superconductor

SuperconductivityMaterials ScienceStrongly Correlated Electrons
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