Energy- and momentum-resolved Cooper-pair emission from a cuprate superconductor
Authors: Henry Amir, Jack Zwettler, Ka Ho Wong, Genda Gu, Rafael M. Fernandes, Jorge Noronha, Dirk K. Morr, Fahad Mahmood
Abstract
Superconductivity arises from Cooper pairing, but conventional photoemission probes electrons individually rather than as pairs. Here we report the observation of Cooper-pair emission from an optimally doped cuprate superconductor using two-electron angle-resolved photoemission (2e-ARPES). Below the superconducting transition, we observe a distinct two-electron emission peak at zero pair binding energy and zero pair momentum that disappears in the normal state, revealing the characteristic fingerprint of a Cooper pair. Unexpectedly, the joint energy distribution broadens markedly along the relative-energy axis as temperature decreases, while the total energy width remains nearly unchanged. This anomalous behavior cannot be explained by instrumental resolution, static disorder or thermal broadening, and instead points to scattering processes involving collective excitations of the superconductor. Our results establish 2e-ARPES as a probe of both Cooper-pair emission and the many-body dynamics of the superconducting state.
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Directly observes non-local fermion pairs in an attractive Fermi-Hubbard gas, whereas this paper detects emitted Cooper pairs in a cuprate.
Abstract
Pairing of fermions lies at the heart of superconductivity, the hierarchy of nuclear binding energies and superfluidity of neutron stars. The Hubbard model of attractively interacting fermions provides a paradigmatic setting for fermion pairing, featuring a crossover between Bose-Einstein condensation (BEC) of tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of long-range Cooper pairs, and a "pseudo-gap" region where pairs form already above the superfluid critical temperature. We here directly observe the non-local nature of fermion pairing in a Hubbard lattice gas, employing spin- and density-resolved imaging of $\sim$1000 fermionic ${}^{40}$K atoms under a bilayer mic…
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The model studies electron pairing and superconductivity in an incoherent-electron system, rather than measuring pair emission from a cuprate.
Abstract
We introduce and solve a model of interacting electrons and phonons that is a natural generalization of the Sachdev-Ye-Kitaev-model and that becomes superconducting at low temperatures. In the normal state two Non-Fermi liquid fixed points with distinct universal exponents emerge. At weak coupling superconductivity prevents the onset of low-temperature quantum criticality, reminiscent of the behavior in several heavy-electron and iron-based materials. At strong coupling, pairing of highly incoherent fermions sets in deep in the Non-Fermi liquid regime, a behavior qualitatively similar to that in underdoped cuprate superconductors. The pairing of incoherent time-reversal partners is protected…
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The study probes local and superconducting pairs in optimally doped YBa2Cu3O7-δ, using terahertz recovery dynamics rather than two-electron photoemission.
Abstract
Pairing states are essential for understanding the underlying mechanisms of high-temperature superconductivity. Here the non-superconducting state in an optimally doped YBa2Cu3O7-{\delta} film was driven out of equilibrium by an optical pump with low fluence at a temperature well below the critical temperature (Tc), and its recovery dynamics were exclusively measured using transient terahertz spectroscopy. The pump-fluence dependent experiments unveiled evidence of local pairs without superconductivity coexisting with the superconducting Cooper pairs. An energy gap opening induced by the local pairing with short-range coherence was invoked to rationalize the temperature-dependent recovery ti…
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Nodeless d-wave pairing in monolayer FeSe revealed by intra-unit-cell Josephson interferometryRunxin Li, Yuchen Huo, Jiong Mei et al. · 2026 · Superconductivity · cited 2 times · AI summary available
The study uses atomic-scale Josephson interferometry to examine d-wave pairing symmetry in monolayer FeSe, rather than detecting emitted Cooper pairs.
In short
Atomic-scale Josephson imaging reveals a bond-centred response with Fe–Se nodal lines in monolayer FeSe, which calculations identify as a signature of nodeless d-wave pairing.
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Abstract
Multiply-excited states in semiconductor quantum dots feature intriguing physics and play a crucial role in nanocrystal-based technologies. While photoluminescence provides a natural probe to investigate these states, room temperature single-particle spectroscopy of their emission has so far proved elusive due to the temporal and spectral overlap with emission from the singly-excited and charged states. Here we introduce biexciton heralded spectroscopy, enabled by a single-photon avalanche diode array based spectrometer. This allows us to directly observe biexciton-exciton emission cascades and measure the biexciton binding energy of single quantum dots at room temperature, even though it is…
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Measuring total density correlations in a Fermi-Hubbard gas via bilayer microscopyThomas Hartke, Botond Oreg, Ningyuan Jia et al. · 2020 · Phys. Rev. Lett. 125, 113601 (2020) · cited 5 times · Not summarized yet
The study measures atom-pair density correlations in a Fermi-Hubbard gas, not Cooper-pair emission from a superconductor.
Abstract
We report on the single atom and single site-resolved detection of the total density in a cold atom realization of the 2D Fermi-Hubbard model. Fluorescence imaging of doublons is achieved by splitting each lattice site into a double well, thereby separating atom pairs. Full density readout yields a direct measurement of the equation of state, including direct thermometry via the fluctuation-dissipation theorem. Site-resolved density correlations reveal the Pauli hole at low filling, and strong doublon-hole correlations near half filling. These are shown to account for the difference between local and non-local density fluctuations in the Mott insulator. Our technique enables the study of ato…
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Competing itinerant and local spin interactions in kagome metal FeGeLebing Chen, Xiaokun Teng, Hengxin Tan et al. · 2023 · Nat Commun 15, 1918 (2024) · cited 25 times · AI summary available
The study examines competing magnetic and charge-density-wave phases in kagome FeGe, a neighbouring problem in correlated-electron materials.
Abstract
Two-dimensional kagome metals consisting of corner-sharing triangles offer a unique platform for studying strong electron correlations and band topology due to its geometrically frustrated lattice structure. The similar energy scales between spin, lattice, and electronic degrees of freedom in these systems give rise to competing quantum phases such as charge density wave (CDW), magnetic order, and superconductivity. For example, kagome metal FeGe first exhibits A-type collinear antiferromagnetic (AFM) order at T_N ~ 400 K, then establishes a CDW phase coupled with AFM ordered moment below T_CDW ~ 100 K, and finally forms a $c$-axis double cone AFM structure around T_Canting ~ 60 K. Here we u…
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Superradiance as a witness to multipartite entanglementFrederik Lohof, Daniel Schumayer, David A. W. Hutchinson et al. · 2023 · Phys. Rev. Lett. 131, 063601 (2023) · cited 16 times · AI summary available
The study connects correlated emission to multipartite entanglement in quantum emitters, rather than measuring Cooper-pair emission.
Abstract
Generation and detection of entanglement is at the forefront of most quantum information technologies. There is a plethora of techniques that reveal entanglement on the basis of only partial information about the underlying quantum state including, in particular, entanglement witnesses. Superradiance refers to the phenomenon of highly synchronized photon emission from an ensemble of quantum emitters that is caused by correlations among the individual particles and has been connected by Dicke himself to the presence of multipartite entangled states. We investigate this connection in a quantitative way and discuss, whether or not signatures of superradiance from semiconductor nanolasers, manif…
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