Coincidence Detection Probability in (γ, 2e) Photoemission Measurements: Revealing Center-of-Mass Physics of Two-Body Correlations

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While limited in revealing the inner-pair structure of two-body correlations, (γ, 2e) photoemission measurements can effectively probe the center-of-mass physics of correlated electrons, offering potential applications in studying Cooper pairs in superconductors.

Samenvatting

• Bibliographic Information: Su, Y., Cao, K., & Zhang, C. (2024, October 4). Coincidence detection probability of (γ, 2e) photoemission measurement. arXiv.org. https://arxiv.org/abs/2307.12857v3
• Research Objective: This theoretical study aims to develop a comprehensive second-order perturbation theory for (γ, 2e) photoemission measurements, focusing on their ability to probe two-body correlations in condensed matter systems.
• Methodology: The authors utilize a second-order perturbation approach, incorporating electron-photon and electron-electron interactions, to derive expressions for the coincidence detection probability of two emitted electrons in (γ, 2e) photoemission. They introduce a two-body Bethe-Salpeter wave function to describe the dynamical two-body correlations of the target electrons.
• Key Findings: The study reveals that while the arbitrary momentum and energy transfer during the electron-electron scattering process in (γ, 2e) photoemission prevents the resolution of inner-pair structures within the two-body correlations, the technique can effectively probe the center-of-mass momentum and energy of the two-body Bethe-Salpeter wave function. This finding highlights the potential of (γ, 2e) photoemission for investigating the center-of-mass physics of correlated electron systems.
• Main Conclusions: The authors conclude that (γ, 2e) photoemission, despite its limitations in resolving inner-pair structures, offers a valuable tool for studying the center-of-mass physics of two-body correlations, particularly in the context of Cooper pairs in superconductors. They suggest that the technique can be applied to investigate collective excitations of macroscopic superconducting condensates, such as plasmon modes and Higgs amplitude modes.
• Significance: This research provides a theoretical framework for understanding and interpreting (γ, 2e) photoemission measurements, paving the way for their application in studying a wider range of correlated electron systems beyond superconductors, including Mott insulators and heavy fermion systems.
• Limitations and Future Research: The study primarily focuses on the theoretical aspects of (γ, 2e) photoemission. Further experimental investigations are needed to validate the theoretical predictions and explore the full potential of the technique. Future research could also focus on extending the theoretical framework to incorporate more complex interactions and material properties.

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Citaten

"The (γ, 2e) photoemission technique has been developed to investigate the two-body correlations of the target correlated electrons."
"The coincidence detection probability of the two emitted electrons in the (γ, 2e) photoemission measurement is shown to be relevant to a two-body Bethe-Salpeter wave function, which describes the dynamical two-body correlations of the target correlated electrons near the Fermi energy."
"Thus, the (γ, 2e) photoemission technique can provide the center-of-mass physics of the two-body correlations of the target correlated electrons. It will be one potential technique to study the center-of-mass physics of the Cooper pairs in superconductor."

Belangrijkste Inzichten Gedestilleerd Uit

Coincidence detection probability of $(\gamma, 2e)$ photoemission measurement

by Yuehua Su, K... om arxiv.org 10-07-2024

https://arxiv.org/pdf/2307.12857.pdf

Diepere vragen

How does the resolution of (γ, 2e) photoemission spectroscopy compare to other techniques used to study correlated electron systems, and what advancements in experimental techniques could potentially improve its resolution?

(γ, 2e) photoemission spectroscopy, while a promising tool for studying correlated electron systems, currently lags behind other techniques in terms of resolution. This is primarily due to the inherent challenge posed by the arbitrary momentum and energy transfer during the electron-electron scattering process, which limits its ability to resolve inner-pair structures of the two-body Bethe-Salpeter wave function.
Here's a comparative look at its resolution capabilities:

Techniques:
Resolution:
Advantages:
Limitations:

(γ, 2e) Photoemission
Lower
Direct access to two-body correlations, Sensitivity to center-of-mass physics of Cooper pairs
Limited resolution of inner-pair structures due to arbitrary momentum/energy transfer during electron-electron scattering

cARPES
Higher
Direct access to two-body correlations, Can resolve both inner-pair and center-of-mass physics
Experimentally challenging due to the requirement of detecting two photoelectrons from two photons

ARPES
High
Provides detailed information about single-particle electronic structure, band dispersion, and Fermi surface topology
Limited information about many-body correlations

cINS
Moderate
Directly probes spin-spin correlations, Sensitive to magnetic excitations
Limited to momentum and energy scales accessible by neutrons

Advancements for improved resolution:

Time-resolved (γ, 2e) photoemission: Incorporating pump-probe techniques could provide temporal resolution, allowing for the study of dynamic processes and potentially disentangling the electron-electron scattering event.
Spin-resolved (γ, 2e) photoemission: Detecting the spin of emitted electrons could provide additional information about the spin correlations within the two-body Bethe-Salpeter wave function.
Improved energy and momentum resolution detectors: Advancements in detector technology, such as time-of-flight or momentum microscopy, could enhance the resolution of the emitted electron energies and momenta, leading to a clearer picture of the center-of-mass physics.
Advanced theoretical modeling: Developing sophisticated theoretical models that incorporate the complexities of electron-electron interactions and scattering processes could help in interpreting the experimental data and extracting more information about the correlated electron system.

Could the limitations in resolving inner-pair structures in (γ, 2e) photoemission be advantageous in specific scenarios, allowing for a clearer focus on center-of-mass physics by effectively averaging out the inner-pair details?

Yes, the limitations of (γ, 2e) photoemission in resolving inner-pair structures could indeed be advantageous in specific scenarios where the focus is on the center-of-mass physics of the correlated electron system.
Here's why:

Effective averaging: The arbitrary momentum and energy transfer during electron-electron scattering, while hindering inner-pair resolution, effectively averages over these details. This averaging can provide a cleaner signal when studying properties that are primarily governed by the center-of-mass behavior.
Focus on collective excitations: In the study of collective excitations in superconductors, such as plasmon modes or Higgs amplitude modes, the center-of-mass motion of Cooper pairs is of paramount importance. The (γ, 2e) technique's ability to probe this aspect directly, even with limited inner-pair resolution, makes it a valuable tool.
Simplified analysis: By effectively integrating out the inner-pair degrees of freedom, the analysis of experimental data can be simplified, allowing for a more direct extraction of center-of-mass properties like the energy and momentum of collective excitations.
Scenarios where this could be advantageous:

Investigating the dispersion relation of collective modes: The energy-momentum relationship of collective excitations can be directly probed by varying the incident photon energy and detecting the emitted electron energies in (γ, 2e) photoemission.
Studying the temperature dependence of collective modes: The evolution of collective excitations with temperature, particularly their softening or hardening, can be tracked using this technique.
Probing the effects of doping or external fields: The influence of external stimuli on the center-of-mass physics of correlated electron systems, and consequently on collective excitations, can be studied.

Considering the potential of (γ, 2e) photoemission in studying collective excitations in superconductors, could this technique be extended to investigate and manipulate these excitations, potentially leading to novel applications in superconducting devices?

The potential of (γ, 2e) photoemission to study collective excitations in superconductors extends beyond mere observation. By extending the technique, it might be possible to not only investigate but also manipulate these excitations, potentially opening doors to novel applications in superconducting devices.
Here are some possibilities:

Selective excitation of collective modes: By tuning the incident photon energy and momentum, specific collective modes, such as plasmon or Higgs modes, could be selectively excited. This could lead to a deeper understanding of their individual properties and dynamics.
Ultrafast control of superconductivity: Combining (γ, 2e) photoemission with ultrafast laser pulses could enable the manipulation of collective excitations on extremely short timescales. This could pave the way for ultrafast switching or modulation of superconducting properties.
Generation of non-equilibrium superconducting states: By driving the system out of equilibrium through controlled excitation of collective modes, novel non-equilibrium superconducting states with potentially exotic properties could be realized.
Enhanced superconducting properties: Manipulating collective excitations could potentially be used to enhance desirable properties in superconducting devices, such as critical temperature or critical current density.
Challenges and future directions:

Developing experimental techniques for manipulation: Extending (γ, 2e) photoemission to manipulate collective excitations will require significant advancements in experimental techniques, such as incorporating ultrafast laser systems and developing methods for precise control of photon energy, momentum, and polarization.
Understanding the interplay of collective excitations: Superconductors exhibit a complex interplay of various collective excitations. Decoupling and selectively manipulating these modes will be crucial for developing practical applications.
Material challenges: Identifying and synthesizing materials that exhibit strong coupling to light and exhibit robust collective excitations at technologically relevant temperatures will be essential.
While significant challenges remain, the potential of (γ, 2e) photoemission to not only study but also manipulate collective excitations in superconductors presents an exciting avenue for future research with potential for groundbreaking applications in superconducting devices.