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Towards Stirling cooler operable single-photon sources based on low-noise GaAs quantum dots
Authors:
Maximilian Aigner,
Jana Schlücking,
Eva Schöll,
Christian Weidinger,
Gabriel Undeutsch,
Ievgen Brytavskyi,
Thomas Oberleitner,
Tobias Maria Krieger,
Ailton Jose Garcia Junior,
Melina Peter,
Thomas K. Bracht,
Michał Gawełczyk,
Saimon Filipe Covre da Silva,
Santanu Manna,
Yusuf Karli,
Gregor Weihs,
Doris E. Reiter,
Armando Rastelli
Abstract:
For photonic quantum technology applications, sources capable of emitting photons with indistinguishability close to unity are essential. Ideally, these sources should not require demanding cooling systems. Here, we present temperature-dependent two-photon-interference measurements on photons produced by the radiative decay of the negative trion in a low-noise GaAs quantum dot, which are in quanti…
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For photonic quantum technology applications, sources capable of emitting photons with indistinguishability close to unity are essential. Ideally, these sources should not require demanding cooling systems. Here, we present temperature-dependent two-photon-interference measurements on photons produced by the radiative decay of the negative trion in a low-noise GaAs quantum dot, which are in quantitative agreement with theoretical calculations accounting for carrier-phonon interactions and coupling to excited states. While at at the lowest explored temperatures the emission linewidth reaches values only 6(2) % above the Fourier limit and the indistinguishability I between subsequently emitted photons reaches 0.966(6), the latter drops to 0.05(4) at 55 K. We show that this loss can be explained with the coupling with energetically close excited trion states and suggest that the photon indistinguishability at elevated temperatures can be increased by employing Purcell enhancement of the emission rate or by increasing the energy separation of the excited states. Using cavity-enhanced emission, we experimentally verify the first route and demonstrate an improvement in photon indistinguishability from 0.314(25) to 0.80(3) at 32 K, which - to our knowledge - is the highest reported value at such temperature.
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Submitted 25 August, 2026;
originally announced August 2026.
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Coherent Control of Quantum-Dot Spins with Cyclic Optical Transitions
Authors:
Zhe Xian Koong,
Urs Haeusler,
Jan M. Kaspari,
Christian Schimpf,
Benyam Dejen,
Ahmed M. Hassanen,
Daniel Graham,
Yusuf Karli,
Ailton J. Garcia Jr.,
Melina Peter,
Edmund Clarke,
Maxime Hugues,
Michał Gawełczyk,
Armando Rastelli,
Doris E. Reiter,
Mete Atatüre,
Dorian A. Gangloff
Abstract:
Solid-state spins are promising as interfaces from stationary qubits to single photons for quantum communication technologies. Semiconductor quantum dots have excellent optical coherence, exhibit near unity collection efficiencies when coupled to photonic structures, and possess long-lived spins for quantum memory. However, the incompatibility of performing optical spin control and single-shot rea…
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Solid-state spins are promising as interfaces from stationary qubits to single photons for quantum communication technologies. Semiconductor quantum dots have excellent optical coherence, exhibit near unity collection efficiencies when coupled to photonic structures, and possess long-lived spins for quantum memory. However, the incompatibility of performing optical spin control and single-shot readout simultaneously has been a challenge faced by almost all solid-state emitters. To overcome this, we leverage light-hole mixing to realize a highly asymmetric lambda system in a negatively charged heavy hole exciton in Faraday configuration. By compensating GHz-scale differential Stark shifts, induced by unequal coupling to Raman control fields, and by performing nuclear-spin cooling, we achieve quantum control of an electron-spin qubit with a $π$-pulse contrast of 97.4% while preserving spin-selective optical transitions with a cyclicity of 471 (50). We demonstrate this scheme for both GaAs and InGaAs quantum dots, and show that it is compatible with the operation of a nuclear quantum memory. Our approach thus enables repeated emission of indistinguishable photons together with qubit control, as required for single-shot readout, photonic cluster-state generation, and quantum repeater technologies.
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Submitted 24 June, 2026; v1 submitted 17 September, 2025;
originally announced September 2025.
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Low-density InGaAs/AlGaAs Quantum Dots in Droplet-Etched Nanoholes
Authors:
Saimon F. Covre Da Silva,
Ailton J. Garcia Jr,
Maximilian Aigner,
Christian Weidinger,
Tobias M. Krieger,
Gabriel Undeutsch,
Christoph Deneke,
Ishrat Bashir,
Santanu Manna,
Melina Peter,
Ievgen Brytavskyi,
Johannes Aberl,
Armando Rastelli
Abstract:
Over the past two decades, epitaxial semiconductor quantum dots (QDs) have demonstrated very promising properties as sources of single photons and entangled photons on-demand. Among different growth methods, droplet etching epitaxy has allowed the growth of almost strain-free QDs, with low and controllable surface densities, small excitonic fine structure splitting (FSS), and fast radiative decays…
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Over the past two decades, epitaxial semiconductor quantum dots (QDs) have demonstrated very promising properties as sources of single photons and entangled photons on-demand. Among different growth methods, droplet etching epitaxy has allowed the growth of almost strain-free QDs, with low and controllable surface densities, small excitonic fine structure splitting (FSS), and fast radiative decays. Here, we extend the local droplet etching technique to In(Ga)As QDs in AlGaAs, thereby increasing the achievable emission wavelength range beyond that accessible to GaAs/AlGaAs QDs, while benefiting from the aforementioned advantages of this growth method. We observe QD densities of $\sim 0.2\ μ\mathrm{m}^{-2}$, FSS values as small as $3\ μ\mathrm{eV}$, and short radiative lifetimes of $\sim 300\ \mathrm{ps}$, while extending the achievable emission range to $\sim 920\ \mathrm{nm}$ at cryogenic temperatures. We envision these QDs to be particularly suitable for integrated quantum photonics applications.
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Submitted 11 August, 2025;
originally announced August 2025.
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Electric-field control of photon indistinguishability in cascaded decays in quantum dots
Authors:
Gabriel Undeutsch,
Maximilian Aigner,
Ailton J. Garcia Jr.,
Johannes Reindl,
Melina Peter,
Simon Mader,
Christian Weidinger,
Saimon F. Covre da Silva,
Santanu Manna,
Eva Schöll,
Armando Rastelli
Abstract:
Photon indistinguishability, entanglement, and antibunching are key ingredients in quantum optics and photonics. Decay cascades in quantum emitters offer a simple method to create entangled photon-pairs with negligible multi-pair generation probability. However, the degree of indistinguishability of the photons emitted in a cascade is intrinsically limited by the lifetime ratio of the involved tra…
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Photon indistinguishability, entanglement, and antibunching are key ingredients in quantum optics and photonics. Decay cascades in quantum emitters offer a simple method to create entangled photon-pairs with negligible multi-pair generation probability. However, the degree of indistinguishability of the photons emitted in a cascade is intrinsically limited by the lifetime ratio of the involved transitions. Here we show that, for the biexciton-exciton cascade in a quantum dot, this ratio can be widely tuned by an applied electric field. Hong-Ou-Mandel interference measurements of two subsequently emitted biexciton photons show that their indistinguishability increases with increasing field, following the theoretically predicted behavior. At the same time, the emission linewidth stays close to the transform-limit, favoring applications relying on the interference among photons emitted by different sources.
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Submitted 27 February, 2025;
originally announced February 2025.
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Passive Demultiplexed Two-photon State Generation from a Quantum Dot
Authors:
Yusuf Karli,
Iker Avila Arenas,
Christian Schimpf,
Ailton José Garcia Junior,
Santanu Manna,
Florian Kappe,
René Schwarz,
Gabriel Undeutsch,
Maximilian Aigner,
Melina Peter,
Saimon F Covre da Silva,
Armando Rastelli,
Gregor Weihs,
Vikas Remesh
Abstract:
High-purity multi-photon states are essential for photonic quantum computing. Among existing platforms, semiconductor quantum dots offer a promising route to scalable and deterministic multi-photon state generation. However, to fully realize their potential we require a suitable optical excitation method. Current approaches of multi-photon generation rely on active polarization-switching elements…
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High-purity multi-photon states are essential for photonic quantum computing. Among existing platforms, semiconductor quantum dots offer a promising route to scalable and deterministic multi-photon state generation. However, to fully realize their potential we require a suitable optical excitation method. Current approaches of multi-photon generation rely on active polarization-switching elements (e.g., electro-optic modulators, EOMs) to spatio-temporally demultiplex single photons. Yet, the achievable multi-photon rate is fundamentally limited by the switching speed of the EOM. Here, we introduce a fully passive demultiplexing technique that leverages a stimulated two-photon excitation process to achieve switching rates that are only limited by the quantum dot lifetime. We demonstrate this method by generating two-photon states from a single quantum dot without requiring any active switching elements. Our approach significantly reduces the cost of demultiplexing while shifting it to the excitation stage, enabling loss-free demultiplexing and effectively doubling the achievable multi-photon generation rate when combined with existing active demultiplexing techniques.
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Submitted 20 February, 2025;
originally announced February 2025.
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Experimental measurement of the reappearance of Rabi rotations in semiconductor quantum dots
Authors:
L. Hanschke,
T. K. Bracht,
E. Schöll,
D. Bauch,
E. Berger,
P. Kallert,
M. Peter,
A. J. Garcia Jr.,
S. F. Covre da Silva,
S. Manna,
A. Rastelli,
S. Schumacher,
D. E. Reiter,
K. D. Jöns
Abstract:
Phonons in solid-state quantum emitters play a crucial role in their performance as photon sources in quantum technology. For resonant driving, phonons dampen the Rabi oscillations resulting in reduced preparation fidelities. The phonon spectral density, which quantifies the strength of the carrier-phonon interaction, is non-monotonous as a function of energy. As one of the most prominent conseque…
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Phonons in solid-state quantum emitters play a crucial role in their performance as photon sources in quantum technology. For resonant driving, phonons dampen the Rabi oscillations resulting in reduced preparation fidelities. The phonon spectral density, which quantifies the strength of the carrier-phonon interaction, is non-monotonous as a function of energy. As one of the most prominent consequences, this leads to the reappearance of Rabi rotations for increasing pulse power, which was theoretically predicted in Phys. Rev. Lett. 98, 227403 (2007). In this paper we present the experimental demonstration of the reappearance of Rabi rotations.
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Submitted 27 September, 2024;
originally announced September 2024.
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(Fe,Sn)4N alloy as a model spin-glass system with short-range competing interactions on a nonfrustrated simple cubic lattice
Authors:
Khmelevskyi Sergii,
Mohn Peter
Abstract:
The origin of the spin-glass state in (Fe,Sn)4N alloys is studied on the basis of a Heisenberg Hamiltonian with parameters derived from first principles within the magnetic force theorem applied in the framework of the disordered local moments method and local spin-density approximation. We show that in the alloy concentration range where the spin-glass state is stable only one Fe sublattice is in…
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The origin of the spin-glass state in (Fe,Sn)4N alloys is studied on the basis of a Heisenberg Hamiltonian with parameters derived from first principles within the magnetic force theorem applied in the framework of the disordered local moments method and local spin-density approximation. We show that in the alloy concentration range where the spin-glass state is stable only one Fe sublattice is intrinsically magnetic and the interatomic exchange magnetic interactions are essentially short ranged due to effects of chemical and magnetic disorder. The magnetic Fe atoms with well-localized spin moments are randomly distributed over the nongeometrically frustrated simple cubic lattice. The magnetic frustration, which generally is believed to be an essential ingredient of the spin-glass state formation condition, may occur only due to the competition of the two nearest-neighbor interactions. We thus argue that (Fe,Sn)4N is a rare example of a spin-glass system where the mechanism of spin-glass state formation might be studied in the framework of the minimal random-site model on a simple cubic lattice with competing interactions, while the effects of the geometrical frustration can be excluded.
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Submitted 6 February, 2019;
originally announced February 2019.
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Microseconds, milliseconds and seconds: deconvoluting the dynamic behaviour of planar perovskite solar cells
Authors:
Adam Pockett,
Giles Eperon,
Nobuya Sakai,
Henry Snaith,
Laurence M Peter,
Petra J Cameron
Abstract:
Perovskite solar cells (PSC) are shown to behave as coupled ionic-electronic conductors with strong evidence that the ionic environment moderates both the rate of electron-hole recombination and the band offsets in planar PSC. Numerous models have been presented to explain the behavior of perovskite solar cells, but to date no single model has emerged that can explain both the frequency and time d…
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Perovskite solar cells (PSC) are shown to behave as coupled ionic-electronic conductors with strong evidence that the ionic environment moderates both the rate of electron-hole recombination and the band offsets in planar PSC. Numerous models have been presented to explain the behavior of perovskite solar cells, but to date no single model has emerged that can explain both the frequency and time dependent response of the devices. Here we present a straightforward coupled ionic-electronic model that can be used to explain the large amplitude transient behavior and the impedance response of PSC.
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Submitted 14 October, 2016;
originally announced October 2016.
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Emissivity of freestanding membranes with thin metal coatings
Authors:
P. J. van Zwol,
D. F. Vles,
W. P. Voorthuijzen,
M. Péter,
H. Vermeulen,
W. J. van der Zande,
J. M. Sturm. R. W. E. van de Kruijs,
F. Bijkerk
Abstract:
Freestanding silicon nitride membranes with thicknesses down to a few tens of nanometers find use as TEM windows or soft X-ray spectral purity filters. As the thickness of a membrane decreases, emissivity vanishes, which limits radiative heat emission and resistance to heat loads. We show that thin metal layers with thicknesses in the order of 1 nm enhance the emissivity of thin membranes by two t…
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Freestanding silicon nitride membranes with thicknesses down to a few tens of nanometers find use as TEM windows or soft X-ray spectral purity filters. As the thickness of a membrane decreases, emissivity vanishes, which limits radiative heat emission and resistance to heat loads. We show that thin metal layers with thicknesses in the order of 1 nm enhance the emissivity of thin membranes by two to three orders of magnitude close to the theoretical limit of 0.5. This considerably increases thermal load capacity of membranes in vacuum environments. Our experimental results are in line with classical theory in which we adapt thickness dependent scattering terms in the Drude and Lorentz oscillators.
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Submitted 19 November, 2015;
originally announced November 2015.
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Electric-field induced switching from fcc to hcp stacking of a single layer of Fe/Ni(111)
Authors:
Lukas Gerhard,
Moritz Peter,
Wulf Wulfhekel
Abstract:
We present a detailed study of an electric-field induced phase transition of a single layer of Fe on a Ni(111) substrate. Scanning tunneling microscopy at 4 K substrate temperature is used to provide the necessary electric field and to follow the transition from face-centered cubic to hexagonal closepacked stacking with atomic resolution.
We present a detailed study of an electric-field induced phase transition of a single layer of Fe on a Ni(111) substrate. Scanning tunneling microscopy at 4 K substrate temperature is used to provide the necessary electric field and to follow the transition from face-centered cubic to hexagonal closepacked stacking with atomic resolution.
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Submitted 26 February, 2015;
originally announced February 2015.
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Singular spin-wave theory and scattering continua in the cone state of Cs_2CuCl_4
Authors:
Andreas Kreisel,
Michael Peter,
Peter Kopietz
Abstract:
For temperatures below 0.6 K the geometrically frustrated layered quantum antiferromagnet Cs$_2$CuCl$_4$ in a magnetic field perpendicular to the layers orders magnetically in a so-called cone state, where the magnetic moments have a finite component in the field direction while their projection onto the layers forms a spiral. Modeling this system by a two-dimensional spatially anisotropic quantum…
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For temperatures below 0.6 K the geometrically frustrated layered quantum antiferromagnet Cs$_2$CuCl$_4$ in a magnetic field perpendicular to the layers orders magnetically in a so-called cone state, where the magnetic moments have a finite component in the field direction while their projection onto the layers forms a spiral. Modeling this system by a two-dimensional spatially anisotropic quantum Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interaction, we find that even for vanishing temperature the usual spin-wave expansion is plagued by infrared divergencies which are due to the coupling between longitudinal and transverse spin fluctuations in the cone state. Similar divergencies appear also in the ground state of the interacting Bose gas in two and three dimensions. Using known results for the correlation functions of the interacting Bose gas, we present a non-perturbative expression for the dynamic structure factor in the cone state of Cs$_2$CuCl$_4$. We show that in this state the spectral line shape of spin fluctuations exhibits singular scattering continua which can be understood in terms of the well-known anomalous longitudinal fluctuations in the ground state of the two-dimensional Bose gas.
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Submitted 4 September, 2014; v1 submitted 21 May, 2014;
originally announced May 2014.
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Modeling scanning tunneling spectra of $Bi_2 Sr_2 CaCu_2 O_{8+δ}$
Authors:
B. W. Hoogenboom,
C. Berthod,
M. Peter,
Ø. Fischer,
A. A. Kordyuk
Abstract:
Recent angle-resolved photoemission and neutron scattering data have provided new ingredients for the interpretation of scanning tunneling spectra on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. We analyze the low-temperature tunneling spectra, from oxygen overdoped to underdoped samples, including details about the bilayer splitting and the neutron resonance peak. Two van Hove singularities are identified: t…
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Recent angle-resolved photoemission and neutron scattering data have provided new ingredients for the interpretation of scanning tunneling spectra on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. We analyze the low-temperature tunneling spectra, from oxygen overdoped to underdoped samples, including details about the bilayer splitting and the neutron resonance peak. Two van Hove singularities are identified: the first is integrated in the coherence peaks, the second is heavily broadened at higher binding energy. The shape of the tunneling spectra suggests a strong coupling of the quasiparticles with a collective mode, and a comparison with photoemission shows that the scattering rate in tunneling is an order of magnitude smaller than in ARPES. Finally, the theoretical spectra calculated with an isotropic tunneling matrix element are in better agreement with the experimental data than those obtained with anisotropic matrix elements.
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Submitted 13 December, 2002;
originally announced December 2002.
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Electron transport in the dye sensitized nanocrystalline cell
Authors:
A Kambili,
A B Walker,
F Qiu,
A C Fisher,
A D Savin,
L M Peter
Abstract:
Dye sensitised nanocrystalline solar cells (Grätzel cells) have achieved solar-to-electrical energy conversion efficiencies of 12% in diffuse daylight. The cell is based on a thin film of dye-sensitised nanocrystalline TiO$_2$ interpenetrated by a redox electrolyte. The high surface area of the TiO$_2$ and the spectral characteristics of the dye allow the device to harvest 46% of the solar energ…
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Dye sensitised nanocrystalline solar cells (Grätzel cells) have achieved solar-to-electrical energy conversion efficiencies of 12% in diffuse daylight. The cell is based on a thin film of dye-sensitised nanocrystalline TiO$_2$ interpenetrated by a redox electrolyte. The high surface area of the TiO$_2$ and the spectral characteristics of the dye allow the device to harvest 46% of the solar energy flux. One of the puzzling features of dye-sensitised nano-crystalline solar cells is the slow electron transport in the titanium dioxide phase. The available experimental evidence as well as theoretical considerations suggest that the driving force for electron collection at the substrate contact arises primarily from the concentration gradient, ie the contribution of drift is negligible. The transport of electrons has been characterised by small amplitude pulse or intensity modulated illumination. Here, we show how the transport of electrons in the Grätzel cell can be described quantitatively using trap distributions obtained from a novel charge extraction method with a one-dimensional model based on solving the continuity equation for the electron density. For the first time in such a model, a back reaction with the I$_3^-$ ions in the electrolyte that is second order in the electron density has been included.
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Submitted 26 July, 2001;
originally announced July 2001.
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Topological asymmetry in the damping-pairing contribution of electron-boson scattering
Authors:
Georgios Varelogiannis,
Martin Peter
Abstract:
We make a harmonic analysis of the pairing and damping contribution of a finite $k$ range isotropic electron-phonon (or other boson) scattering in an anisotropic two-dimensional electronic system. We show that the pairing contribution of the anisotropic part of the electronic system can be much larger than its damping contribution enhancing significantly T_c. The higher is the order of the harmo…
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We make a harmonic analysis of the pairing and damping contribution of a finite $k$ range isotropic electron-phonon (or other boson) scattering in an anisotropic two-dimensional electronic system. We show that the pairing contribution of the anisotropic part of the electronic system can be much larger than its damping contribution enhancing significantly T_c. The higher is the order of the harmonic of the electronic anisotropy, smaller is its damping contribution and higher can be the asymmetry in its damping-pairing contribution. This could explain the puzzle of a much broader quasiparticle peak in the n-doped than in the p-doped cuprates, their smaller T_c's being also attributed to larger damping effects.
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Submitted 8 May, 1997;
originally announced May 1997.
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s and d-wave symmetries of the solutions of the Eliashberg equations
Authors:
G. Santi,
T. Jarlborg,
M. Peter,
M. Weger
Abstract:
We examine the different possible symmetries of the superconducting gap obtained by solving the Eliashberg equations. We consider an electron-phonon interaction in a strong coupling scenario. The Coulomb pseudopotential plays the crucial role of providing the repulsion needed to favour the d-wave symmetry. But the key parameter that allows very anisotropic solutions even with very strong couplin…
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We examine the different possible symmetries of the superconducting gap obtained by solving the Eliashberg equations. We consider an electron-phonon interaction in a strong coupling scenario. The Coulomb pseudopotential plays the crucial role of providing the repulsion needed to favour the d-wave symmetry. But the key parameter that allows very anisotropic solutions even with very strong coupling is the small angular range of the interaction due to predominantly electron-phonon forward scattering that is found in the high-Tc superconductors. We find both s and d-wave solutions whose stability depends mainly on the angular range of the interaction.
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Submitted 23 February, 1996;
originally announced February 1996.