Special Issue "Fluctuations and Highly Non-Linear Phenomena in Superfluids and Superconductors VI"

A special issue of Condensed Matter (ISSN 2410-3896). This special issue belongs to the section "Superconductivity".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 5568

Special Issue Editors

Prof. Dr. Andrea Perali
E-Mail Website
Guest Editor
Scuola del Farmaco e Divisione di Fisica, Edificio di Fisica, Università di Camerino, Via Madonna delle Carceri 9, 62032 Camerino, MC, Italy
Interests: high-Tc superconductivity (theory and phenomenology); multiband superconductivity; quantum size effects and shape resonances in superconductors; nanoscale superconductors; superconducting heterostructures; BCS-BEC crossover; pseudogap; superconducting fluctuations; ultracold fermions: superfluidity and BCS-BEC crossover; electron–hole superfluidity
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Special Issue Information

Dear Colleagues,

This Special Issue is dedicated to the proceedings of the conference SuperFluctuations 2021 (http://www.multisuper.org/superfluctuations-2021), which will be held online on 14–15 June 2021. This international conference will highlight recent advances in superconductivity, superfluidity, Bose–Einstein condensation, and related areas. You are invited to submit a full manuscript for consideration and possible publication in this joint Special Issue. Submissions will be rapidly reviewed and published immediately if accepted. Invited and leading contributed papers will focus on the following topics:

  • Fluctuations and BCS–BEC crossover phenomena in multicomponent and low dimensional systems;
  • Quantum technologies and novel phenomena with Bose and Fermi mixtures;
  • Highly nonlinear phenomena: Josephson and Andreev effects, topological defects, skyrmions and solitons, vortex states;
  • Novel quantum phenomena in multicomponent/multigap superconductors and superfluids;
  • Innovative numerical methods: machine learning and its applications.

Prof. Dr. Andrea Perali
Prof. Dr. Luca Dell'Anna
Prof. Dr. Luca Salasnich
Guest Editors

Manuscript Submission Information

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Published Papers (5 papers)

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Research

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Article
Mimicking Multiorbital Systems with SU(N) Atoms: Hund’s Physics and Beyond
Condens. Matter 2022, 7(1), 18; https://doi.org/10.3390/condmat7010018 - 01 Feb 2022
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Abstract
The physics of many interesting correlated materials can be captured by multiorbital Hubbard models, where conduction electrons feature an additional orbital degree of freedom. The multiorbital characteristic is not a mere complication, but it leads to an immensely richer landscape of physical regimes. [...] Read more.
The physics of many interesting correlated materials can be captured by multiorbital Hubbard models, where conduction electrons feature an additional orbital degree of freedom. The multiorbital characteristic is not a mere complication, but it leads to an immensely richer landscape of physical regimes. One of the key features is the interplay between Hubbard repulsion and Hund’s exchange coupling, which has been shown to lead to orbital-selective correlations and to the existence of correlation-resilient metals (usually called Hund’s metals) defying Mott localization. Here, we show that experimentally available platforms of SU(N)-symmetric ultracold atoms can indeed mimic the rich physics disclosed by multiorbital materials, by exploiting the internal degrees of freedom of multicomponent atoms. We discuss in detail the SU(N) version of interaction-resilient Hund’s metal and some other interesting regimes. Full article
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Article
Evolution of Charge-Lattice Dynamics across the Kuramoto Synchronization Phase Diagram of Quantum Tunneling Polarons in Cuprate Superconductors
Condens. Matter 2021, 6(4), 52; https://doi.org/10.3390/condmat6040052 - 16 Dec 2021
Cited by 1 | Viewed by 975
Abstract
Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to [...] Read more.
Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to hole-doped cuprate superconductors, EXAFS has revealed the presence of internal quantum tunneling polarons (IQTPs). An IQTP arises in EXAFS as a two-site distribution for certain Cu–O pairs, which is also duplicated in inelastic scattering but not observed in standard diffraction measurements. The Cu–Sr pair distribution has been found to be highly anharmonic and strongly correlated to both the IQTPs and to superconductivity, as, for example, in YSr2Cu2.75Mo0.25O7.54(Tc=84 K). In order to describe such nontrivial, anharmonic charge-lattice dynamics, we have proposed a model Hamiltonian for a prototype six-atom cluster, in which two Cu-apical-O IQTPs are charge-transfer bridged through Cu atoms by an O atom in the CuO2 plane and are anharmonically coupled via a Sr atom. By applying an exact diagonalization procedure to this cluster, we have verified that our model indeed produces an intricate interplay between charge and lattice dynamics. Then, by using the Kuramoto model for the synchronization of coupled quantum oscillators, we have found a first-order phase transition for the IQTPs into a synchronized, phase-locked phase. Most importantly, we have shown that this transition results specifically from the anharmonicity. Finally, we have provided a phase diagram showing the onset of the phase-locking of IQTPs as a function of the charge-lattice and anharmonic couplings in our model. We have found that the charge, initially confined to the apical oxygens, is partially pumped into the CuO2 plane in the synchronized phase, which suggests a possible connection between the synchronized dynamic structure and high-temperature superconductivity (HTSC) in doped cuprates. Full article
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Article
Reliability of the Ginzburg–Landau Theory in the BCS-BEC Crossover by Including Gaussian Fluctuations for 3D Attractive Fermions
Condens. Matter 2021, 6(4), 49; https://doi.org/10.3390/condmat6040049 - 01 Dec 2021
Cited by 1 | Viewed by 977
Abstract
We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian [...] Read more.
We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian fluctuations strongly modifies the values of the Ginzburg–Landau parameters approaching the BEC regime of the crossover. We investigate the reliability of the Ginzburg–Landau theory, with fluctuations, studying the behavior of the coherence length and of the critical rotational frequencies throughout the BCS-BEC crossover. The effect of the Gaussian fluctuations gives qualitative correct trends of the considered physical quantities from the BCS regime up to the unitary limit of the BCS-BEC crossover. Approaching the BEC regime, the Ginzburg–Landau equation with the inclusion of Gaussian fluctuations turns out to be unreliable. Full article
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Article
Uniformly Frustrated XY Model: Strengthening of the Vortex Lattice by Intrinsic Disorder
Condens. Matter 2021, 6(4), 42; https://doi.org/10.3390/condmat6040042 - 06 Nov 2021
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Abstract
In superconducting films, the role of intrinsic disorder is typically to compete with superconductivity by fragmenting the global phase coherence and lowering the superfluid density. Nonetheless, when a transverse magnetic field is applied to the system and an Abrikosov vortex lattice form, the [...] Read more.
In superconducting films, the role of intrinsic disorder is typically to compete with superconductivity by fragmenting the global phase coherence and lowering the superfluid density. Nonetheless, when a transverse magnetic field is applied to the system and an Abrikosov vortex lattice form, the presence of disorder can actually strengthen the superconducting state against thermal fluctuations. By means of Monte Carlo simulations on the uniformly frustrated XY model in two dimensions, we show that while for weak pinning the superconducting critical temperature Tc increases with the applied field H, for strong enough pinning, the experimental decreasing dependence between Tc and H is recovered with a resulting more robust vortex lattice. Full article
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Review

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Review
Extremely Overdoped Superconducting Cuprates via High Pressure Oxygenation Methods
Condens. Matter 2021, 6(4), 50; https://doi.org/10.3390/condmat6040050 - 01 Dec 2021
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Abstract
Within the cuprate constellation, one fixed star has been the superconducting dome in the quantum phase diagram of transition temperature vs. the excess charge on the Cu in the CuO2-planes, p, resulting from O-doping or cation substitution. However, a more [...] Read more.
Within the cuprate constellation, one fixed star has been the superconducting dome in the quantum phase diagram of transition temperature vs. the excess charge on the Cu in the CuO2-planes, p, resulting from O-doping or cation substitution. However, a more extensive search of the literature shows that the loss of the superconductivity in favor of a normal Fermi liquid on the overdoped side should not be assumed. Many experimental results from cuprates prepared by high-pressure oxygenation show Tc converging to a fixed value or continuing to slowly increase past the upper limit of the dome of p = 0.26–0.27, up to the maximum amounts of excess oxygen corresponding to p values of 0.3 to > 0.6. These reports have been met with disinterest or disregard. Our review shows that dome-breaking trends for Tc are, in fact, the result of careful, accurate experimental work on a large number of compounds. This behavior most likely mandates a revision of the theoretical basis for high-temperature superconductivity. That excess O atoms located in specific, metastable sites in the crystal, attainable only with extreme O chemical activity under HPO conditions, cause such a radical extension of the superconductivity points to a much more substantial role for the lattice in terms of internal chemistry and bonding. Full article
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