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Condensed Matter
Special Issues
Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III
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Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III

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

Deadline for manuscript submissions: closed (15 March 2021) | Viewed by 16339

Special Issue Editors

Prof. Dr. Andrea Perali

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Guest Editor
Scuola del Farmaco e Divisione di Fisica, Edificio di Fisica, Università di Camerino, Via Madonna delle Carceri 9, 62032 Camerino, 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
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Luca Dell'Anna

E-Mail Website
Guest Editor
Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova, Via F. Marzolo 8, 35131 Padova, Italy
Interests: ultracold atoms; disordered systems; mesoscopic physics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Luca Salasnich

E-Mail Website
Guest Editor
Department of Physics and Astronomy “Galileo Galilei”, University of Padova, Via Marzolo 8, 35131 Padova, Italy
Interests: Bose-Einstein condensation; ultracold atoms; quantum statistical physics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue is dedicated to the proceedings of the conference SuperFluctuations 2020 (http://www.multisuper.org/superfluctuations-2020), which will be held online on 22–23 June 2020. This international conference will highlight recent advances in diverse fields of superconductivity and superfluidity. 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 Salasnich
Prof. Dr. Luca Dell'Anna
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Condensed Matter is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • BCS-BEC crossover
  • multicomponent superfluids
  • Bose–Fermi mixtures
  • machine learning
  • topological quantum matter
  • quantum technologies
  • vortex states

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Published Papers (6 papers)

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Research

13 pages, 3534 KiB  
Article
Nonlinear Excitations in Ultracold Atoms Trapped in Triple Optical Lattices
by Pradosh Basu, Barun Halder, Sriganapathy Raghav and Utpal Roy
Condens. Matter 2022, 7(3), 52; https://doi.org/10.3390/condmat7030052 - 09 Sep 2022
Viewed by 1453
Abstract
Various solitary wave excitations are found for a Bose-Einstein condensate in presence of two hybrid potentials in the form of triple mixtures of optical lattices. One of these potentials comprises of a combination of two important lattice profiles, such as frustrated optical lattice [...] Read more.
Various solitary wave excitations are found for a Bose-Einstein condensate in presence of two hybrid potentials in the form of triple mixtures of optical lattices. One of these potentials comprises of a combination of two important lattice profiles, such as frustrated optical lattice and double-well super-lattice, within one. Another represents a composite lattice combination, resulting in a wider and deeper frustrated optical lattice. The dynamical equation for such a system is solved by the exact analytical method to obtain a bright solitary wave, periodic wave and cnoidal wave excitations. We also report Anderson localization, bifurcation of condensate at the center and a competition between two different types of localizations upon trap engineering. Dynamical and structural stability analyses are also carried out, which reveal the obtained solutions as extremely stable for structural noise incorporation and sufficiently stable for dynamical stability. These triple mixtures of optical lattices impart better tunability on the condensate profile, which has made this system a true quantum simulator. Full article
(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III)
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19 pages, 781 KiB  
Article
The Role of Orbital Nesting in the Superconductivity of Iron-Based Superconductors
by Raquel Fernández-Martín, María J. Calderón, Laura Fanfarillo and Belén Valenzuela
Condens. Matter 2021, 6(3), 34; https://doi.org/10.3390/condmat6030034 - 14 Sep 2021
Cited by 1 | Viewed by 2226
Abstract
We analyze the magnetic excitations and the spin-mediated superconductivity in iron-based superconductors within a low energy model that operates in the band basis, but fully incorporates the orbital character of the spin excitations. We show how the orbital selectivity, encoded in our low [...] Read more.
We analyze the magnetic excitations and the spin-mediated superconductivity in iron-based superconductors within a low energy model that operates in the band basis, but fully incorporates the orbital character of the spin excitations. We show how the orbital selectivity, encoded in our low energy description, simplifies substantially the analysis and allows for analytical treatments, while retaining all the main features of both spin excitations and gap functions computed using multiorbital models. Importantly, our analysis unveils the orbital matching between the hole and electron pockets as the key parameter to determine the momentum dependence and the hierarchy of the superconducting gaps, instead of the Fermi surface matching, as in the common nesting scenario. Full article
(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III)
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59 pages, 608 KiB  
Article
Critical Temperature in the BCS-BEC Crossover with Spin-Orbit Coupling
by Luca Dell’Anna and Stefano Grava
Condens. Matter 2021, 6(2), 16; https://doi.org/10.3390/condmat6020016 - 30 Apr 2021
Cited by 3 | Viewed by 3314
Abstract
We review the study of the superfluid phase transition in a system of fermions whose interaction can be tuned continuously along the crossover from Bardeen–Cooper–Schrieffer (BCS) superconducting phase to a Bose–Einstein condensate (BEC), also in the presence of a spin–orbit coupling. Below a [...] Read more.
We review the study of the superfluid phase transition in a system of fermions whose interaction can be tuned continuously along the crossover from Bardeen–Cooper–Schrieffer (BCS) superconducting phase to a Bose–Einstein condensate (BEC), also in the presence of a spin–orbit coupling. Below a critical temperature the system is characterized by an order parameter. Generally a mean field approximation cannot reproduce the correct behavior of the critical temperature Tc over the whole crossover. We analyze the crucial role of quantum fluctuations beyond the mean-field approach useful to find Tc along the crossover in the presence of a spin–orbit coupling, within a path integral approach. A formal and detailed derivation for the set of equations useful to derive Tc is performed in the presence of Rashba, Dresselhaus and Zeeman couplings. In particular in the case of only Rashba coupling, for which the spin–orbit effects are more relevant, the two-body bound state exists for any value of the interaction, namely in the full crossover. As a result the effective masses of the emerging bosonic excitations are finite also in the BCS regime. Full article
(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III)
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12 pages, 2990 KiB  
Article
Topological Edge States of a Majorana BBH Model
by Alfonso Maiellaro and Roberta Citro
Condens. Matter 2021, 6(2), 15; https://doi.org/10.3390/condmat6020015 - 09 Apr 2021
Cited by 9 | Viewed by 3359
Abstract
We investigate a Majorana Benalcazar–Bernevig–Hughes (BBH) model showing the emergence of topological corner states. The model, consisting of a two-dimensional Su–Schrieffer–Heeger (SSH) system of Majorana fermions with π flux, exhibits a non-trivial topological phase in the absence of Berry curvature, while the Berry [...] Read more.
We investigate a Majorana Benalcazar–Bernevig–Hughes (BBH) model showing the emergence of topological corner states. The model, consisting of a two-dimensional Su–Schrieffer–Heeger (SSH) system of Majorana fermions with π flux, exhibits a non-trivial topological phase in the absence of Berry curvature, while the Berry connection leads to a non-trivial topology. Indeed, the system belongs to the class of second-order topological superconductors (HOTSC2), exhibiting corner Majorana states protected by C4 symmetry and reflection symmetries. By calculating the 2D Zak phase, we derive the topological phase diagram of the system and demonstrate the bulk-edge correspondence. Finally, we analyze the finite size scaling behavior of the topological properties. Our results can serve to design new 2D materials with non-zero Zak phase and robust edge states. Full article
(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III)
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13 pages, 392 KiB  
Article
Effect of Mismatched Electron-Hole Effective Masses on Superfluidity in Double Layer Solid-State Systems
by Sara Conti, Andrea Perali, François M. Peeters and David Neilson
Condens. Matter 2021, 6(2), 14; https://doi.org/10.3390/condmat6020014 - 07 Apr 2021
Cited by 1 | Viewed by 2428
Abstract
Superfluidity has been predicted and now observed in a number of different electron-hole double-layer semiconductor heterostructures. In some of the heterostructures, such as GaAs and Ge-Si electron-hole double quantum wells, there is a strong mismatch between the electron and hole effective masses. We [...] Read more.
Superfluidity has been predicted and now observed in a number of different electron-hole double-layer semiconductor heterostructures. In some of the heterostructures, such as GaAs and Ge-Si electron-hole double quantum wells, there is a strong mismatch between the electron and hole effective masses. We systematically investigate the sensitivity to unequal masses of the superfluid properties and the self-consistent screening of the electron-hole pairing interaction. We find that the superfluid properties are insensitive to mass imbalance in the low density BEC regime of strongly-coupled boson-like electron-hole pairs. At higher densities, in the BEC-BCS crossover regime of fermionic pairs, we find that mass imbalance between electrons and holes weakens the superfluidity and expands the density range for the BEC-BCS crossover regime. This permits screening to kill the superfluid at a lower density than for equal masses. Full article
(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III)
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9 pages, 599 KiB  
Article
Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor
by Hiroyuki Tajima, Pierbiagio Pieri and Andrea Perali
Condens. Matter 2021, 6(1), 8; https://doi.org/10.3390/condmat6010008 - 07 Feb 2021
Cited by 1 | Viewed by 2649
Abstract
We investigate single-particle excitation properties in the normal state of a two-band superconductor or superfluid throughout the Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein-condensation (BEC) crossover, within the many-body T-matrix approximation for multichannel pairing fluctuations. We address the single-particle density of states and the spectral [...] Read more.
We investigate single-particle excitation properties in the normal state of a two-band superconductor or superfluid throughout the Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein-condensation (BEC) crossover, within the many-body T-matrix approximation for multichannel pairing fluctuations. We address the single-particle density of states and the spectral functions consisting of two contributions associated with a weakly interacting deep band and a strongly interacting shallow band, relevant for iron-based multiband superconductors and multicomponent fermionic superfluids. We show how the pseudogap state in the shallow band is hidden by the deep band contribution throughout the two-band BCS-BEC crossover. Our results could explain the missing pseudogap in recent scanning tunneling microscopy experiments in FeSe superconductors. Full article
(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors III)
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