Special Issue "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).

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
Special Issues and Collections in MDPI journals
Prof. Dr. Luca Dell'Anna
E-Mail Website
Guest Editor
Prof. Dr. Luca Salasnich
E-Mail Website
Guest Editor

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

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Keywords

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

Published Papers (4 papers)

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Research

Article
Critical Temperature in the BCS-BEC Crossover with Spin-Orbit Coupling
Condens. Matter 2021, 6(2), 16; https://doi.org/10.3390/condmat6020016 - 30 Apr 2021
Viewed by 455
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
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Article
Topological Edge States of a Majorana BBH Model
Condens. Matter 2021, 6(2), 15; https://doi.org/10.3390/condmat6020015 - 09 Apr 2021
Viewed by 536
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 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
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Article
Effect of Mismatched Electron-Hole Effective Masses on Superfluidity in Double Layer Solid-State Systems
Condens. Matter 2021, 6(2), 14; https://doi.org/10.3390/condmat6020014 - 07 Apr 2021
Cited by 1 | Viewed by 454
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
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Article
Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor
Condens. Matter 2021, 6(1), 8; https://doi.org/10.3390/condmat6010008 - 07 Feb 2021
Viewed by 676
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
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