Special Issue "Control and Enhancement of Quantum Coherence in Nanostructured Materials"

A special issue of Condensed Matter (ISSN 2410-3896).

Deadline for manuscript submissions: closed (31 May 2018)

Special Issue Editors

Guest Editor
Prof. Andrea Perali

Università di Camerino, Scuola del Farmaco e Divisione di Fisica, Edificio di Fisica, Via Madonna delle Carceri 9, 62032 Camerino (MC), Italy
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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
Guest Editor
Dr. Alessandro Ricci

Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg, Germany
Website | E-Mail
Interests: inhomogeneous high temperature superconductors; complex geometries in quantum materials; nanoscale phase separation; charge-density-waves; spin-density-waves; quantum materials dynamic

Special Issue Information

Dear Colleagues,

The problem of controlling and enhancing the properties of quantum coherent phenomena in nanostructured materials is attracting a large research effort, involving international research collaborations with cross-topic character. In particular, the understanding and control of superconductivity at the nanoscale and in complex configurations is a central issue in condensed matter physics, but after several decades of work the role of competition/cooperation of charge, spin and lattice orders in these systems is still not well established. Recently, a renewed excitement followed results showing important effects of complex geometries in the quantum coherence mechanism that govern magnetism, ferroelectricity and superconductivity in hybrid systems and other novel nanostructures, that can drive electron–hole superfluidity in layered heterostructures. The goal of this special issue is to collect state of the art results (from experiments, theory and simulations) around this problem and to provide a view on how the control and enhancement of quantum coherence in nanostructured materials can be converted into new technological applications and quantum devices.

Key topics include:

  • control and enhancement of superconductivity at the nanoscale;
  • competition/cooperation of charge, spin and lattice orders in quantum materials;
  • effects of complex geometries in the quantum coherence;
  • magnetism, ferroelectricity, and superconductivity in hybrid systems and other novel nanostructures;
  • electron–hole superfluidity in layered heterostructures (graphene, GaAs and other systems);
  • quantum devices for technological applications: nano-squids, single-photon detectors, qubits, metrology, switches.

Prof. Dr. Andrea Perali
Dr. Alessandro Ricci
Guest Editors

Manuscript Submission Information

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Keywords

  • superconductivity at the nanoscale
  • charge
  • spin and lattice orders
  • complex geometries
  • hybrid magnetic
  • ferroelectric
  • superconducting systems
  • electron-hole superfluidity
  • quantum devices

Published Papers (8 papers)

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Research

Open AccessArticle Microscopic Linear Response Theory of Spin Relaxation and Relativistic Transport Phenomena in Graphene
Condens. Matter 2018, 3(2), 18; https://doi.org/10.3390/condmat3020018
Received: 23 April 2018 / Revised: 17 May 2018 / Accepted: 18 May 2018 / Published: 22 May 2018
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Abstract
We present a unified theoretical framework for the study of spin dynamics and relativistic transport phenomena in disordered two-dimensional Dirac systems with pseudospin-spin coupling. The formalism is applied to the paradigmatic case of graphene with uniform Bychkov-Rashba interaction and shown to capture spin
[...] Read more.
We present a unified theoretical framework for the study of spin dynamics and relativistic transport phenomena in disordered two-dimensional Dirac systems with pseudospin-spin coupling. The formalism is applied to the paradigmatic case of graphene with uniform Bychkov-Rashba interaction and shown to capture spin relaxation processes and associated charge-to-spin interconversion phenomena in response to generic external perturbations, including spin density fluctuations and electric fields. A controlled diagrammatic evaluation of the generalized spin susceptibility in the diffusive regime of weak spin-orbit interaction allows us to show that the spin and momentum lifetimes satisfy the standard Dyakonov-Perel relation for both weak (Gaussian) and resonant (unitary) nonmagnetic disorder. Finally, we demonstrate that the spin relaxation rate can be derived in the zero-frequency limit by exploiting the SU(2) covariant conservation laws for the spin observables. Our results set the stage for a fully quantum-mechanical description of spin relaxation in both pristine graphene samples with weak spin-orbit fields and in graphene heterostructures with enhanced spin-orbital effects currently attracting much attention. Full article
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Open AccessArticle Electronic Properties of Curved Few-Layers Graphene: A Geometrical Approach
Condens. Matter 2018, 3(2), 11; https://doi.org/10.3390/condmat3020011
Received: 19 December 2017 / Revised: 21 March 2018 / Accepted: 30 March 2018 / Published: 5 April 2018
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Abstract
We show the presence of non-relativistic Lévy-Leblond fermions in flat three- and four-layers graphene with AB stacking, extending the results obtained in Cariglia et al. 2017 for bilayer graphene. When the layer is curved we obtain a set of equations for Galilean fermions
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We show the presence of non-relativistic Lévy-Leblond fermions in flat three- and four-layers graphene with AB stacking, extending the results obtained in Cariglia et al. 2017 for bilayer graphene. When the layer is curved we obtain a set of equations for Galilean fermions that are a variation of those of Lévy-Leblond with a well defined combination of pseudospin, and that admit Lévy-Leblond spinors as solutions in an approriate limit. The local energy of such Galilean fermions is sensitive to the intrinsic curvature of the surface. We discuss the relationship between two-dimensional pseudospin, labelling layer degrees of freedom, and the different energy bands. For Lévy-Leblond fermions, an interpretation is given in terms of massless fermions in an effective 4D spacetime, and in this case the pseudospin is related to four dimensional chirality. A non-zero energy band gap between conduction and valence electronic bands is obtained for surfaces with positive curvature. Full article
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Open AccessFeature PaperArticle Nanoscale Phase Separation and Lattice Complexity in VO2: The Metal–Insulator Transition Investigated by XANES via Auger Electron Yield at the Vanadium L23-Edge and Resonant Photoemission
Condens. Matter 2017, 2(4), 38; https://doi.org/10.3390/condmat2040038
Received: 28 September 2017 / Revised: 27 November 2017 / Accepted: 7 December 2017 / Published: 10 December 2017
Cited by 2 | PDF Full-text (1465 KB) | HTML Full-text | XML Full-text
Abstract
Among transition metal oxides, VO2 is a particularly interesting and challenging correlated electron material where an insulator to metal transition (MIT) occurs near room temperature. Here we investigate a 16 nm thick strained vanadium dioxide film, trying to clarify the dynamic behavior
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Among transition metal oxides, VO2 is a particularly interesting and challenging correlated electron material where an insulator to metal transition (MIT) occurs near room temperature. Here we investigate a 16 nm thick strained vanadium dioxide film, trying to clarify the dynamic behavior of the insulator/metal transition. We measured (resonant) photoemission below and above the MIT transition temperature, focusing on heating and cooling effects at the vanadium L23-edge using X-ray Absorption Near-Edge Structure (XANES). The vanadium L23-edges probe the transitions from the 2p core level to final unoccupied states with 3d orbital symmetry above the Fermi level. The dynamics of the 3d unoccupied states both at the L3- and at the L2-edge are in agreement with the hysteretic behavior of this thin film. In the first stage of the cooling, the 3d unoccupied states do not change while the transition in the insulating phase appears below 60 °C. Finally, Resonant Photoemission Spectra (ResPES) point out a shift of the Fermi level of ~0.75 eV, which can be correlated to the dynamics of the 3d// orbitals, the electron–electron correlation, and the stability of the metallic state. Full article
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Open AccessArticle Role of H Distribution on Coherent Quantum Transport of Electrons in Hydrogenated Graphene
Condens. Matter 2017, 2(4), 37; https://doi.org/10.3390/condmat2040037
Received: 7 October 2017 / Revised: 28 November 2017 / Accepted: 29 November 2017 / Published: 4 December 2017
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Abstract
Using quantum mechanical methods, in the framework of non-equilibrium Green’s function (NEGF) theory, we discuss the effects of the real space distribution of hydrogen adatoms on the electronic properties of graphene. Advanced methods for the stochastic process simulation at the atomic resolution are
[...] Read more.
Using quantum mechanical methods, in the framework of non-equilibrium Green’s function (NEGF) theory, we discuss the effects of the real space distribution of hydrogen adatoms on the electronic properties of graphene. Advanced methods for the stochastic process simulation at the atomic resolution are applied to generate system configurations in agreement with the experimental realization of these systems as a function of the process parameters (e.g., temperature and hydrogen flux). We show how these Monte Carlo (MC) methods can achieve accurate predictions of the functionalization kinetics in multiple time and length scales. The ingredients of the overall numerical methodology are highlighted: the ab initio study of the stability of key configurations, on lattice matching of the energetic configuration relation, accelerated algorithms, sequential coupling with the NEGF based on calibrated Hamiltonians and statistical analysis of the transport characteristics. We demonstrate the benefit to this coupled MC-NEGF method in the study of quantum effects in manipulated nanosystems. Full article
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Open AccessArticle Enhanced Manifold of States Achieved in Heterostructures of Iron Selenide and Boron-Doped Graphene
Condens. Matter 2017, 2(4), 34; https://doi.org/10.3390/condmat2040034
Received: 5 September 2017 / Revised: 17 October 2017 / Accepted: 25 October 2017 / Published: 29 October 2017
Cited by 2 | PDF Full-text (4444 KB) | HTML Full-text | XML Full-text
Abstract
Enhanced superconductivity is sought by employing heterostructures composed of boron-doped graphene and iron selenide. Build-up of a composite manifold of near-degenerate noninteracting states formed by coupling top-of-valence-band states of FeSe to bottom-of-conduction-band states of boron-doped graphene is demonstrated. Intra- and intersubsystem excitons are
[...] Read more.
Enhanced superconductivity is sought by employing heterostructures composed of boron-doped graphene and iron selenide. Build-up of a composite manifold of near-degenerate noninteracting states formed by coupling top-of-valence-band states of FeSe to bottom-of-conduction-band states of boron-doped graphene is demonstrated. Intra- and intersubsystem excitons are explored by means of density functional theory in order to articulate a normal state from which superconductivity may emerge. The results are discussed in the context of electron correlation in general and multi-band superconductivity in particular. Full article
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Open AccessArticle X-Rays Writing/Reading of Charge Density Waves in the CuO2 Plane of a Simple Cuprate Superconductor
Condens. Matter 2017, 2(3), 26; https://doi.org/10.3390/condmat2030026
Received: 4 July 2017 / Revised: 2 August 2017 / Accepted: 8 August 2017 / Published: 11 August 2017
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Abstract
It is now well established that superconductivity in cuprates competes with charge modulations giving an electronic phase separation at nanoscale. More specifically, superconducting electronic current takes root in the available free space left by electronic charge ordered domains, called charge density wave (CDW)
[...] Read more.
It is now well established that superconductivity in cuprates competes with charge modulations giving an electronic phase separation at nanoscale. More specifically, superconducting electronic current takes root in the available free space left by electronic charge ordered domains, called charge density wave (CDW) puddles. This means that CDW domain arrangement plays a fundamental role in the mechanism of high temperature superconductivity in cuprates. Here we report about the possibility of controlling the population and spatial organization of the charge density wave puddles in a single crystal La2CuO4+y through X-ray illumination and thermal treatments. We apply a pump-probe method—based on X-ray illumination as a pump and X-ray diffraction as a probe—setting a writing/reading procedure of CDW puddles. Our findings are expected to allow new routes for advanced design and manipulation of superconducting pathways in new electronics. Full article
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Open AccessArticle Goldstone and Higgs Hydrodynamics in the BCS–BEC Crossover
Condens. Matter 2017, 2(2), 22; https://doi.org/10.3390/condmat2020022
Received: 23 April 2017 / Revised: 7 June 2017 / Accepted: 7 June 2017 / Published: 20 June 2017
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Abstract
We discuss the derivation of a low-energy effective field theory of phase (Goldstone) and amplitude (Higgs) modes of the pairing field from a microscopic theory of attractive fermions. The coupled equations for Goldstone and Higgs fields are critically analyzed in the Bardeen–Cooper–Schrieffer (BCS)-to-Bose–Einstein
[...] Read more.
We discuss the derivation of a low-energy effective field theory of phase (Goldstone) and amplitude (Higgs) modes of the pairing field from a microscopic theory of attractive fermions. The coupled equations for Goldstone and Higgs fields are critically analyzed in the Bardeen–Cooper–Schrieffer (BCS)-to-Bose–Einstein condensate (BEC) crossover—both in three spatial dimensions and in two spatial dimensions. The crucial role of pair fluctuations is investigated, and the beyond-mean-field Gaussian theory of the BCS–BEC crossover is compared with available experimental data of the two-dimensional ultracold Fermi superfluid. Full article
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Open AccessArticle Inverse Spin Galvanic Effect in the Presence of Impurity Spin-Orbit Scattering: A Diagrammatic Approach
Condens. Matter 2017, 2(2), 17; https://doi.org/10.3390/condmat2020017
Received: 31 March 2017 / Revised: 2 May 2017 / Accepted: 2 May 2017 / Published: 11 May 2017
Cited by 5 | PDF Full-text (874 KB) | HTML Full-text | XML Full-text
Abstract
Spin-charge interconversion is currently the focus of intensive experimental and theoretical research both for its intrinsic interest and for its potential exploitation in the realization of new spintronic functionalities. Spin-orbit coupling is one of the key microscopic mechanisms to couple charge currents and
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Spin-charge interconversion is currently the focus of intensive experimental and theoretical research both for its intrinsic interest and for its potential exploitation in the realization of new spintronic functionalities. Spin-orbit coupling is one of the key microscopic mechanisms to couple charge currents and spin polarizations. The Rashba spin-orbit coupling in a two-dimensional electron gas has been shown to give rise to the inverse spin galvanic effect, i.e., the generation of a non-equilibrium spin polarization by a charge current. Whereas the Rashba model may be applied to the interpretation of experimental results in many cases, in general, in a given real physical system, spin-orbit coupling also occurs due to other mechanisms such as Dresselhaus bulk inversion asymmetry and scattering from impurities. In this work, we consider the inverse spin galvanic effect in the presence of Rashba, Dresselhaus and impurity spin-orbit scattering. We find that the size and form of the inverse spin galvanic effect is greatly modified by the presence of the various sources of spin-orbit coupling. Indeed, spin-orbit coupling affects the spin relaxation time by adding the Elliott–Yafet mechanism to the Dyakonov–Perel, and, furthermore, it changes the non-equilibrium value of the current-induced spin polarization by introducing a new spin generation torque. We use a diagrammatic Kubo formula approach to evaluate the spin polarization-charge current response function. We finally comment about the relevance of our results for the interpretation of experimental results. Full article
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