Fermi-Bose Mixtures and BCS-BEC Crossover in High-Tc Superconductors

Kagan, M. Yu.; Bianconi, A.

doi:10.3390/condmat4020051

Cited by 29 publications

(16 citation statements)

References 195 publications

(306 reference statements)

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“…For the cuprates specifically, effects of hydrostatic and uniaxial pressure for multi-band models [1] or microstrains [27] have also been discussed. For attractively interacting two-band systems, the effects of the second band have been studied with Nozières-Schmitt-Rink formalism [28], BCS pairing Hamiltonian [29], and/or in the context of the BCS-BEC crossover [30] or Lifshitz transitions [31]. Thus a future problem is how these would apply to the flat-band cases.…”

Section: Discussionmentioning

confidence: 99%

Theoretical Possibilities for Flat Band Superconductivity

Aoki

2020

J Supercond Nov Magn

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One novel arena for designing superconductors with high T C is the flat-band systems. A basic idea is that flat bands, arising from quantum mechanical interference, give unique opportunities for enhancing T C with (i) many pair-scattering channels between the dispersive and flat bands, and (ii) an even more interesting situation when the flat band is topological and highly entangled. Here we compare two routes, which comprise a multi-band system with a flat band coexisting with dispersive ones, and a one-band case with a portion of the band being flat. Superconductivity can be induced in both cases when the flat band or portion is "incipient" (close to, but away from, the Fermi energy). Differences are, for the multi-band case, we can exploit large entanglement associated with topological states, while for the one-band case a transition between different (d and p) wave pairings can arise. These hint at some future directions.

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Section: Discussionmentioning

confidence: 99%

Theoretical Possibilities for Flat Band Superconductivity

Aoki

2020

J Supercond Nov Magn

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“…Moreover, today there is a high interest on electron-phonon interaction [43,95] and on lattice heterogeneity as proposed by Alex [120]. A new rapidly developing field is at the crossing point between the research a) on mixed boson-fermion systems in ultracold gases [121] b) shape resonances in multigap superconductivity near Lifshitz transitions in complex heterostructures and c) percolation of filamentary superconductivity in a granular landscape showing mesoscale correlated disorder [105][106] after the accumulated information on complex spatial distribution of defects, strain fluctuations, SDW puddles [122] after many works made in these last ten years [123][124][125][126][127].…”

Section: Discussionmentioning

confidence: 99%

Superconductivity in Quantum Complex Matter: the Superstripes Landscape

Bianconi

2020

J Supercond Nov Magn

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While in XX century the theory of superconductivity has focused on a homogeneous metal with a rigid lattice which can be reduced to a single effective conduction band in the dirty limit. Today in the XXI century, the physics of superconductivity is focusing on complexity of quantum matter where novel quantum functionalities with lattice inhomogeneity at nanoscale (between 1 nm and 100 nm) and at mesoscopic scale (in the range 100-10000 nm), where the electronic structure need to be described by multiple Fermi surfaces and multiple gaps in the superconducting phase in the clean limit. The present issue of Journal of superconductivity and Novel magnetism collects papers presented at the

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“…Finally, we have reported new information on the quantum complex scenario near criticality in nickelates which opens new venues to applications and developments of new magnetic and electronic devices. In fact, in the proximity of a topological Lifshitz transition it is possible to control novel macroscopic functionalities by a weak external stimulus such as stress [25][26][27][28][29][30][31][32][33][34][35][36][71][72][73][74][75], current density [64,65] or photon illumination dose [5,[76][77][78][79].…”

Section: Discussionmentioning

confidence: 99%

Direct Visualization of Spatial Inhomogeneity of Spin Stripes Order in La1.72Sr0.28NiO4

et al. 2019

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In several strongly correlated electron systems, the short range ordering of defects, charge and local lattice distortions are found to show complex inhomogeneous spatial distributions. There is growing evidence that such inhomogeneity plays a fundamental role in unique functionality of quantum complex materials. La 1.72 Sr 0.28 NiO 4 is a prototypical strongly correlated perovskite showing spin stripes order. In this work we present the spatial distribution of the spin order inhomogeneity by applying micro X-ray diffraction to La 1.72 Sr 0.28 NiO 4 , mapping the spin-density-wave order below the 120 K onset temperature. We find that the spin-density-wave order shows the formation of nanoscale puddles with large spatial fluctuations. The nano-puddle density changes on the microscopic scale forming a multiscale phase separation extending from nanoscale to micron scale with scale-free distribution. Indeed spin-density-wave striped puddles are disconnected by spatial regions with negligible spin-density-wave order. The present work highlights the complex spatial nanoscale phase separation of spin stripes in nickelate perovskites and opens new perspectives of local spin order control by strain.Condens. Matter 2019, 4, 77 2 of 10 the stripes phases have been the object of interest for decades [1][2][3], while in this last decade new scanning X-ray diffraction methods have been developed due to the ability to focus X-ray synchrotron radiation to micron and sub-micron spots. These methods have made it possible to obtain visualization of spatial topological inhomogeneity of charge density wave order in doped cuprate perovskites [4,5]. Short range generalized Wigner charge density waves have been found to be spatially inhomogeneous with the formation of "striped charge puddles" anti-correlated with competing puddles of "striped dopants rich clusters" [4][5][6]. These experimental results have opened a new era in the long-standing research of complexity in doped strongly correlated perovskites, since they have falsified popular stripes theories which for decades have assumed a homogeneous spatial distribution of spin stripes and charge-stripes. In this work we focus on the spin stripes phase in doped nickelate perovskites. In order to determine the role that the spatial distribution of ordered phases in cuprates plays for the superconductivity, it is instructive to study a non-superconducting reference system like the layered nickelates [7]. Keeping this idea in mind, we push forward the investigation of the spatial distribution of spin-density-wave stripes ordering (SDW-stripes) in La 2-x Sr x NiO 4 nickelates.It is well known that spin stripes appear in layered nickelates [7] in the doping interval 0.15 ≤ x ≤ 0.5 [7]. In the doping range 0.25 < x < 0.3 magnetic stripes and charge stripes can be easily investigated separately. In La 2-x Sr x NiO 4 the spin-order scattering exhibits peaks in the k-space for (1−ε; 0; l) with odd and even l, whereas charge-order scattering always peaks at (2ε; 0; l) with odd l, [7,8] where t...

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Fermi-Bose Mixtures and BCS-BEC Crossover in High-Tc Superconductors

Cited by 29 publications

References 195 publications

Theoretical Possibilities for Flat Band Superconductivity

Theoretical Possibilities for Flat Band Superconductivity

Superconductivity in Quantum Complex Matter: the Superstripes Landscape

Direct Visualization of Spatial Inhomogeneity of Spin Stripes Order in La1.72Sr0.28NiO4

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