Explanation of Superfluidity Using the Berry Connection for Many-Body Wave Functions

Koizumi, Hiroyasu

doi:10.1007/s10948-020-05438-w

Cited by 20 publications

(37 citation statements)

References 28 publications

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“…It is shown to be identified as A fic . According to our previous work [30], A MB is stabilized by the electron-pairing, meaning that the A fic is stabilized by the electron-pairing; thus, a stable nontrivial A fic necessary fo superconductivity is realized. In Section 6, we succinctly summarize part of our previous work that utilizes the particle-number fixed version of the BCS ground state [30], and conclude the present work by discussing implications for it.…”

Section: Introductionmentioning

confidence: 86%

“…Motivated by the above developments, we have reinvestigated the superfluidity problem in general [30]. Then, we have found that the particle number non-fixed formalism, such as the standard BCS formalism or the Bogoliubov-de Gennes formalism [31,32], can be cast in a particle number fixed formalism if the Berry connection is employed.…”

Section: Introductionmentioning

confidence: 99%

“…The energy reduction is shown to be optimum when the Berry connection is given by A fic = − h 2e ∇χ, and the Meissner effect is realized if the nontrivial A fic is stable. In Section 5, the Berry connection from the many-body wave function [30], A MB , is calculated for the present model. It is shown to be identified as A fic .…”

Section: Introductionmentioning

confidence: 99%

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Possible Occurrence of Superconductivity by the π-flux Dirac String Formation Due to Spin-Twisting Itinerant Motion of Electrons

Koizumi

2020

Symmetry

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We show that the Rashba spin-orbit interaction causes spin-twisting itinerant motion of electrons in metals and realizes the quantized cyclotron orbits of conduction electrons without an external magnetic field. From the view point of the Berry connection, the cause of this quantization is the appearance of a non-trivial Berry connection A fic = − ℏ 2 e ∇ χ ( χ is an angular variable with period 2 π ) that generates π flux (in the units of ℏ = 1 , e = 1 , c = 1 ) inside the nodal singularities of the wave function (a “Dirac string”) along the centers of spin-twisting. Since it has been shown in our previous work that the collective mode of ∇ χ is stabilized by the electron-pairing and generates supercurrent, the π -flux Dirac string created by the spin-twisting itinerant motion will be stabilized by the electron-pairing and produce supercurrent.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

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Possible Occurrence of Superconductivity by the π-flux Dirac String Formation Due to Spin-Twisting Itinerant Motion of Electrons

Koizumi

2020

Symmetry

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“…In some recent studies [32][33][34][35][36], the shortcomings of the standard Eliashberg formalism in explaining some of the fundamental observation related to unconventional superconductivity has been highlighted and alternative formulation for a better theory is proposed. While our particle-particle ladder approximation does not use the standard Eliashberg formalism, it is an important task for future efforts, also for our own approach, to see how these proposed formulations can be adapted for better description of unconventional superconductivity.…”

Section: Methodsmentioning

confidence: 99%

Electronic Origin of Tc in Bulk and Monolayer FeSe

et al. 2021

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FeSe is classed as a Hund’s metal, with a multiplicity of d bands near the Fermi level. Correlations in Hund’s metals mostly originate from the exchange parameter J, which can drive a strong orbital selectivity in the correlations. The Fe-chalcogens are the most strongly correlated of the Fe-based superconductors, with dxy the most correlated orbital. Yet little is understood whether and how such correlations directly affect the superconducting instability in Hund’s systems. By applying a recently developed ab initio theory, we show explicitly the connections between correlations in dxy and the superconducting critical temperature Tc. Starting from the ab initio results as a reference, we consider various kinds of excursions in parameter space around the reference to determine what controls Tc. We show small excursions in J can cause colossal changes in Tc. Additionally we consider changes in hopping by varying the Fe-Se bond length in bulk, in the free standing monolayer M-FeSe, and M-FeSe on a SrTiO3 substrate (M-FeSe/STO). The twin conditions of proximity of the dxy state to the Fermi energy, and the strength of J emerge as the primary criteria for incoherent spectral response and enhanced single- and two-particle scattering that in turn controls Tc. Using c-RPA, we show further that FeSe in monolayer form (M-FeSe) provides a natural mechanism to enhance J. We explain why M-FeSe/STO has a high Tc, whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls Tc in bulk, layers, and interfaces of Hund’s metals by hole pocket and electron screening cloud engineering.

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“…In both cases, in the end, it is possible to describe the superconductor with a 3-band model [25]. For completeness, it is necessary to mention an alternative approach to explain the superconductivity in the iron pnictides based on the appearance of the nontrivial Berry connection [30][31][32].…”

Section: The Modelmentioning

confidence: 99%

Eliashberg Theory of a Multiband Non-Phononic Spin Glass Superconductor

Ummarino

2020

Magnetochemistry

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I solved the Eliashberg equations for a multiband non-phononic s± wave spin-glass superconductor, calculating the temperature dependence of the gaps and of superfluid density. Their behaviors were revealed to be unusual: showing non-monotonic temperature dependence and reentrant superconductivity. By considering particular input parameters values that could describe the iron pnictide EuFe2(As1−xPx)2, a rich and complex phase diagram arises, with two different ranges of temperature in which superconductivity appears.

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Explanation of Superfluidity Using the Berry Connection for Many-Body Wave Functions

Cited by 20 publications

References 28 publications

Possible Occurrence of Superconductivity by the π-flux Dirac String Formation Due to Spin-Twisting Itinerant Motion of Electrons

Possible Occurrence of Superconductivity by the π-flux Dirac String Formation Due to Spin-Twisting Itinerant Motion of Electrons

Electronic Origin of Tc in Bulk and Monolayer FeSe

Eliashberg Theory of a Multiband Non-Phononic Spin Glass Superconductor

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