scholarly journals Observation of preformed electron-hole Cooper pairs in highly excited ZnO

2012 ◽  
Vol 85 (19) ◽  
Author(s):  
Marijn A. M. Versteegh ◽  
A. J. van Lange ◽  
H. T. C. Stoof ◽  
Jaap I. Dijkhuis
Keyword(s):  
Cooper Pairs ◽  
Electron Hole ◽  
Hole Cooper Pairs

Fano-Resonance Gain by Dephasing Electron–Hole Cooper Pairs in Semiconductors

2012 ◽  
Vol 81 (9) ◽  
pp. 093706 ◽  
Author(s):  
Kenji Kamide ◽  
Masahiro Yoshita ◽  
Hidefumi Akiyama ◽  
Makoto Yamaguchi ◽  
Tetsuo Ogawa
Keyword(s):  
Fano Resonance ◽  
Cooper Pairs ◽  
Electron Hole ◽  
Hole Cooper Pairs

scholarly journals Tunneling and fluctuating electron-hole Cooper pairs in double bilayer graphene

2020 ◽  
Vol 101 (3) ◽  
Author(s):  
Dmitry K. Efimkin ◽  
G. William Burg ◽  
Emanuel Tutuc ◽  
Allan H. MacDonald
Keyword(s):  
Bilayer Graphene ◽  
Cooper Pairs ◽  
Electron Hole ◽  
Hole Cooper Pairs

scholarly journals Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

2021 ◽  
Vol 118 (32) ◽  
pp. e2107874118
Author(s):  
Tommaso Cea ◽  
Francisco Guinea
Keyword(s):  
Fermi Surface ◽  
Coulomb Interaction ◽  
Crucial Role ◽  
Bilayer Graphene ◽  
Combined Effect ◽  
Large Momentum ◽  
Superconducting Gap ◽  
Cooper Pairs ◽  
Electron Hole ◽  
Twisted Bilayer Graphene

The polarizability of twisted bilayer graphene, due to the combined effect of electron–hole pairs, plasmons, and acoustic phonons, is analyzed. The screened Coulomb interaction allows for the formation of Cooper pairs and superconductivity in a significant range of twist angles and fillings. The tendency toward superconductivity is enhanced by the coupling between longitudinal phonons and electron–hole pairs. Scattering processes involving large momentum transfers, Umklapp processes, play a crucial role in the formation of Cooper pairs. The magnitude of the superconducting gap changes among the different pockets of the Fermi surface.

INTRIGUING ROLE OF HOLE-COOPER-PAIRS IN SUPERCONDUCTORS AND SUPERFLUIDS

2008 ◽  
Author(s):  
M. GRETHER ◽  
M. de LLANO ◽  
S. RAMÍREZ ◽  
O. ROJO
Keyword(s):  
Cooper Pairs ◽  
Hole Cooper Pairs

INTRIGUING ROLE OF HOLE-COOPER-PAIRS IN SUPERCONDUCTORS AND SUPERFLUIDS

2008 ◽  
Vol 22 (25n26) ◽  
pp. 4367-4378 ◽  
Author(s):  
M. GRETHER ◽  
M. de LLANO ◽  
S. RAMÍREZ ◽  
O. ROJO
Keyword(s):  
Free Energy ◽  
Helmholtz Free Energy ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Superconducting Transition ◽  
Electron Phonon Interaction ◽  
Bose Einstein ◽  
Hole Cooper Pairs

The role in superconductors of hole-Cooper-pairs (CPs) are examined and contrasted with the more familiar electron-CPs, with special emphasis on their “background” effect in enhancing superconducting transition temperatures Tc — even when electron-CPs drive the transition. Both kinds of CPs are, of course, present at all temperatures. An analogy is drawn between the hole CPs in any many-fermion system with the antibosons in a relativistic ideal Bose gas that appear in substantial numbers only at higher and higher temperatures. Their indispensable role in yielding a lower Helmholtz free energy equilibrium state is established. For superconductors, the problem is viewed in terms of a generalized Bose-Einstein condensation (GBEC) theory that is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that the GBEC theory includes hole CPs as well as electron-CPs — thereby containing as well as further extending BCS theory to higher temperatures with the same weak-coupling electron-phonon interaction parameters. We show that the Helmholtz free energy of both 2e- and 2h-CP pure condensates has a positive second derivative, and are thus stable equilibrium states. Finally, it is conjectured that the role of hole pairs in ultra-cold fermionic atom gases will likely be negligible because the very low densities involved imply a “shallow” Fermi sea.

Two-Electron and Two-Hole Cooper Pairs in Superconductivity

2018 ◽  
Vol 32 (6) ◽  
pp. 1633-1638
Author(s):  
I. Chávez ◽  
L. A. García ◽  
M. Grether ◽  
M. de Llano ◽  
V. V. Tolmachev
Keyword(s):  
Cooper Pairs ◽  
Hole Cooper Pairs

Role of superconducting energy gap in extended BCS-Bose crossover theory

2017 ◽  
Vol 31 (25) ◽  
pp. 1745004 ◽  
Author(s):  
I. Chávez ◽  
L. A. García ◽  
M. de Llano ◽  
M. Grether
Keyword(s):  
Energy Gap ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Number Density ◽  
Superconducting Energy Gap ◽  
Special Cases ◽  
Bose Einstein ◽  
Hole Cooper Pairs ◽  
Theory Of Superconductivity

The generalized Bose–Einstein condensation (GBEC) theory of superconductivity (SC) is briefly surveyed. It hinges on three distinct new ingredients: (i) Treatment of Cooper pairs (CPs) as actual bosons since they obey Bose statistics, in contrast to BCS pairs which do not obey Bose commutation relations; (ii) inclusion of two-hole Cooper pairs (2hCPs) on an equal footing with two-electron Cooper pairs (2eCPs), thus making this a complete boson–fermion (BF) model; and (iii) inclusion in the resulting ternary ideal BF gas with particular BF vertex interactions that drive boson formation/disintegration processes. GBEC subsumes as special cases both BCS (having its 50–50 symmetry of both kinds of CPs) and ordinary BEC theories (having no 2hCPs), as well as the now familiar BCS-Bose crossover theory. We extended the crossover theory with the explicit inclusion of 2hCPs and construct a phase diagram of [Formula: see text] versus [Formula: see text], where [Formula: see text] and [Formula: see text] are the critical and Fermi temperatures, [Formula: see text] is the total number density and [Formula: see text] that of unbound electrons at [Formula: see text]. Also, with this extended crossover one can construct the energy gap [Formula: see text] versus [Formula: see text] for some elemental SCs by solving at least two equations numerically: a gap-like and a number equation. In 50–50 symmetry, the energy gap curve agrees quite well with experimental data. But ignoring 2hCPs altogether leads to the gap curve falling substantially below that with 50–50 symmetry which already fits the data quite well, showing that 2hCPs are indispensable to describe SCs.

BCS-Bose crossover theory extended with hole Cooper pairs

2017 ◽  
Vol 31 (25) ◽  
pp. 1745013 ◽  
Author(s):  
I. Chávez ◽  
L. A. García ◽  
M. de Llano ◽  
M. Grether
Keyword(s):  
Einstein Condensation ◽  
Dimensionless Number ◽  
Cooper Pairs ◽  
Number Density ◽  
Phonon Dynamics ◽  
Perfect Symmetry ◽  
Pure Phases ◽  
Bose Einstein ◽  
Special Case ◽  
Hole Cooper Pairs

Applying the generalized Bose–Einstein condensation (GBEC) formalism, we extend the BCS-Bose crossover theory by explicitly including hole Cooper pairs (2hCPs). From this follows a phase diagram with two pure phases, one with 2hCPs and the other with electron Cooper pairs (2eCPs), plus a mixed phase with arbitrary proportions of 2eCPs and 2hCPs. One has a special-case phase when there is perfect symmetry (i.e., with ideal 50–50 proportions between 2eCPs and 2hCPs). Explicitly including 2hCPs leads to an extended BCS-Bose crossover which predicts [Formula: see text] values for some well-known conventional superconductors (SCs) (i.e., assuming electron–phonon dynamics). These compare reasonably well with experimental data. We compare with experimental [Formula: see text] values for some conventional SCs associated with the new dimensionless number density [Formula: see text] with theoretical curves associated with the extended crossover for the special case of perfect symmetry. They all obey the Bogoliubov et al. upper limit, thus vindicating it.

Sign in / Sign up

Export Citation Format

Share Document