Unveiling the Superconducting Mechanism of Ba0.51K0.49BiO3

Abstract

The mechanism of high superconducting transition temperatures (T_{c}) in bismuthates remains under debate despite more than 30 years of extensive research. Our angle-resolved photoemission spectroscopy studies on Ba_{0.51}K_{0.49}BiO_{3} reveal an unexpectedly 34% larger bandwidth than in conventional density functional theory calculations. This can be reproduced by calculations that fully account for long-range Coulomb interactions-the first direct demonstration of bandwidth expansion due to the Fock exchange term, a long-accepted and yet uncorroborated fundamental effect in many body physics.Furthermore, we observe an isotropic superconducting gap with 2Δ_{0}/k_{B}T_{c}=3.51±0.05, and strong electron-phonon interactions with a coupling constant λ∼1.3±0.2. These findings solve a long-standing mystery-Ba_{0.51}K_{0.49}BiO_{3} is an extraordinary Bardeen-Cooper-Schrieffer superconductor, where long-range Coulomb interactions expand the bandwidth, enhance electron-phonon coupling, and generate the high T_{c}. Such effects will also be critical for finding new superconductors.

Toward a predictive theory of correlated materials

“…This correlation-enhanced electron-phonon coupling provides a natural explanation for the superconductivity in this and related systems. Recent photoemission experiments have confirmed the main predictions of the theory (70).…”

Strong- to weak-coupling superconductivity in high- Tc bismuthates: Revisiting the phase diagram via μSR

“…Our suc-cessful systematic synthesis of Ba 1−x K x BiO 3 samples with different K-doping values, made it possible to reliably construct the Ba 1−x K x BiO 3 phase diagram using different techniques and to confirm once more (this time over the whole phase diagram, and not only for one composition, as in Ref. 14 ), the conventional nature of its superconductivity.…”

“…The polarons then bind into Cooper pairs through a retarded electron-phonon interaction with the low-energy phonon modes [11][12][13] . Recently, a large electron-phonon coupling constant λ ep > 1, strong enough to account for the high T c in Ba 1−x K x BiO 3 , has been experimentally and theoretically proposed 14,15 . An alternative mechanism suggests that the pairing is mediated by high-energy charge excitations 16 .…”

Топологические Лазерно Индуцированные Квантовые Состояния В Нанокластерных Структурах: Фундаментальные Эффекты И Возможные Применения (Электрофизика И Оптика)

“…Если говорить о тенденциях в проблеме высокотемпературной сверхпроводимости, то связанные (куперовские) электронные пары в нанокластерных системах определяются новыми механизмами электронной когерентной связи. Она может возникать по нескольким причинам, включая фононные, экситонные/поляритонноэкситонные, магнонные и другие взаимодействия с квазичастицами, а также из-за размерных эффектов [33][34][35][36][37][38][39][40][41]. В последнем случае речь идет о структурах в топологически неоднородной среде в условиях пространственного распределения пустот между заряженными кластерами с различными размерами.…”