Strong pairing from a small Fermi surface beyond weak coupling: Application to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>La</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mi>Ni</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>7</mml:mn> </mml:msub> </mml:mrow> </mml:math>
Hui Yang, Hanbit Oh, Yahui Zhang
Abstract
One of the central questions in condensed matter theory is: can a small Fermi surface phase, which violates the Luttinger theorem, give rise to superconductivity? This paper offers an answer to the question by developing an effective model with the large interlayer exchange coupling ${J}_{\ensuremath{\perp}}$ limit in the bilayer model. The model is dubbed the ESD $t$-$J$ model with six states: one empty state(E), four single states (S), and one double state(D). The authors find that in the normal state with a small doping regime ($x$=0), the small Fermi surface manifests without symmetry breaking or fractionalization, while the conventional Fermi surface appears at the $x$=1 limit. Moreover, the superconducting phase at low temperatures is different from the cuprate. The author predicts a doping-tuned BCS to BEC crossover from Feshbach resonance accompanied by superconducting domes near $x\ensuremath{\sim}0.5$. The theory can be applied to the recently observed high-${T}_{c}$ superconductor La${}_{3}$Ni${}_{2}$O${}_{7}$ under pressure.