High-temperature superconductivity from kinetic energy

TL;DR

This paper demonstrates that high-temperature superconductivity can arise solely from kinetic energy effects in a simple lattice model, challenging the traditional attraction-based understanding of superconductivity.

Contribution

The study introduces a kinetic energy-driven superconductivity model, showing high pairing gaps and phase stiffness increase with doping, and connects it to realistic bilayer materials.

Findings

Superconductivity can originate from kinetic energy without net attraction.

Pairing gaps exceed 1.5 times the hopping parameter $t$.

Potential for high critical temperatures approaching 500 K.

Abstract

Superconductivity is usually assumed to arise from attractive interaction. In this work we show that strong pairing is possible soley from kinetic energy even without a net attraction. We demonstrate a high-temperature kinetic superconductor in a simple lattice model with nearest-neighbor hopping ($t$) projected onto a constrained Hilbert space, analogous to the $t$-$J$ model with $J=0$, where kinetic magnetism has been previously studied. Using density matrix renormalization group (DMRG) on cylinders up to width $L_y=8$, we find a superconducting ground state exhibiting a key difference from high-$T_c$ cuprates: both the pairing gap and phase stiffness \textit{increase} with doping ($x$). We find pairing gaps, determined from spin and single-electron charge gaps, exceeding $1.5t$. This model can be realized within the double Kondo lattice model, relevant to bilayer nickelates, in the limit of strong inter-layer spin coupling ($J_\perp/t \rightarrow +\infty$) and a balancing inter-layer repulsion ($V$). Importantly, the double Kondo model does not fundamentally restrict $J_\perp/t$, suggesting the potential for high critical temperatures ($T_c$) approaching $0.5t$. While this idealized limit predicts large pairing gaps, we show a smooth connection to the more realistic regime with $J_\perp \sim t$, albeit with a reduced pairing gap of approximately $0.1t$. Assuming $t \sim 10^3$ K in typical solid state systems, our model suggests the exciting possibility of achieving $T_c$ of hundreds of Kelvin. We propose searching for bilayer materials with reduced out-of-plane lattice constants to better approximate the conditions of our ideal model.