Superconductivity in Systems with Arbitrary Interaction Sign

Grzegorz Litak A, Thereza Paiva, Raimundo Dos Santos +2 more

Runyu Ma, Zenghui Fan, Tianxing Ma +1 more

Abstract Recent discovery of high transition temperature superconductivity in La 3 Ni 2 O 7 has sparked renewed theoretical and experimental interests in unconventional superconductivity. It is crucial to understand the influence of various factors on its superconductivity. By refining the determinant quantum Monte Carlo algorithm, we characterize the parameter dependence of the superconducting transition temperature within a bilayer Hubbard model, which is sign-problem-free at arbitrary filling. A striking feature of this model is its similarity to the bilayer nickelate-based superconductor La 3 Ni 2 O 7 , where superconductivity emerges from the bilayer NiO 2 planes. We find that interlayer spin-exchange J is critical to interlayer pairing, and that on-site interaction U contributes negatively to superconductivity at low doping levels but positively at high doping levels. Our findings can provide a reference for the next step in theoretical research on nickelate-based superconductors.

Cristian D. Batista, Gerardo Ortíz

We present the quantum phase diagram of the one-dimensional t- J(z) model for arbitrary spin (integer or half-integer) and sign of the spin-spin interaction J(z), using an exact mapping to a spinless fermion model that can be solved exactly using the Bethe ansatz. We discuss its superconducting phase as a function of hole doping nu. Motivated by the new paradigm of high temperature superconductivity, the stripe phase, we also consider the effect the antiferromagnetic background has on the t- J(z) chain intended to mimic the stripe segments.

Leon N. Cooper

Hong‐Chen Jiang, Shuai A. Chen, Zheng-Yu Weng

The mechanism of superconductivity in a purely interacting electron system has been one of the most challenging issues in condensed matter physics. In the BCS theory, the Landau's Fermi liquid is the ground state of weakly interacting fermions dictated by the fermion sign structure, and the superconducting instability only occurs when an additional pairing force is added. By contrast, as shown by density matrix renormalization group calculation, a quasi-one-dimensional superconducting state (specifically a Luther-Emery state) is an intrinsic ground state of the $t\ensuremath{-}J$ two-leg ladder and four-leg cylinder at finite doping. Such a Luther-Emery state with pairing can be directly turned into a Fermi-gas-like normal state without pairing by merely switching off the phase-string signs hidden in the model via two schemes, which reduce the sign structure to the trivial fermion signs associated with doped holes. It thus demonstrates a new pairing paradigm in a model-doped Mott insulator as due to the generic phase-string sign structure. Finally, as an example, the latter is explicitly shown to lead to a ``stringlike'' pairing force after adiabatically connecting to a strong anisotropic limit of the model.

G. M. Vujčić