Superconductivity from doping symmetric mass generation insulators: application to La3Ni2O7 under pressure

Abstract

Abstract We investigate the bilayer nickelates as a platform to realize the symmetric mass generation (SMG) insulator, a featureless Mott insulator that arises due to the Lieb-Schultz-Mattis (LSM) anomaly cancellation in bilayer spin-1/2 lattice systems. Through a single-orbital bilayer square lattice model involving intralayer hopping t and interlayer superexchange interaction J , we demonstrate the emergence of high-temperature superconductivity (SC) upon doping the SMG insulator. The SC phase features s -wave interlayer spin-singlet pairing and exhibits a crossover between the Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensation (BEC) limits by tuning the J / t ratio. We estimate the SC transition temperature T c from both the weak and strong coupling limits at the mean-field level. Our findings offer insights into the experimentally observed decrease in T c with pressure and the strange metal behavior above T c . Additionally, we propose that both Ni $$3{d}_{{z}^{2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3</mml:mn> <mml:msub> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> and $$3{d}_{{x}^{2}-{y}^{2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3</mml:mn> <mml:msub> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>−</mml:mo> <mml:msup> <mml:mrow> <mml:mi>y</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> orbitals can exhibit superconductivity in La 3 Ni 2 O 7 under pressure, but their T c should vary in opposite ways under doping. This characteristic difference suggests a potential experimental pathway to identify which electronic orbital plays the principal role in the formation of superconductivity in this system.