Formation of magnetic moments and resistance upturn at grain boundaries of two-dimensional electron systems

TL;DR

This paper investigates how electronic correlations in two-dimensional systems can lead to magnetic moments at grain boundaries, causing increased resistance at low temperatures, aligning with experimental observations.

Contribution

It demonstrates the formation of magnetic moments at grain boundaries in correlated 2D electron systems using an inhomogeneous Hubbard model and mean-field analysis.

Findings

Magnetic moments form at grain boundaries with strong bond energy variance.

Local magnetic moments influence conductance, creating confined channels.

Resistance increases at low temperatures due to suppressed current correlations.

Abstract

Electronic correlations control the normal state of bulk high-Tc cuprates. Strong correlations also suppress the charge transport through cuprate grain boundaries (GBs). The question then arises if these correlations can produce magnetic states at cuprate GBs. We analyze the formation of local magnetic moments at the GB of a correlated two-dimensional electron systems which is represented by an inhomogeneous Hubbard model. The model Hamiltonian is diagonalized after the implementation of a mean-field decoupling. The formation of local magnetic moments is supported by a sufficiently strong variance in the bond kinetic energies at the GB. Local scattering potentials can assist or suppress the formation of a magnetic GB state, depending on the details of their spacial distribution. Grain boundary induced stripes are formed in the vicinity the GB and decay into the bulk. Moreover, we observe the build-up of conducting channels which are confined by magnetic clusters. The grain boundary resistance increases at decreasing temperatures. This low-temperature behavior is caused by the suppression of current correlations in the state with local magnetic GB moments. The resistance upturn at low temperatures is in qualitative agreement with experiments.