[Paper Review] Programming Correlated Magnetic States via Gate Controlled Moiré Geometry

Eric Anderson, Feng‐Ren Fan+7 more|arXiv (Cornell University)|Mar 29, 2023

Magnetic properties of thin films9 citations

TL;DR

The paper demonstrates in-situ gate switching between honeycomb and triangular moiré lattices in R-stacked MoTe2 bilayers, enabling switchable magnetic exchange interactions and tunable magnetic states.

ABSTRACT

Understanding quantum many-body systems is at the heart of condensed matter physics. The ability to control the underlying lattice geometry of a system, and thus its many-body interactions, would enable the realization of and transition between emergent quantum ground states. Here, we report in-situ gate switching between honeycomb and triangular lattice geometries of an electron many-body Hamiltonian in R-stacked MoTe2 moiré bilayers, resulting in switchable magnetic exchange interactions. At zero electric field, we observe a correlated ferromagnetic insulator near one hole per moiré unit cell (ν=-1), i.e., a quarter-filled honeycomb lattice, with a widely tunable Curie temperature up to 14K. Fully polarizing layer pseudospin via electric field switches the system into a half-filled triangular lattice with antiferromagnetic interactions. Further doping this layer-polarized superlattice introduces carriers into the empty layer, tuning the antiferromagnetic exchange interaction back to ferromagnetic. Our work demonstrates R-stacked MoTe2 moirés to be a new laboratory for engineering correlated states with nontrivial topology.

Motivation & Objective

• Motivate control of lattice geometry to realize and switch between emergent quantum ground states in correlated electron systems.
• Demonstrate gate-tunable transitions between different moiré lattice geometries (honeycomb vs. triangular) in R-stacked MoTe2 bilayers.
• Characterize how lattice geometry and layer polarization affect magnetic exchange interactions and correlated insulating behavior.

Proposed method

• Fabricate and study R-stacked MoTe2 moiré bilayers under in-situ gate control.
• Observe magnetic states and exchange interactions as a function of filling and electric field.
• Switch lattice geometry by polarizing layer pseudospin with an applied electric field.
• Tune magnetic interactions by moving carriers between layers through gating and doping.

Experimental results

Research questions

• RQ1 Can gate control switch the effective moiré lattice geometry from honeycomb to triangular in a moiré bilayer?
• RQ2 How do lattice geometry and layer polarization influence magnetic exchange interactions (FM vs AFM) in the system?
• RQ3 What is the relationship between carrier filling, gate-induced polarization, and the resulting magnetic state?
• RQ4 Can gate-induced changes in the moiré geometry enable reversible control of correlated magnetic states?

Key findings

• At zero electric field, the system exhibits a correlated ferromagnetic insulator near one hole per moiré unit cell, with a tunable Curie temperature up to 14 K.
• Fully polarizing the layer pseudospin via an electric field switches the system to a half-filled triangular lattice with antiferromagnetic interactions.
• Further doping the layer-polarized superlattice introduces carriers into the empty layer and tunes the antiferromagnetic exchange back toward ferromagnetic.
• These results establish R-stacked MoTe2 moirés as a platform for engineering correlated states with nontrivial topology via gate control.