# Searching for an Exotic Spin-Dependent Interaction between Electrons at the Nanometer Scale with Molecular Rulers

## TL;DR

This study uses molecular rulers with adjustable electron spins to set new, more stringent bounds on exotic spin-dependent interactions at nanometer scales, improving previous limits significantly.

## Contribution

It introduces a novel method employing molecular rulers to constrain electron spin interactions at nanometer distances, achieving more precise bounds than prior experiments.

## Key findings

- Established new upper bounds on exotic dipole-dipole interactions between electrons.
- Improved the laboratory limit at 200 nm by a factor of 20.
- Demonstrated the feasibility of molecular rulers for probing fundamental spin interactions.

## Abstract

We propose that a type of molecular rulers, which contains two electron spins with precisely adjustable distance by varying the length of the shape-persistent polymer chains, can be utilized to constrain the axial-vector mediated interaction between electron spins at the nanometer scale. With measurements of the coupling strengths between two electron spins within different molecular rulers, an improved laboratory bound of exotic dipole-dipole interaction between electrons is established within the force range from 3 to 220 nm. The upper bound of the coupling $g_A^e g_A^e/4\pi\hbar c $ at 200 nm is $|g_A^e g_A^e/4\pi\hbar c| \leq 4.9\times10^{-13}$, which is about 20 times more stringent than previous limits.