Infrared Investigation of the Charge Ordering Pattern in the Organic Spin Ladder Candidate (DTTTF)2Cu(mnt)2

TL;DR

This study uses infrared spectroscopy to analyze the charge ordering in (DTTTF)2Cu(mnt)2, providing evidence that supports a zigzag ladder model over a rectangular one, and reveals charge asymmetry within molecules.

Contribution

It distinguishes between two competing ladder models in (DTTTF)2Cu(mnt)2 using infrared response, favoring the zigzag model and identifying intramolecular charge asymmetry.

Findings

Distortion below 235 K indicates a doubling along b.

Transverse distortion rules out the rectangular ladder model.

Intramolecular distortions cause on-site charge asymmetry.

Abstract

We measured the variable temperature infrared response of the spin ladder candidate (DTTTF)2Cu(mnt)2 in order to distinguish between two competing ladder models, rectangular versus zigzag, proposed for this family of materials. The distortion along the stack direction below 235 K is consistent with a doubling along b through the metal-insulator transition. While this would agree with either of the ladder models, the concomitant transverse distortion rules out the rectangular ladder model and supports the zigzag scenario. Intramolecular distortions within the DTTTF building block molecule also give rise to on-site charge asymmetry.