Defect Control via Cu Enrichment Enhances Multifunctional Properties in the Polar Semiconductor Cu1+xMn1-ySiTe3

TL;DR

This study shows that increasing Cu content in Cu1-xMn1+ySiTe3 reduces stacking faults, enhances nonlinear optical response, and maintains magnetic order, enabling tunable multifunctional properties in this polar semiconductor.

Contribution

It demonstrates that Cu enrichment suppresses crystal defects and improves multifunctional properties, providing a new approach to design tunable magnetic polar semiconductors.

Findings

Cu-enriched samples are nearly stacking-fault-free.

Enhanced second-harmonic generation response in Cu-enriched samples.

Retention of antiferromagnetic order with a spin-flop transition in Cu-enriched samples.

Abstract

Polar materials have recently attracted significant interest due to their rich multifunctional properties. The chalcogenide polar semiconductor Cu1-xMn1+ySiTe3 (Cu-deficient) is an emerging multiferroic system in which electric polarization is coupled to magnetization. However, its macroscopic ferroelectric polarization is strongly suppressed due to the presence of a high density of stacking faults. In this work, we demonstrate that these crystal defects, likely originating from non-stoichiometry, can be substantially reduced by increasing the Cu content. Cu-enriched samples, Cu1+xMn1-ySiTe3, crystallize in a noncentrosymmetric monoclinic structure (space group Pm) as the Cu-deficient counterpart but show a nearly stacking-fault-free phase, which is attributed to the emergence of an interstitial site. Consequently, the Cu-enriched samples show a pronounced enhancement of the second-harmonic generation (SHG) response compared to Cu-deficient compositions. Magnetically, the Cu-enriched crystals retain long-range antiferromagnetic order with a Neel temperature of TN ~ 33 K without a glassy state but manifest a distinct spin-flop transition along the polar b-axis that is absent in the Cu-deficient compositions. Furthermore, the electronic ground state evolves from insulating to doped semiconducting behavior upon Cu enrichment. Together, these results establish this material system as a unique and versatile platform for elucidating the interplay among composition, crystal defects, and multifunctional properties, offering a route to design magnetic polar systems with tunable quantum functionalities.