Two-gap to Single-gap Transition and Two-dome-like Superconductivity in Alkali-Metal Intercalated Bilayer PdTe2

TL;DR

This study uses first-principles calculations to show how alkali-metal intercalation and strain influence superconductivity and electronic topology in bilayer PdTe2, revealing a two-gap to single-gap transition and two-dome Tc behavior.

Contribution

It uncovers the effects of alkali-metal intercalation and strain on superconductivity, gap structure, and topology in bilayer PdTe2, providing insights for tuning its properties.

Findings

Intercalation boosts Tc from 1.4 K to up to 13.5 K.

Lithium induces a two-gap state, larger alkali metals lead to single-gap.

Strain causes a two-dome Tc evolution and modifies band structure.

Abstract

PdTe2 has been synthesized with controllable thickness down to the monolayer limit. Based on first-principles calculations within the fully anisotropic Migdal-Eliashberg framework, this work reveals that alkali-metal intercalation markedly enhances the weak superconductivity of bilayer PdTe2, boosting the transition temperature from 1.4 K to 5.0 -13.5 K and yielding a two-dome-like evolution of Tc. Rubidium intercalation induces the highest Tc of 13.5 K, which can be further increased to 14.5 K under biaxial tensile strain. The strain-dependent evolution of Tc also exhibits a two-dome-like behavior, reflecting the interplay between strain-induced band structure modifications and electron-phonon coupling (EPC). Moreover, a systematic correlation is identified between interlayer interaction and superconducting gap. Lithium intercalation induces a distinct two-gap state, whereas intercalants with larger atomic radii (Na, K, Rb, and Cs) drive the system into a single-gap character. The two-gap to single-gap transition originates from the modulation of interlayer coupling through intercalation-induced interlayer expansion. In addition, pristine and Li/Na-intercalated bilayers exhibit nontrivial band topology, suggesting that layered PdTe2 provides a promising platform for realizing the coexistence of superconductivity and nontrivial topology. These results provide detailed anisotropic insights into EPC and offer viable pathways for enhancing Tc and achieving diverse properties in layered PdTe2 systems.