Engineering a Correlated Narrow-Gap Semiconductor: Effects of Ga Substitution in EuZn${}_2$P${}_2$

Abstract

The effect of Ga substitution on the electronic, magnetic, and low-energy responses of the Zintl phase EuZn${}_2$P${}_2$ is investigated by electrical transport, electron spin resonance (ESR), and terahertz time-domain spectroscopy (THz-TDS). Incorporating Ga into EuZn${}_2$P${}_2$ (EuZn${}_{1.8}$Ga${}_{0.2}$P${}_2$) reduces the electrical resistivity, indicating enhanced free-carrier density and a narrowed semiconducting gap. ESR confirms the persistence of Eu${}^{2+}$ moments while showing a crossover from a Lorentzian to a Dysonian lineshape, consistent with reduced skin depth, increased carrier density, and the emergence of diffusive contributions. Ga-substituted compound display pronounced negative magnetoresistance linked to magnetic-polaron formation. THz-TDS reveals strong low-frequency absorption and a notable enhancement of the Drude conductivity in the substituted material, together with an increased carrier scattering time and enhanced carrier-density--to--effective-mass ratio. These results demonstrate that Ga substitution tunes charge transport, carrier dynamics, and short-range magnetic correlations in EuZn${}_2$P${}_2$, establishing EuZn${}_{1.8}$Ga${}_{0.2}$P${}_2$ as a promising platform for engineering correlated narrow-gap magnetic semiconductors with enhanced electronic and spin-dependent functionalities.

16 pages, 9 figures

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