Piezovalley and piezoelectric altermagnetism in a 2D Ti2ClIO semiconductor.

Altermagnetic materials with high-performance multipiezo effect have attracted tremendous attention for their potential applications in information storage and logic operations. Here, we propose an altermagnetic monolayer Ti2ClIO with excellent dynamic, thermal, and mechanical stabilities. The monolayer Ti2ClIO presents zero net magnetization with an easy xy-plane. Moreover, it is a semiconductor with a direct band gap of 792 meV. The band structure shows a pronounced spin splitting of 914/811 meV for the valence/conduction band. Interestingly, a reversible valley polarization as high as 293 meV is induced in monolayer Ti2ClIO by applying a uniaxial strain, resulting in the piezovalley effect. Moreover, an out-of-plane piezoelectricity emerges in the present monolayer Ti2ClIO due to the broken horizontal mirror symmetry, showing the piezoelectric behavior with a strain coefficient of -0.03 pm/V. This study unveils a promising candidate for developing multifunctional electronic devices.