Using ferroelectric $0.67\text{Pb}\left({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}\right){\text{O}}_3\text{−}0.33{\text{PbTiO}}_3$ single crystals as substrates, we studied the effects of the ferroelectric poling and the converse piezoelectric effect on the strain state, resistance, insulator-to-metal transition temperature $\left(T_C\right)$, and magnetoresistance (MR) of ${\text{La}}_{0.7}{\text{Ba}}_{0.3}{\text{MnO}}_3$ (LBMO) thin films. In situ x-ray diffraction measurements indicate that the ferroelectric poling (or the converse piezoelectric effect) induces a substantial reduction in the in-plane tensile strain in the LBMO film, giving rise to a decrease in the resistance and an increase in $T_C$. The relative changes of the resistance and $T_C$ are proportional to the induced reduction in the in-plane tensile strain $\left(\delta {\epsilon }_{xx}\right)$ in the film. The reduction in the in-plane tensile strain leads to opposite effects on MR below and above $T_C$, namely, MR is reduced for $T<T_C$ while MR is enhanced for $T>T_C$. We discuss these strain effects within the framework of the Jahn-Teller (JT) electron-lattice coupling and phase separation scenario that are relevant to the induced strain. Similar studies on ${\text{CaMnO}}_3$ thin films, for which there is no JT distortion of ${\text{MnO}}_6$ octahedra, show that the resistance of the films also decreases when the tensile strain is reduced, indicating that the resistance change arising from the reduction in Mn-O bond length dominates over that arising from the reduction in Mn-O-Mn bond angle.

A comprehensive understanding of strain coupling across heterointerfaces and its impact on physical properties of oxide heterostructures is important for elucidating the mechanisms of certain novel physical phenomena occurring at heterointerfaces, such as magnetoelectric coupling, tunneling electroresistance effects, and strain-driven exchange bias. Using the $\mathrm{L}{\mathrm{a}}_{0.5}\mathrm{C}{\mathrm{a}}_{0.5}\mathrm{Mn}{\mathrm{O}}_3/\mathrm{Pb}\left(\mathrm{I}{\mathrm{n}}_{1/2}\mathrm{N}{\mathrm{b}}_{1/2}\right){\mathrm{O}}_3\text{−}\mathrm{Pb}\left(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}\right){\mathrm{O}}_3\text{−}\mathrm{PbTi}{\mathrm{O}}_3$ (PINT) multiferroic heterostructure as a model system, we systematically investigated the influences of interface strain coupling on the electronic transport and magnetic properties as well as the electronic phase separation of charge-ordered $\mathrm{L}{\mathrm{a}}_{0.5}\mathrm{C}{\mathrm{a}}_{0.5}\mathrm{Mn}{\mathrm{O}}_3$ thin films through electric-field-induced ferroelectric domain switching. Upon the irreversible initial poling of the PMNT substrate, the induced in-plane compressive strain $({\varepsilon }_{xx\left(\mathrm{film}\right)}=-0.045\%)$ causes a decrease in $T_{\mathrm{CO}}(\Delta T_{\mathrm{CO}}=180\mathrm{K})$ and resistance $[{(\Delta R/R)}_{\mathrm{strain}}\sim -99.4\%]$, resulting in a gauge factor ${(\Delta R/R)}_{\mathrm{strain}}/{\varepsilon }_{xx\left(\mathrm{film}\right)}\sim 220800\%$. Such a large strain-tunability of resistance is unprecedented and magnetic-field tunable. This, together with the strain-tunable magnetoresistance (MR) and magnetization of the films, demonstrates strong coupling between the strain and the magnetic field. Further analysis indicates that this coupling is essentially mediated by the electronic phase separation, whose relative strength could be monitored by measuring ${(\Delta R/R)}_{\mathrm{strain}}$ against magnetic field and temperature. By combining 180° ferroelectric domain switching and x-ray diffraction and transport measurements, we identify that this electric-field modulation of the physical properties is strain-mediated but not interface charge-mediated. In addition, we observed that the non-180° ferroelastic domain switching-induced in-plane tensile strain $({\varepsilon }_{xx\left(\mathrm{film}\right)}=0.1\%)$ induces a large increase in the resistance (up to ∼87.4%) and $T_{\text{CO}}$ and a drop in MR, signaling the stabilizing of the charge-ordered phase. Our findings provide further insight into the strain effect and essential physics of perovskite manganites, particularly the electronic phase separation.

Topological semimetals represent one of the most interesting classes of materials that continue to attract worldwide interest. Here, we report magnetotransport properties of MPn₂-type (M = Nb, Ta; Pn = P, As, Sb) NbSb₂ single-crystal semimetals with a centrosymmetric C12/m1 space group, paramagnetic ground state, and non-saturation parabolic-like magnetoresistance. The NbSb₂ crystals show metallic conductivity down to 2 K and undergo a metal-to-insulator-like transition under a magnetic field B (B ≥ 4 T) and exhibit a resistivity plateau in the low-temperature region (T ≤ 10 K), where the value of resistivity strongly depends on the magnitude and direction of the magnetic field. Upon sweeping the magnetic field from 0 to 14.5 T in the transverse configuration at T = 1.5 K, the NbSb₂ crystal shows a large positive magnetoresistance (4.2 × 10³% at B = 14.5 T) with Shubnikov–de Haas (SdH) oscillation. Hall measurements reveal that both the carrier compensation between electrons and holes and the high mobility and large mean free path of carriers contribute to the large magnetoresistance. Fast Fourier transform analyses of angle-resolved SdH oscillation indicate that the Fermi surface of the NbSb₂ crystal is quasi-two-dimensional with three-dimensional components. These findings, together with the theoretically calculated electronic band structure obtained within the framework of density functional theory, suggest that NbSb₂ is a good candidate compensated semimetal for further theoretical and experimental investigation of this family of materials.