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.

We report the epitaxial growth of the $\mathrm{Cr}$-doped ${\mathrm{In}}_{2-x}{\mathrm{Cr}}_x{\mathrm{O}}_3$ (x = 0.05) ($\mathrm{Cr}$:${\mathrm{In}}_2{\mathrm{O}}_3$) semiconducting thin films on perovskite-type (111)-oriented $0.7\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3$−$0.3{\mathrm{Pb}\mathrm{Ti}\mathrm{O}}_3$ (PMN-PT) ferroelectric single-crystal substrates in the form of ferroelectric field-effect devices that allow us to obtain an in situ tuning of the electron carrier density and magnetoresistance (MR) as well as the resistance in a reversible and nonvolatile manner, thereby stringently disclosing the relationship between the MR and the electron carrier density. Specifically, for the thinnest 25-nm $\mathrm{Cr}$:${\mathrm{In}}_2{\mathrm{O}}_3$ film the polarization switching of the PMN-PT from the positively polarized $P_r^{+}$ state to the negatively polarized $P_r^{-}$ state results in a large increase in the resistance and MR. Particularly, at T = 10 K, the polarization switching induces reversible and nonvolatile changes in the magnitude and sign of MR, demonstrating strong coupling between the MR and the electron carrier density. Moreover, regardless of the polarization states of PMN-PT, MR for films with different thicknesses can be quite well described by a combination of the two-band model and the semiempirical model proposed by Khosla and Fischer based on which the positive MR (PMR) and negative MR (NMR) could be disentangled into positive component [MR(+)] and negative component [MR(−)], respectively. We find that the polarization-switching-induced large decrease in the PMR and the change in the sign of MR from positive to negative is mainly due to the rapid decrease in the MR(+), demonstrating that the coupling between MR(+) and electron carrier density plays a dominant role in controlling the magnitude and sign of MR.

The electric-field-modulated resistance switching in VO2 thin films grown on piezoelectric (111)-0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) substrates has been investigated. Large relative change in resistance (10.7%) was observed in VO2/PMN-PT(111) hererostructures at room temperature. For a substrate with a given polarization direction, stable resistive states of VO2 films can be realized even when the applied electric fields are removed from the heterostructures. By sweeping electric fields across the heterostructure appropriately, multiple resistive states can be achieved. These stable resistive states result from the different stable remnant strain states of substrate, which is related to the rearrangements of ferroelectric domain structures in PMN-PT(111) substrate. The resistance switching tuned by electric field in our work may have potential applications for novel electronic devices.