The study of magnetoresistance and Hall effect variations under high pressure in semiconductors provides critical insights into the behavior of charge carriers in extreme conditions. High-pressure environments significantly alter the electronic and structural properties of materials, leading to phenomena not observable at ambient conditions. Semiconductors such as indium antimonide (InSb) serve as ideal candidates for such investigations due to their narrow bandgap, high electron mobility, and pronounced response to external perturbations like pressure and magnetic fields.
Under high pressure, the lattice constants of semiconductors contract, modifying the band structure and carrier dynamics. In InSb, the application of hydrostatic pressure increases the direct bandgap, altering the effective mass of electrons and holes. This change directly impacts carrier mobility, a key parameter governing magnetotransport properties. The magnetoresistance effect, defined as the change in electrical resistance under an applied magnetic field, becomes more pronounced under pressure due to enhanced Landau level splitting and modified scattering mechanisms.
The Hall effect, which measures the transverse voltage generated by a magnetic field perpendicular to the current flow, is another essential tool for probing carrier behavior. At high pressures, the Hall coefficient provides information on carrier concentration and type, while deviations from classical behavior reveal the influence of quantum corrections. In InSb, the high electron mobility results in well-resolved quantum oscillations, such as Shubnikov-de Haas (SdH) oscillations, under sufficiently high magnetic fields. These oscillations arise from the quantization of electron orbits into Landau levels, and their periodicity is linked to the Fermi surface cross-section.
A critical distinction between high-pressure and ambient transport studies lies in the pressure-induced modifications to scattering mechanisms. At ambient conditions, ionized impurity scattering and phonon scattering dominate, but under high pressure, deformation potential scattering and intervalley scattering gain significance due to lattice strain. This shift alters the temperature and magnetic field dependence of mobility, leading to non-monotonic trends in magnetoresistance. For instance, in InSb, the magnetoresistance transitions from a quadratic dependence at low fields to a linear regime at higher fields under pressure, a behavior attributed to the interplay between Landau level spacing and scattering rates.
Landau level splitting under high pressure is further influenced by spin-orbit coupling and the non-parabolicity of the conduction band. In narrow-gap semiconductors like InSb, the non-parabolic dispersion relation causes the Landau levels to deviate from the equidistant spacing predicted by simple effective mass theory. High pressure exacerbates this effect by increasing bandgap non-parabolicity, leading to observable changes in the quantum oscillation spectra. Additionally, the Zeeman splitting of Landau levels becomes more significant under pressure due to enhanced g-factors, further complicating the magnetotransport behavior.
Experimental studies on InSb under pressures exceeding 5 GPa reveal a crossover from semiconducting to semi-metallic behavior, accompanied by a Lifshitz transition in the Fermi surface topology. This transition is marked by a sudden change in the SdH oscillation frequency, indicating a reconstruction of the electronic states. The Hall coefficient also exhibits anomalies at critical pressures, signaling changes in carrier density or type. Such phenomena are absent in ambient studies, underscoring the unique insights gained from high-pressure investigations.
The interplay between pressure and magnetic field also affects the quantum Hall regime. In two-dimensional electron systems, high pressure can tune the carrier density and subband spacing, leading to pressure-induced quantum Hall plateaus. While such effects are more commonly studied in layered materials, bulk semiconductors like InSb under extreme conditions offer complementary perspectives on quantum transport.
A comparison of key parameters under ambient and high-pressure conditions highlights the distinct physics at play:
Parameter Ambient Conditions High-Pressure Conditions
Bandgap 0.17 eV (InSb) Increases with pressure
Electron Mobility ~78,000 cm²/Vs Reduced due to enhanced scattering
Landau Level Spacing Regular Non-equidistant due to non-parabolicity
Magnetoresistance Quadratic at low fields Linear at high fields
Hall Coefficient Constant Pressure-dependent anomalies
The practical implications of these findings extend to high-pressure sensors, quantum devices, and materials for extreme environments. For example, the pressure sensitivity of magnetoresistance in InSb can be exploited for piezoresistive transducers, while the tunability of Landau levels offers avenues for pressure-modulated quantum devices.
In summary, high-pressure magnetotransport studies uncover rich physics beyond ambient conditions, revealing pressure-induced modifications to carrier mobility, Landau level splitting, and scattering mechanisms. Semiconductors like InSb serve as versatile platforms for exploring these effects, bridging fundamental knowledge and technological applications. The distinct behaviors observed under pressure underscore the necessity of dedicated high-pressure transport studies, complementing conventional ambient investigations.