Pressure-induced Lifshitz transition in black phosphorus

Abstract: In a semimetal, both electron and hole carriers contribute to the density of states at the Fermi level. The small band overlaps and multi-band effects give rise to many novel electronic properties, such as relativistic Dirac fermions with linear dispersion, titanic magnetoresistance and unconventional superconductivity. Black phosphorus has recently emerged as an exceptional semiconductor with high carrier mobility and a direct, tunable bandgap. Of particular importance is the search for exotic electronic states in black phosphorus, which may amplify the material's potential beyond semiconductor devices. Here we show that a moderate hydrostatic pressure effectively suppresses the band gap and induces a Lifshitz transition from semiconductor to semimetal in black phosphorus; a colossal magnetoresistance is observed in the semimetallic phase. Quantum oscillations in high magnetic field reveal the complex Fermi surface topology of the semimetallic black phosphorus. In particular, a Dirac-like fermion emerges at around 1.2 GPa, which is continuously tuned by external pressure. The observed semi-metallic behavior greatly enriches black phosphorus's material property, and sets the stage for the exploration of novel electronic states in this material. Moreover, these interesting behaviors make phosphorene a good candidate for the realization of a new two-dimensional relativistic electron system, other than graphene.

Pressure-Induced Electronic Transition in Black Phosphorus

The study titled "Pressure-Induced Electronic Transition in Black Phosphorus" investigates the effects of hydrostatic pressure on the electronic properties of black phosphorus, a layered semiconducting material. Herein, the research team examines the transition from semiconductor to semimetal induced by pressure and observes significant changes in transport properties and electronic structure.

Black phosphorus is recognized for its unique layered structure and high mobility due to its puckered honeycomb lattice arrangement. This leads to the formation of a direct bandgap mainly influenced by the $p_z$-like orbitals and interlayer coupling. Under the influence of hydrostatic pressure, this bandgap can be suppressed, leading to intriguing transitions in electronic properties. The paper delineates a pressure-driven electronic topological transition—specifically, a Lifshitz transition—which occurs at approximately 1.2 GPa, characterized by black phosphorus transitioning to a semimetal.

The experimental setup involved single crystals of black phosphorus under pressures up to 2.4 GPa. With pressures applied using BeCu piston-cylinder cells, the authors conducted magneto-transport measurements, recording significant changes in resistivity with pressure. The research highlights a robust semiconductor-to-metal transition, confirmed by a distinct suppression of the low-temperature resistive divergence at 1.25 GPa and above.

Further analysis involving Hall resistivity underscores the emergence of co-existing electron and hole bands above the transition pressure. At this point, black phosphorus demonstrates multiband conduction properties, with the Hall resistivity experiencing a sign reversal indicative of nearly compensated electron and hole concentrations in its semimetal state. This claims consistency with phenomena observed in other semimetals, which results in colossal magnetoresistance (MR) values, observed up to 80000% in a magnetic field of 9 T.

To understand Fermi surface dynamics further, the study employed Shubnikov-de Haas (SdH) oscillations, which revealed complex Fermi surface topologies in the resulting semimetal phase. These oscillations provided insight into the newly emerged band structures, which exhibited a non-trivial Berry's phase—a significant indication of Dirac-like dispersion and hence a Dirac semimetalic nature.

The implications of these findings extend to both practical applications and theoretical frameworks. The ability to induce semimetallic behavior into black phosphorus via moderate pressure tuning showcases the versatility of this material for exploring novel electronic states and potential device applications, especially where tuning electronic properties in situ is desirable.

This investigation into the pressure-dependent electronic transitions in black phosphorus enriches our understanding of the material's band structure and emphasizes its suitability for future research focusing on pressure or strain engineering. Furthermore, observing potential Dirac fermions under such conditions suggests the viability of black phosphorus as a candidate for exploring Dirac particle physics, with implications for future developments in materials science and condensed matter physics. Future work could aim at mapping the detailed band structure evolution under such conditions more comprehensively, clarifying the presence of all potential Dirac points and further exploring the topological nature of the pressure-induced state in black phosphorus.