Two-dimensional layered material is the frontier research area in the field of the semiconducting material due to its superior electronic properties. The extraordinary large mobility and turn on-off ratio in high-quality multilayer black phosphorus demonstrate that black phosphorus may be a prospective fundamental material for electronic circuits and photoelectric devices for substituting the silicon material, which triggers great research enthusiasm on the physical properties of black phosphorus. These properties make black phosphorus a new exciting field both in material sciences and condensed matter physics. On the other hand, due to the development of topological material, searching for tunable three-dimensional Dirac semimetal remains as an unsettled and hot topic.

A recent collaborative research performed by Prof. CHEN Xianhui in the University of Science and Technology of China (USTC), Prof. ZHANG Yuanbo in the Fudan University, and Prof. ZOU Liangjian in the Institute of Solid State Physics (ISSP), Hefei Institutes of Physical Sciences reports an anomaly Shubnikov-de Haas oscillation on the black phosphorus sample at pressure, a Lifshitz transition from semiconductor from semimetal induced by hydrostatic pressure in black phosphorus, showing that the hydrostatic pressure is an effective modulation method on quantum properties of electrons in black phosphorus (Physical Review Letter115, 186403 (2015)). However, it is very difficult to experimentally determine the pressure evolutions of the crystal structures, electronic structure and electronic properties of black phosphorus.

More recently, in order to uncover the modulation mechanism of hydrostatic pressure on black phosphorus, Prof. ZOU Liangjian in the Key Laboratory of Materials Physics, ISSP together with Prof. CHEN Xianhui in the Department of Physics, USTC, and Prof. SHEN Shunqing in the Department of Physics, University of Hong Kong, combine several first-principle methods to determine the detail evolutions of crystal structures and electronic structures of the bulk black phosphorus at hydrostatic pressure.

They found that the energy bands crossover around the critical pressure Pc = 1.23 GPa, as shown in Fig. 1. With increasing pressure, the band reversal occurs at the Z point and evolves into 4 twofold-degenerate Dirac cones around the Z point, suggesting that pressured black phosphorus is a 3D Dirac semimetal. A clear Lifshitz transition occurs at Pc from semiconductor to 3D Dirac semimetal. The Dirac cones are sketched as in Fig. 2.

They demonstrated that such a 3D Dirac semimetal is protected by the nonsymmorphic space symmetry of bulk black phosphorus. With further increasing pressure, the Γ-Z Dirac cones evolve into two hole-type Fermi pockets, and the Z-M ones evolve into two tiny electron-type Fermi pockets, and a band above the Z-M line sinks below E_F and contributes four electron-type pockets, as seen in Fig. 3.

In addition, the researchers also predicted its anisotropic effective masses of carriers, mobilities and Fermi velocities under various hydrostatic pressures. These show that layered black phosphorus may have potential applications in quantum optoelectronic and electronic devices.

The related experimental and theoretical works have been published in Phys. Rev. Lett. entitled Pressure-Induced Electronic Transition in Black Phosphorus, and Physical Review B entitled Hydrostatic pressure induced three-dimensional Dirac semimetal in black phosphorus, respectively.

This work is supported by the NSF of China under Grant Nos. 11474287, 11274310, 11574315 and the Key Project 11534010. Numerical calculations were performed at the Center for Computational Science of CASHIPS.

Figure 1. Semiconductor-3D Semimetal evolution of bulk black phosphorus with increasing hydrostatic pressures. (Image by GONG Penglai) 

Figure 2. Sketched distribution of four Dirac cones in the first Brillouin zone of bulk black phosphorus under hydrostatic pressure P= 2 GPa. (Image by GONG Penglai) 

Figure 3. Fermi surfaces for bulk black phosphorus under various pressures. (Image by GONG Penglai)