Artificial gravity field, astrophysical analogues, and topological phase transitions in strained topological semimetals

Effective gravity and gauge fields are emergent properties intrinsic for low-energy quasiparticles in topological semimetals. Here, taking two Dirac semimetals as examples, we demonstrate that applied lattice strain can generate warped spacetime, with fascinating analogues in astrophysics. Particularly, we study the possibility of simulating black-hole/white-hole event horizons and gravitational lensing effect. Furthermore, we discover strain-induced topological phase transitions, both in the bulk materials and in their thin films. Especially in thin films, the transition between the quantum spin Hall and the trivial insulating phases can be achieved by a small strain, naturally leading to the proposition of a novel piezo-topological transistor device. Possible experimental realizations and analogue of Hawking radiation effect are discussed. Our result bridges multiple disciplines, revealing topological semimetals as a unique table-top platform for exploring interesting phenomena in astrophysics and general relativity; it also suggests realistic materials and methods to achieve controlled topological phase transitions with great potential for device applications. Condensed matter: Creating black holes in materials A material that mimics the behavior of a black hole is developed by researchers in China and Singapore. Yugui Yao from the Beijing Institute of Technology and colleagues show that mechanical strain in a material known as Dirac semimetal can imitate the warping of space–time predicted by general relativity. Simulations of the Universe predict a wide range of counter-intuitive phenomenon. But many of these are beyond state-of-the-art technology to detect. Instead, scientists can engineer materials that are governed by equations similar to those that define astrophysical phenomena. Yao et al. investigate Dirac semimetals whose electronic bandstructure gives rise to massless quasiparticles that resemble relativistic particles. They show that altering the uniaxial strain enables control over these quasiparticles so that they emulate the behavior associated with black and white holes, event horizons and gravitational lensing.