The quantum Hall effect in the third dimension

The Quantum Hall Effect (QHE) in two-dimensional (2D) metals is a macroscopic quantum phenomenon and has helped to solve many important aspects of quantum physics. In common three-dimensional (3D) metals, the QHE is usually forbidden, because the third dimension destroys the quantization. However, our studies on the 3D metals ZrTe ₅ and HfTe ₅ show that their Hall resistance can be quasi-quantized if there are enough electrons in the materials. This makes the Hall effect in ZrTe ₅ and HfTe ₅ a real 3D counterpart to QHE in 2D systems.