An international team of scientists has investigated the topological properties of grey tin (α-Sn), a low-temperature form of tin. They have successfully stabilized this form at room temperature by applying small compressive forces. Through a combination of complementary experimental techniques, the researchers demonstrated that α-Sn belongs to the class of Dirac topological semimetals and, under the influence of an external magnetic field, transforms into a Weyl semimetal phase. A significant part of the experiments exploring the fascinating electronic properties of this material was conducted at the URANOS beamline of the SOLARIS National Synchrotron Radiation Centre.
Tin, a seemingly ordinary and well-known material, reveals unique electronic properties under extreme conditions. Historically, α-Sn caused problems during harsh winters by destroying organ pipes in churches. However, this form now shows fascinating electronic properties. Scientists from the International Research Centre MagTop at the Institute of Physics of the Polish Academy of Sciences have stabilized and strained grey tin at room temperature on insulating substrates. The unusual electronic structure of α-Sn has been experimentally visualized using angle-resolved photoemission spectroscopy at the URANOS beamline at the SOLARIS Synchrotron Centre. The electron energy spectrum of α-Sn resembles a Dirac spectrum, typically observed in particles accelerated to speeds close to the speed of light. This discovery was further supported by magneto-optical experiments and theoretical calculations conducted by researchers from Johannes Kepler Universität in Linz and Ecole Normale Supérieure in Paris. Electrical transport measurements at the MagTop center revealed that applying a magnetic field parallel to the electrical current results in an unusual drop in resistance, manifesting the chiral anomaly, a phenomenon known from high-energy physics. The unique electronic structure of grey tin paves the way for its application as a functional material in novel spintronic devices.
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Image: Left panel: Crystal structure of the α-Sn layer grown by molecular beam epitaxy on CdTe/GaAs substrate is subject to in-plane biaxial compressive strain (black arrows) and thus uniaxial tensile strain along normal to the layer. Magnetic field B can be applied in the layer plane; Middle panel: Dirac-like surface states revealed by Angle Resolved Photoemission Spectroscopy studies of α-Sn in Dirac semimetal phase induced by strain for B=0. Right panel: negative longitudinal magnetoresistance (current I ǁ B, see right inset) indicative of chiral anomaly in Weyl semimetal phase induced by an in-plane B. At low temperature, Shubnikov-de Hass oscillations are also visible. Insets to middle and right panels show calculated band structure of Dirac and Weyl semimetal phases, respectively.
Credit: Jakub Polaczyński, Valentine V. Volobuev