Image courtesy of Ali Yazdani
Low-temperature scanning tunneling spectroscopy image of a heavy electron material in its superconducting state. These measurements reveal the structure of the superconducting state.
Scanning tunneling microscopy (STM) experiments have been used to visualize the formation of composite particles called “heavy electrons” with the lowering of temperature. These heavy electrons pair coherently upon further cooling to form an unconventional superconducting state, allowing electricity to be conducted by the material without losses.
Heavy electron superconductivity belongs to the class of unconventional superconductors, which also includes well-publicized high-temperature superconductors that are superconducting at far higher temperatures than conventional superconductors. High temperature superconductors can conduct electricity with no losses at liquid nitrogen temperatures, around 196 °C. A detailed understanding of the common factors among unconventional superconductors may have implications for further improvement of the properties of superconductors for potential applications in electric power generation and transmission and in computing.
In metallic compounds containing actinide and rare earth elements at the bottom of the periodic table, the interaction between electrons localized on one atomic site and surrounding itinerant electrons (electrons that move freely among atoms due to overlap of the electron orbitals that surround the nuclei of atoms) leads to the development of composite particles, referred to as “heavy electrons” that behave at low temperatures as if they are much more massive than free electrons. Strong correlations between these heavy electrons persist with continued cooling and ultimately drive the appearance of unconventional superconductivity. Researchers at Princeton University have used scanning tunneling spectroscopy to detect the emergence of these heavy electrons in a prototypical family of cerium-based heavy-electron materials (e.g., CeCoIn5) synthesized at Los Alamos National Laboratory, in which the localized electron is provided by cerium. By probing the scattering and interference of these electrons, the experiments reveal their energy-momentum structure and mass enhancement with decreasing temperature. Through further technical advancement to enable measurement at temperatures below one Kelvin (lower than 272 °C), the technique’s fine spatial and spectroscopic resolution can be used to directly image how an impurity locally perturbs superconductivity, uncovering the nanoscale fingerprint of the symmetry of superconductivity in this compound.
Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ 08540 firstname.lastname@example.org
DOE Office of Science, Basic Energy Sciences program provided primary support for the research at Princeton University and Los Alamos National Lab. The instrumentation at the Princeton Nanoscale Microscopy Laboratory is supported by the National Science Foundation, the W.M. Keck Foundation, and the Eric and Linda Schmidt Transformative Fund at Princeton. B.B.Z. was supported by a National Defense Science and Engineering Graduate Fellowship. P.A. was supported by a fellowship through the Princeton Center for Complex Materials funded by the National Science Foundation. Z.F. was supported by the National Science Foundation.
B.B. Zhou, S. Misra, E.H. da Silva Neto, P. Aynajian, R.E. Baumbach, J.D. Thompson, E.D. Bauer, and A. Yazdani, Nature Physics, 9, 474 (2013)
P. Aynajian, E.H. da Silva Neto, A. Gyenis, R.E. Baumbach, J.D. Thompson, Z. Fisk, E.D. Bauer, and A. Yazdani, Nature, 486, 201 (2012)
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