Researchers have directly visualized robust two-dimensional superconductivity confined to the surface of $gamma$-PtBi$_2$, a topological semimetal composed of platinum and bismuth, according to a collaborative team from the Universidad Autónoma de Madrid and Iowa State University and Ames National Laboratory. This research is outlined by Isabel Guillamón, Paul C. Canfield, Hermann Suderow, Jose Antonio Moreno, Pablo García Talavera, Edwin Herrera, Sara López Valle, Zhuoqi Li, Lin-Lin Wang, Sergey Bud’ko, and Alexander I. Buzdin, revealing a critical temperature of 2.9 K and a critical field of approximately 1.8 T through very low temperature Scanning Tunneling Microscopy.
Atomic-Scale Visualization and Quantum Properties of $gamma$-PtBi$_2$
The material’s surface state, addressing macroscopic quantum phase coherence and two-dimensional behavior is shown through observations of the Josephson effect and quantized superconducting vortices, answering previous questions regarding the stability of this unusual behavior. The layered material $gamma$-PtBi$_2$ possesses a unique electronic structure without inversion symmetry. A thorough examination of this trigonal arrangement uncovers a make-up of bismuth and platinum elements, leading to cleavage surfaces that are primarily ended with bismuth atoms. Atomic-resolution Scanning Tunneling Microscopy imaging demonstrates two distinct terminations, each exhibiting a hexagonal pattern formed by bismuth atoms with differing atomic arrangements.
Unlike most known superconductors where phenomena occur throughout the bulk material, the team’s findings demonstrate robust two-dimensional superconductivity specifically linked to Fermi arcs present on the surface. These arcs are conducting pathways connecting bulk Weyl points. The research team stated, “We find homogeneous superconductivity down to atomic scale with a critical temperature of T_c = 2.9 K,” emphasizing consistency with established BCS theory. The observed superconducting gap size of 0.48 meV and its temperature dependence closely align with these theoretical predictions.
Role of Fermi Arcs and Weyl Points in Surface Superconductivity
The material’s layered trigonal structure without inversion symmetry contributes to wide bands crossing the Fermi level and Weyl points approximately 50 meV above it, according to the published findings. The surface Fermi arcs visible on the material trace their origin directly back to these Weyl points, which were previously mapped via quantum oscillations and angle-resolved photoemission spectroscopy. The Fermi arcs appear to act as conduits for this unusual superconducting behavior, differing from proposals to induce superconductivity through proximity with other materials.
Did you know? Unlike traditional superconductors that conduct electricity without resistance throughout their entire volume, $gamma$-PtBi$_2$ displays this macroscopic quantum state exclusively across its atomic-scale surface layers, linked directly to its unique topological Fermi arcs.
Using a dilution refrigerator scanning tunneling microscopy setup under applied magnetic fields, the researchers resolved this by observing quantized superconducting vortices arranged in a repeating lattice pattern. These vortices confirm the presence of persistent currents and support a critical field ($H_{c2}$) of approximately 1.8 Tesla, characterizing the strength of the two-dimensional superconducting state.
Implications for Future Quantum Devices
The confirmation of two-dimensional macroscopic quantum phase coherence opens potential advantages for quantum device applications, complementing ongoing research into two-dimensional superconductivity observed in materials like graphene.
Frequently Asked Questions
What is $gamma$-PtBi$_2$?
It is a topological Weyl semimetal composed of platinum and bismuth, featuring a layered trigonal crystal structure without inversion symmetry.
What is the critical temperature of the surface superconductivity in $gamma$-PtBi$_2$?
According to the research team, the material exhibits homogeneous surface superconductivity down to the atomic scale with a critical temperature of 2.9 K and a critical field of about 1.8 T.
How was the surface superconductivity detected?
Researchers used very low temperature Scanning Tunneling Microscopy and a dilution refrigerator STM to directly visualize quantized superconducting vortices and observe the Josephson effect.
Explore More Quantum Research
Worth a look