The hunting of the Majorana fermions - particles that are their own antiparticles - in topological superconductors is one of paramount research targets in condensed matter physics today. Recently, a research team led by Professor Qi-Kun Xue of Tsinghua University in China has succeeded to reveal experimental evidence of topological superconductivity near the surface of epitaxial β-Bi2Pd films, and possible Majorana zero modes at magnetic vortices.
A topological superconductor is superconducting inside the bulk like usual superconductors, while on the boundary/surface it harbors the long-sought Majorana fermions. Such unusual particles obey non-Abelian braiding statistics and could be potential for fault-tolerant quantum computing, which can operate much more efficiently than any current computers.
Topological superconductivity and Majorana zero modes of epitaxial β-Bi2Pd films by molecular beam epitaxy. (a) Topographic image of β-Bi2Pd films, with the insert as the schematic crystal structure of β-Bi2Pd. (b) Typical differential conductance dI/dV spectrum at 0.4 K, revealing two distinct superconducting gaps from bulk (Δb) and topological surface (Δs) states, respectively. (c) Zero-bias conductance map, showing an individual magnetic vortex (bright yellow region). (d) Tunneling conductance dI/dV spectrum taken at the vortex center, signifying a salient zero bias conductance peak. (e) The dI/dV spectra acquired at positions with varying radial distance r from the vortex center. The peaks shows no splitting and is invariably fixed to the zero energy, anticipated for Majorana zero modes.
Credit: ©Science China Press
A handful of topological superconductors have hitherto been proposed in topological insulators or other systems with strong spin-orbital coupling when they are interfaced with a superconductor or driven into the superconducting states by chemical doping. However, little attention is paid to the other way of thinking, to wit, searching for topologically nontrivial band structure in classical s-wave superconductors.
Tetragonal β-Bi2Pd was found to be superconducting below 5.4 K in 1957. Just recently, it was revealed from angle-resolved photoemission spectroscopy that topologically protected surface bands cross the Fermi level of β-Bi2Pd.
The two major ingredients of realizing topological superconductivity are coincidently existing in this single-component compound. Subsequent experimental search for the buried topological superconductivity in β-Bi2Pd all fell flat. The researchers in Tsinghua University have caught the rare opportunity and unmasked the veil of topologically nontrivial superconducting states in β-Bi2Pd.
"We are motivated to unravel why the topological superconductivity failed to be observed in all previous studies of β-Bi2Pd crystals, it is now known that tuning the chemical potential to isolate the topological surface states from bulk bands near the Fermi level is the key to observe such topologically nontrivial superconducting states," said Yanfeng Lv, the first author of this study, now is a postdoctoral researcher at Texas Center for Superconductivity, University of Houston.
Published in the journal of Science Bulletin, the study utilized a state-of-the-art molecular beam epitaxy technique under ultrahigh vacuum to prepare successfully high-quality β-Bi2Pd thin films on SrTiO3 substrates, which was then in-situ transferred to a cryogenic scanning tunneling microscopy chamber.
The tunneling spectrum revealed a pronounced and impurity-resistant superconducting gap opening on the surface, which appears much larger than the bulk on owing to Dirac-fermion enhanced parity mixing of surface pair potential. The direct visualization of superconducting gap opening on the topological surface states, as well as its expected variation with the Fermi level, compellingly reveals β-Bi2Pd as a promising candidate for topological superconductor. Salient zero bias conductance peaks, probably from Majorana zero modes supported by such superconducting states, were identified at the end of magnetic vortex lines.
"This research provides the convincing evidence of topological superconductivity on β-Bi2Pd and signature of Majorana zero modes at vortices," said the researchers, "and more importantly points to a novel avenue for searching topological pairing states on usual superconductors that might exhibit topologically nontrivial band structure by the engineering of Fermi level."
This work was financially supported by National Science Foundation, Ministry of Science and Technology and Ministry of Education of China, the National Thousand-Young-Talents Program and the Tsinghua University Initiative Scientific Research Program.
See the article:
Yan-Feng Lv, Wen-Lin Wang, Yi-Min Zhang, Hao Ding, Wei Li, Lili Wang, Ke He, Can-Li Song, Xu-Cun Ma, Qi-Kun Xue. Experimental signature of topological superconductivity and Majorana zero modes on β-Bi2Pd thin films. Science Bulletin 2017, 62(12): 852-856. https:/
Can-Li Song | EurekAlert!
Writing and deleting magnets with lasers
19.04.2018 | Helmholtz-Zentrum Dresden-Rossendorf
Ultrafast electron oscillation and dephasing monitored by attosecond light source
19.04.2018 | Yokohama National University
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
In an article that appears in the journal “Review of Modern Physics”, researchers at the Laboratory for Attosecond Physics (LAP) assess the current state of the field of ultrafast physics and consider its implications for future technologies.
Physicists can now control light in both time and space with hitherto unimagined precision. This is particularly true for the ability to generate ultrashort...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
19.04.2018 | Materials Sciences
19.04.2018 | Physics and Astronomy
19.04.2018 | Physics and Astronomy