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Welcome to

Ando lab

The Ando Laboratory, nicknamed Topological Matter Laboratory Cologne, focuses on experimental studies of topological matter and their devices. Topological matter is a peculiar class of materials in which a nontrivial topology of the quantum-mechanical wavefunctions leads to unusual, and often useful, physical properties. We use nanofabrication and ultra-low-temperature techniques to explore the novel physics of topological matter, in particular topological superconductors hosting Majorana zero-modes. One of our main goals is to confirm the prediction that Majorana zero-modes obey non-Abelian statistics, which has never been observed in nature and would be the key for topological quantum computing. Our main experimental platform is hybrid nanodevices consisting of topological insulator and superconductor. Such devices present fascinating phenomena reflecting the interplay between unconventional superconductivity, mesoscopic physics, and topology. Our experiments are performed in a dedicated lab building, which houses a state-of-the-art clean room, as well as in the new wing of the main physics building. 

Keywords to characterize our research:

  • Topological insulator (TI)
  • Quantum anomalous Hall insulator
  • Hybrid devices
  • Mesoscopic superconductivity
  • Unconventional superconductivity
  • Ultra-low-noise measurements in the mK region
  • Superconducting qubits
  • circuit-QED technique
  • Bulk-insulating TI flakes and MBE thin films

group mail address

ando-group(at)ph2.uni-koeln(dot)de

What is Topological Insulator?

In the topologically-protected surface states of topological insulators, the orientation of electron spin is perpendicularly locked to the momentum.

Topological insulators are an exotic class of materials where an insulating bulk state supports an intrinsically metallic surface state that is “topologically protected” by time reversal symmetry. In this topological surface state, right- and left-moving electrons carry opposite spins, which is the key property to realize topological superconductivity when such electrons are made to form Cooper pairs. Professor Ando is one of the pioneers of the research field of topological insulators, and his pedagogical review article (http://journals.jps.jp/doi/pdf/10.7566/JPSJ.82.102001) provides a good introduction to this field.

What is Topological Superconductor?

The first data which probed the existence of Majorana fermions on the surface of a topological superconductor. This is a plot of differential conductivity vs bias voltage, measured in Ando Laboratory by point-contact spectroscopy on CuxBi2Se3, which is a superconductor derived from the topological insulator Bi2Se3. [Sasaki et al., Phys. Rev. Lett. 107, 217001 (2011).

Even more exotic state of matter is topological superconductors. The nontrivial topology of their electronic wavefunctions gives rise to gapless boundary states, which sometimes present the properties of Majorana fermions conceived originally in high-energy physics. There are various ways to realize topological superconductivity. Professor Ando is also a pioneer of the research field of topological superconductors, and his pedagogical review article (https://iopscience.iop.org/article/10.1088/1361-6633/aa6ac7) provides a good introduction to this fascinating field.

For Non-specialists

The research area of Ando Lab is so-called solid state physics, which concerns the properties of materials. For example, the questions such as why copper conducts electricity while glasses do not, or why iron can be magnetized and used as a compass --- those question are answered in solid state physics. 

In this field, researchers keep discovering new materials to exhibit unexpected properties that will allow for making better machines and infrastructures. Our specialty lies in "topological matter", which are expected to revolutionize information technologies. 

At the University of Cologne, we have installed state-of-the-art facilities to perform the research in this promising field at the top level. Our goal is to deepen the fundamental understanding of topological matter and bring this knowledge to build foundations of future information technologies.

 

Who should join?

We offer excellent research environment and interesting projects to talented young physicists (or physicists to be) at all levels: Bachelor students, Master students, PhD students, and Postdocs. 

For possible thesis topics, please see here.

At the PhD and postdoc level, we are looking for talented individuals with a strong background in experimental condensed matter physics. More specifically, it is required that the applicant has experience/interest in one of the following areas: low-temperature physics, mesoscopic physics, superconductivity, nanodevice fabrications, or circuit-QED. It is advised NOT to apply to us if your main interest is quantum computing, since our research is still miles away from such an application. 

If you are interested in joining us, please take a look at our lab manual to have a glimpse on the philosophy and practicalities of our lab. If it resonates with you, please inquire Professor Ando about possibilities.

Lab Manual

“In my lab, I hope to foster an environment of scientific excellence and personal development, where we have fun doing curiosity-driven science. I would like all the lab members to be happy and productive in their lab life. This manual was written to help achieve these goals by providing guidance to the current lab members, as well as to give general introduction to prospective members.”
- Yoichi Ando
 

We are a part of the Cluster of Excellence "Matter and Light for Quantum Computing” (ML4Q) funded from 2017 to 2032 through the Excellence Strategy of Germany. It is a cooperation by the universities of Cologne, Aachen, and Bonn, as well as the Research Center Jülich. We are responsible for the realization of topological qubits that might become a game-changer in quantum computing.