Hot Topics in Quantum Nanoscience - Laurens Molenkamp (Würzburg) on 'HgTe as a topological insulator'



11 AM - 1 PM


Leiden University, Huygens building, room HL 204


Hot Topics in Quantum Nanoscience

Course Content: Speakers from all over the world will be asked to present pedagogical introductions to their field with an emphasis on basic concepts. Besides such an introductory lecture open for everybody, the participants of this course will have an additional discussion with the speaker discussing a recent paper and the holy grails of the field.

Exemplary topics are topological insulators, mesoscopic quantum gravity, string theory for condensed matter, measurement-based quantum computing, quantum-limited sensors, Majorana Fermions, fast-light with single photons, etc., etc.

Audience: The tutorial, as a one hour lecture, is open to everybody. A second hour will be reserved as a discussion hour for the registered class of PhD students and postdocs with the lecturer.

Course teachers: Gary Steele, Leo DiCarlo, Leo Kouwenhoven and Tjerk Oosterkamp

Preparation: PhD students who have registered for the hot topics course need to prepare for the session by reading the two articles mentioned in the below.

Date & Speaker:

Thursday 21 November, professor Laurens W. Molenkamp (Physics Institute (EP3), Würzburg University, Germany)

Topic: "HgTe as a Topological Insulator"


"Topological insulators are a new class of materials, insulating in the bulk but supporting an unusual metal on their surfaces. HgTe was the first material that was demonstrated to be a topological insulator, and in this talk I will discuss our research on this compound to illustrate the main trends in the field.

While bulk HgTe is a semimetal, it can be turned into a topological insulator by lowering the crystalline symmetry.

The most straightforward way to do so is by growing a quantum well with (Hg,Cd)Te barriers.  Such structures exhibit the quantum spin Hall effect, where a pair of spin polarized helical edge channels (one-dimensional conductors) develops when the bulk of the material is insulating. Our transport data provide very direct evidence for the existence of this third quantum Hall effect, which now is seen as the prime manifestation of a 2-dimensional topological insulator.

To turn the material into a 3-dimensional topological insulator, we utilize growth induced strain in relatively thick (ca. 100 nm) HgTe epitaxial layers. The high electronic quality of such layers allows a direct observation of the quantum Hall effect of the 2-dimensional topological surface states. These states appear to be decoupled from the bulk.

The topological metallic states are unusual in that their bandstructure closely mimics that found for elementary particles, yielding experimental access to a number celebrated predictions of quantum field theory. E.g., it should be possible to generate Majorana fermions by fabricating a Josephson junction involving the surface states.

I will discuss our experiments on such structures."

Host: Tjerk Oosterkamp

Location: Leiden University, Huygens building, room HL 204.

Time: 11:00 - 12:00 lecture
          12:00 - 13:00 lunch/hot topics session 

Please note: registration for lunch was only possible until Monday 18 November. If you registered after this date, please take your own lunch with you. 

Links to the articles:

Required reading for Hot Topics session 21 November:

For more information, we suggest you to read (optional, not obligatory as two articles mentioned above are):

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