Write your bachelor thesis in the Scheer group!

The main research of the Scheer group is concentrated on physics at the nanometer scale. Single atoms, single molecules or other nanoobjects are used to characterize phenomena only found in these restricted geometries.

An often used technical realization is the so-called mechanically controllable break junction (MCBJ) which offers the possibility of analyzing single-atom contacts by, simply speaking, controlled thinning of a metallic wire down to only a few atoms in diameter. Another way of how we investigate nano scale physics is the scanning tunneling microscope (STM). Here an atomically sharp tip electronically scans the surface layers of a sample to record its electronic signature.

Low-temperature cryostat for STM measurements.

Our low-temperature setups are capable of cooling down to only 10 mK above the absolute zero, which is needed to do physics with superconducting structures in combination with ferromagnetic materials. These are possible building blocks for a new generation of spin-based computers in the future.

Experimental techniques which you will learn

  • Electron microscopy
  • Micro- and nanotechnology
  • Vacuum- and pumping techniques
  • Low-temperature techniques
  • High-resolution transport measurements
  • Numerical data acquisition and evaluation

Some possible projects to join

S-F-S contacts under ferromagnetic resonance

In this project you will use advanced nano-lithography to fabricate samples consisting of a superconductor and a ferromagnet. The measurements will be carried out at very low temperatures in the milli Kelvin range.

Strong paramagnet - superconductor heterostructures

A possibility to test the magnetic state of nanoscale conductors, one possibility is to measure the spin-polarization of the current. To do so we use break junctions made of two different materials, a superconductors, and a strong paramagnet. The aim of this thesis project is to develop a novel fabrication process for these samples by using two successive lithography steps for the two metals. After successful sample fabrication you will also contribute to the transport measurements at low temperature.

Electronic transport in mechanically tuned graphene

Vibrational motion of bending waves provides a controllable way to tune the out of plane deflection of 2D nanomembrane resonators [1,2,3]. In a graphene mechanical free-standing membrane system, such deformations can split an electronic transport current into two beams of almost completely valley polarized electrons [4]. However, although graphene is mechanically very strong [5] devices to study the combination of the electronic transport and strong deflections made from freestanding graphene alone are not stable enough. Therefore, a combination with thicker membrane, e.g. made of siliconnitride is investigated here.

In this Bachelor Thesis project, the fabrication of graphene-siliconnitride bilayer resonators using optical lithography is developed. The success of the fabrication process is monitored by measurements of the electronic transport while vibrating.

The project can be extended to a Master Thesis with systematic studies of the electronic properties of the resonator with different vibrational motion, as function of temperature and magnet field.

[1] R. Waitz, S. Nößner, M. Hertkorn, O. Schecker, and E. Scheer, Mode shape and dispersion relation of bending waves in thin silicon membranes, Phys. Rev. B 85, 035324 (2012).
[2] R. Waitz, C. Lutz, S. Nößner, M. Hertkorn, and E. Scheer, Spatially resolved measurement of the stress tensor in thin membranes using bending waves, Phys. Rev. Appl. 3, 044002 (2015).
[3] F. Yang, R. Waitz, and E. Scheer, Quantitative Determination of the Mechanical Properties of Nanomembrane Resonators by Vibrometry In Continuous Light, arXiv preprint arXiv:1704.05328 (2017).
[4] T. Stegmann and N. Szpak, Current splitting and valley polarization in elastically deformed graphene, 2D Materials 6, 015024 (2018).
[5] X. Zhang, R. Waitz, F. Yang, C. Lutz, P. Angelova, A. Gölzhäuser, and E. Scheer, Vibrational modes of ultrathin carbon nanomembrane mechanical resonators, Appl. Phys. Lett. 106, 063107 (2015).