Atomic-scale visualization of strain effects

In many strongly correlated electron materials, a delicate interplay between structural distortions, charge and magnetic orders has a strong influence on macroscopic properties and the overall phase diagram. This interplay is what makes these materials exciting both for fundamental research to understand the driving interactions behind these as well as potentially for technological applications. Recently, it has been demonstrated [1, 2] that uniaxial pressure can have a substantial impact on these emergent orders and the electronic structure of these materials, providing an additional tuning parameter and a new handle which can be used to unravel the underlying physics.

This project aims to establish atomic-scale visualization of strain-controlled emergent orders in quantum materials by scanning tunneling microscopy and spectroscopy. To this end, you will develop a novel strain device, starting from existing designs used for transport experiments [3] and existing low temperature scanning tunneling microscopy set-ups [4, 5]. Both will be combined into a powerful new method, combining in-situ strain control with atomic-scale imaging and spectroscopy.

The aim of this project is to study the influence of the strain on electronic states, magnetic and orbital orders near the Fermi energy at the atomic scale, e.g. via quasi-particle interference or spin-polarized scanning tunnelling microscopy [6]. This will provide new insights into the interplay between symmetry breaking electronic states [7] with superconductivity in iron- and copper-oxide based superconductors.

[1] C. W. Hicks, D. O. Brodsky, E. A. Yelland, A. S. Gibbs, J. A. N. Bruin, M. E. Barber, S. D. Edkins, K. Nishimura, S. Yonezawa, Y. Maeno, A. P. Mackenzie
Strong Increase of Tc of Sr2RuO4 Under Both Tensile and Compressive Strain
Science 344, 283–285 (2014)
[2] A. Steppke, L. Zhao, M. E. Barber, T. Scaffidi, F. Jerzembeck, H. Rosner, A. S. Gibbs, Y. Maeno, S. H. Simon, A. P. Mackenzie, C. W. Hicks
Strong peak in Tc of Sr2RuO4 under uniaxial pressure
Science 355, eaaf9398 (2017)
[3] C. W. Hicks, M. E. Barber, S. D. Edkins, D. O. Brodsky, A. P. Mackenzie
Piezoelectric-based apparatus for strain tuning
Review of Scientific Instruments 85, 065003 (2014)
[4] S. C. White, U. R. Singh, and P. Wahl
A stiff scanning tunneling microscopy head for measurement at low temperatures and in high magnetic fields
Review of Scientific Instruments 82, 113708 (2011)
[5] U. R. Singh, M. Enayat, S. C. White, and P. Wahl
Construction and performance of a dilution-refrigerator based spectroscopic-imaging scanning tunneling microscope
Review of Scientific Instruments 84, 013708 (2013)
[6]  M. Enayat, Z. Sun, U. R. Singh, R. Aluru, S. Schmaus, A. Yaresko, Y. Liu, C. Lin, V. Tsurkan, A. Loidl, J. Deisenhofer, P. Wahl
Real-space imaging of the atomic-scale magnetic structure of Fe1+yTe
Science 345, 653–656 (2014)
[7] U. R. Singh, S. C. White, S. Schmaus, V. Tsurkan, A. Loidl, J. Deisenhofer and P. Wahl
Evidence for orbital order and its relation to superconductivity in FeSe0.4Te0.6
Science Advances 1, e1500206 (2015)

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