Peter Wahl, PhD
    Phone: +44 (0)1334 463122
    Andrew Mackenzie, Prof. Dr.
    Phone: +49 351 4646-5900
    Fax: +49 351 4646-5902

    Imaging emergent orders near quantum phase transitions

    Close to quantum critical points, emerging phases appear with often unexpected properties. Examples include superconductivity as well as putative electron-nematic orders [1, 2]. This project takes a microscopic approach to study these emergent electronic phases at the atomic scale with the aim to relate atomic-scale electronic and magnetic properties to macroscopic observables and sample properties.

    One of the materials for which you will explore this is Sr3Ru2O7, a metamagnetic material which exhibits a well-studied magnetic field-tuned quantum critical point [3]. Close to the quantum critical point, evidence for symmetry breaking electronic states has been found in the magnetoresistance [1]. In the same region of the phase diagram, the material also shows magnetic order [4]. It remains an important open question whether the symmetry breaking electronic states are driven by the magnetic order, or whether electronic correlation effects might drive this possible electron nematicity.

    This project aims at using spin-polarized scanning tunnelling microscopy using a dilution-refrigerator-based low temperature scanning tunneling microscope [5, 6] to study the reconstruction of the electronic structure as well as emergent magnetic orders as the material is tuned through the quantum critical point. By studying both the electronic structure through quasi-particle interference imaging as well as the magnetic order in the same atomic-scale area, it will become possible to establish the relation between the two orders, i.e. whether the magnetic order drives a reconstruction of the electronic structure which leads to an anisotropy of the transport properties, or whether they are independent phenomena.

    The project will involve standard characterization of the physical properties of the crystals selected for measurement, operating the scanning tunnelling microscope and extensive data analysis, including modelling of quasi-particle interference for comparison with the experimental data.


    [1] Borzi, R. A. et al. Formation of a Nematic Fluid at High Fields in Sr3Ru2O7.
         Science 315, 214–217 (2007).

    [2] Ronning, F. et al. Nature 548, 313–317 (2017).

    [3] S.A. Grigera, et al., Science 294, 329 (2001).

    [4] Lester, C. et al. Field-tunable spin-density-wave phases in Sr3Ru2O7.
         Nat Mater 14, 373–378 (2015).

    [5] Enayat, M. et al. Science 345, 653–656 (2014).

    [6] Singh, U. R., et al. Review of Scientific Instruments 84, 013708 (2013).

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