Project - Unveiling the nature of electronic phase transitions in Dirac systems.

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This project is funded by the Polish National Science center (NCN) within the POLINEZ-3 grant scheme, under the number 2016/23/P/ST3/03514 Trulli. Here you will find more information about it.

The work is currently being carried out in the group ON 2.4 at the institute of physics of the Polish Academy of Sciences.You can find more information about the group and what me and my colleagues do by clicking here.

This webpage will be updated as the work develops. Mostly whenever a scientific report will be produced.

What is this project about?

In this project, we are studying the properties of materials known as Dirac semimetals. These are electrical conductors in which electrons behave as highly energetic particles. More specifically, we are interested to see how we can transform these materials from insulators to metals to superconductors by tuning external parameters such as applied magnetic field, disorder and chemical doping. You can find a laymen description of the project here.

What has been done so far?

This project consists of several steps, which are listed below:

Sample growth,

The samples used for the current project are commercial graphite HOPG and bismuth (purchased from SPI-supplies), Bi and Bi-Sb single crystals grown by Dr. Przemislaw Iwanowski, and the Dirac semimetals SnTe and PbSnTe.

  • HOPG samples have already been purchased.
  • Bismuth crystals have been both purchsed and molten from high purity chunks into small policrystaline samples
  • Bi-Sb samples have been grown by the Birminghan method at ON 3.1 at IFPAN
  • Bi-Sb policrystals have been grown by evaporating thin (<1 nm) Bi and Sb layers subsequently. Resulting samples were homogeneous thin Bi-Sb films with various stoichiometries.
  • Micrographite samples have been prepared by ultrasonic exfoliation and contacted for electrical measurements as a function of magnetic field and disorder.
  • SnTe and PbSnTe samples were obtained in collaboration with Grzegor Mazurek and Krzystof Dybko.

    • Sample modification (doping, adding disorder, etc...),

  • Bismuth and graphite devices have been outfited with superconducting electrodes, revealing an annomalously long-ranged proximity effect. Read more about our findings here.
  • The same experiments were carried out in different Dirac systems and conventional materials. Results reveal an apparently universal phenomenon in Dirac systems (manuscript under preparation).
  • Bismuth and antimony thin films have been subjected to different heat treatments, in an attempt to modulate their properties.
    • Structural caracterization,

  • HOPG samples have been charactetrized by Raman spectroscopy and X-ray diffraction (XRD).
  • HOPG samples have been charactetrized low temperature STM measurements, to identify the origin of superconducting signatures in transport measurements.
  • Bismuth poli- and single-crystals have been characterized by EDS (electron dispersive spectroscopy) and XPS (x-ray photoemission spectroscopy) for impurities.
  • The remaining crystals (Bi-Sb based) will be characterized by XRD and energy-dispersive x-ray spectroscopy (EDAX).
  • Bi-Sb thin films have been characterized by XRD, allowing to determine wheter samples were grown as Bi-Sb multilayers, or homogeneous BiSb alloys.
  • Bulk Bi crystals were characterized by XRD, EDX and SEM to obtain structural parameters later correlated with its magnetic properties.

    • Electrical and magnetic caracterization,

  • Resistance vs. temperature and resistance vs. magnetic field measurements in a series of graphite and pristine bismuth samples have been carried out, resulting in the report seen here
  • Electrical transport and magnectic measurements have been performed in pristine and policrystalline bismuth, resulting in the report seen here.
  • High magnetic field measurements in graphite ribbons revealed samples with intrinsic charge carrier concentration 10 times above the conventional value obtained in bulk graphite. These devices revealed the same anomaly on high magnetic fields as the one obtained in priesine graphite, suggesting that features observed in graphite at high magnetic fields are not well-described by the current models of the material.
  • Magnetotransport measurements in PbSnTe, SnTe, Bi, Sb and HOPG have been caried out. Results revealed an apparent universal phenomenon in Dirac systems, associated with the surface of these materials (Manuscript under preparation).
  • Development of a torque magnetometer in collaboration with Bogdan Semenenko, University of Leipzig, well-suited for the characterization og Bi-Sb multilayers. First result of the collaboration can be seen here.
  • Collaboration with Marta Cieplak and Iryna Zaytseva on the study of a "strange metal phase" in Nb, which can also be used to describe the metal-insulator transition observed in different Dirac systems. This collaboration resulted in this report.

    • Can I see your data?

    Absolutely. You can reach me by clicking in "contact" below.

    See what has been published so far.

    Papers

    The following manuscripts have been accepted:

  • Anomalous Hall Effect in Bismuth - Journal of Magnetism and Magnetic materials (2020)
  • Magnetization of Bi2Sr2CaCu2O8+δ Micrometer Thin Ring and Its Depinning Line - Journal of Superconductivity and Novel Magnetism (2020)
  • Upper critical field and superconductor-metal transition in ultrathin niobium films - Scientific Reports (2020)

    • The following papers have been submitted, but are still under review:

  • Submillimeter - sized proximity effect in graphite and bismuth

    • Conferences

    Below is a list of conferences where results have been presented:

  • MAGNETIC-FIELD-INDUCED TRANSITIONS IN BISMUTH - 17th Czech and Slovak Conference on Magnetism (CSMAG2019)
  • Anomalous Hall effect in bismuth - 19th National Polish conference on superconductivity and strongly correlated systems (KKN-XIX)

    • About NCN and the POLONEZ-3 grant funding scheme.

    The POLONEZ programme has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 665778. It is a grant scheme awarded by the polish Nacional Science Center (NCN) and is intended to attract scientists to Poland by providing attractive employment conditions. More information about this can be found in the POLONEZ website.

    Contact.

    You can drop by (address here), give me a call (number here), or send me an email on camargo[SHIFT-2]ifpan.edu.pl

    updated on 01/12/2020.