Two-dimensional van-der-Waals materials, which can be exfoliated as nanometer-thin flakes, are a novel class of materials which can be tuned by electrical gating, and where new materials can be created “by design” by stacking different material layers [1]. In recent years, evidence of unconventional superconductivity has been found in several 2D materials, such as monolayer WTe2 [2] and in heterostructures such as twisted bilayer graphene [3] and twisted cuprate superconductors [4,5].
Figure 1. A thin (~20 nm) exfoliated flake of the high temperature superconductor BSCCO, with evaporated gold contacts to form a Hall bar. Such a device can be placed in a uniaxial pressure cell, to explore its superconducting properties in an entirely new regime.
Figure 1. A thin (~20 nm) exfoliated flake of the high temperature superconductor BSCCO, with evaporated gold contacts to form a Hall bar. Such a device can be placed in a uniaxial pressure cell, to explore its superconducting properties in an entirely new regime.
To understand the internal structure of a material and observe new phases of matter, it is highly useful to have a tunable parameter where change can be observed. Typical tuning parameters (e.g. temperature, magnetic field, doping) have significant drawbacks and limitations, and so any new “tuning knob” can revolutionize the field and give us access to a new regime of physical effects. Recently, the ability the apply uniaxial pressure to a material, as pioneered by the MPI CPfS, has led to a tremendous success in exploring novel phases in unconventional superconductors [5]. Such a technique could be highly beneficial to the study of van-der-Waals superconductors, and particularly high-temperature superconductors where the application of uniaxial pressure has demonstrated multiple step changes in the critical temperature [7] and interpreted in a variety of layered cuprates compounds as an increase of the electron density of states at the Fermi level through an alteration of the Fermi surface topology of the CuO2 layers within the unit-cell [8].
The project combines novel device fabrication, the study of quantum devices in cryogenic conditions, and a unique measurement technique under controlled uniaxial pressure. Through this project, the student can gain expertise in a broad range of topics in condensed matter physics and quantum technology.
References:
[1] K. S. Novoselov , A. Mishchenko, A. Carvalho, and A. H. Castro Neto
[5] Y. Lee, M. Martini, T. Confalone, S. Shokri, C.N. Saggau, D. Wolf, G. Gu, K. Watanabe, T. Taniguchi, D. Montemurro, V.M. Vinokur, K. Nielsch, N. Poccia
Encapsulating High-Temperature Superconducting Twisted van der Waals Heterostructures Blocks Detrimental Effects of Disorder
[6] Y.-S. Li, M. Garst, J. Schmalian, S. Ghosh, N. Kikugawa, D.A. Sokolov, C.W. Hicks, F. Jerzembeck, M.S. Ikeda, Z. Hu, B.J. Ramshaw, A.W. Rost, M. Nicklas, and A.P. Mackenzie
Elastocaloric determination of the phase diagram of Sr2RuO4
