Discovering novel states of matter and understanding their formation marks one of the central goals of research on quantum materials. To this end, it is essential to apply powerful external tuning parameter and to consequently establish the entropy landscape, one of the most fundamental thermodynamic quantities. Among the tuning parameters available, uniaxial pressure has gained significant importance in the study of quantum materials in the last years [1,2], followed by the development of devices that allow to apply large and in situ tunable uniaxial pressures in the MPI CPfS [3,4]. The in situ tunability has inspired the introduction of a new experimental approach [5] that provides direct access to the entropy landscape of tuned quantum materials: the elastocaloric effect, i.e., the temperature change that is induced by an adiabatic change of strain.

Whereas the idea of the experiment sounds simple to apply to mechanically robust samples, a bottleneck for the use of the technique for the wider class of quantum materials is that many of those are mechanically delicate [6,7]. One example is the class of van-der-Waals materials. As known from e.g., graphene, these materials tend to cleave easily. This makes this material class interesting for the study of quantum phenomena in low dimensions [8], but also hinders the application of homogeneous and large uniaxial pressures to bulk materials. Nonetheless, understanding the effect of strain on magnetic and superconducting properties of van-der-Waals bonded materials is of significant importance in view of basic quantum material research as well as applications.

This undergraduate project will focus on establishing the elastocaloric effect as a measurement technique for van-der-Waals ferromagnets [9] and superconductors [6]. You will develop a wide range of skill sets, including the design of novel experiments, modelling of the mechanical and thermal behavior of the components, the use of in-house Focused Ion Beam facilities for sample preparation as well as the use of cryogenic equipment.

Fig. 1: Sketch of elastocaloric effect measurements on mechanically delicate samples: The sample of interest is glued to a rigid platform that is strained in situ [7]. As a result, the temperature of the sample is changed which can be measured using a thermocouple that is attached to the sample.  Quasi-adiabatic conditions can be obtained using an a.c. method that overcomes the coupling for the sample to its environment.
 

 

[1] Steppke et al., Science 355, 6321 (2017);

[2] Gati et al., Ann. Phys. 532, 2000248 (2020);

[3] Hicks et al., Review of Scientific Instruments 85, 065003 (2014);

[4] Barber et al., Review of Scientific Instruments 90, 023904 (2019);

[5] Ikeda et al., Review of Scientific Instruments 90, 083902 (2019);

[6] Bartlett et al., Phys. Rev. X 11, 021038 (2021);

[7] Park et al., Rev. Sci. Instrum. 91, 083902 (2020);

[8] Burch et al., Nature 563, 47–52 (2018);

[9] Gati et al., Phys. Rev. B 100, 094408 (2019);

 

For further details please contact

Elena Gati (elena.gati@cpfs.mpg.de)

Andrew Mackenzie (andy.mackenzie@cpfs.mpg.de)

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