Magnetic and Electronic Phase Transitions in 2D-Materials Probed by Nanomechanical Resonators

Credit: TU Delft

Phase transitions play an important role in materials. However, in two-dimensional materials, the most famous of which is graphene, phase transitions can be very difficult to study. Researchers from Delft University of Technology and the University of Valencia have developed a new method that helps to solve this problem. They suspended ultrathin layers of 2D-materials over a cavity and tracked the resonance frequency of the resulting membranes using lasers. The results of their work have been published inNature Communications. 

Since the discovery of the exceptional electrical and mechanical properties of graphene — the first-ever two-dimensional (2D) material — layers with thicknesses down to a single atom are attracting scientific interest. New functionalities and phenomena emerge with the recent discoveries of unique types of magnetic and electronic phases in these layers, including superconducting, charge density waves, 2D Ising antiferromagnetic and ferromagnetic phases. Phase transitions play an important role in materials: for instance water is a liquid at room temperature and freezes below zero centigrade, forming a material with completely different properties.

Resonant motion

In large samples, there are several techniques to measure these phase transition, for instance by measuring the specific heat which can show abrupt changes at the phase transition. However, only a few methods are available to study these transitions in atomically thin samples with a mass of less than a picogram. This is particularly challenging for ultrathin insulating antiferromagnets that only weakly couple to magnetic and electronic probes.

Researchers at Delft University of Technology have now demonstrated that these phases can be studied by looking at the resonant motion of membranes made of these 2D materials. These membranes can be formed by suspending an ultrathin crystal over a cavity in a substrate, thereby creating a nanoscale drum. “We track the mechanical resonance frequency of these membranes using a red laser while bringing them in motion at MHz frequencies by a power-modulated blue laser,” researcher Makars Šiškins explains

Sudden expansion

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