Three-Layer Graphene Reveals Interesting Magnetic Properties



Three-Layer Graphene Reveals Interesting Magnetic Properties - Featured Graphene research
The image shows the density of electrons as a function of gating voltage Vbg and Magnetic field B.  Credit: Nature Communication

Metals have a large density of electrons and to be able to see the wave nature of electrons one has to make metallic wires that are only a few atoms wide. However, in – one atom thick graphite — the density of electrons is much smaller and can be changed by making a transistor. As a result of the low density of electrons the wave nature of electrons, as described by quantum mechanics, is easier to observe in graphene.

Often in metals like copper the electron is scattered every 100 nanometers, a distance roughly 1000 times smaller than the diameter of human hair, due to impurities and imperfections. Electrons can travel much longer in graphene, upto distances of 10 micrometer, a distance roughly 10 times smaller than the diameter of human hair. This is realized by sandwiching graphene between layers of boron nitride. The layers of boron nitride have few imperfections to impede the flow of electrons in graphene.

Once electrons travel long distances, implying there are few imperfections, one notices the faint whispers of electrons “talking to each other”. Reducing the imperfections is akin to making a room quiet to enable the faint whispers of electronic interactions to develop between many electrons.

In a study, led by PhD student Biswajit Datta, Professor Mandar Deshmukh’s group at TIFR realized just this kind of silence allowing electronic interactions to be observed in three layers of graphene. The study reveals a new kind of magnet and provides insight on how electronic devices using graphene could be made for fundamental studies as well as applications. This work discovers the magnetism of electrons in three layers of graphene at a low temperature of -272 Celsius. The magnetism of electrons arises from the coordinated “whispers” between many electrons.

This work is published in journal of Nature Communication.

Publication Journal:Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene ” Biswajit Datta, Santanu Dey, Abhisek Samanta, Hitesh Agarwal, Abhinandan Borah, Kenji Watanabe, Takashi Taniguchi, Rajdeep Sensarma & Mandar M. Deshmukh, Nature Communications 8, 14518 (2017) 

Publication Abstract:
Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ?500,000?cm2?V?1?s?1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree–Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field.