A novel twist in the conventional understanding of the Quantum Hall systems

Researchers from IIT Delhi in collaboration with their counterparts in UK have given a novel twist to the conventional understanding of the Quantum Hall systems, paving way for a broader study of the traditional experimentation.

What are Quantum Hall Systems?
Quantum Hall systems (Nobel Prize1985, 1998), had made a paradigm shift in our understanding of phase transitions in condensed matter systems through the introduction of topological phases (Nobel 2016). Such topological phases in Quantum Hall systems are realized in two dimensional gases of electrons formed in a sandwich piece between two semiconductors called heterostructure in the presence of a very high uniform transverse magnetic field and at extremely low temperature. In this phase of matter the interior is perfectly insulating like a piece of wood that does not conduct electric current, but on the border ( edge) there are robust conductors that carries current like a copper wire, but with a strictly uni-directional flow manifesting a property called chirality. As of now in most of such systems these current carrying states are due to the application of electric field and hence called chiral electric edge states.

The Work
Researchers in UK (Group of Alain Nogaret in Bath and his collaborators in Cambridge) and in IIT Delhi (Puja Mondal, Ankip Kumar and Sankalpa Ghosh), have demonstrated that such chiral edge states can be created in the bulk of the system purely by varying the uniform magnetic field of conventional Quantum Hall systems in a highly controlled manner. These states are called magnetic edge states and lies at the border of two insulating zones in the bulk.

The experiment, supported by a detailed theoretical analysis, not only created such chiral magnetic edge states, but also been able to change the separation between such magnetic edge states in the bulk with the conventional electric edge states at the physical edge of the system. The experiment recorded a transition from the magnetic edge state dominated transport to conventional electrostatic edge dominated transport in a highly controlled way by measuring the resistivity of the sample as a function of the applied magnetic field and the bias voltage which nicely agrees with the accompanying theory.

The results might be interesting in general to the explore the rich bulk-edge correspondence in various topological phases in condensed matter systems in general. The work is funded by a UGC-UKIERI grant. The results were recently published as a rapid communication in https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.081302