Quantized Heat Flow as a Probe of Thermal Equilibration and Edge Structures of Quantum Hall Phases in Graphene

This book describes the quantized thermal conductance measurements of integer and several fractional quantum Hall (QH) states realized in graphene devices. Although the electrical conductance quantization of the QH effect in graphene was demonstrated in 2005, a heat flow study of QH states needed to be included. This becomes particularly essential for the hole-conjugate fractional QH phases, where counterpropagating edge modes lead to complex transport behavior. The experimental results reported in this thesis are the first set of experiments done for the quantized heat flow in graphene devices since the first mechanical isolation of graphene flakes. The book devotes two detailed introductory chapters to the electronic properties of the graphene and its bilayer and trilayer parts at zero magnetic fields, and to the essential physics of the integer and fractional quantum Hall (FQH) states, the topological order of FQH phases and the experiments that can detect them.

The book has a dedicated chapter for the details of the device fabrication and thermal conductance measurement technique. The rest of the chapters are dedicated to the systematic and detailed documentation of the new experimental findings of quantized heat flow in quantum Hall phases in graphene.

Electronic properties of graphene.- Electron in Magnetic field Quantum Hall effect.- Device Fabrication and Measurement Setup.- Universal quantization of thermal conductance in graphene.- Vanishing thermal equilibration for hole conjugate fractional quantum Hall states in graphene.

Saurabh Kumar Srivastav received his B.Sc. (Hons) in Physics from Banaras Hindu University, Varanasi, in 2015. After this, He joined the Department of Physics, Indian Institute of Science, Bengaluru, India, as an Integrated PhD student. He completed his PhD under the supervision of Prof. Anindya Das in 2022. His PhD thesis was focused on understanding the edge structure of the several integers and fractional quantum Hall (QH) phases realized in graphene-based devices. It turns out that by measuring the transport coefficients, one can determine the topological quantum numbers of edge modes and hence the bulk topological order of the integer and fractional quantum Hall (QH) phases. Saurabh mainly focused on the measurement of the quantized thermal Hall conductance instead of the conventional electrical conductance measurement because it can provide additional insight, which is limited in electrical conductance measurement. By measuring the thermal conductance of hole conjugate states in the asymptotic limit of the thermal equilibration, He successfully measured the exact number of the topological edge modes of these phases in graphene, which remained an open question for decades. His PhD research offers an efficient route to determine the exact topological order of non-abelian fractional quantum Hall states. In his postdoctoral research at the Weizmann Institute of Science with Prof. Eli Zeldov, Saurabh is utilizing the SQUID-on-tip magnetic and thermal imaging techniques to explore the novel electronic phases realized in two-dimensional materials and their hybrid devices.