Rotational stacking faults and mechanical instabilities in two-dimensional systems have added a new dimension to engineering its physical properties. Observation of unconventional superconductivity at magic angles, reduction in thermal conductivity with an increase in twist angle between layers, and observation of long-range Moire superstructures with the formation of flat bands in twisted bilayer graphene are a few of the recent intriguing discoveries. Turbostratic multilayer graphene is another exciting system of the same family. It is a multi-layered system containing a distribution of rotational stacking faults, and the interfaces in this system also have variable twist angles. We have studied the influence of turbostratic single-layer graphene content on the thermal conductivity of a defect-free multilayer graphene system. Thermal transport in these systems is investigated with Raman optothermal technique supported with finite element analysis simulations. Thermal conductivity of AB-stacked graphene diminishes by a factor of 2.59 for 1% of turbostratic single-layer graphene content. In comparison, the decrease at 19% turbostratic content is by an order in magnitude. Thermal conductivity obeys the relation, κ ∼ exp(-F), where F is the fraction of turbostratic single-layer graphene content in the system. Mechanical instabilities such as wrinkles have been predicted to decrease the thermal conductivity of single-layer graphene. Our studies show an interesting local enhancement of thermal conductivity across wrinkles in multilayer graphene with rotational stacking faults. Finally, the temperature and laser excitation energy-dependent Raman spectroscopy of turbostratic multilayer graphene is presented. The resonant window for laser excitation indicates lowered positions of the van Hove singularities, and the twist angles associated with the buried interfaces are revealed.

REFERENCES:
[1]. A. Mohapatra, M. S. Ramachandra Rao, & M. Jaiswal, Thermal transport in turbostratic multilayer graphene, Carbon, 2023 201,120-128
[2]. A. Mohapatra, S. Das, K. Majumdar, M. S. Ramachandra Rao, & M. Jaiswal, Thermal transport across wrinkles in few-layer graphene stacks, Nanoscale Adv., 2021,3,1708-1716
[3]. A Mohapatra, M. S. Ramachandra Rao, & M. Jaiswal, Thermal expansion coefficient of multi-layer graphene with rotational stacking faults, AIP Conference Proceedings, 2021, 2408, 020002