PhD defence

Strongly interacting electrons in Sachdev-Ye-Kitaev models and Twisted Bilayer Graphene

• A.S. Shankar

Date

Tuesday 7 January 2025

Time

13:00 - 14:00 hour

Address

Academy Building
Rapenburg 73
2311 GJ Leiden

Supervisor(s)

• Prof.dr. V. Cheianov
• Prof.dr. K. Schalm

Summary

The electrical properties of materials are governed by the movement of charged particles known as electrons. It has been a landmark success of quantum physics in the twentieth century to identify that in many materials, complicated interactions between electrons can be simplified using composite excitations of electrons known as quasiparticles, which behave as if they move independently of each other. This thesis is concerned with situations in which the electronic correlations are so strong that such a simplified quasiparticle description breaks down, most famously in the case of the cuprate high temperature superconductors.

The first half of the work focuses on extensions to the Sachdev-Ye-Kitaev (SYK) model, a minimalist example of quasiparticle breakdown in a system of interacting electrons. Through the holographic duality, this model equivalently describes black holes in a hypothetical contracting universe. An example of the duality manifesting itself is reflected in how both systems scramble quantum information at the same rate, which also is the theoretical speed limit. The thesis also explores how a junction made of strongly correlated superconducting systems may correspond to wormholes in this framework.

The latter half of the thesis is concerned with a novel material known as twisted bilayer graphene. Owing to features of its electronic structure, it is predisposed to accentuate any electronic correlations that may exist. Its ability to screen away magnetic impurities is discussed, and has an impact for potential RAM devices that may be constructed using it.

PhD dissertations

Approximately one week after the defence, PhD dissertations by Leiden PhD students are available digitally through the Leiden Repository, that offers free access to these PhD dissertations. Please note that in some cases a dissertation may be under embargo temporarily and access to its full-text version will only be granted later.

Press enquiries (journalists only)

[phone]
[e-mail]

General information

Beadle's Office
[e-mail]
[phone]