Exploring the strongly correlated realm of electrons using scanning tunneling spectroscopy

Strong correlations between electrons in materials give rise to a wide variety of exotic and unusual phenomena like unconventional superconductivity, spin and charge ordering and fractionalization of quasiparticles. This dissertation comprises three bodies of experiments, where strongly correlated electron systems have been studied to unearth novel phenomena using the technique of scanning tunneling microscopy and spectroscopy. The first work is an experimental discovery of long lifetime spin excitations near the domain walls (DWs) of a transition metal dichalcogenide Mott insulator, namely 1T − TaS2. 1T − TaS2 is a Mott insulator on a triangular lattice with a frustrated, putative quantum spin liquid ground state. However, charge denity wave (CDW) DWs give rise to short ranged antiferromagnetic spin-ordering with long lifetimes. These results have been published in Proceedings of the National Academy of Sciences, 119 (22) e2121740119, (2022). The second work is the development of a novel form of spectroscopic technique using nanowires of topological Kondo insulators as probe tips. In this work, using state-of-the-art nanofabrication techniques we have harvested nanowires of SmB6, a strongly correlated electron system and a candidate topological Kondo insulator, as probe tips for tunneling microscopy. Our work paves the way for a new generation of STM spectroscopy using functionalized nanowires to probe and manipulate emergent excitations in materials. The detailed results have been published in Science, 377, 6611 (2022). The final set of experiments are on UTe2, which combines triplet-superconductivity and non-trivial topology with strong correlations. In this work we have employed scanning tunneling microscopy and spectroscopy at 300 mK to uncover the existence of an unusual incommensurate CDW order which is suppressed by an external magnetic field and vanishes at the upper critical field Hc2 of the superconducting order. This behavior has been explained by using a Ginzburg-Landau theory for a uniform triplet superconductor coexisting with triplet pair density wave (PDW) state. PDWs in the absence of magnetic field need strong correlations to exist. While many previous works describe singlet PDW states, triplet PDWs have not been considered before by theory or observed in experiments. This work has been accepted to be published in Nature 2023 but can be accessed at arXiv:2207.09491v2.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Aishwarya, Anuva

Contributors dc:contributor

• Madhavan, Vidya
• Mason, Nadya
• Fradkin, Eduardo H
• Gadway, Bryce

• Scanning Tunneling Microscope
• Spectroscopy
• Correlated Electrons
• Mott Insulators
• Superconductors
• Spins
• Triplet
• Topology
• Kondo
• Low Temperature

Statement dc:rights

• Copyright 2023 Anuva Aishwarya

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/121489

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F121489