Using ultrafast laser pulses we demonstrate adiabatic control of the bandstructure of monolayer WS2 through Floquet engineering. In other words the periodic electric field of the laser pulse dresses the Bloch bands of the semiconductors. Interactions between the dressed bands then cause energy shifts, avoided crossings and the potential to induce a topological phase transition. The use of coherent spectroscopy …
Using Light to Probe and Manipulate Topologically Non-Trivial States
In this talk I will present the case for using high-electric field, ultrashort femtosecond pulses of light to controllably switch the behaviour of topologically interesting systems such as the Dirac semimetal, graphene. I will also outline our research efforts in this space and why quasi-single cycle terahertz probe pulses provide a unique window into the dynamics and optical properties …
Electronic properties of highly ordered wide bandgap intrinsic magnetic topological insulator thin films
Intrinsic magnetic topological insulators offer the potential of low disorder and large magnetic bandgaps for robust magnetic topological phases operating at higher temperatures, enabling observation of phenomena such as the quantum anomalous Hall effect (QAHE) and axion insulator phases [1,2]. However, these observations occur at temperatures significantly lower than the Neel temperature of bulk MnBi2Te4, and measurement of the magnetic energy …
Interactions and correlations in exciton-polariton systems
I will give an update on recent theoretical progress in understanding the nature of interactions in exciton-polariton systems. About the presenter CI A/Prof Meera Parish develops many-body theories that span electron-hole systems and ultracold atomic gases. In Research Theme 2, she is investigating the fundamental properties of exciton-polariton condensates, while in Research Theme 3, she is studying quantum systems out of …
Double Moire superlattices in hBN encapsulated graphene
Isolation of monolayer and few-layer graphene and other two-dimensional materials provides an opportunity to fabricate new types of heterostructures by stacking them layer by layer in a designed sequence [1]. Previous studies show that putting a graphene on a hexagonal boron nitride (hBN) substrate could form a Moiré pattern which generates a periodic potential and creates new Dirac points in …
Room-temperature polaritonics in FLEET
Exciton-polaritons (polaritons herein) are bosonic quasiparticles with unique physical properties arising from strong coupling between excitons and confined photons. Since their first demonstration, exciton-polaritons became a convenient platform for studies of collective quantum effects such as Bose-Einstein condensation and superfluidity. To date, the most striking effects were cleanly demonstrated in GaAs- based microcavities due to the very low defect densities …
Micromagnetic manipulation of resistance in a 2-dimensional viscous electron flow
Electron transport in most solid state systems is dominated by extrinsic factors, such as sample geometry and scattering from impurities, and is essentially independent of the intrinsic properties of the electron system. An exception is the hydrodynamic regime, where Coulomb interactions transform the electron motion from independent particles to the collective motion of a viscous ‘electron fluid’. The fluid viscosity …
Quantum Hall steps and Massive Dirac Fermion in Sm,Fe:Bi2Se3 single crystals
Intrinsic TIs are nonmagnetic or antiferromagnetic materials, possessing linear dispersed surface states with helical-textured spin configuration. With ferromagnetic ordering, a so-called massive Dirac state is achieved, in which the spin texture near Dirac gap is hedgehog like. Particularly, with fully spin polarization at Fermi surface, one can obtained the half-metallic TI, which should also exhibite the massive Dirac states, and …
Anisotropic ion conduction in van der Waals ferroelectrics: Implications for emergent electronic device design
Two-dimensional layered materials have been at the forefront of material research ever since the discovery of graphene about a decade ago. The dangling-bond-free lattice has made it feasible to integrate these materials with highly disparate atomic layers, such as industrial silicon substrates, to create a wide spectrum of van der Waals heterostructures without the constraints of lattice matching and processing …
High-resolution scanning transmission electron microscopy to understand topological materials
With a strong chemical sensitivity, high-resolution high angle annular dark field (HADDF)-scanning transmission electron microscopy (STEM) is widely used for acquiring detailed structural information in materials. The precise displacement of B-site ions with respect to the center of A-site ions in perovskites can be further mapped which is direct evidence for topological structures. As the topological entities have great potential …
Universal scaling of a quenched 2D Bose gas
We numerically study the phase ordering dynamics of a uniform 2D Bose gas following a quench into the superfluid phase, using the classical field methodology. We explore the crossover between conservative and dissipative evolution, finding clear evidence for universal behaviour in the dynamics, regardless of the dissipation strength. This universal behaviour manifests as a power-law growth of the correlation length …
Realisation of Wide Bandgap Quantum Anomalous Hall Insulator in Ultra-thin MnBi2Te4 and Bi2Te3 Heterostructures
The recently discovered anti-ferromagnetic topological insulator MnBi2Te4 (MBT) has been proved to host rich topological phases such as quantum anomalous Hall (QAH) and axion insulator phase in its thin films. A transition from a large gap 2D Ferromagnetic (FM) insulator in 1 Septuple layer (SL) to 5SL QAH insulator has been reported [1]. 1SL MBT has a wide gap exceeding …
Nanoscale topological defects in ferroelectric thin films Topology and control of self-assembled domain patterns in low-dimensional ferroelectrics
Whilst often discussed as non-trivial phases of low-dimensional ferroelectrics, modulated polar phases such as the dipolar maze and the nano-bubble state have been appraised as essentially distinct. Here we emphasize their topological nature and show that these self-patterned polar states, but also additional mesophases such as the disconnected labyrinthine phase and the mixed bimeron-skyrmion phase, can be fathomed in …
Disruption of helical edge states in topological insulators by magnetic impurities
Topological insulators (Tis) are a promising candidate for future low-energy electronics technologies, and the 2D or quantum spin hall (QSH) insulator (Bernevig, 2006) has attracted much attention for its 2e^2/h conductance regardless of width. This conductance is characterised by two helical edge states that have correlated spin polarization and momenta (Qi, 2011). This correlation acts to explicitly prevent backscatter, as …
Topotactic Phase Transformation in Epitaxial SrCo0.67Fe0.33O3−δ Thin Films
About the presenter Hien Nguyen is a PhD candidate in materials science and engineering working with Prof Jan Seidel at UNSW Sydney, where she studies nanoscale properties of multiferroic materials and growth of atomically thin films by pulsed laser deposition on different substrates, and investigates electric, magnetic properties of these materials as well as phase transitions and topotactic transformations in …
Polariton-Polariton Interaction: a four-body calculation
About the presenter Dr Guangyao Li is a postdoc researcher working with A/Prof Meera Parish and Dr Jesper Levinsen at Monash University within FLEET’s Research themes 2 (exciton superfluids) and 3 (light-transformed materials). His research interests include dynamics of polariton condensates, chiral states at exceptional points, topological excitations in open-dissipative superfluid, and the spin-orbit interaction of light.
Spin-gapless materials for in-plane QAHE PdBr3
About the presenter Frank Yun is a Research Fellow working with CI Xiaolin Wang at the University of Wollongong.
Kondo effect in a 2D Kagome metal-organic framework on a metal
About the presenter Dhaneesh Kumar Gopalakrishnan is an PhD student working with Dr Agustin Schiffrin at Monash University. Within FLEET’s research theme 1 and Enabling technology theme A, Dhaneesh synthesises and characterises 2D organic-based materials, searching for those that exhibit topological electronic properties. Synthesis and characterisation of these materials are carried out in the state-of-the-art scanning probe microscopy set-up in …
Electronic and Optical Properties of BiInO3 thin films
About the presenter Dr Daniel Sando is a postdoctoral researcher working with Prof Nagy Valanoor at UNSW to fabricate and characterise topological materials for FLEET’s Research Theme 1 and Enabling technology theme A. Dr Sando’s research is focused on the growth of 2-dimensional electron systems (2DES) comprising oxide perovskite materials LaAlO3 and SrTiO3, by pulsed laser deposition (PLD). A specific …
Electronic and Magnetic Structure of Metal-Organic Lattices on Substrates
About the presenter Bernard is pursuing a PhD with CIs Agustin Schiffrin and Nikhil Medhekar, working on calculating the properties of novel electronic materials using ab initio (first principles) calculations with density functional theory within FLEET’s Research Theme 1. In 2018, Bernard received the Rodney L Turner Prize for the Best Honours Thesis in Physics and Astronomy, and the JJ …
Atomic-Scale Evidence of Surface-Catalyzed Gold-Carbon Covalent Bonding
About the presenter Benjamin Lowe is a PhD student at Monash University where he works in Research theme 1 with Dr Agustin Schiffrin studying the self-assembly of metal-organic systems using a state-of-the-art scanning probe microscopy (SPM)facility that allows metal-organic systems to be engineered and probed with atomic-scale precision. He seeks to develop systems with electronic and opto-electronic properties that are …
Aharonov-Bohm interference as a probe of Majorana fermions
About the presenter Tommy is a PhD student and condensed matter theoretical physicist at RMIT university under the supervision of Jared Cole. Within FLEET he works in Research theme 1: topological materials.
Coherent dynamics and excitation density dependence in exciton-polaritons system
About the presenter Tatek Lemma is a PhD student working with CI Jeff Davis in FLEET’s Research Theme 3 and in Research theme 2. For his PhD, he is working on the investigation of topological phase transition in a 2D semiconductor using the state-of-the-art Coherent multidimensional spectroscopy.
Multidimensional Coherent Spectroscopy to reveal interactions in strongly correlated materials
About the presenter Rishabh Mishra is a PhD Student working with A/Prof Jeff Davis‘s Ultrafast Spectroscopy group at Swinburne University of Technology. Contributing to FLEET’s Research Theme 3, Light-transformed Materials, Rishabh and Jeff aim to study the electronic correlations and ultrafast coherent dynamics in non-equilibrium quantum matter using coherent multi-dimensional spectroscopy.
Oxidation Kinetics of WTe2 Surfaces in Different Environments
About the presenter Dr Pankaj Sharma is a postdoctoral research associate working with A/Prof Jan Seidel at UNSW. Dr Sharma’s expertise lies in the area of scanning probe microscopy techniques and ferroelectric complex-oxides. Within FLEET, Dr Sharma is working on electric-field induced controlled rewritable manipulation of topological interfaces such as ferroelectric domain walls, and LaAlO3/SrTiO3 hetero-interfaces at the nanometre length …
Non-collinear magnetism in oxide superlattices
About the presenter Oliver is a PhD student studying with Nagarajan Valanoor (UNSW). Oliver specialises in fabrication and characterisation of thin film heterostructures. He uses pulsed laser deposition (PLD) and laser molecular beam epitaxy (LMBE) to fabricate the desired materials, and uses high-resolution X-ray diffraction, piezoresponse force microscopy (PFM), magnetometry and neutron scattering in characterization of the materials. In terms …
Long-Range Surface-Assisted Molecule-Molecule Hybridization
About the presenter Dr Jack Hellerstedt is a research fellow working with CI Agustin Schiffrin at Monash University.
Toward high-performance tungsten diselenide field-effect transistors
About the presenter Yi-Hsun Chen is an experimental physicist working with Prof Michael Fuhrer and Dr Chen Shao-Yu at Monash University, where he researches Bose-Einstein condensates using devices constructed using 2D materials, seeking exciton superfluids in 2D material quantum wells. His research falls under FLEET research theme 2 exciton superfluids. For his PhD project, he is using 2D materials to create …
Topological spin-plasma waves at the interface of a topological insulator and a magnet
About the presenter Dr Dmitry Efimkin is a Scientific Associate Investigator at Monash University specialising in novel materials such as Dirac materials, graphene and topological insulators, and optical phenomena in solids. Within FLEET, Dmitry works with Michael Fuhrer, Meera Parish, and Nkhil Medhekar in Research theme 2: exciton superfluids and Enabling technology A: atomically-thin materials, studying optical and collective phenomena …
Towards long-lifetime excitons in 2D semiconductors
About the presenter Daniel McEwen is an Honours student working with CI Michael Fuhrer at Monash University.