Quantum Materials Theory and Mesoscopics
1 Dec 2023 - Our group's experiment-theory collaboration with the Loh group showing that Bernal stacked tetralayer graphene can exhibit ferromagnetism and an anomalous Hall effect was published in Nature Communications as "Gate-tunable anomalous Hall effect in Bernal tetralayer graphene". Congratulations Arpit and Chen Hao!
18 Aug 2023 - Ma Da's paper unveiling a type new nonlinear Hall effect in PT symmetric magnetic metals was published in Physical Review Letters: "Anomalous Skew-Scattering Nonlinear Hall Effect and Chiral Photocurrents in PT- Symmetric Antiferromagnets". This nonlinear Hall effect arises from the cooperative action of Berry curvature (quantum geometric) as well as skew scattering (extrinsic). While both individually do not contribute to Hall effects in PT symmetric materials, when combined they can provide the leading contribution to the nonlinear Hall effect. Congratulations Ma Da!
8 Feb 2023 - Our group's review article detailing the multi-physics and multi-scale nature of photocurrent in quantum materials was published in Nature Reviews Physics: "Photocurrent as a multiphysics diagnostic of quantum materials". It describes how photocurrent can probe and disentagle a variety of different aspects of out-of-equilibrium quantum states. This was an in-depth and worthwhile collaboration between our group and Qiong Ma (BC), Su-Yang Xu (Harvard) and Frank Koppens (ICFO).
4 Jan 2023 - Our group's experiment-theory collaboration with THz experimentalist Elbert Chia showing large THz emission in PtSe2 was published in Science Advances: "Giant photon momentum locked THz emission in a centrosymmetric Dirac semimetal". Xiong Ying helped spearhead the theoretical effort! Congratulations!
29 Nov 2022 - Xiong Ying's paper detailing how photon drag cam be used to track a momentum resolve quantum geometry in an ARPES like fashion was published in Physical Review B as "Polariton drag enabled quantum geometric photocurrents in high-symmetry materials". Congratulations Xiong Ying!
16 Nov 2022 - Arpit's paper detailing how a nonreciprocity of quantum origin can be achieved for plasmonic modes was published in NanoLetters. See "Quantum plasmonic nonreciprocity in parity violating magnets" Congratulations Arpit!
5 Jul 2022 - Our group's experiment-theory collaboration with Nathan Gabor's group on imaging vibronic exciton-phonon states in stacks of van der Waals materials was published in NanoLetters. See "Vibronic Exciton−Phonon States in Stack-Engineered van der WaalsHeterojunction Photodiodes"
31 May 2022 -Xiong Ying's paper on how to achieve a "Multistable excitonic Stark effect" was published in Physical Review Research. This work the Stark effect in a nanophotonic cavity can achieve a highly nonlinear and multiple stable states. Congratulations Xiong Ying!
25 March 2022 - Our group's experiment-theory collaboration with Frank Koppens group (ICFO) on realizing a giant Hall photoconductivity in gapped bilayer graphene was published in "Tunable and giant valley-selective Hall effect in gapped bilayer graphene" in Science.
16 Dec 2021 - Arpit's paper "Strain-induced large injection current in twisted bilayer graphene" was published in Physical Review B (Letters). This work predicts how moire materials can host a large circular photogalvanic effect. Congratulations Arpit!
10 May 2021 - Likun's paper "Geometric photon drag effect and nonlinear shift current in centrosymmetric crystals" was published in Physical Review Letters. This work shows how to activate the shift current (typically absent in centrosymmetric crystals) by using Photon Drag. This paper was also featured as an "Editor's Suggestion". Congratulations Likun!
24 Mar 2021 - Xiong Ying's paper on "Atomic configuration photocurrent in van der Waals homostructures" was published in 2D Materials. This work shows how the stacking arrangement and configuration of 2D bilayers can dramatically change its bulk photovoltaic response. Congratulations Xiong Ying!
5 Oct 2020 - Arpit and Likun's paper on "Cooperative Orbital Moments and Edge Magnetoresistance in monolayer WTe2" is published in Physical Review B (Rapid Communications. This work proposes how an unusual cooperative orbital moment can emerge in WTe2 to provide a large edge magnetoresistance. Congratulations Arpit!
12 June 2020 - Our group is highlighted in "A*STAR Research" online magazine in a feature on "Shining light on quantum materials".
11 Dec 2019 - Likun and Jing's paper on "Gate tunable flatbands in van der Waals patterned dielectric superlattices" in published in 2D materials (Open-access). This work a simple strategy for creating gate tunable flat bands in materials such as WS2 without the need for a magic angle. Congratulations Likun and Jing!
21 Nov 2019 - Likun's paper "Shift vector as geometric origin of beam shifts" is published in Physical Review B (Rapid Communication). This work describes how the unusual displacement of a wave beam as it reflects off a boundary can be captured by the geometry of wavefunctions in the propagating media. Congratulations Likun!
18 October 2019 - Our group's theory-experiment collaboration with the Deshmukh group @TIFR on how a topologically trivial band can pick up a non-trivial quantum oscillation phase shift is published in Science Advances. This work showed a Berry phase "proximity effect" that arises from a filling induced coupling between trivial and non-trivial bands.
12 August 2019 - Hasdeo's paper on "Cyclotron motion without magnetic field" (open access) is published in the New Journal of Physics. This work describes how the familiar circulating motion of that electrons experience in a magnetic field (called cyclotron motion) can be achieved in special materials even without magnetic field. Congratulations Hasdeo!
9 July 2019 - Our group's new proposal on "Self-induced Berry flux and out-of-equilibrium plasmonic magnetism" is published in Nature Physics. This work shows that collective modes can take on a life of their own and exhibit symmetry breaking distinct from the ground state they emerged from. See also Nature Physics news and views feature "A sudden twist".
21 Jan 2019 - Our group's experiment-theory collaboration with the Chia group@NTU on giant spin injection from a Ferromagnet (Co) into a semiconductor (MoS2) is published in Nature Physics. See also feature in Asian Scientist "Injecting fresh hope into spintronics".
2 Jan 2019 - Likun's paper on controlling quantum geometry in monolayer WTe2 is published in Physical Review B.
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Group contact information:justinsong [at] ntu [dot] edu
Who we are and what we do:
We are a theoretical group that focuses on unveiling the inner workings and physics of quantum materials. These include topological materials such as Dirac/Weyl semimetals, topological insulators, and 2D van der Waals materials, amongst many others. While focussing on theory, our group has an unusually close rapport with experimental groups. The unique interactions arising from these often lead to new scientific discovery.
A selection of popular material about the group's work:
Collective mode symmetry breaking
Nature Physics news and views commentary - "A sudden twist"
Phys.org feature - "Spontaneous magnetization in a non-magnetic interacting metal"
NTU media release - "Light may magnetize non-magnetic metals"
Metametarial strategies for designer quantum materials
Phys.org feature - "Physicists name and codify new field"
SPMS research highlight - "Synthetic quantum materials"
Geometry and Topology in plasmonics
Physics news and commentary - "Hidden structure of plasmons"
SPMS research highlight - "Theory of internal structure of plasmons"
Manipulating Valleys in 2D Materials
Science magazine perspective - "Harnessing Chirality for Valleytronics"
MIT news - "Physicists find a new way to push electrons around"
IEEE Spectrum - "Weird New Graphene Effect Makes Electrons Scoot Sideways"
Condensed Matter Journal Club - "Topological features and gauge fields in graphene superlattices"
[Click for full list of popular material]
Funding: Our work is supported by the Singapore Ministry of Education, Singapore National Research Foundation, as well as the Nanyang Technological University Singapore.