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(July 14, 2023) Monolayer Chemistry - In this work, we report a chamber-free, on-chip approach for synthesizing 2D crystalline structures directly in a nanoscale surface-confined 2D space defined by a template 2D material. The method is based on a surprising discovery of a rapid, long-distance, non-Fickian transport of a uniform layer of atomically thin palladium (Pd) on a monolayer crystal of tungsten ditelluride (WTe2), at temperatures well below the known melting points of all materials involved (watch the video to the right). The resulting nanoconfined growth realizes a controlled formation of a stable new 2D crystalline material. The reaction and approach are generalizable to various combinations of metal and template 2D materials and highly compatible with nanodevice fabrication, promising to expand the library of 2D materials and their functionalities. This work is led by Yanyu Jia, in collaboration with groups of Prof. Schoop and Prof. Yao.
2D chemistry is interesting!
Pdtransport_vd.mp4Read More: Our work on Surface-Confined Two-Dimensional MassTransport and Crystal Growth on Monolayer Materials arXiv:2307.06477 (2023) Nature Synthesis Link
Extended reading: Prof. Wu's previous works on vapor deposition growth of monolayer TMDs and their lateral heterojunctions.
(August 1, 2023) Ultralow Temperature Optics - Optical spectroscopy of quantum materials at ultralow temperatures is rarely explored, yet it may provide critical characterizations of quantum phases not possible using other approaches. In the past 2 years, we have been focusing on developing a new instrumental platform based on which we hope to explore optics of 2D quantum phases at millikelvin temperatures inside a dilution refrigerator. In the current setup, we achieve spectroscopic measurements in the far-infrared regime at a base temperature as low as ~ 43 mK and a sample electron temperature of ~ 450 mK. We are very excited about the potential use of this instrument in the coming years!!
This project is led by Ayelet, Mike, Pengjie and Yue, supported by the entire Wu lab members. A wonderful team effort!!
Read more: Our work on A Platform for Far-Infrared Spectroscopy of Quantum Materials at Millikelvin Temperatures arXiv:2308.00610 Review of Scientific Instruments (2023) Link
(March 12, 2023) Monolayer WTe2 - Quantum critical points (QCP) associated with quantum phase transitions are highly intriguing states of matter; yet they are difficult to study. An example is the superconductor to insulator or metal transition in two dimensions (2D), a topic that has a long history in condensed matter research, but many problems remain unsolved. In a project led by Tiancheng Song and supported by the entire Wu lab members, we recently developed novel devices that enable the precise measurements of superconducting fluctuations in 2D materials at millikelvin temperatures, based on the Nernst effect. We discover a unconventional QCP in monolayer WTe2. The observed superconducting quantum fluctuations are anomalous and have no prior analogue. The phenomena, especially including the abrupt disappearance of fluctuations right below the critical density (we call it "sudden death"), are unexpected in the conventional Landau-Ginzburg picture. It triggers one to ask whether an "order-to-order" continuous quantum phase transition is realized here. Examining this question in a spin model at theoretical level two decades ago led to many discussions on the idea of "deconfined quantum criticality". Independent to theories, our work raises intriguing questions experimentally regarding the nature of superconducting transition in WTe2. While the explanation to the anomalous fluctuations is widely open at this stage, we are excited about the opportunities offered by WTe2 here for examining novel QCPs and phase transitions.
Read more:
Our work on Unconventional Superconducting Quantum Criticality in Monolayer WTe2 arXiv:2303.06540 Nature Physics (2023) Link
Extended reading: a review on Phuan Ong's previous works on Nernst effect in cuprates.
(May 04, 2022) tWTe2 (5 degree) - The Luttinger liquid model of 1D electronic systems provides a powerful tool for understanding strongly correlated physics, e.g., the phenomena of spin-charge separation. In a recent experiment led by Pengjie and Guo, we have found that twisted bilayer WTe2 (tWTe2), stacked at a small interlayer twist angle (~ 5 degree), hosts a 2D array of 1D electronic channels. Transport measurements reveal Luttinger liquid behaviors in such a 2D anisotropic phase. We are excited about the results because they are expanding the Luttinger liquid physics from 1D to 2D systems and are potentially relevant to various coupled-wire models!
Read more:
One Dimensional Luttinger Liquids in a Two Dimensional Moire Lattice (arXiv, Nature 2022)
(Oct 21, 2020) Congratulations: Our first work - on the surprising observation of Landau quantization in the insulator state of monolayer WTe2 - is now accepted to Nature! Congratulations to Pengjie, Guo and Yanyu!!! A lot of hard work!
This has triggered a lot of excitement in our lab to search for very exotic quantum particles and phases hidden in insulators, including ground-state excitons, charge neutral fermions and fractionalized insulators. Fascinating new opportunities offered by 2D crystals and devices!
Read more:
Our Paper on Landau Quantization in the Monolayer Insulator (Nature, 2021) (Princeton University News)
Our Paper on the Monolayer Excitonic Insulator (Nature Physics 2021)
(Oct 25, 2018) Monolayer WTe2: In this 2D crystal, two interesting quantum states of matter – topological insulator and superconductor – can be chosen at will! -- Ready for Majorana? Let's see.
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