M-point Twist: Unlocking Quantum Phases in Moiré Materials
Researchers Discover New Twistable Materials Like M-Point and k-Point, Opening Up Unprecedented Quantum Potential.
Revolutionising Quantum Physics using Moiré Structures
Twisted materials, or moiré structures, have altered current physics by creating new phases of matter by geometric manipulation. When two periodic patterns are stacked with a slight misalignment, they form rippling patterns called “moiré”—an atomic-level physics principle.
Stacking two atomically thin sheets of the same or different material and gently rotating one layer causes a fundamental alteration. The composite material has distinct qualities from its layers. By creating new quantum states through careful twist angle manipulation, physicists can investigate new experimental fields. Moiré structures have great potential for basic science and practical applications including single-photon detectors, ultrasensitive terahertz sensors, and quantum simulators.
Twisted bilayer graphene is a stunning example of superconductivity, a situation in which electrons flow without resistance, which occurs unexpectedly.
M-point Twist Unlocks Quantum Possibilities
Before this, twisting material research focused on hexagonal lattices spun around “K-points,” unique regions of electrical momentum symmetrical under 120-degree rotations. Few materials have been experimentally explored, including graphene, MoTe₂, MoSe₂, and WSe₂. The recent Nature study expands the "moiré landscape" by introducing a new twisting paradigm based on the electron momentum's M-point Twist.
Dumitru Călugăru (PhD 2024, Princeton), a Leverhulme-Peierls fellow at Oxford, explained that K-point twisting limited inquiry to “a small corner of the material universe.” By focussing on M-point Twist, scientists “unlock a completely new class of twisted quantum materials with entirely new quantum behavior,” where the electronic band minimum is key.
M-point Twisted Materials' Unique Properties
M-point Twist bands are flat and topologically trivial, unlike K-point twisting bands. Princeton postdoctoral researcher Haoyu Hu says the bands at the M-point Twist have a “previously unnoticed type of symmetry,” making them rare and sometimes one-dimensional, affecting their quantum behaviour.
Yi Jiang and Hanqi Pi (Donostia International Physics Centre) proved through microscopic ab initio calculations that electron bands flatten considerably at low twist angles of about three degrees after more than six months of computational work. Flattening electron bands increases electron-to-electron interactions and introduces new quantum phenomena by slowing electrons.
Paths to exotic quantum states
Due to electron localisation, scientists may now experimentally achieve several quantum states. Jiang says this flattening can localise electrons in kagome or hexagonal lattices. Pi claimed this localisation allows them to experimentally realise many quantum states, including quantum spin liquids.
High-temperature superconductivity may be made possible by quantum spin liquids, which have long captivated physicists.Doping (adding or withdrawing electrons) and other critical material properties are difficult to manage, hence they have never been experimentally detected in bulk materials. More experimental control is possible because to the customisable structure of twisted materials and electrostatic gating, which allows electron doping without material degradation and overcomes numerous historical difficulties.
A crucial step towards seeing these states in practical materials is the research team's theoretical predictions and thorough electrical models. Unidirectional spin liquids and orthonormal dimer valence bond phases are peculiar to the M-point Twist system and newly discovered.
Experimental Progress and International Collaboration
Princeton University, the Donostia International Physics Centre, Oxford University, the Max Planck Society, Cornell University, Ludwig Maximilian University of Munich, the University of Sherbrooke, and the University of Florida conducted this research. Materials experts, chemists, theoretical and computational physicists from around the world are on the team.
Scientists found hundreds of possible materials for this novel bending and classified them by electrical band minimum. We selected SnSe₂ and ZrS₂, two materials exhibiting band minimums near the M-point Twist, for further study.
This research goes beyond theory, which matters. Quantum materials chemistry collaborators Leslie Schoop (Princeton University) and Claudia Felser (Max Planck Institute, Dresden) have synthesised bulk crystals of several candidate materials, a crucial first step towards practical implementation. World-renowned 2D material experts Dmitri Efetov from Ludwig Maximilian University of Munich, Jie Shan, and Kin Fai Mak from Cornell University are exfoliating these bulk crystals into single-layer sheets to prove the platform is experimentally achievable.
Once twisted, gated, and measured, Princeton University physics professor B said these new quantum states may be tangible. Andrei Bernevig emphasises experimental realisation. It seems like every new twist we do brings shocks, he said. In essence, these materials open the door to quantum states of matter never before conceived. Due to their experimental controllability, the possibilities are infinite.
