An official website of the United States government
Abstract Motivated by recent experimental observations of opposite Chern numbers in R-type twisted MoTe2and WSe2homobilayers, we perform large-scale density-functional-theory calculations with machine learning force fields to investigate moiré band topology across a range of twist angles in both materials. We find that the Chern numbers of the moiré frontier bands change sign as a function of twist angle, and this change is driven by the competition between moiré ferroelectricity and piezoelectricity. Our large-scale calculations, enabled by machine learning methods, reveal crucial insights into interactions across different scales in twisted bilayer systems. The interplay between atomic-level relaxation effects and moiré-scale electrostatic potential variation opens new avenues for the design of intertwined topological and correlated states, including the possibility of mimicking higher Landau level physics in the absence of magnetic field.
more »
« less
Anomalous superconductivity in twisted MoTe 2 nanojunctions
Introducing superconductivity in topological materials can lead to innovative electronic phases and device functionalities. Here, we present a unique strategy for quantum engineering of superconducting junctions in moiré materials through direct, on-chip, and fully encapsulated 2D crystal growth. We achieve robust and designable superconductivity in Pd-metalized twisted bilayer molybdenum ditelluride (MoTe2) and observe anomalous superconducting effects in high-quality junctions across ~20 moiré cells. Unexpectedly, the junction develops enhanced, instead of weakened, superconducting behaviors, exhibiting fluctuations to a higher critical magnetic field compared to its adjacent Pd7MoTe2superconductor. In addition, the critical current further exhibits a notable V-shaped minimum at zero magnetic field. These features are unexpected in conventional Josephson junctions and absent in junctions of natural bilayer MoTe2created using the same approach. We discuss implications of these observations, including the possible formation of mixed even- and odd-parity superconductivity at the moiré junctions. Our results also demonstrate a pathway to engineer and investigate superconductivity in fractional Chern insulators.
more »
« less
- PAR ID:
- 10585805
- Publisher / Repository:
- Science Advances
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 11
- Issue:
- 5
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The heavy fermion material UTe2is a candidate topological superconductor that exhibits multiple magnetic field–induced superconducting phases. One such phase exists only at fields greater than 40 tesla, a considerable scale given its critical temperature of only 2 K. Here, we extend measurements of this state with fields outside of thebccrystallographic plane and reveal its core structure: The superconducting phase wraps around thebaxis in a halo-like fashion and appears to be stabilized by a field component perpendicular to the magnetic easy axis. This angle dependence points to a multicomponent spin-triplet order parameter with a finite angular momentum of the Cooper pairs. The pairing mechanism remains enigmatic, and UTe2’s specific magnetophilic superconducting tendencies seem incompatible with existing models for field-enhanced superconductivity.more » « less
-
Abstract Twisted transition metal dichalcogenide (TMD) bilayers have enabled the discovery of superconductivity, ferromagnetism, correlated insulators, and a series of new topological phases of matter. However, the connection between these electronic phases of matter and the underlying band structure singularities has remained largely unexplored. Here, combining magnetic circular dichroism and exciton sensing measurements, we investigate the influence of a van Hove singularity (vHS) on the correlated phases in bilayer WSe2with twist angle between 2 and 3 degrees. By tuning the vHS across the Fermi level using electric and magnetic fields, we observe Stoner ferromagnetism below moiré lattice filling one and Chern insulators at filling one. The experimental observations are supported by the continuum model band structure calculations. Our results highlight the prospect of engineering electronic phases of matter in moiré materials by tunable van Hove singularities.more » « less
-
Abstract MoTe2possesses two polymorphs: semiconducting (2H) and semi‐metallic (1T') phases, separated by a small energy barrier. The 1T' phase of MoTe2provides an excellent platform for forming low‐resistance contacts with the 2H phase, where the low density of states in the semimetal suppresses metal‐induced gap states (MIGS) and reduces Fermi‐level pinning. However, existing fabrication methods encounter significant challenges in location control, contact quality, and device scaling. In this work, a new method is developed to synthesize 1T'‐2H heterophase structures using chemical vapor deposition (CVD). By depositing pre‐patterned molybdenum, seamless in‐plane 1T'‐2H MoTe2heterophase junctions are synthesized in a single‐step process, achieving precise control over the location of each phase and uniform MoTe2coverage across centimeter‐scale surfaces. Field‐effect transistors incorporating 1T' MoTe2contacts and 2H MoTe2channels show p‐type dominant transfer characteristics and exceptionally low contact resistance. The unique attributes of these 1T' MoTe2contacts, including pristine interfaces, reduced Schottky barrier heights, and seamless edge contacts, combined with the pronounced ambipolarity of the grown 2H MoTe2, demonstrate the commercial viability of this process for 2D transistors, addressing the long‐standing challenge of contact resistance in 2D transistor technology.more » « less
-
ABSTRACT Interface‐induced superconductivity has recently been achieved by stacking a magnetic topological insulator layer on an antiferromagnetic FeTe layer. However, the mechanism driving this emergent superconductivity remains unclear. Here, we employ molecular beam epitaxy to grow a 1T‐CrTe2layer, a 2D ferromagnet with a Curie temperature up to room temperature, on a FeTe layer. These 1T‐CrTe2/FeTe heterostructures show superconductivity with a critical temperature of ∼12 K. Through magnetic force microscopy measurements, we observe the Meissner effect on the surface of the 1T‐CrTe2layer. Our electrical transport measurements reveal that the 1T‐CrTe2/FeTe heterostructures exhibit nonreciprocal charge transport behavior, characterized by a large magneto‐chiral anisotropy coefficient. The enhanced nonreciprocal charge transport in 1T‐CrTe2/FeTe heterostructures provides a promising platform for exploring the magnetically controllable superconducting diode effect.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1126/sciadv.adq5712
