An official website of the United States government
Abstract Emergent color centers with accessible spins hosted by van der Waals materials have attracted substantial interest in recent years due to their significant potential for implementing transformative quantum sensing technologies. Hexagonal boron nitride (hBN) is naturally relevant in this context due to its remarkable ease of integration into devices consisting of low-dimensional materials. Taking advantage of boron vacancy spin defects in hBN, we report nanoscale quantum imaging of low-dimensional ferromagnetism sustained in Fe 3 GeTe 2 /hBN van der Waals heterostructures. Exploiting spin relaxometry methods, we have further observed spatially varying magnetic fluctuations in the exfoliated Fe 3 GeTe 2 flake, whose magnitude reaches a peak value around the Curie temperature. Our results demonstrate the capability of spin defects in hBN of investigating local magnetic properties of layered materials in an accessible and precise way, which can be extended readily to a broad range of miniaturized van der Waals heterostructure systems.
more »
« less
Hall signal dominated microwave transmission through graphene-loaded waveguides
This paper reports the discovery that resistively-coupled coplanar waveguides in van der Waals heterostructures are dominated by Hall conductivity rather than longitudinal conductivity, unlike traditional capacitively-coupled systems. We observed clear integer quantum Hall effect plateaus that were frequency-independent from below 1 GHz to over 7 GHz, with sensitivity strongly dependent on device geometry. We developed a T-network circuit model that successfully explains the nearly threefold enhancement in measurement sensitivity observed in samples with long contact regions compared to theoretical predictions. This work establishes important design principles for microwave measurements of two-dimensional electron systems in van der Waals materials and opens pathways for contactless characterization of materials where Ohmic contacts are challenging to achieve.
more »
« less
- Award ID(s):
- 1943389
- PAR ID:
- 10642701
- Publisher / Repository:
- APS Physical Review
- Date Published:
- Journal Name:
- Physical Review B
- Volume:
- 111
- Issue:
- 19
- ISSN:
- 2469-9950
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Semiconductor microcavities with a high quality‐factor are an important component for photonics research and technology, especially in the strong coupling regime. While van der Waals semiconductors have emerged as an interesting platform for photonics due to their strong exciton–photon interaction strength and engineering flexibility, incorporating them in photonic devices requires heterogeneous integration and remains a challenge. This study demonstrates a method to assemble high quality factor microcavities for van der Waals materials, using high reflectance top mirrors which, similar to van der Waals materials themselves, can be nondestructively and reliably peeled off the substrate and transferred onto the rest of the device. Microcavities are created with quality factors consistently above 2000 and up to 11000 ± 800; and the strong coupling regime is demonstrated. The method can be generalized to other types of heterogeneously integrated photonic structures and will facilitate research on cavity quantum electrodynamic and photonic systems using van der Waals materials.more » « less
-
The developing material class of van der Waals (vdW) magnets has attracted great interest due to their novel properties such as gate and strain tunable magnetism. Magnetism at the atomic limit remains difficult to explore however due to the air instability of most vdW ferromagnets. In this work, we demonstrate that pre-fabricated Hall bar electrodes can be used to probe magnetism in Fe3GeTe2 (FGT) flakes via the anomalous Hall effect. Utilizing this device structure, we systematically investigated the magnetic properties of FGT. Clear ferromagnetic hysteresis windows were clearly observed at temperatures up to 200 K. These vdW Hall bar structures provides a highly efficient and damage-free strategy for metal integration, which could be used in many other 2D magnetic materials.more » « less
-
Abstract Group IV‐VI van der Waals crystals (MX, where M = Ge, Sn, and X = S, Se) are receiving increasing attention as semiconducting thermoelectric materials with nontoxic, earth‐abundant composition. Among them, SnSe is considered the most promising as it exhibits a remarkably high thermoelectric figure of merit (ZT), initially attributed to its low lattice thermal conductivity. However, it has been shown that the electronic band structure plays an equally important role in thermoelectric performance. A certain band shape, described as a “pudding mold” and characteristic for all MXs, has been predicted to significantly improveZTby combining good electrical conductivity with high Seebeck coefficient. This subtle feature is explored experimentally for GeS, SnS, and SnSe by means of angle‐resolved photoemission spectroscopy. The technique also allows for the determination of the effective mass and Fermi level position of as‐grown undoped crystals. The findings are supported by ab initio calculations of the electronic band structure. The results greatly contribute to the general understanding of the valence band dispersion of MXs and reinforce their potential as high‐performance thermoelectric materials, additionally giving prospects for designing systems consisting of van der Waals heterostructures.more » « less
-
2D materials have attracted broad attention from researchers for their unique electronic proper-ties, which may be been further enhanced by combining 2D layers into vertically stacked van der Waals heterostructures. Among the superlative properties of 2D systems, thermoelectric energy (TE) conversion promises to enable targeted energy conversion, localized thermal management, and thermal sensing. However, TE conversion efficiency remains limited by the inherent tradeoff between conductivity and thermopower. In this paper, we use first-principles calculation to study graphene-based van der Waals heterostructures (vdWHs) composed of graphene layers and hexagonal boron nitride (h-BN). We compute the electronic band structures of heterostructured systems using Quantum Espresso and their thermoelectric (TE) properties using BoltzTrap2. Our results have shown that stacking layers of these 2D materials opens a bandgap, increasing it with the number of h-BN interlayers, which significantly improves the power factor (PF). We predict a PF of ~1.0x10 11 W/K 2 .m.s for the vdWHs, nearly double compared to 5x10 10 W/K 2 .m.s that we obtained for single-layer graphene. This study gives important information on the effect of stacking layers of 2D materials and points toward new avenues to optimize the TE properties of vdWHs.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1103/PhysRevB.111.195410
