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Register a new userGiant Tunneling Magnetoresistance in Spin-Filter van der Waals Heterostructures
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Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here we report novel multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. These devices also show multiple resistance states as a function of magnetic field, suggesting the potential for multi-bit functionalities using an individual vdW sf-MTJ. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI3. Our work reveals the possibility to push magnetic information storage to the atomically thin limit, and highlights CrI3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.
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In this article we review recent work on van der Waals (vdW) systems in which at least one of the components has strong spin-orbit coupling. We focus on a selection of vdW heterostructures to exemplify the type of interesting electronic properties that can arise in these systems. We first present a general effective model to describe the low energy electronic degrees of freedom in these systems. We apply the model to study the case of (vdW) systems formed by a graphene sheet and a topological insulator. We discuss the electronic transport properties of such systems and show how they exhibit much stronger spin-dependent transport effects than isolated topological insulators. We then consider vdW systems in which the layer with strong spin-orbit coupling is a monolayer transition metal dichalcogenide (TMD) and briefly discuss graphene-TMD systems. In the second part of the article we discuss the case in which the vdW system includes a superconducting layer in addition to the layer with strong spin-orbit coupling. We show in detail how these systems can be designed to realize odd-frequency superconducting pair correlations. Finally, we discuss twisted graphene-NbSe2 bilayer systems as an example in which the strength of the proximity-induced superconducting pairing in the normal layer, and its Ising character, can be tuned via the relative twist angle between the two layers forming the heterostructure.
We develop a theory for interlayer tunneling in van der Waals heterostructures driven under a strong electromagnetic field, using graphene/{it h}-BN/graphene as a paradigmatic example. Our theory predicts that strong anti-resonances appear at bias voltage values equal to an integer multiple of the light frequency. These features are found to originate from photon-assisted resonant tunneling transitions between Floquet sidebands of different graphene layers, and are unique to two-band systems due to the interplay of both intraband and interband tunneling transitions. Our results point to the possibility of tunneling localization in van der Waals heterostructures using strong electromagnetic fields.
The development of van der Waals (vdW) crystals and their heterostructures has created a fascinating platform for exploring optoelectronic properties in the two-dimensional (2D) limit. With the recent discovery of 2D magnets, the control of the spin degree of freedom can be integrated to realize 2D spin-optoelectronics with spontaneous time-reversal symmetry breaking. Here, we report spin photovoltaic effects in vdW heterostructures of atomically thin magnet chromium triiodide (CrI3) sandwiched by graphene contacts. In the absence of a magnetic field, the photocurrent displays a distinct dependence on light helicity, which can be tuned by varying the magnetic states and photon energy. Circular polarization-resolved absorption measurements reveal that these observations originate from magnetic-order-coupled and thus helicity-dependent charge-transfer exciton states. The photocurrent displays multiple plateaus as the magnetic field is swept, which are associated with different spin configurations enabled by the layered antiferromagnetism and spin-flip transitions in CrI3. Remarkably, giant photo-magnetocurrent is observed, which tends to infinity for a small applied bias. Our results pave the way to explore emergent photo-spintronics by engineering magnetic vdW heterostructures.
In van der Waals (vdW) heterostructures formed by stacking two monolayer semiconductors, lattice mismatch or rotational misalignment introduces an in-plane moire superlattice. While it is widely recognized that a moire superlattice can modulate the electronic band structure and lead to novel transport properties including unconventional superconductivity and insulating behavior driven by correlations, its influence on optical properties has not been investigated experimentally. We present spectroscopic evidence that interlayer excitons are confined by the moire potential in a high-quality MoSe2/WSe2 heterobilayer with small rotational twist. A series of interlayer exciton resonances with either positive or negative circularly polarized emission is observed in photoluminescence, consistent with multiple exciton states confined within the moire potential. The recombination dynamics and temperature dependence of these interlayer exciton resonances are consistent with this interpretation. These results demonstrate the feasibility of engineering artificial excitonic crystals using vdW heterostructures for nanophotonics and quantum information applications.
Discoveries of interfacial topological Hall effect (THE) provide an ideal platform for exploring physics arising from the interplay between topology and magnetism. The interfacial topological Hall effect is closely related to the Dzyaloshinskii-Moriya interaction (DMI) at interface and topological spin textures. However, it is difficult to achieve a sizable THE in heterostructures due to the stringent constraints on the constituents of THE heterostructures such as strong spin-orbit coupling (SOC). Here we report the observation of a giant THE signal of 1.39 $muOmegacdot$cm in the van der Waals heterostructures of CrTe2/Bi2Te3 fabricated by molecular beam epitaxy, a prototype of two-dimensional (2D) ferromagnet (FM)/topological insulator (TI). This large magnitude of THE is attributed to an optimized combination of 2D ferromagnetism in CrTe2, strong SOC in Bi2Te3, and an atomically sharp interface. Our work reveals CrTe2/Bi2Te3 as a convenient platform for achieving large interfacial THE in hybrid systems, which could be utilized to develop quantum science and high-density information storage.
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