arXiv subjects

Haozhe Yang

Publications and source records attributed to Haozhe Yang.

18 recordsLinked to original sources

arXiv2026

Gate-tunable charge-spin interconversion in graphene/heavy-metal heterostructures

Spintronics has emerged as a promising field for next-generation devices, offering functionalities beyond complementary metal-oxide-semiconductor (CMOS). A critical challenge in spintronics is to develop systems that can efficiently generate spin currents and enable their long-distance transport. Here, we demonstrate a graphene (Gr)/heavy metal (HM) heterostructure system that combines strong charge-spin interconversion efficiency, induced by the spin Hall effect, with a long spin diffusion length. By employing an industry-friendly magnetron sputtering technique, we deposit HM layers onto few-layer Gr while minimizing structural damage. The proximity effect from the HM enhances the spin Hall angle of Gr while limiting the reduction in its spin diffusion length. Additionally, the spin Hall angle can be tuned via an applied gate voltage, offering high controllability of the system. Importantly, these properties are observed across heterostructures composed of different HMs, indicating the generality of this approach. Our findings establish Gr/HM heterostructures as a scalable and versatile platform for spin current generation, paving the way for advanced spintronic devices with high efficiency, long spin propagation, and straightforward fabrication processes.

cond-mat.mes-hall↗

arXiv2025

Gate tunable spin-charge interconversion in a graphene/ReS$_{2}$ heterostructure up to room temperature

Graphene is a material with great potential in the field of spintronics, combining good conductivity with low spin--orbit coupling (SOC), which allows for the transport of spin currents over long distances. However, this lack of SOC also limits the capacity for manipulating spin current. A key strategy to address this limitation is to induce SOC in graphene via proximity to other two-dimensional (2D) materials. Such proximity-induced SOC can enable spin--charge interconversion (SCI) in graphene, with potential applications in next-generation logic devices. Here, we place graphene in close proximity to the room-temperature ferroelectric candidate ReS$_\mathrm{2}$, inducing SCI for both in-plane and out-of-plane polarized spin current. We attribute the SCI for in-plane polarized current to either the Rashba--Edelstein effect (REE) or the unconventional spin Hall effect (SHE) at the graphene/ReS$_\mathrm{2}$ interface, and the SCI for out-of-plane polarized current to either the conventional SHE in the proximitised graphene, or the unconventional SHE in the bulk of the ReS$_\mathrm{2}$. SCI due to in-plane spin is characterised over a wide range of temperature, up to 300 K and a range of gate voltages.

cond-mat.mes-hall↗

arXiv2025

Geometric Asymmetry-Enhanced Nonreciprocal Supercurrent Transport Revealed by Second-Harmonic Response

Nonreciprocal transport in superconducting systems serves as a powerful probe of symmetry-breaking mechanisms, with the superconducting diode effect emerging as a key manifestation enabling cryogenic rectification. While theoretical models have extensively explored superconducting nonreciprocity, experimental verification remains challenging, as conventional transport measurements struggle to disentangle intrinsic and extrinsic contributions. Nonlinear transport analysis, particularly second-harmonic response, offers an alternative approach by providing a sensitive probe for detecting spatial inversion symmetry breaking in the presence of time-reversal symmetry violation. Here, we systematically investigate the influence of geometric symmetry on nonreciprocal transport by comparing two triangular-extended Hall bar configurations with a symmetric Hall bar control. Second-harmonic nonlinear transport measurements reveal that the triangular extension significantly enhances nonreciprocal response, exhibiting a clear dependence on the base angle of the extension. These findings establish a direct connection between mesoscopic geometry and macroscopic nonreciprocity, demonstrating how spatial symmetry and vortex dynamics govern nonlinear transport. This insight offers a guiding principle for designing superconducting rectification architectures.

cond-mat.supr-con↗

arXiv2025

Dimensionality Enhanced Out-of-Plane Spin Currents in NbIrTe$_4$ for Efficient Field-Free Switching of Perpendicular Magnetization

Efficient generation of out-of-plane (OOP) spin currents is crucial for advanced spintronic memory applications. However, the theoretical understanding and experimental implementation of robust OOP spin currents for high-density and low-power magnetization switching remain significant challenges of spintronics. Here, we demonstrate that transitioning NbIrTe$_4$ from a two-dimensional quantum spin Hall insulator to a three-dimensional type-II Weyl semimetal markedly enhances OOP spin current generation. The bulk topological Weyl semimetal nature of NbIrTe$_4$, characterized by its Weyl cone, significantly enhances the OOP spin Berry curvature, enabling an unprecedented OOP spin Hall conductivity exceeding $10^5\hbar/2e$ $Ω^{-1}m^{-1} $. This enhancement, surpassing the in-plane component by more than fourfold, enables efficient and field-free spin-orbit torque (SOT) switching of perpendicular magnetization with a low current density of 1.4 MA/cm$^2$. The improved spin Hall conductivity reduces the overall power consumption by more than two orders of magnitude compared to existing systems, such as heavy metals. Our findings highlight the pivotal role of dimensionality in harnessing robust OOP spin currents in topological Weyl semimetals, paving the way for the development of high-density, low-power spintronic memory technologies.

cond-mat.mes-hall↗

arXiv2024

Gate-tunable spin Hall effect in trilayer graphene/group-IV monochalcogenide van der Waals heterostructures

Spintronic devices require materials that facilitate effective spin transport, generation, and detection. In this regard, graphene emerges as an ideal candidate for long-distance spin transport owing to its minimal spin-orbit coupling, which, however, limits its capacity for effective spin manipulation. This problem can be overcome by putting spin-orbit coupling materials in close contact to graphene leading to spin-orbit proximity and, consequently, efficient spin-to-charge conversion through mechanisms such as the spin Hall effect. Here, we report and quantify the gate-dependent spin Hall effect in trilayer graphene proximitized with tin sulfide (SnS), a group-IV monochalcogenide which has recently been predicted to be a viable alternative to transition-metal dichalcogenides for inducing strong spin-orbit coupling in graphene. The spin Hall angle exhibits a maximum around the charge neutrality point of graphene up to room temperature. Our findings expand the library of materials that induce spin-orbit coupling in graphene to a new class, group-IV monochalcogenides, thereby highlighting the potential of two-dimensional materials to pave the way for the development of innovative spin-based devices and future technological applications.

cond-mat.mes-hall↗

arXiv2024

Role of hydrogen in decarbonizing China's electricity and hard-to-abate sectors

Green hydrogen has the potential to address two pressing problems in a zero-carbon energy system: balancing seasonal variability of solar and wind in the electricity sector, and replacing fossil fuels in hard-to-abate sectors. However, the previous research only separately modeled the electricity and hard-to-abate sectors, which is unable to capture how the interaction between the two sectors influences the energy system cost. In this study, focusing on China, we deploy an electricity system planning model to examine the cost implications of green hydrogen to fully decarbonize the electricity system and hard-to-abate sectors. Our results reveal that green hydrogen enables a 17% reduction in the levelized cost of a zero-carbon electricity system relative to that without hydrogen. However, cost savings hinge on the availability of underground hydrogen storage capacities and electric transmission expansion. More importantly, coupling hydrogen infrastructure in the electricity and hard-to-abate sectors not only reduces energy costs compared to a decoupled energy system but also makes green hydrogen cost-competitive compared to fossil fuel-based gray and blue hydrogen in China.

eess.SY↗

arXiv2024

A seamless graphene spin valve based on proximity to van der Waals magnet Cr$_2$Ge$_2$Te$_6$

Pristine graphene is potentially an ideal medium to transport spin information. Proximity effects, where a neighbouring material is used to alter the properties of a material in adjacent (or proximitized) regions, can also be used in graphene to generate and detect spins by acquiring spin-orbit coupling or magnetic exchange coupling. However, the development of seamless spintronic devices that are based uniquely on proximity effects remains challenging. Here, we report a two-dimensional graphene spin valve that is enabled by proximity to the van der Waals magnet Cr$_2$Ge$_2$Te$_6$. Spin precession measurements show that graphene acquires both spin-orbit coupling and magnetic exchange coupling when interfaced with the Cr$_2$Ge$_2$Te$_6$. This leads to spin generation by both electrical spin injection and the spin Hall effect, while retaining long-distance spin transport. The simultaneous presence of spin-orbit coupling and magnetic exchange coupling also leads to a sizeable anomalous Hall effect.

cond-mat.mes-hall↗

arXiv2024

Large spin-charge interconversion induced by interfacial spin-orbit coupling in a highly conducting all-metallic system

Spin-charge interconversion in systems with spin-orbit coupling has provided a new route for the generation and detection of spin currents in functional devices for memory and logic such as spin-orbit torque switching in magnetic memories or magnetic state reading in spin-based logic. Disentangling the bulk (spin Hall effect) from the interfacial (inverse spin galvanic effect) contribution has been a common issue to properly quantify the spin-charge interconversion in these systems, being the case of Au paradigmatic. Here, we obtain a large spin-charge interconversion at a highly conducting Au/Cu interface which is experimentally shown to arise from the inverse spin galvanic effect of the interface and not from the spin Hall effect of bulk Au. We use two parameters independent of the microscopic details to properly quantify the spin-charge interconversion and the spin losses due to the interfacial spin-orbit coupling, providing an adequate benchmarking to compare with any spin-charge interconversion system. The good performance of this metallic interface, not based in Bi, opens the path to the use of much simpler light/heavy metal systems.

cond-mat.mes-hall↗

arXiv2024

Control of charge-spin interconversion in van der Waals heterostructures with chiral charge density waves

A charge density wave (CDW) represents an exotic state in which electrons are arranged in a long range ordered pattern in low-dimensional materials. Although our understanding of the fundamental character of CDW has been enriched after extensive studies, its relationship with functional phenomena remains relatively limited. Here, we show an unprecedented demonstration of a tunable charge-spin interconversion (CSI) in graphene/1T-TaS$_2$ van der Waals heterostructures by manipulating the distinct CDW phases in 1T-TaS$_2$. Whereas CSI from spins polarized in all three directions are observed in the heterostructure when the CDW phase does not show commensurability, the output of one of the components disappears and the other two are enhanced when the CDW phase becomes commensurate. The experimental observation is supported by first-principles calculations, which evidence that chiral CDW multidomains are at the origin of the switching of CSI. Our results uncover a new approach for on-demand CSI in low-dimensional systems, paving the way for advanced spin-orbitronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Percolating Superconductivity in Air-Stable Organic-Ion Intercalated MoS2

When doped into a certain range of charge carrier concentrations, MoS2 departs from its pristine semiconducting character to become a strongly correlated material characterized by exotic phenomena such as charge density waves or superconductivity. However, the required doping levels are typically achieved using ionic-liquid gating or air-sensitive alkali-ion intercalation, which are not compatible with standard device fabrication processes. Here, we report on the emergence of superconductivity and a charge density wave phase in air-stable organic cation intercalated MoS2 crystals. By selecting two different molecular guests, we show that these correlated electronic phases depend dramatically on the intercalated cation, demonstrating the potential of organic ion intercalation to finely tune the properties of 2D materials. Moreover, we find that a fully developed zero-resistance state is not reached in few-nm-thick flakes, indicating the presence of three-dimensional superconductive paths which are severed by the mechanical exfoliation. We ascribe this behavior to an inhomogeneous charge carrier distribution, which we probe at the nanoscale using scanning near-field optical microscopy. Our results establish organic-ion intercalated MoS2 as a platform to study the emergence and modulation of correlated electronic phases.

cond-mat.supr-con↗

arXiv2024

Gate-tunable spin Hall effect in an all-light-element heterostructure: graphene with copper oxide

Graphene is a light material for long-distance spin transport due to its low spin-orbit coupling, which at the same time is the main drawback to exhibit a sizeable spin Hall effect. Decoration by light atoms has been predicted to enhance the spin Hall angle in graphene while retaining a long spin diffusion length. Here, we combine a light metal oxide (oxidized Cu) with graphene to induce the spin Hall effect. Its efficiency, given by the product of the spin Hall angle and the spin diffusion length, can be tuned with the Fermi level position, exhibiting a maximum (1.8 $\pm$ 0.6 nm at 100 K) around the charge neutrality point. This all-light-element heterostructure shows a larger efficiency than conventional spin Hall materials. The gate-tunable spin Hall effect is observed up to room temperature. Our experimental demonstration provides an efficient spin-to-charge conversion system free from heavy metals and compatible with large-scale fabrication.

cond-mat.mes-hall↗

arXiv2024

Towards General Visual-Linguistic Face Forgery Detection

Deepfakes are realistic face manipulations that can pose serious threats to security, privacy, and trust. Existing methods mostly treat this task as binary classification, which uses digital labels or mask signals to train the detection model. We argue that such supervisions lack semantic information and interpretability. To address this issues, in this paper, we propose a novel paradigm named Visual-Linguistic Face Forgery Detection(VLFFD), which uses fine-grained sentence-level prompts as the annotation. Since text annotations are not available in current deepfakes datasets, VLFFD first generates the mixed forgery image with corresponding fine-grained prompts via Prompt Forgery Image Generator (PFIG). Then, the fine-grained mixed data and coarse-grained original data and is jointly trained with the Coarse-and-Fine Co-training framework (C2F), enabling the model to gain more generalization and interpretability. The experiments show the proposed method improves the existing detection models on several challenging benchmarks. Furthermore, we have integrated our method with multimodal large models, achieving noteworthy results that demonstrate the potential of our approach. This integration not only enhances the performance of our VLFFD paradigm but also underscores the versatility and adaptability of our method when combined with advanced multimodal technologies, highlighting its potential in tackling the evolving challenges of deepfake detection.

cs.CV↗

arXiv2023

Twist-angle tunable spin texture in WSe$_2$/graphene van der Waals heterostructures

Angle-twisting engineering has emerged as a powerful tool for modulating electronic properties in van der Waals heterostructures. Recent theoretical works have predicted the modulation of spin texture in graphene-based heterostructures by twist angle, although an experimental verification is missing. Here, we demonstrate the tunability of the spin texture and associated spin-charge interconversion with twist angle in WSe$_2$/graphene heterostructures by using spin precession experiments. For specific twist angles, we experimentally detect a spin component radial with the electron's momentum, in addition to the standard orthogonal component. Our results show that the helicity of the spin texture can be reversed by angle twisting, highlighting its critical role on the spin-orbit properties of WSe$_2$/graphene heterostructures and paving the way for the development of novel spin-twistronic devices.

cond-mat.mes-hall↗

arXiv2022

Unconventional charge-to-spin conversions in graphene/MoTe2 van der Waals heterostructures

Spin-charge interconversion (SCI) is a central phenomenon to the development of spintronic devices from materials with strong spin-orbit coupling (SOC). In the case of materials with high crystal symmetry, the only allowed SCI processes are those where the spin current, charge current and spin polarization directions are orthogonal to each other. Consequently, standard SCI experiments are designed to maximize the signals arising from the SCI processes with conventional mutually orthogonal geometry. However, in low-symmetry materials, certain non-orthogonal SCI processes are also allowed. Since the standard SCI experiment is limited to charge current flowing only in one direction in the SOC material, certain allowed SCI configurations remain unexplored. In this work, we performed a thorough SCI study in a graphene-based lateral spin valve combined with low-symmetry MoTe$_2$. Due to a very low contact resistance between the two materials, we could detect SCI signals using both a standard configuration, where the charge current is applied along the MoTe$_2$, and a recently introduced (3D-current) configuration, where the charge current flow can be controlled in three directions within the heterostructure. As a result, we observed three different SCI components, one orthogonal and two non-orthogonal, giving new insight into the SCI processes in low-symmetry materials. The large SCI signals obtained at room temperature, along with the versatility of the 3D-current configuration, provide feasibility and flexibility to the design of the next generation of spin-based devices.

cond-mat.mes-hall↗

arXiv2022

All-electrical spin-to-charge conversion in sputtered Bi$_x$Se$_{1-x}$

One of the major obstacles to realizing spintronic devices such as MESO logic devices is the small signal magnitude used for magnetization readout, making it important to find materials with high spin-to-charge conversion efficiency. Although intermixing at the junction of two materials is a widely occurring phenomenon, its influence on material characterization and the estimation of spin-to-charge conversion efficiencies is easily neglected or underestimated. Here, we demonstrate all electrical spin-to-charge conversion in Bi$_x$Se$_{1-x}$ nanodevices and show how the conversion efficiency can be overestimated by tens of times depending on the adjacent metal used as a contact. We attribute this to the intermixing-induced compositional change and the properties of a polycrystal that lead to drastic changes in resistivity and spin Hall angle. Strategies to improve the spin-to-charge conversion signal in similar structures for functional devices are discussed.

cond-mat.mes-hall↗

arXiv2022

Effect of Chiral Damping on the dynamics of chiral domain walls and skyrmions

Friction plays an essential role in most physical processes that we experience in our everyday life. Examples range from our ability to walk or swim, to setting boundaries of speed and fuel efficiency of moving vehicles. In magnetic systems, the displacement of chiral domain walls (DW) and skyrmions (SK) by Spin Orbit Torques (SOT), is also prone to friction. Chiral damping, the dissipative counterpart of the Dzyaloshinskii Moriya Interaction (DMI), plays a central role in these dynamics. Despite experimental observation, and numerous theoretical studies confirming its existence, the influence of chiral damping on DW and SK dynamics has remained elusive due to the difficulty of discriminating from DMI. Here we unveil the effect that chiral damping has on the flow motion of DWs and SKs driven by current and magnetic field. We use a static in-plane field to lift the chiral degeneracy. As the in-plane field is increased, the chiral asymmetry changes sign. When considered separately, neither DMI nor chiral damping can explain the sign reversal of the asymmetry, which we prove to be the result of their competing effects. Finally, numerical modelling unveils the non-linear nature of chiral dissipation and its critical role for the stabilization of moving SKs.

cond-mat.mes-hall↗

arXiv2022

Gate-tuneable and chirality-dependent charge-to-spin conversion in Tellurium nanowires

Chiral materials are the ideal playground for exploring the relation between symmetry, relativistic effects, and electronic transport. For instance, chiral organic molecules have been intensively studied to electrically generate spin-polarized currents in the last decade, but their poor electronic conductivity limits their potential for applications. Conversely, chiral inorganic materials such as Tellurium are excellent electrical transport materials, but have not been explored to enable the electrical control of spin polarization in devices. Here, we demonstrate the all-electrical generation, manipulation, and detection of spin polarization in chiral single-crystalline Tellurium nanowires. By recording a large (up to 7%) and chirality-dependent unidirectional magnetoresistance, we show that the orientation of the electrically generated spin polarization is determined by the nanowire handedness and uniquely follows the current direction, while its magnitude can be manipulated by an electrostatic gate. Our results pave the way for the development of magnet-free chirality-based spintronic devices.

cond-mat.mes-hall↗

arXiv2021

Mechanism of Spin-Orbit Torques in Platinum Oxide Systems

Spin-Orbit Torque (SOT) Magnetic Random-Access Memories (MRAM) have shown promising results towards the realization of fast, non-volatile memory systems. Oxidation of the heavy-metal (HM) layer of the SOT-MRAM has been proposed as a method to increase its energy efficiency. But the results are widely divergent due to the difficulty in controlling the HM oxidation because of its low enthalpy of formation. Here, we reconcile these differences by performing a gradual oxidation procedure, which allows correlating the chemical structure to the physical properties of the stack. As an HM layer, we chose Pt because of the strong SOT and the low enthalpy of formation of its oxides. We find evidence of an oxide inversion layer at the FM/HM interface: the oxygen is drawn into the FM, while the HM remains metallic near the interface. We further demonstrate that the oxygen migrates in the volume of the FM layer rather than being concentrated at the interface. Consequently, we find that the intrinsic magnitude of the SOT is unchanged compared to the fully metallic structure. The previously reported apparent increase of SOTs is not intrinsic to platinum oxide and instead arises from systemic changes produced by oxidation.

cond-mat.mes-hall↗