arXiv subjects

Chen-Yu Hu

Publications and source records attributed to Chen-Yu Hu.

6 recordsLinked to original sources

arXiv2026

Distinct Surface and Bulk Superconductivity in the Kagome Superconductor SrSn$_3$

Surface and bulk superconductivity may possess fundamentally different superconducting properties in quantum materials with nontrivial electronic structures, yet their superimposed spectroscopic signatures often prevent direct experimental access to each superconducting channel. Here we reveal, in epitaxial films of the kagome superconductor SrSn$_3$, distinct surface and bulk superconducting channels with markedly different superconducting gaps, upper critical fields, and vortex-core electronic states by tuning the tunneling junction resistance in scanning tunneling spectroscopy. The surface superconductivity is characterized by a thickness-independent superconducting gap and an enhanced upper critical field, whereas the bulk superconducting channel exhibits a larger superconducting gap that decreases with reducing film thickness and a much lower upper critical field. Within magnetic vortex cores, robust non-split zero-bias conductance peaks are observed exclusively in the surface superconducting channel, while pronounced zero-bias suppression is consistently associated with the bulk superconducting channel. These findings demonstrate that the vortex-core electronic structure depends sensitively on the underlying superconducting channel, providing new insight into vortex-bound states in topological quantum materials.

cond-mat.supr-con↗

arXiv2025

Evaluation of Wafer-Scale SOT-MRAM for Analog Crossbar Array Applications

Analog crossbar arrays consisting of emerging memory devices can greatly alleviate the computational strain required by vector matrix multiplications for neural network applications. The ability to produce spin orbit torque-magnetic random-access memory (SOT-MRAM) at wafer-scale positions SOT-MRAM as a strong memory candidate. In this work, we fabricate and measure 300 mm-compatible SOT-MRAM with 150% tunnel magnetoresistance ratio, fast (2 ns) and low voltage (<1 V) operation, low energy dissipation (350 fJ), low write noise (0.1%), and low device-to-device variation of 10%. Through 2-bit quantization aware training and noisy training as mitigation techniques, the measured SOT-MRAM devices attain 95% on MNIST. The bi-stable anisotropy and stochastic switching of SOT-MRAM can additionally be leveraged for stochastic training of binary neural networks, able to reach ideal accuracy for a single device. Lastly, the devices were evaluated on implementation of probabilistic graph modeling and the interplay of tunnel magnetoresistance ratio, probability curve distribution, and conductance noise was shown to reduce potential errors in implementation. Through these results, SOT-MRAM is shown to be a uniquely effective candidate for implementation of crossbar accelerators in memory- and energy-limited applications, able to take advantage of stochastic operation and bi-stability to beneficial results in neural network applications.

cond-mat.mes-hall↗

arXiv2023

Tailoring Interlayer Chiral Exchange by Azimuthal Symmetry Engineering

Recent theoretical and experimental studies of the interlayer Dzyaloshinskii-Moriya interaction (DMI) has sparked great interest in its implementation into practical magnetic random-access memory (MRAM) devices, due to its capability to mediate long-range chiral spin textures. So far, experimental reports focused on the observation of interlayer DMI, leaving the development of strategies to control interlayer DMI's magnitude unaddressed. Here, we introduce an azimuthal symmetry engineering protocol capable of additive/subtractive tuning of interlayer DMI through the control of wedge deposition of separate layers, and demonstrate its capability to mediate field-free spin-orbit torque (SOT) magnetization switching in both orthogonally magnetized and synthetic antiferromagnetically coupled systems. Furthermore, we showcase the spatial inhomogeneity brought about by wedge depositon can be suppressed by specific azimuthal engineering design, ideal for practical implementation. Our findings provide guidelines for effective manipulations of interlayer DMI strength, beneficial for future design of SOT-MRAM or other spintronic devices utilizing interlayer DMI.

physics.app-ph↗

arXiv2023

The Central Role of Tilted Anisotropy for Field-Free Spin-Orbit Torque Switching of Perpendicular Magnetization

The discovery of efficient magnetization switching activated by the spin Hall effect (SHE)-induced spin-orbit torque (SOT) changed the course of magnetic random-access memory (MRAM) research and development. However, for systems with perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by the necessity of a longitudinal magnetic field to break the magnetic symmetry to achieve deterministic switching. In this work, we first demonstrate that a robust and tunable field-free current-driven SOT switching of perpendicular magnetization can be controlled by the growth protocol in Pt-based magnetic heterostructures. It is further elucidated that such growth-dependent symmetry breaking is originated from the laterally tilted magnetic anisotropy of the ferromagnetic layer with PMA, which has been largely neglected in previous studies and its critical role should be re-focused. We show by both experiments and simulations that in a PMA system with tilted anisotropy, the deterministic field-free switching possesses a conventional SHE-induced damping-like torque feature and the resulting current-induced effective field has a non-linear dependence on the applied current density, which could be potentially misattributed to an unconventional SOT origin.

cond-mat.mes-hall↗

arXiv2022

Toward 100% Spin-Orbit Torque Efficiency with High Spin-Orbital Hall Conductivity Pt-Cr Alloys

5d transition metal Pt is the canonical spin Hall material for efficient generation of spin-orbit torques (SOTs) in Pt/ferromagnetic layer (FM) heterostructures. However, for a long while with tremendous engineering endeavors, the damping-like SOT efficiencies ($ξ_{DL}$) of Pt and Pt alloys have still been limited to $ξ_{DL}$<0.5. Here we present that with proper alloying elements, particularly 3d transition metals V and Cr, a high spin-orbital Hall conductivity ($σ_{SH}{\sim}6.5{\times}10^{5}({\hbar}/2e)Ω^{-1}{\cdot} m^{-1}$) can be developed. Especially for the Cr-doped case, an extremely high $ξ_{DL}{\sim}0.9$ in a Pt$_{0.69}$Cr$_{0.31}$/Co device can be achieved with a moderate Pt$_{0.69}$Cr$_{0.31}$ resistivity of $ρ_{xx}{\sim}133 μΩ{\cdot}cm$. A low critical SOT-driven switching current density of $J_{c}{\sim}3.2{\times}10^{6} A{\cdot}cm^{-2}$ is also demonstrated. The damping constant ($α$) of Pt$_{0.69}$Cr$_{0.31}$/FM structure is also found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall high $σ_{SH}$, giant $ξ_{DL}$, moderate $ρ_{xx}$, and reduced $α$ of such a Pt-Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.

cond-mat.mtrl-sci↗

arXiv2020

Benchmarking of spin-orbit torque switching efficiency in Pt alloys

We systematically survey on Pt$_{x}$Cu$_{1-x}$/Co/MgO magnetic heterostructure with perpendicular magnetic anisotropy and report a significant improvement on spin-orbit torque switching efficiency in Pt-Cu alloy system. The largest damping-like spin-orbit torque efficiency determined by hysteresis loop shift measurement is about 0.44 for Pt$_{0.57}$Cu$_{0.43}$, which is originated from the higher resistivity tuned by alloying. Moreover, from the results of current-induced switching measurements, a lower critical switching current density is achieved by proper alloying due to the simultaneous enhancement of spin-orbit torque efficiency and reduction of coercivity of the Co layer. Finally, the ability to lower power consumption and preserve good thermal stability using Pt$_{x}$Cu$_{1-x}$ alloy is demonstrated, which suggests that Pt$_{x}$Cu$_{1-x}$ is an attractive candidate for future SOT-MRAM applications.

cond-mat.mtrl-sci↗