arXiv subjects

Shu-Hui Zhang

Publications and source records attributed to Shu-Hui Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Interfacial Noncollinear Filtering of Spin Hall Currents

Spin Hall currents generated in nonmagnetic materials are conventionally regarded as bulk responses whose polarization is fixed by crystal symmetry. This view has motivated the search for intrinsically low-symmetry spin sources when unconventional spin polarizations are required. Here we point out that, in realistic heterostructures, the device-relevant quantity is not the fully symmetry-averaged bulk spin Hall current, but the emitted spin current transmitted across the interface. We therefore establish emitted spin currents as bulk-interface hybrid responses and propose interfacial noncollinear filtering as a mechanism to bypass the bulk-symmetry constraint. A low-symmetry interfacial spin-orbit field, generally noncollinear with the momentum-resolved spin polarization of the incident spin Hall current, imposes spin-dependent transmission and converts hidden momentum-resolved spin-polarization components into an observable unconventional emitted spin current. Using both a rotationally symmetric minimal model and a realistic high-symmetry Dirac-semimetal model, we show that conventional spin Hall sources can emit sizable out-of-plane spin currents when their hidden bulk spin Hall textures are selectively transmitted by the interfacial spin-orbit field. Our results reveal that spin-current polarization emerges from the cooperative action of bulk and interfacial responses, providing a strategy for reprogramming spin-current polarization in high-efficiency, CMOS-compatible spin Hall materials without relying on intrinsically low-symmetry bulk crystals or external symmetry-breaking schemes.

cond-mat.mes-hall↗

arXiv2026

Antiferromagnetic pseudospintronics without spin splitting

Antiferromagnets (AFMs) are promising for high-density spintronics due to their zero net magnetization, yet conventional AFM spintronics relies on spin splitting-a requirement that excludes many collinear AFMs with compensated spin sublattices. Here we exploit the sublattice degree of freedom in a honeycomb AFM with zero spin splitting. We uncover a coupling between spin and sublattice: the out-of-plane pseudospin polarization is spin-dependent, a mechanism we term partial pseudospin-spin coupling. This allows switching of the pseudospin polarization by reversing the N\'eel vector. Introducing an impurity into a specific sublattice induces Friedel oscillations with a sublattice-resolved amplitude ratio dictated solely by the pseudospin polarization, which is directly measurable by spin-polarized scanning tunneling microscopy. Furthermore, we demonstrate N\'eel-vector-controlled transmission and a large nonvolatile tunneling magnetoresistance in an all-in-one AFM junction, with pronounced resonant enhancement in gate-tunable two-dimensional devices. Our work establishes a new paradigm-AFM pseudospintronics-that utilizes the sublattice pseudospin in zero-spin-splitting AFMs, extending spintronics beyond the conventional spin-splitting paradigm.

cond-mat.mes-hall↗

arXiv2026

Spin-polarized scanning tunneling microscopy measurement scheme for determining the quantum geometric tensor

The quantum geometric tensor (QGT) embodies the geometry of the eigenstates of a system's Hamiltonian, and its full characterization across diverse quantum systems is essential. However, it is challenging to characterize the QGT of solid-state systems. Here we present an electric scheme to measure the complete QGT of two-dimensional solid-state systems by using spin-polarized scanning tunneling microscopy (STM), in which the spin texture is extracted from geometric amplitudes of Friedel oscillations induced by the intentionally introduced magnetic impurity, and then the QGT is derived from the momentum differential of spin texture. As a canonical spin model, the surface states of a topological insulator offer a promising way to demonstrate the scheme. In a slab of topological insulator, the gapped surface states host complete QGT, i.e., nonvanishing quantum metric and Berry curvature as its symmetric real part and the antisymmetric imaginary part. Thus, a detailed derivation guides the use of the developed scheme to measure the QGT of gapped surface states, even with an external magnetic field. This study opens a new avenue to directly measure the complete QGT of two-dimensional solid-state systems by using spin-polarized STM.

cond-mat.mes-hall↗

arXiv2025

Anomalous-Hall Neel textures in altermagnetic materials

Recently, the altermagnets, a new kind of collinear antiferromagnet with nearly zero net magnetization and momentum-dependent spin-splitting of bands, have sparked great interest. Despite simple magnetic structures, these altermagnets exhibit intriguing and intricate dependence of anomalous Hall effect (AHE) on the Néel vector, in contrast to the conventional perpendicular configuration of Hall current with magnetization in ferromagnets. However, the fundamental relationship between the AHE and the Néel vector remains largely elusive. Here, we reveal all the unconventional anomalous Hall textures in the Néel vector space, dubbed anomalous-Hall Néel textures (AHNTs) for altermagnets. Specifically, we identify 10 types across four categories of AHNTs for all altermagnets. Notably, we find that AHNTs resemble the known spin textures in momentum space, and further reveal their symmetry origin. Meanwhile, we examine our key discoveries in prototypical altermagnets. Our work offers a thorough understanding of AHE in altermagnets and a complete and pictorial classification of altermagnets based on the geometry of response functions.

cond-mat.mtrl-sci↗

arXiv2025

Interface-controlled antiferromagnetic tunnel junctions

Magnetic tunnel junctions (MTJs) are the key building blocks of high-performance spintronic devices. While conventional MTJs rely on ferromagnetic (FM) materials, employing antiferromagnetic (AFM) compounds can significantly increase operation speed and packing density. Current prototypes of AFM tunnel junctions (AFMTJs) exploit antiferromagnets either as spin-filter insulating barriers or as metal electrodes supporting bulk spin-dependent currents. Here, we highlight a largely overlooked AFMTJ prototype, where bulk-spin-degenerate electrodes with an A-type AFM stacking form magnetically uncompensated interfaces, enabling spin-polarized tunneling currents and a sizable tunneling magnetoresistance (TMR) effect. Using first-principles quantum-transport calculations and the van der Waals (vdW) metal Fe$_{4}$GeTe$_{2}$ as a representative A-type AFM electrode, we demonstrate a large negative TMR arising solely from the alignment of interfacial magnetic moments. This prototype of AFMTJs can also be realized with various non-vdW A-type AFM metals that support roughness-insensitive surface magnetization. Beyond TMR, AFMTJs based on A-type antiferromagnets allow convenient switching of the Néel vector, opening a new paradigm for AFM spintronics that leverages spin-dependent properties at AFM interfaces.

cond-mat.mtrl-sci↗

arXiv2025

X-type stacking in cross-chain antiferromagnets

Physical phenomena in condensed matter normally arise from the collective effect of all atoms, while selectively addressing a lone atomic sublattice by external stimulus is elusive. The later functionality may, however, benefit various applications, as the response may differ when the external stimulus affects only a specific sublattice rather than the entire solid. Here, we introduce cross-chain antiferromagnets, where the stacking of two magnetic sublattices forms a pattern of intersecting atomic chains, allowing for the sublattice selectivity. We dub this antiferromagnetic (AFM) stacking X-type and demonstrate that it exhibits unique spin-dependent transport properties not present in conventional magnets. Through high-throughput analyses and computations, we unveil three prototypes of X-type AFM stacking and identify 15 candidate candidates. Using $β$-Fe$_{2}$PO$_{5}$ as a representative X-type antiferromagnet, we predict sublattice-selective spin-polarized transport driven by the X-type stacking, where one magnetic sublattice conducts, while the other does not. Consequently, a spin torque can be exerted solely on a single sublattice, leading to unconventional ultrafast dynamics of the Nèel vector capable of deterministic switching of the AFM domains. Our work uncovers a previously overlooked type of magnetic moment stacking and reveals sublattice-selective physical properties promising for high-performance spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Emerging Challenges in Molecular Paleontology: Misapplication of Environmental DNA Fragments and Misconception of Deamination as a Key Criterion for In Situ DNA Identification

This article critically examines the methodologies applied in ancient DNA (aDNA) research, particularly those developed by Dr. Pääbo's team, which have significantly influenced the field. The focus is on the challenges of distinguishing original in situ DNA (oriDNA) from environmental DNA (eDNA) contamination in fossil samples. Recent analyses indicate that even with rigorous extraction and sequencing protocols, a considerable amount of eDNA remains present, often misinterpreted as oriDNA. This misidentification risks the accuracy of species ascription and evolutionary interpretations derived from fossil analyses. The paper explores fossil preservation's physical and chemical dynamics, which allow eDNA from similar and disparate species to infiltrate bone matrices. We propose enhancements to methodological frameworks, such as broader BLAST database usage and stringent E-value criteria, to improve species-specific aDNA identification. Additionally, the article critiques the reliance on deamination patterns as a definitive marker for aDNA, suggesting a reevaluation of this criterion due to its inconsistency and the potential for misleading sequencing results. Ultimately, our findings advocate for a more cautious and refined approach to aDNA research, ensuring more reliable and verifiable scientific outcomes

q-bio.GN↗

arXiv2024

Skin Effect of Nonlinear Optical Responses in Antiferromagnets

Nonlinear optics plays important roles in the research of fundamental physics and the applications of high-performance optoelectronic devices. The bulk nonlinear optical responses arise from the uniform light absorption in noncentrosymmetric crystals, and hence are usually considered to be the collective phenomena of all atoms. Here we show, in contrast to this common expectation, the nonlinear optical responses in antiferromagnets can be selectively accumulated near the surfaces, representing a skin effect. This is because the inversion symmetry, despite being broken globally by magnetism, is barely violated locally deeply inside these antiferromagnets. Using A-type layered antiferromagnets as the representatives, we predict that the spatial-dependent nonlinear optical responses, such as bulk photovoltaic effect (BPVE) and second harmonic generation (SHG), are notable in the top- and bottom-most layers and decay rapidly when moving away from the surfaces. Such a phenomenon is strongly associated with the antiferromagnetism and exists in a broad range of antiferromagnets composed of centrosymmetric sublattices, offering promising device applications using these antiferromagnets. Our work uncovers a previously overlooked property of nonlinear optical responses and opens new opportunities for high-performance antiferromagnetic optospintronics.

cond-mat.mtrl-sci↗

arXiv2023

Prediction of Giant Tunneling Magnetoresistance in RuO$_{2}$/TiO$_{2}$/RuO$_{2}$ (110) Antiferromagnetic Tunnel Junctions

Using first-principles quantum-transport calculations, we investigate spin-dependent electronic and transport properties of antiferromagnetic tunnel junctions (AFMTJs) that consist of (110)-oriented antiferromagnetic (AFM) metal RuO$_{2}$ electrodes and an insulating TiO$_{2}$ tunneling barrier. We predict the emergence of a giant tunneling magnetoresistance (TMR) effect in a wide energy window, a series of barrier layer thicknesses, and different interface terminations, indicating the robustness of this effect. We show that the predicted TMR cannot be explained in terms of the global transport spin-polarization of RuO$_{2}$ (110) but is well understood based on matching the momentum-dependent spin-polarized conduction channels of the two RuO$_{2}$ (110) electrodes. We predict oscillations of TMR with increasing barrier thickness, indicating a non-negligible contribution from the perfectly epitaxial interfaces. Our work helps the understanding of the physics of TMR in AFMTJs and aids in realizing efficient AFM spintronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Geometric density of states of electronic structures for local responses: Phase information from the amplitudes of STM measurement

Electronic band structures underlie the physical properties of crystalline materials, their geometrical exploration renovates the conventional cognition and brings about novel applications. Inspired by geometry phases, we introduce a geometric amplitude named as the geometric density of states (GDOS) dictated by the differential curvature of the constant-energy contour. The GDOS determines the amplitude of the real-space Green's function making it attain the ultimate expression with transparent physics. The local responses of crystalline materials are usually formulated by the real-space Green's function, so the relevant physics should be refreshed by GDOS. As an example of local responses, we suggest using scanning tunneling microscopy (STM) to characterize the surface states of three-dimensional topological insulator under an in-plane magnetic field. The GDOS favors the straightforward simulation of STM measurement without resorting to Fourier transform of the real-space measurement, and also excavates the unexplored potential of STM measurement to extract the phase information of wavefunction through its amplitude, i.e., the spin and curvature textures. Therefore, the proposed GDOS deepens the understanding of electronic band structures and is indispensable in local responses, and it should be universal for any periodic systems.

cond-mat.mes-hall↗

arXiv2023

Tunneling valley Hall effect driven by tilted Dirac fermions

Valleytronics is a research field utilizing a valley degree of freedom of electrons for information processing and storage. A strong valley polarization is critical for realistic valleytronic applications. Here, we predict a tunneling valley Hall effect (TVHE) driven by tilted Dirac fermions in all-in-one tunnel junctions based on a two-dimensional (2D) valley material. Different doping of the electrode and spacer regions in these tunnel junctions results in momentum filtering of the tunneling Dirac fermions, generating a strong transverse valley Hall current dependent on the Dirac-cone tilting. Using the parameters of an existing 2D valley material, we demonstrate that such a TVHE is much stronger than that induced by the intrinsic Berry curvature mechanism reported previously. Finally, we predict that resonant tunneling can occur in a tunnel junction with properly engineered device parameters such as the spacer width and transport direction, providing significant enhancement of the valley Hall angle. Our work opens a new approach to generate valley polarization in realistic valleytronic systems.

cond-mat.mes-hall↗

arXiv2022

Néel Spin Currents in Antiferromagnets

Ferromagnets are known to support spin-polarized currents that control various spin-dependent transport phenomena useful for spintronics. On the contrary, fully compensated antiferromagnets are expected to support only globally spin-neutral currents. Here, we demonstrate that these globally spin-neutral currents can represent the Néel spin currents, i.e. staggered spin currents flowing through different magnetic sublattices. The Néel spin currents emerge in antiferromagnets with strong intra-sublattice coupling (hopping) and drive the spin-dependent transport phenomena such as tunneling magnetoresistance (TMR) and spin-transfer torque (STT) in antiferromagnetic tunnel junctions (AFMTJs). Using RuO$_{2}$ and Fe$_{4}$GeTe$_{2}$ as representative antiferromagnets, we predict that the Néel spin currents with a strong staggered spin-polarization produce a sizable field-like STT capable of the deterministic switching of the Néel vector in the associated AFMTJs. Our work uncovers the previously unexplored potential of fully compensated antiferromagnets and paves a new route to realize the efficient writing and reading of information for antiferromagnetic spintronics.

cond-mat.mes-hall↗

arXiv2022

Spin-Neutral Tunneling Anomalous Hall Effect

Anomalous Hall effect (AHE) is a fundamental spin-dependent transport property that is widely used in spintronics. It is generally expected that currents carrying net spin polarization are required to drive the AHE. Here we demonstrate that, in contrast to this common expectation, a spin-neutral tunneling AHE (TAHE), i.e. a TAHE driven by spin-neutral currents, can be realized in an antiferromagnetic (AFM) tunnel junction where an AFM electrode with a non-spin-degenerate Fermi surface and a normal metal electrode are separated by a non-magnetic barrier with strong spin-orbit coupling (SOC). The symmetry mismatch between the AFM electrode and the SOC barrier results in an asymmetric spin-dependent momentum filtering of the spin-neutral longitudinal current generating the transverse Hall current in each electrode. We predict a sizable spin-neutral TAHE in an AFM tunnel junction with a RuO$_{2}$-type AFM electrode and a SnTe-type SOC barrier and show that the Hall currents are reversible by the Néel vector switching. With the Hall angle being comparable to that in conventional AHE bulk materials, the predicted spin-neutral TAHE can be used for the Néel vector detection in antiferromagnetic spintronics.

cond-mat.mes-hall↗

arXiv2021

Spin-neutral currents for spintronics

Electric currents carrying a net spin polarization are widely used in spintronics, whereas globally spin-neutral currents are expected to play no role in spin-dependent phenomena. Here we show that, in contrast to this common expectation, spin-independent conductance in compensated antiferromagnets and normal metals can be efficiently exploited in spintronics, provided their magnetic space group symmetry supports a non-spin-degenerate Fermi surface. Due to their momentum-dependent spin polarization, such antiferromagnets can be used as active elements in antiferromagnetic tunnel junctions (AFMTJs) and produce a giant tunneling magnetoresistance (TMR) effect. Using RuO$_{2}$ as a representative compensated antiferromagnet exhibiting spin-independent conductance along the [001] direction but a non-spin-degenerate Fermi surface, we design a RuO$_{2}$/TiO$_{2}$/RuO$_{2}$ (001) AFMTJ, where a globally spin-neutral charge current is controlled by the relative orientation of the Néel vectors of the two RuO$_{2}$ electrodes, resulting in the TMR effect as large as ~500%. These results are expanded to normal metals which can be used as a counter electrode in AFMTJs with a single antiferromagnetic layer or other elements in spintronic devices. Our work uncovers an unexplored potential of the materials with no global spin polarization for utilizing them in spintronics.

cond-mat.mes-hall↗

arXiv2021

Oblique and asymmetric Klein tunneling across smooth NP junctions or NPN junctions in 8-Pmmn borophene

The tunneling of electrons and holes in quantum structures plays a crucial role in studying the transport properties of materials and the related devices. 8-Pmmn borophene is a new two-dimensional Dirac material, which hosts tilted Dirac cone and chiral, anisotropic massless Dirac fermions. We develop the transfer matrix method to investigate the Klein tunneling of massless fermions across the smooth NP junctions and NPN junctions of 8-Pmmn borophene. Like the sharp NP junctions of 8-Pmmn borophene, the tilted Dirac cones induce the oblique Klein tunneling. The angle of perfect transmission to the normal incidence is 20.4 degrees, a constant determined by the Hamiltonian of 8-Pmmn borophene. For the NPN junction, there are branches of the Klein tunneling in the phase diagram. We find that the asymmetric Klein tunneling is induced by the chirality and anisotropy of the carriers. Furthermore, we show the oscillation of electrical resistance related to the Klein tunneling in the NPN junctions. One may analyze the pattern of electrical resistance and verify the existence of asymmetric Klein tunneling experimentally.

cond-mat.mes-hall↗

arXiv2021

Robust wavefront dislocations of Friedel oscillations in gapped graphene

Friedel oscillation is a well-known wave phenomenon, which represents the oscillatory response of electron waves to imperfection. By utilizing the pseudospin-momentum locking in gapless graphene, two recent experiments demonstrate the measurement of the topological Berry phase by corresponding to the unique number of wavefront dislocations in Friedel oscillations. Here, we study the Friedel oscillations in gapped graphene, in which the pseudospin-momentum locking is broken. Unusually, the wavefront dislocations do occur as that in gapless graphene, which expects the immediate verification in the current experimental condition. The number of wavefront dislocations is ascribed to the invariant pseudospin winding number in gaped and gapless graphene. This study deepens the understanding of correspondence between topological quantity and wavefront dislocations in Friedel oscillations, and implies the possibility to observe the wavefront dislocations of Friedel oscillations in intrinsic gapped two-dimensional materials, e.g., transition metal dichalcogenides.

cond-mat.mes-hall↗

arXiv2021

Interfacial crystal Hall effect reversible by ferroelectric polarization

The control of spin-dependent properties by voltage, not involving magnetization switching, has significant advantages for low-power spintronics. Here, we predict that the interfacial crystal Hall effect (ICHE) can serve for this purpose. We show that the ICHE can occur in heterostructures composed of compensated antiferromagnetic metals and non-magnetic insulators due to reduced symmetry at the interface, and it can be made reversible if the antiferromagnet is layered symmetrically between two identical ferroelectric layers. We explicitly demonstrate this phenomenon using density functional theory calculations for three material systems: MnBi$_{2}$Te$_{4}$/GeI$_{2}$ and topological In$_{2}$Te$_{3}$/MnBi$_{2}$Te$_{4}$/In$_{2}$Te$_{3}$ van der Waals heterostructures, and GeTe/Ru$_{2}$MnGe/GeTe heterostructure composed of three-dimensional materials. We show that all three systems reveal a sizable ICHE, while the latter two exhibit a quantum ICHE and ICHE, respectively, reversible with ferroelectric polarization. Our proposal opens an alternative direction for voltage controlled spintronics and offers not yet explored possibilities for functional devices by heterostructure design.

cond-mat.mtrl-sci↗

arXiv2020

Nonlinear anomalous Hall effect for Néel vector detection

Antiferromagnetic (AFM) spintronics exploits the Néel vector as a state variable for novel spintronic devices. Recent studies have shown that the field-like and antidamping spin-orbit torques (SOT) can be used to switch the Néel vector in antiferromagnets with proper symmetries. However, the precise detection of the Néel vector remains a challenging problem. In this letter, we predict that the nonlinear anomalous Hall effect (AHE) can be used to detect the Néel vector in most compensated antiferromagnets supporting the antidamping SOT. We show that the magnetic crystal group symmetry of these antiferromagnets combined with spin-orbit coupling produce a sizable Berry curvature dipole and hence the nonlinear AHE. As a specific example, we consider half-Heusler alloy CuMnSb, which Néel vector can be switched by the antidamping SOT. Based on density functional theory calculations, we show that the nonlinear AHE in CuMnSb results in a measurable Hall voltage under conventional experimental conditions. The strong dependence of the Berry curvature dipole on the Néel vector orientation provides a new detection scheme of the Néel vector based on the nonlinear AHE. Our predictions enrich the material platform for studying non-trivial phenomena associated with the Berry curvature and broaden the range of materials useful for AFM spintronics.

cond-mat.mtrl-sci↗