arXiv subjects

Shiming Zhou

Publications and source records attributed to Shiming Zhou.

8 recordsLinked to original sources

arXiv2024

Unveiling the nonrelativistic spin current polarization in an altermagnet

Spin current plays a central role in spintronics for driving exotic spin-dependent phenomena and high-performance device applications. Recently, a magnetic spin Hall effect has been discovered in spin-split antiferromagnets including noncollinear antiferromagnets and altermagnets, allowing the efficient generation of unconventional spin currents even in the absence of spin-orbit coupling. However, although such nonrelativistic spin currents are proposed to have a magnetic origin, the direct connection between the Neel vector and the spin current polarization is still missing. Here, using the altermagnetic RuO2 as a representative example, we unveil the spin current polarization by disentangling the conventional and magnetic spin Hall effects using a technique we developed based on the spin Hall magnetoresistance measurement. The results suggest that the nonrelativistic spin current hosts a polarization very close to the Neel vector. Our work offers unambiguous evidence of the magnetic origin of the nonrelativistic spin current in altermagnetic RuO2, and paves a straightforward route to understand the unconventional spin currents that are crucial in spintronics.

cond-mat.mes-hall↗

arXiv2024

A Powder Diffraction-AI Solution for Crystalline Structure

Determining the atomic-level structure of crystalline solids is critically important across a wide array of scientific disciplines. The challenges associated with obtaining samples suitable for single-crystal diffraction, coupled with the limitations inherent in classical structure determination methods that primarily utilize powder diffraction for most polycrystalline materials, underscore an urgent need to develop alternative approaches for elucidating the structures of commonly encountered crystalline compounds. In this work, we present an artificial intelligence-directed leapfrog model capable of accurately determining the structures of both organic and inorganic-organic hybrid crystalline solids through direct analysis of powder X-ray diffraction data. This model not only offers a comprehensive solution that effectively circumvents issues related to insoluble challenges in conventional structure solution methodologies but also demonstrates applicability to crystal structures across all conceivable space groups. Furthermore, it exhibits notable compatibility with routine powder diffraction data typically generated by standard instruments, featuring rapid data collection and normal resolution levels.

cond-mat.mtrl-sci↗

arXiv2024

Quantum oscillations in kagome metals (Ti, Zr, Hf)V6Sn6 at Van Hove filling

Kagome materials have recently drawn great attention due to the interplay between nontrivial band topology, electron correlations, and Van Hove singularities related many-body orders. Here we report three new vanadium-based kagome metals, TiV6Sn6, ZrV6Sn6, and HfV6Sn6, and conduct a comprehensive investigation of their structural, magnetic, and electrical transport properties. All three compounds exhibit large unsaturated magnetoresistances and multiband Hall effects at low temperatures, indicating the existence of multiple highly mobile carriers. Both the diagonal and off-diagonal resistivity show quantum oscillations with nontrivial Berry phases and high quantum mobilities. First-principles calculations together with quantum oscillation analyses suggest the Van Hove singularities at the M point for the three compounds all located in close vicinity of the Fermi level, and there also exist multiple topological nontrivial band crossings, including a nodal ring and a massive Dirac cone. Our work extends the kagome AM6X6 family and paves the way for searching possible Van Hove physics in the V kagome lattice.

cond-mat.str-el↗

arXiv2024

Evidence for an Excitonic Insulator State in Ta$_2$Pd$_3$Te$_5$

The excitonic insulator (EI) is an exotic ground state of narrow-gap semiconductors and semimetals arising from spontaneous condensation of electron-hole pairs bound by attractive Coulomb interaction. Despite research on EIs dating back to half a century ago, their existence in real materials remains a subject of ongoing debate. In this study, through systematic experimental and theoretical investigations, we provide evidence for the existence of an EI ground state in a van der Waals compound Ta$_2$Pd$_3$Te$_5$. Density-functional-theory calculations suggest that it is a semimetal with a small band overlap, whereas various experiments exhibit an insulating ground state with a clear band gap. Upon incorporating electron-hole Coulomb interaction into our calculations, we obtain an EI phase where the electronic symmetry breaking opens a many-body gap. Angle-resolved photoemission spectroscopy measurements exhibit that the band gap is closed with a significant change in the dispersions as the number of thermally excited charge carriers becomes sufficiently large in both equilibrium and nonequilibrium states. Structural measurements reveal a slight breaking of crystal symmetry with exceptionally small lattice distortion in the insulating state, which cannot account for the significant gap opening. Therefore, we attribute the insulating ground state with a gap opening in Ta$_2$Pd$_3$Te$_5$ to exciton condensation, where the coupling to the symmetry-breaking electronic state induces a subtle change in the crystal structure.

cond-mat.mtrl-sci↗

arXiv2023

Discovery of a long-ranged charge order with 1/4 Ge1-dimerization in an antiferromagnetic Kagome metal

Exotic quantum states arise from the interplay of various degrees of freedom such as charge, spin, orbital, and lattice. Recently, a novel short-ranged charge order (CO) was discovered deep inside the antiferromagnetic phase of Kagome magnet FeGe, exhibiting close relationships with magnetism. Despite extensive investigations, the CO mechanism remains controversial, mainly because the short-ranged behavior hinders precise identification of CO superstructure. Here, combining multiple experimental techniques, we report the observation of a long-ranged CO in high-quality FeGe samples, which is accompanied with a first-order structural transition. With these high-quality samples, the distorted 2 * 2 * 2 CO superstructure is characterized by a strong dimerization along the c-axis of 1/4 of Ge1-sites in Fe3Ge layers, and in response to that, the 2 * 2 in-plane charge modulations are induced. Moreover, we show that the previously reported short-ranged CO might be related to large occupational disorders at Ge1-site, which upsets the equilibrium of the CO state and the ideal 1 * 1 * 1 structure with very close energies, inducing nanoscale coexistence of these two phases.Our study provides crucial clues for further understanding the CO properties in FeGe and helps to identify the CO mechanism.

cond-mat.str-el↗

arXiv2021

Efficient field-free perpendicular magnetization switching by a magnetic spin Hall effect

Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows generation of the out-of-plane spin current carrying spin polarization induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing deterministic switching of perpendicular magnetization of an adjacent Ni/Co multilayer. Compared to the conventional spin-orbit torque devices, the observed switching does not need any external magnetic field and requires much lower current density. Our results demonstrate great prospects of exploiting the magnetic spin Hall effect in noncollinear antiferromagnets for low-power spintronics.

cond-mat.mtrl-sci↗

arXiv2015

Electrical control of exchange spring in antiferromagnetic metals

Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. In spite of the electrical modulation of insulated AFMs through coupling between their intrinsic ferroelectricity and antiferromagnetism, direct electrical control of AFM metals remains challenging due to the screening effect by the surface charge, and the manipulation is confined to a limited depth of atomic dimensions, which is insufficient to form a stable AFM exchange spring. In the present letter we primarily report a reversible electrical control of exchange spring in AFM metals, using an ionic liquid to exert a substantial electric-field effect. The exchange spring could transfer the force to the ferromagnet/antiferromagnet interface, enabling a deeper modulation depth in AFM metals. The manipulation of AFM moments by gate voltage is demonstrated in [Co/Pt]/IrMn model system and a single IrMn layer with the IrMn thickness up to 5 nm. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.

cond-mat.mtrl-sci↗

arXiv2012

Griffiths singularity and magnetic phase diagram of La1-xCaxCoO3

Magnetic properties of La$_{1-x}$Ca$_{x}$CoO$_{3}$ (0.10 $\leq x\leq$ 0.25) are systemically studied in this work. All the samples exhibits the ferromagnetic state at low temperatures. However, their inverse low-field magnetic susceptibilities shows a sharply downward deviation from high-temperature Curie-Weiss paramagnetic behavior well above the ferromagnetic transition temperature ($T_C$), which indicates the presence of a ferromagnetic clustered state above $T_C$. A detailed analysis on the susceptibilities reveals that the short-range state in these Ca-doped samples can be well described as the Griffiths phase. This characteristic is quite different from those of the clustered states above $T_C$ recently reported in Sr- and Ba-doped cobaltites, which are non-Griffith-like. It is proposed that this difference possibly arises from the unique dependence of magnetic interactions among Co$^{3+}$ ions on the size of the dopant in the doped cobaltites. Based on these results, the magnetic diagram of the Ca-doped cobaltites is established.

cond-mat.str-el↗