arXiv subjects

Yinwei Li

Publications and source records attributed to Yinwei Li.

At least 19 recordsLinked to original sources

arXiv2026

Strain induced magnetic phase transition and anomalous transport phenomena in RuO$_2$ and MnF$_2$

Collinear antiferromagnets with broken time-reversal symmetry have emerged as a fertile platform for spintronics. Using a general tight-binding model and first-principles calculations, we show that strain engineering provides a simple route to control magnetic phase transition and activate transverse responses in representative altermagnets RuO$_2$ and MnF$_2$. For pristine RuO$_2$ and MnF$_2$ with N\'eel vector $\mathbf{n}\parallel$ [001], symmetry constrains the off-diagonal elements of the Hall conductivity tensor to vanish, thereby forbidding anomalous transport and magneto-optical responses. Shear strain applied along the $ac$ direction preserves the spin symmetry relating the two spin-opposite magnetic sublattices and therefore maintains the altermagnetic phase. By contrast, shear strain applied along the $ab$ direction breaks this spin symmetry and drives a transition from an altermagnetic phase to a partially compensated ferrimagnetic phase in metallic RuO$_2$ and to a fully compensated ferrimagnetic phase in semiconducting MnF$_2$. In addition, the lowered symmetry enables finite anomalous Hall, anomalous Nernst, and anomalous thermal Hall conductivities, as well as magneto-optical rotation angles, which are prohibited in the pristine systems. These responses exhibit a clear strain dependence and become progressively stronger as the strain amplitude increases. Our results establish strain engineering as an effective route to manipulate magnetic phases and functional responses in unconventional antiferromagnets, thereby expanding opportunities for antiferromagnetic spintronics and magneto-optical applications.

cond-mat.mtrl-sci↗

arXiv2026

Theoretical prediction of strong-coupling superconductivity in a hypothetical NaAlH3 phase at ambient pressure

We present a comprehensive first-principles investigation of a hypothetical cubic Pm-3m phase of the ternary hydride NaAlH3, focusing on its lattice dynamics, electronic structure, and electron-phonon-mediated superconducting properties at ambient pressure. Using density functional theory and the Migdal-Eliashberg formalism, we find an exceptionally strong electron-phonon coupling ($\lambda=2.23$), resulting in a superconducting critical temperature of up to 73.7 K for a Coulomb pseudopotential $\mu^* = 0.1$. Phonon dispersion calculations, complemented by ab initio molecular dynamics simulations, indicate dynamic and thermal stability within the adopted theoretical framework. The electronic structure exhibits a metallic character with substantial contributions from Al- and Na-derived states at the Fermi level. The resulting superconducting gap ratio ($2\Delta(0)/k_B T_c \approx 4.8$) and specific heat jump ($\Delta C/\gamma T_c \approx 2.2$) significantly exceed BCS weak-coupling predictions, highlighting the strong-coupling nature of superconductivity in this hypothetical phase.

cond-mat.supr-con↗

arXiv2025

High-Tc superconductivity above 130 K in cubic MH4 compounds at ambient pressure

Hydrides have long been considered promising candidates for achieving room-temperature superconductivity; however, the extremely high pressures typically required for high critical temperatures remain a major challenge in experiment. Here, we propose a class of high-Tc ambient-pressure superconductors with MH4 stoichiometry. These hydrogen-based compounds adopt the bcc PtHg4 structure type, in which hydrogen atoms occupy the one-quarter body-diagonal sites of metal lattices, with the metal atoms acting as chemical templates for hydrogen assembly. Through comprehensive first-principles calculations, we identify three promising superconductors, PtH4, AuH4 and PdH4, with superconducting critical temperatures of 84 K, 89 K, and 133 K, respectively, all surpassing the liquid-nitrogen temperature threshold of 77 K. The remarkable superconducting properties originate from strong electron-phonon coupling associated with hydrogen vibrations, which in turn arise from phonon softening in the mid-frequency range. Our results provide crucial insights into the design of high-Tc superconductors suitable for future experiments and applications at ambient pressure.

cond-mat.supr-con↗

arXiv2025

Longwave-transparent low-emissivity material

Low emissivity (low-e) materials are crucial for conserving thermal energy in buildings, cold chain logistics and transportation by minimizing unwanted radiative heat loss or gain. However, their metallic nature intrinsically causes severe longwave attenuation, hindering their broad applications. Here, we introduce, for the first time, an all-dielectric longwave-transparent low-emissivity material (LLM) with ultra-broadband, high transmittance spanning 9 orders of magnitude, from terahertz to kilohertz frequencies. This meter-scale LLM not only achieves energy savings of up to 41.1% over commercial white paint and 10.2% over traditional low-e materials, but also unlocks various fundamentally new capabilities including high-speed wireless communication in energy-efficient buildings, wireless energy transfer with radiative thermal insulation, as well as non-invasive terahertz security screening and radio frequency identification in cold chain logistics. Our approach represents a new photonic solution towards carbon neutrality and smart city development, paving the way for a more sustainable and interconnected future.

physics.optics↗

arXiv2025

Ferroelectric Antiferromagnetic Lifting of Spin-Valley Degeneracy

The generation and control of spin- and valley-polarization in antiferromagnets (AFMs) have garnered increasing attention due to their potential for enabling faster and more stable multifunctional spintronic and valleytronic memory and logic devices. However, the two primary categories of AFMs, altermagnets and TP-symmetric AFMs, either lack intrinsic valley-polarization or net spin-polarization. Here, we propose an effective approach for achieving spontaneous spin-valley polarization in TP-broken layered ferroelectric antiferromagnets (FE-AFMs). The FE-AFMs exhibit lifted spin degeneracy across the entire Brillouin zone, along with uncompensated spin density of states. They combine the benefits of spin-polarization in altermagnets with valley-polarization in TP-symmetric AFMs. Furthermore, the FE-AFMs feature layer-dependent spin-polarization, rooted in their intrinsic ferroelectric property, allowing for the flexible control over spin-valley polarization by interlayer sliding. This tunability facilitates sign-reversible and size-tunable valley Hall and Nernst effects, along with other spin-valley-dependent transport properties. Our findings are demonstrated in a broad class of TP-broken bilayer antiferromagnets such as Nb3X8 (X = Cl, Br, I), VX2 (X = S, Se), and VSi2X4 (X = N, P), underscoring the potential of FE-AFMs for advancing next-generation spin- and valley-based information technologies.

cond-mat.mes-hall↗

arXiv2025

Magnetic-Field and Strain Engineering of Modulated Transverse Transport in Altermagnetic Topological Materials

Here, we explore the role of inherent altermagnetic topology in transverse transport phenomena (such as crystal/anomalous Hall, Nernst, and thermal Hall effects) in several famous altermagnets, including tetragonal \textit{X}V$_2$\textit{Y}$_2$O (\textit{X} = K, Rb, Cs; \textit{Y} = S, Se, Te), RuO$_2$, MnF$_2$, as well as hexagonal CrSb and MnTe. Notably, in \textit{X}V$_2$\textit{Y}$_2$O, the first experimentally realized layered altermagnets, transverse transport is governed by altermagnetic pseudonodal surfaces, emphasizing the purely topological contributions to transverse transport. Interestingly, we demonstrate that strain engineering and magnetic field, two unique methods for selectively controlling crystal and anomalous transport, can substantially enhance the magnitude of these phenomena while preserving the alternating spin characteristics in both real and momentum space. Moreover, due to the spin symmetry breaking via shear strain, a new magnetic phase, fully compensated ferrimagnetism, with isotropic spin splitting, can be induced. Our findings provide effective strategies not only for manipulating transverse transport in altermagnets but also for controlling magnetic phase transitions, offering valuable insights for their potential applications in spintronics and spin caloritronics.

cond-mat.mtrl-sci↗

arXiv2024

Prediction of high-Tc superconductivity in ternary actinium beryllium hydrides at low pressure

Hydrogen-rich superconductors are promising candidates to achieve room-temperature superconductivity. However, the extreme pressures needed to stabilize these structures significantly limit their practical applications. An effective strategy to reduce the external pressure is to add a light element M that binds with H to form MHx units, acting as a chemical precompressor. We exemplify this idea by performing ab initio calculations of the Ac-Be-H phase diagram, proving that the metallization pressure of Ac-H binaries, for which critical temperatures as high as 200 K were predicted at 200 GPa, can be significantly reduced via beryllium incorporation. We identify three thermodynamically stable (AcBe2H10, AcBeH8, and AcBe2H14) and four metastable compounds (fcc AcBeH8, AcBeH10, AcBeH12 and AcBe2H16). All of them are superconductors. In particular, fcc AcBeH8 remains dynamically stable down to 10 GPa, where it exhibits a superconducting transition temperature Tc of 181 K. The Be-H bonds are responsible for the exceptional properties of these ternary compounds and allow them to remain dynamically stable close to ambient pressure. Our results suggest that high-Tc superconductivity in hydrides is achievable at low pressure and may stimulate experimental synthesis of ternary hydrides.

cond-mat.supr-con↗

arXiv2024

Prediction of high-Tc superconductivity under submegabar pressure in ternary actinium borohydrides

Ternary hydrides are considered as the ideal candidates with high critical temperature (Tc) stabilized at submegabar pressure, evidenced by the recent discoveries in LaBeH8 (110 K at 80 GPa) and LaB2H8 (106 K at 90 GPa). Here, we investigate the crystal structures and superconductivity of an Ac-B-H system under pressures of 100 and 200 GPa by using an advanced structure method combined with first-principles calculations. As a result, nine stable compounds were identified, where B atoms are bonded with H atoms in the formation with diverse BHx motifs, e.g., methanelike (BH4), polythenelike, (BH2)n,andBH6 octahedron. Among them, seven Ac-B-H compounds were found to become superconductive. In particular, AcBH7 was estimated to have a Tc of 122 K at 70 GPa. Our in-depth analysis reveals that the B-H interactions in the BH6 units play a key role in its high superconductivity and stability at submegabar pressure. Our current results provide a guidance for future experiments to synthesize ternary hydride superconductors with high-Tc at moderate pressure.

cond-mat.supr-con↗

arXiv2024

Creating cyclo-N$_5$$^{+}$ cation and assembling N$_5$$^{+}$N$_5$$^{-}$ salt via electronegativity co-matching in tailored ionic compounds

The recent discovery of crystalline pentazolates marks a major advance in polynitrogen science and raises prospects of making the long-touted potent propellant N$_5$$^{+}$N$_5$$^{-}$ salt. However, despite the synthesis of cyclo-N$_5$$^{-}$ anion in pentazolates, counter cation cyclo-N$_5$$^{+}$ remains elusive due to the strong oxidizing power of pentazole ion; moreover, pure N$_5$$^{+}$N$_5$$^{-}$ salt is known to be unstable. Here, we devise a new strategy for making rare cyclo-N$_5$$^{+}$ cation and assembling the long-sought N$_5$$^{+}$N$_5$$^{-}$ salt in tailored ionic compounds, wherein the negative/positive host ions act as oxidizing/reducing agents to form cyclo-N$_5$$^{+}$/N$_5$$^{-}$ species. This strategy is implemented via an advanced computational crystal structure search, which identifies XN$_5$N$_5$F (X = Li, Na, K) compounds that stabilize at high pressures and remain viable at ambient pressure-temperature conditions based on \textit{ab initio} molecular dynamics simulations. This finding opens an avenue for creating and stabilizing N$_5$$^{+}$N$_5$$^{-}$ salt assembly in ionic compounds, where cyclo-N$_5$ species are oxidized/reduced via co-matching with host ions of high/low electronegativity. The present results demonstrate novel polynitrogen chemistry, and these findings offer new insights and prospects in the design and synthesis of diverse chemical species that exhibit unusual charge states, bonding structures, and superior functionality.

cond-mat.mtrl-sci↗

arXiv2024

Layer Control of Magneto-Optical Effects and Their Quantization in Spin-Valley Splitting Antiferromagnets

Magneto-optical effects (MOE), interfacing the fundamental interplay between magnetism and light, have served as a powerful probe for magnetic order, band topology, and valley index. Here, based on multiferroic and topological bilayer antiferromagnets (AFMs), we propose a layer control of MOE (L-MOE), which is created and annihilated by layer-stacking or an electric field effect. The key character of L-MOE is the sign-reversible response controlled by ferroelectric polarization, the Neel vector, or the electric field direction. Moreover, the sign-reversible L-MOE can be quantized in topologically insulating AFMs. We reveal that the switchable L-MOE originates from the combined contributions of spin-conserving and spin-flip interband transitions in spin-valley splitting AFMs, a phenomenon not observed in conventional AFMs. Our findings bridge the ancient MOE to the emergent realms of layertronics, valleytronics, and multiferroics and may hold immense potential in these fields.

cond-mat.mes-hall↗

arXiv2023

A Beam-Segmenting Polar Format Algorithm Based on Double PCS for Video SAR Persistent Imaging

Video synthetic aperture radar (SAR) is attracting more attention in recent years due to its abilities of high resolution, high frame rate and advantages in continuous observation. Generally, the polar format algorithm (PFA) is an efficient algorithm for spotlight mode video SAR. However, in the process of PFA, the wavefront curvature error (WCE) limits the imaging scene size and the 2-D interpolation affects the efficiency. To solve the aforementioned problems, a beam-segmenting PFA based on principle of chirp scaling (PCS), called BS-PCS-PFA, is proposed for video SAR imaging, which has the capability of persistent imaging for different carrier frequencies video SAR. Firstly, an improved PCS applicable to video SAR PFA is proposed to replace the 2-D interpolation and the coarse image in the ground output coordinate system (GOCS) is obtained. As for the distortion or defocus existing in the coarse image, a novel sub-block imaging method based on beam-segmenting fast filtering is proposed to segment the image into multiple sub-beam data, whose distortion and defocus can be ignored when the equivalent size of sub-block is smaller than the distortion negligible region. Through processing the sub-beam data and mosaicking the refocused subimages, the full image in GOCS without distortion and defocus is obtained. Moreover, a three-step MoCo method is applied to the algorithm for the adaptability to the actual irregular trajectories. The proposed method can significantly expand the effective scene size of PFA, and the better operational efficiency makes it more suitable for video SAR imaging. The feasibility of the algorithm is verified by the experimental data.

cs.CV↗

arXiv2022

A THz Video SAR Imaging Algorithm Based on Chirp Scaling

In video synthetic aperture radar (SAR) imaging mode, the polar format algorithm (PFA) is more computational effective than the backprojection algorithm (BPA). However, the two-dimensional (2-D) interpolation in PFA greatly affects its computational speed, which is detrimental to the real-time imaging of video SAR. In this paper, a terahertz (THz) video SAR imaging algorithm based on chirp scaling is proposed, which utilizes the small synthetic angular feature of THz SAR and the inherent property of linear frequency modulation. Then, two-step chirp scaling is used to replace the 2-D interpolation in the PFA to obtain a similar focusing effect, but with a faster operation. Point target simulation is used to verify the effectiveness of the proposed method.

eess.SY↗

arXiv2021

Seven-coordinated Silicon in a SiO2He Compound Formed under the Extreme Conditions of Planetary Interiors

Changes in atomic coordination numbers at high pressures are fundamental to condensed-matter physics because they initiate the emergence of unexpected structures and phenomena. Silicon is capable of forming eight-, nine-, and ten-coordinated structures under compression,in addition to the usual six-coordinated structures. The missing seven-coordinated silicon remains an open question, but here our theoretical study provides evidence for its existence at high pressures. A combination of a crystal-structure prediction method and first-principles calculations allowed prediction of a stable SiO2He compound containing unique SiO7 polyhedrons, which is a configuration unknown in any proposed silica phase. Consequently, seven-coordinated SiO7 is a possible form of silica at high pressures. Further calculations indicate that the SiO2He phase remains energetically stable with a solid character over a wide range of pressures exceeding 607 GPa and temperatures of 0-9000 K, covering the extreme conditions of the core-mantle boundary in super-Earth exoplanets, or even the Solar System's ice giant planets. Our results may provide theoretical guidance for the discovery of other silicides at high pressures, promote the exploration of materials at planetary core-mantle boundaries, and enable planetary models to be refined.

cond-mat.mtrl-sci↗

arXiv2020

Helium Incorporation Stabilized Direct-gap Silicides

The search of direct-gap Si-based semiconductors is of great interest due to the potential application in many technologically relevant fields. This work examines the incorporation of He as a possible route to form a direct band gap in Si. Structure predictions and first-principles calculations have shown that He reacts with Si at high pressure, to form the stable compounds Si2He and Si3He. Both compounds have host-guest structures consisting of a channel-like Si host framework filled with He guest atoms. The Si frameworks in two compounds could be persisted to ambient pressure after removal of He, forming two pure Si allotropes. Both Si-He compounds and both Si allotropes exhibit direct or quasi-direct band gaps of 0.84-1.34 eV, close to the optimal value (~1.3 eV) for solar cell applications. Analysis shows that Si2He with an electric-dipole-transition allowed band gap possesses higher absorption capacity than diamond cubic Si, which makes it to be a promising candidate material for thin-film solar cell.

cond-mat.mtrl-sci↗

arXiv2020

Isotope effect in superconducting lanthanum hydride under high compression

Recently, the discovery of room-temperature superconductivity (SC) was experimentally realized in the fcc phase of LaH$_{10}$ under megabar pressure. Specifically, the isotope effect of $T_{\rm c}$ was measured by the replacement of hydrogen (H) with deuterium (D), demonstrating a driving role of phonons in the observed room-temperature SC. Herein, based on the first-principles calculations within the harmonic approximation, we reveal that (i) the identical electron-phonon coupling constants of fcc LaH$_{10}$ and LaD$_{10}$ decrease monotonously with increasing pressure and (ii) the isotope effect of $T_{\rm c}$ is nearly proportional to $M^{-α}$ ($M$: ionic mass) with $α$ ${\approx}$ 0.465, irrespective of pressure. The predicted value of $α$ agrees well with the experimental one ($α=0.46$) measured at around 150 GPa. Thus, our findings provide a theoretical confirmation of the conventional electron-phonon coupling mechanism in a newly discovered room-temperature superconductor of compressed LaH$_{10}$.

cond-mat.supr-con↗

arXiv2017

Dehydrogenation through the pressure-induced polymerization processes of phosphine

PH3 is studied to understand the superconducting transition and responsible stoichiometry under high pressure by means of Raman, IR, and x-ray diffraction (XRD) measurements, and theoretical calculations. It is found PH3 is stable up to about 8 GPa and then starts to dehydrogenate through two dimerization processes at room temperature as pressure up to 25 GPa. Two resulting phosphorus hydrides, P2H4 and P4H6, are verified experimentally and can be recovered to ambient pressure. On further compression above 35 GPa, P4H6 directly decomposes into elemental phosphorus. The superconductivity transition temperatures of P4H6 at 100 and 200 GPa have been predicted to be 13 and 67 K in agreement with reported results, suggesting it might responsible for the superconductivity at higher pressures. Our results clearly show that P2H4 and P4H6 are only stable P-H compounds between PH3 and elemental phosphorus, shedding light on the superconducting mechanism.

cond-mat.mtrl-sci↗

arXiv2015

Quantum Hydrogen-Bond Symmetrization and High-Temperature Superconductivity in Hydrogen Sulfide

Hydrogen compounds are peculiar as the quantum nature of the proton can crucially affect their structural and physical properties. A remarkable example are the high-pressure phases of H$_2$O, where quantum proton fluctuations favor the symmetrization of the H bond and lower by 30 GPa the boundary between the asymmetric structure and the symmetric one. Here we show that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with the record superconducting critical temperature $T_c=203$ K at 155 GPa. In this system, according to classical theory, superconductivity occurs via formation of a structure of stoichiometry H$_3$S with S atoms arranged on a body-centered-cubic (bcc) lattice. For $P \gtrsim 175$ GPa, the H atoms are predicted to sit midway between two S atoms, in a structure with $Im\bar3m$ symmetry. At lower pressures the H atoms move to an off-center position forming a short H$-$S covalent bond and a longer H$\cdots$S hydrogen bond, in a structure with $R3m$ symmetry. X-ray diffraction experiments confirmed the H$_3$S stoichiometry and the S lattice sites, but were unable to discriminate between the two phases. Our present ab initio density-functional theory (DFT) calculations show that the quantum nuclear motion lowers the symmetrization pressure by 72 GPa. Consequently, we predict that the $Im\bar3m$ phase is stable over the whole pressure range within which a high $T_c$ was measured. The observed pressure-dependence of $T_c$ is closely reproduced in our calculations for the $Im\bar3m$ phase, but not for the $R3m$ phase. Thus, the quantum nature of the proton completely rules the superconducting phase diagram of H$_3$S.

cond-mat.supr-con↗

arXiv2015

Dissociation products and structures of solid H2S at strong compression

Hydrogen sulfides have recently received a great deal of interest due to the record high superconducting temperatures of up to 203 K observed on strong compression of dihydrogen sulfide (H2S). A joint theoretical and experimental study is presented in which decomposition products and structures of compressed H2S are characterized, and their superconducting properties are calculated. In addition to the experimentally known H2S and H3S phases, our first-principles structure searches have identified several energetically competitive stoichiometries that have not been reported previously; H2S3, H3S2, and H4S3. In particular, H4S3 is predicted to be thermodynamically stable within a large pressure range of 25-113 GPa. High-pressure room-temperature X-ray diffraction measurements confirm the presence of H3S and H4S3 through decomposition of H2S that emerge at 27 GPa and coexist with residual H2S, at least up to the highest pressure studied in our experiments of 140 GPa. Electron-phonon coupling calculations show that H4S3 has a small Tc of below 2 K, and that H2S is mainly responsible for the observed superconductivity of samples prepared at low temperature (<100K).

cond-mat.supr-con↗