arXiv subjects

Hongrui Ma

Publications and source records attributed to Hongrui Ma.

6 recordsLinked to original sources

arXiv2026

Achieving Large Uniaxial and Homogeneous Strain in Two-Dimensional Materials

Strain engineering is a powerful tool for tuning the electronic, magnetic, and topological properties of two-dimensional (2D) materials and thin films - particularly at high values of strain (>3%) where many electronic, magnetic, and structural transitions have been predicted. However, most approaches to tuning strain in 2D materials are limited below 1.5%, with poor repeatability when cycling strain and low strain transfer when cooling to cryogenic temperatures. Here, we report a high-yield sample preparation and device strain platform that overcomes these limitations, enabling precise, reversible strain tuning up to the intrinsic strain-to-failure of the materials tested herein. In addition, we show that this platform can be used to controllably design uniform linear strain gradients across of 10's of $\mu$m, providing a novel route to systematically investigate flexoelectric and flexomagnetic phenomena. Using CrSBr as a model system, we demonstrate uniform uniaxial strain, up to ~4%, with negligible slippage and linear strain gradients of up to 0.06%/$\mu$m. We further show that our strain approach is applicable to a broad class of 2D materials, validating its performance for three different phases of transition metal dichalcogenides: 2H-MoTe$_2$, 1T$^\prime$-MoTe$_2$ and T$_\mathrm{d}$-WTe$_2$. In T$_\mathrm{d}$-WTe$_2$, verified by theoretical calculations, we show a continuous redshift of the A$_1^3$ mode, up to a record-breaking ~5.5% strain, with a clear separation of the A$_1^3$ and A$_1^2$ modes starting at 2% strain.

cond-mat.mtrl-sci↗

arXiv2026

The Quotient of Milnor Number by Tjurina Number of Hypersurface Singularities in Arbitrary Characteristic

In this paper, we use Hilbert-Samuel multiplicity, Hilbert-Kunz multiplicity, and s-multiplicity to establish a sharp upper bound for the quotient of the generalized Milnor numbers and the Tjurina numbers for isolated hypersurface singularities of any dimension in positive characteristic. Using this result, we also derive an upper bound for the quotient of the Milnor numbers $\mu$ and the Tjurina numbers $\tau$ for isolated hypersurface singularities of any dimension in characteristic zero. In particular, as a corollary, we obtain that for an isolated surface singularity $(f,0) \subset (\mathbb{C}^3,0)$, $\frac{\mu(f)}{\tau(f)}\leq \frac{3}{2}$, which partially answers a conjecture of P. Almir\'{o}n, replacing the original strict inequality $<$ by $\leq$. This is also a weak version of Durfee's conjecture. We have also constructed a family of hypersurface singularities of any dimension for which $\frac{\mu}{\tau}$ tends to the bound we get, which means that the bound is sharp, and at the same time answers an open problem raised by P. Almir\'{o}n.

math.AG↗

arXiv2025

Sliding multiferroicity in hexagonal stacked CrI3

Developing new multiferroics at the two-dimensional (2D) limit with energy-efficient magnetoelectric coupling can inform the interplay physics of novel orders and advance on-chip high-performance computing applications. Here we apply stacking order engineering to create a new type of 2D multiferroics, namely sliding multiferroics, based on polar hexagonal stacked (H-stacked) CrI3. This new stacking order removes structural inversion symmetry and gives rise to room temperature sliding ferroelectricity, as confirmed by Raman spectroscopy, second harmonic generation spectroscopy and electrical transport measurements. Building upon the gate-dependent reflective magnetic circular dichroism, first-principles calculations, and modeling, sliding ferroelectricity is shown to interplay with an emergent interfacial ferromagnetism via interlayer spin-polarized charge transfer. This coupling mechanism results in non-volatile magnetic switching by as low as 0.4V across the H-stacked CrI3. Our demonstration introduces polar stacking order engineering of 2D magnets as a general approach to create non-volatile 2D multiferroics with efficient magnetoelectric coupling, paving the way for low-power electronics and spintronics at the atomically thin limit.

cond-mat.mtrl-sci↗

arXiv2025

Tjurina Number Jumps and Unimodal Hypersurface Singularities in Positive Characteristic

This paper generalizes existing methods to derive stronger bounds on the modality of hypersurface singularities. Our results demonstrate that each sudden jump in the extended Tjurina number necessarily increases the modality. Furthermore, we provide a full classification of unimodal isolated hypersurface singularities in characteristic p > 3 under contact equivalence.

math.AG↗

arXiv2025

Superconducting Sn-Intercalated TaSe$_2$: Structural Diversity Obscured by Routine Characterization Techniques

Using Sn-intercalated TaSe$_2$ as a model system, we demonstrate the presence of structural heterogeneity captured by single-crystal X-ray diffraction (SCXRD) and scanning transmission electron microscopy (STEM) that eludes the routine characterization techniques of powder X-ray diffraction, Raman spectroscopy, and electronic transport measurements. From a single growth composition (1:1:2 Sn:Ta:Se), we obtained crystals diverse in stoichiometry and structure, with near-continuous intercalation for Sn$_x$TaSe$_2$ from $0\lesssim{x}\lesssim1$. Using SCXRD, we found global structural diversity, identifying three new structure types: Sn$_{0.18}$TaSe$_{2.0}$/Sn$_{0.08}$TaSe$_{1.96}$ ($R3m$), Sn$_{0.16}$TaSe$_{2.0}$ ($P6_3/mmc$), and Sn$_{1.2}$TaSe$_{1.9}$ ($Fmm2$). Using STEM, we observed local structural diversity, manifested as regions of highly variable stacking within a single crystal. In contrast, powder X-ray diffraction did not resolve all observed global structures. Raman spectroscopy was unable to distinguish between different structures or compositions in the standard measurement range. Electronic transport measurements showed consistent superconductivity and charge density wave behavior irrespective of Sn-intercalation amount. Our results indicate that routine approaches to characterization of intercalated transition metal dichalcogenides may be inadequate for capturing the diversity of this family of materials, highlighting the need for high-resolution structural characterization when examining the properties of van der Waals-layered compounds.

cond-mat.mtrl-sci↗

arXiv2025

Classification of unimodal isolated complete intersection singularities in positive characteristic

In this paper we classify the unimodal isolated complete intersection singularities in arbitrary characteristic under contact equivalence. The classification over $\mathbb{C}$ has already done by A. Dimca and C.G. Gibson. We continue and generalize their work. To complete the classification, we generalized the complete transversal method into positive characteristic field, which is also useful in many other classification problem.

math.AG↗