arXiv subjects

Shijun Yuan

Publications and source records attributed to Shijun Yuan.

7 recordsLinked to original sources

arXiv2026

Robust Flat Magnetoresistivity in D0$_3$-Fe$_3$Ga Driven by Chiral Anomaly

Topologically non-trivial nodes emerging from flat-band crossings not only enhance unconventional topological responses but also play a fundamental role in exploring correlation-driven topological physics. Here, we report the exceptionally robust chiral-anomaly-dominated transport in D0_3-Fe_3Ga. First, we observe a combination of positive and negative magnetoresistance, ideal planar longitudinal magnetoresistance (PLMR), and the planar Hall effect (PHE). Second, ultra-low-temperature resistivity exhibits pronounced non-Fermi-liquid (NFL) behavior, accompanied by the emergence of giant intrinsic anomalous Hall conductivity (AHC), in excellent agreement with our DFT calculations, which confirm the existence of tilted Weyl points arising from crossings of nearly three-dimensional (3D) flat bands. Most remarkably, we detect an exceptionally robust flat magnetoresistance (flat-MR) that persists without decay up to 33 T. This set of phenomena provides strong evidence that the Fermi level intersects the flattened Weyl crossings, offering confirmation of a topological flat-band semimetal. D0_3-Fe_3Ga presents a promising magnetic platform for quantum device innovations.

cond-mat.mtrl-sci↗

arXiv2025

Zero-field Anomalous Hall Effect in Bulk Single Crystal Mn3Ir

The L1_2-phase non-collinear antiferromagnet (AFM) Mn_3Ir has emerged as a pioneering platform for realizing the zero-field anomalous Hall effect (AHE), thereby catalyzing rapid advances in antiferromagnetic spintronics. Despite its significant potential, experimental investigations of the intrinsic magnetic and electronic properties of Mn_3Ir have been greatly hindered by the formidable challenges in growing bulk single crystals. Here, we report the growth of stoichiometric Mn_3Ir bulk single crystals and their characterization in terms of magnetization and the AHE. Using a high-throughput flux method, we obtained (111)-oriented hexagonal Mn_3Ir single crystals. A small AHE signal was detected, which we attribute to the coexistence of A- and B-type antiferromagnetic domains that mutually cancel the net AHE response. Our results reveal key aspects of the intrinsic magnetic properties and AHE in bulk Mn_3Ir, providing a critical material platform for the development of advanced spintronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Electron doping induced stable ferromagnetism in two-dimensional GdI_3 monolayer

As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM-FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d-4f hybridization. Moreover, the shortened Gd-Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.

cond-mat.mtrl-sci↗

arXiv2022

Magnetic phase transition induced ferroelectric polarization in BaFeF4 with room temperature weak ferromagnetism

BaMF4 (M=Fe, Co, Ni and Mn) family are typical multiferroic materials, having antiferromagnetism at around liquid nitrogen temperature. In this work, polycrystalline BaFeF4 has been prepared by solid state reaction. The slight deficiency of Fe leads to the coexistence of valence states of +2 and +3, facilitating the electrons to hop between the neighboring Fe2+ and Fe3+ ions through the middle F- ion, leading to the strong double exchange interaction with weak ferromagnetism above room temperature. A bifurcation at about 170 K between the zero-field-cooled and field-cooled temperature dependent magnetization curves indicates the onset of 2-dimensional antiferromagnetism, which is completed at about 125 K with the sudden drop of magnetization. Despite the fact of type-I multiferroic, its magnetoelectricity can be evidenced by the pyroelectric current, which shows a peak starting at about 170 K and finishing at about 125 K. The saturated ferroelectric polarization change of around 34 μC/m2 is observed, which is switchable by the reversed poling electric field and decreases to about 30 μC/m2 under a magnetic field of 90 kOe. This magnetoelectricity can be qualitatively reproduced by first-principles calculations. Our results represent substantial progress to search for high-temperature multiferroics in ferroelectric fluorides.

cond-mat.mtrl-sci↗

arXiv2018

Prediction of Extraordinary Magnetoresistance in Janus Monolayer MoTeB2

Based on first-principles calculations, we studied the geometric configuration, stability and electronic structure of the two-dimensional Janus MoTeB2. The MoTeB2 monolayer is semimetal, and its attractive electronic structure reveals the perfect electron-hole compensation. Moreover, the electron-type and hole-type bands of the MoTeB2 monolayer are easily adjustable by external stain and charge doping, such as the switch of carrier polarity by charge doping, and the metal-semiconductor transition under tensile stain. These properties allow the MoTeB2 monolayer to be a controllable two-dimensional material with extraordinary large magnetoresistance in magnetic field.

cond-mat.mtrl-sci↗

arXiv2014

Two-dimensional Quasi-Freestanding Molecular Crystals for High-Performance Organic Field-Effect Transistors

Two-dimensional atomic crystals are extensively studied in recent years due to their exciting physics and device applications. However, a molecular counterpart, with scalable processability and competitive device performance, is still challenging. Here, we demonstrate that high-quality few-layer dioctylbenzothienobenzothiophene molecular crystals can be grown on graphene or boron nitride substrate via van der Waals epitaxy, with precisely controlled thickness down to monolayer, large-area single crystal, low process temperature and patterning capability. The crystalline layers are atomically smooth and effectively decoupled from the substrate due to weak van der Waals interactions, affording a pristine interface for high-performance organic transistors. As a result, monolayer dioctylbenzothienobenzothiophene molecular crystal field-effect transistors on boron nitride show record-high carrier mobility up to 10cm2V-1s-1 and aggressively scaled saturation voltage around 1V. Our work unveils an exciting new class of two-dimensional molecular materials for electronic and optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2013

Hopping Transport through Defect-induced Localized States in Molybdenum Disulfide

Molybdenum disulfide is a novel two-dimensional semiconductor with potential applications in electronic and optoelectronic devices. However, the nature of charge transport in back-gated devices still remains elusive as they show much lower mobility than theoretical calculations and native n-type doping. Here we report transport study in few-layer molybdenum disulfide, together with transmission electron microscopy and density functional theory. We provide direct evidence that sulfur vacancies exist in molybdenum disulfide, introducing localized donor states inside the bandgap. Under low carrier densities, the transport exhibits nearest-neighbor hopping at high temperatures and variable-range hopping at low temperatures, which can be well explained under Mott formalism. We suggest that the low-carrier-density transport is dominated by hopping via these localized gap states. Our study reveals the important role of short-range surface defects in tailoring the properties and device applications of molybdenum disulfide.

cond-mat.mtrl-sci↗