arXiv subjects

Yusheng Hou

Publications and source records attributed to Yusheng Hou.

At least 19 recordsLinked to original sources

arXiv2026

Quantum oscillation fingerprints of altermagnetism in hole-doped RuO2

Altermagnetism, characterized by its ferromagnetism-like spin-splitting band structure and antiferromagnetism-like magnetic order, has garnered considerable attention recently. Although hole doping may promote magnetism in the debated altermagnet candidate RuO2, the evolution of its electronic and magnetic properties under hole doping remains poorly understood. Based on first-principles calculations, we employ quantum oscillations to study hole-doped RuO2. We find that hole doping can enhance spin splitting and reconstruct the Fermi surface in RuO2, which is revealed by the angle-dependent quantum oscillation frequency. By tracking a pair of closed Fermi-surface pockets, we identify a meaningful correlation between the magnetic moment of Ru and a quantum-oscillation-based signature of spin splitting. This correlation follows a quasi-linear trend over a broad doping range, which can be captured by a minimal two-dimensional d-wave altermagnetic model. In addition, the hole-doped RuO2 exhibits a transition from a nonmagnetic to an altermagnetic state via an intermediate state. The quasi-linear correlation through quantum oscillation and the distinct quantum oscillation frequency of the stable altermagnetic state can serve as useful signatures for identifying the altermagnetic state in RuO2. Our results provide a comprehensive framework for understanding hole-doped RuO2, offering new insights into altermagnetic transitions and their identification.

cond-mat.mtrl-sci↗

arXiv2026

Unconventional Superconductivity in $\mathrm{La_{3}Ni_{2}O_{7}}$ from the Perspective of Symmetry

The recently discovered superconductor $\mathrm{La_{3}Ni_{2}O_{7}}$ has attracted significant attention due to its remarkably high transition temperature ($T_{c}$) under high pressure. Shortly after this discovery, thin-film $\mathrm{La_{3}Ni_{2}O_{7}}$ was demonstrated to exhibit ambient-pressure superconductivity; however, the corresponding $T_c$ is only about half that of the pressurized bulk material. This striking difference raises questions about the underlying mechanisms governing superconductivity in these two structures. To address this issue, we develop a phenomenological symmetry-based method to investigate the superconducting gap structure in $\mathrm{La_{3}Ni_{2}O_{7}}$. Using density-functional theory methods (DFT+$U$), together with the experimentally determined $T_c$ and structural symmetry, we find that both pressurized bulk and thin-film $\mathrm{La_{3}Ni_{2}O_{7}}$ exhibit $s_{\pm}$-wave pairing symmetry and two-gap superconductivity, yet their dominant microscopic pairing configurations are distinct. In the pressurized bulk, superconductivity is dominated by the out-of-plane pairing of the Ni-$d_{z^2}$ orbitals, while in the thin film, the in-plane pairing of the Ni-$d_{x^2-y^2}$ orbitals prevails. Furthermore, the observed reduction in $T_c$ can be attributed to this transition of the dominant pairing type, driven by the decreased ratio of inter-layer to intra-layer hoppings in the thin film. Our result sheds lights on the microscopic pairing in $\mathrm{La_{3}Ni_{2}O_{7}}$ and reveals the significance of the symmetry. This method can potentially be generalized to a broader range of unconventional superconductors.

cond-mat.supr-con↗

arXiv2026

Topological-transition-driven Giant Enhancement of Second-harmonic Generation in Ferroelectric Bismuth Monolayer

The interplay between band topology and light in condensed materials could unlock intriguing nonlinear optical phenomena, enabling modern photonic technologies such as quantum light sources and sub-wavelength topological lasers. Here, we unveil that a buckling-tuned topological transition in ferroelectric bismuth monolayer unleashes a giant second-harmonic generation. Using first-principles calculations, we surprisingly find that ferroelectric bismuth monolayer with a buckling parameter, $Δh$, has a large susceptibility $χ^{(2)}$ on the order of $10^{7}$ $\mathrm{pm}^2/\mathrm{V}$, exceeding monolayer MoS$_2$ by about two orders of magnitude. When $Δh$ is engineered to the critical window where Dirac electrons emerge, a low-frequency resonance appears, boosting $χ^{(2)}$ by an additional order of magnitude. We show that this enhancement is localized on the Dirac cones and dominated by intraband modification contributions. Based on an extended Dirac model, we establish that this enhancement physically originates from the ultralight effective masses $m^{*}$ of Dirac electrons through scaling with the Fermi velocity $v_F$ and band gap $E_g$. Our findings provide a general paradigm for achieving exceptional second-harmonic generation via engineering topological criticality, and could serve as an experimental signature of Dirac electrons in topological materials.

cond-mat.mtrl-sci↗

arXiv2025

Highly tunable Gilbert damping in two-dimensional van der Waals ferromagnet Fe3GaTe2: From bilayer to the twisted bilayer

Van der Waals ferromagnet Fe3GaTe2 possesses both a high Curie temperature and robust perpendicular magnetic anisotropy, holding promise for practical spintronic applications. In particular, understanding and engineering its Gilbert damping which determines magnetization dynamics are crucial for its applications. Here, we investigate the Gilbert damping of bilayer and the twisted bilayer Fe3GaTe2 through first-principles calculations. For the bilayer Fe3GaTe2, we obtain a quite low Gilbert damping when its magnetization is along the z axis at room temperature. In addition, the bilayer Fe3GaTe2 exhibits a large orientational anisotropy of Gilbert damping when its magnetization is rotated from the magnetic easy axis to the hard one. Such anisotropy is attributed to the distinct band structures caused by the anisotropic spin-orbit coupling. Surprisingly, we find that twisting the bilayer Fe3GaTe2 can effectively reduce the Gilbert damping for the perpendicular magnetization, and enhance the orientational anisotropy of Gilbert damping up to 635% when rotating the magnetization from the magnetic easy axis to the hard one. These findings open up an entirely new avenue for the manipulation of Gilbert damping and its anisotropy in two-dimensional van der Waals ferromagnets.

cond-mat.mtrl-sci↗

arXiv2025

Giant Anomalous Hall Conductivity and Gilbert Damping in Room-temperature Ferromagnetic Half-Heusler Alloys PtMnBi

Half-Heusler alloys have emerged as promising candidates for novel spintronic applications due to their exceptional properties including the high Curie temperature (TC) above room temperature and large anomalous Hall conductivity (AHC). In this work, we systematically study the magnetic and electronic properties of PtMnBi in α-, \{beta}-, and γ-phase using first-principles calculations and Monte Carlo simulations. The three phases are found to be ferromagnetic metals. In particular, the α-phase PtMnBi shows a high TC up to 802 K and a relatively large Gilbert damping of 0.085. Additionally, the γ-phase PtMnBi possesses a non-negligible AHC, reaching 203 Ω-1cm-1 at the Fermi level. To evaluate its potential in nanoscale devices, we further investigate the α-phase PtMnBi thin films. The Gilbert dampings of α-phase PtMnBi thin films varies with film thickness and we attribute this variation to the distinct band structures at the high-symmetry point Γ, which arise from differences in film thickness. Moreover, the 1-layer (1L) α-phase thin film retains robust ferromagnetism (TC = 688 K) and shows enhanced Gilbert damping (0.14) and AHC (1116 Ω-1cm-1) compared to the bulk. Intriguingly, under a 2% in-plane biaxial compressive strain, the Gilbert damping of 1L α-phase PtMnBi thin film increases to 0.17 and the AHC reaches 2386 Ω-1cm-1. The coexistence of giant Gilbert damping and large AHC makes α-phase PtMnBi a compelling platform for practical spintronic applications, and highlights the potential of half-Heusler alloys in spintronic device design.

cond-mat.mtrl-sci↗

arXiv2025

Magnetic Anisotropy in Two-dimensional van der Waals Magnetic Materials and Their Heterostructures: Importance, Mechanisms, and Opportunities

Two-dimensional (2D) magnetism in atomically thin van der Waals (vdW) monolayers and heterostructures has attracted significant attention due to its promising potential for next-generation spintronic and quantum technologies. A key factor in stabilizing long-range magnetic order in these systems is magnetic anisotropy, which plays a crucial role in overcoming the limitations imposed by the Mermin-Wagner theorem. This review provides a comprehensive theoretical and experimental overview of the importance of magnetic anisotropy in enabling intrinsic 2D magnetism and shaping the electronic, magnetic, and topological properties of 2D vdW materials. We begin by summarizing the fundamental mechanisms that determine magnetic anisotropy, emphasizing the contributions from strong ligand spin-orbit coupling of ligand atoms and unquenched orbital magnetic moments. We then examine a range of material engineering approaches, including alloying, doping, electrostatic gating, strain, and pressure, that have been employed to effectively tune magnetic anisotropy in these materials. Finally, we discuss open challenges and promising future directions in this rapidly advancing field. By presenting a broad perspective on the role of magnetic anisotropy in 2D magnetism, this review aims to stimulate ongoing efforts and new ideas toward the realization of robust, room-temperature applications based on 2D vdW magnetic materials and their heterostructures.

cond-mat.mtrl-sci↗

arXiv2025

Ambient-pressure superconductivity onset at 10 K and robust Tc under high pressure in TiNbTaN3 medium-entropy nitride

Superconductivity has been one of the focal points in medium and high-entropy alloys (MEAs-HEAs) since the first discovery of the HEA superconductor in 2014. Until now, most HEAs' superconducting transition temperature (Tc) has not exceeded 10 K. Here we report the first observation of superconductivity in a bulk medium-entropy nitride (MEN), TiNbTaN3, which shows a Tc of 10 K at ambient pressure. Notably, the electronic specific heat coefficient γ(H) exhibits nonlinear H-dependence behavior, which is similar to other well-studied multigap superconductors. Furthermore, TiNbTaN3 exhibits extraordinary pressure resilience, maintaining robust superconductivity under high-pressure conditions. Density functional theory (DFT) calculations indicate that pressure exerts a negligible impact on the electronic structures of TiNbTaN3, thereby corroborating the experimental observations. These findings not only advance our understanding of emergent phenomena in entropy-stabilized nitrides but also establish a new material platform for finding more high-Tc superconductors with combinations of 4d/5d transition metal elements and light elements, motivating further investigations into high-entropy functional ceramics for extreme environment applications.

cond-mat.supr-con↗

arXiv2025

First-principles study of electronic and magnetic properties of self-intercalated van der Waals magnet Cr$_3$Ge$_2$Te$_6$

Self-intercalated van der Waals magnets, characterized by self-intercalating native atoms into van der Waals layered structures with intrinsic magnetism, exhibit a variety of novel physical properties. Here, using first-principles calculations and Monte Carlo simulations, we report a self-intercalated van der Waals ferromagnet, Cr$_3$Ge$_2$Te$_6$, which has a high Curie temperature of 492 K. We find that Cr$_3$Ge$_2$Te$_6$ is nearly half-metallic with a spin polarization reaching up to 90.9%. Due to the ferromagnetism and strong spin-orbit coupling effect in Cr$_3$Ge$_2$Te$_6$, a large anomalous Hall conductivity of 138 $Ω^{-1}$ cm$^{-1}$ and 305 $Ω^{-1}$ cm$^{-1}$ can be realized when its magnetization is along its magnetic easy axis and hard axis, respectively. By doping electrons (holes) into Cr$_3$Ge$_2$Te$_6$, these anomalous Hall conductivities can be increased up to 318 $Ω^{-1}$ cm$^{-1}$ (648 $Ω^{-1}$ cm$^{-1}$). Interestingly, a 5-layer Cr$_3$Ge$_2$Te$_6$ thin film retains the room-temperature ferromagnetism with a higher spin polarization and larger anomalous Hall conductivity. Our work demonstrates that Cr$_3$Ge$_2$Te$_6$ is a novel room-temperature self-intercalated ferromagnet with high spin polarization and large anomalous Hall conductivity, offering great opportunities for designing nano-scale electronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Thickness-dependent anisotropic Gilbert damping in heterostructures of ferromagnets and two-dimensional ferroelectric bismuth monolayer

The Gilbert damping parameter, which describes magnetization dynamics, is crucial for the performance of modern spintronic devices, affecting factors such as the switching speed and critical current density of magnetoresistive random access memory. Thus, the ability to engineer it on demand is pivotal for developing novel spintronic applications. In this work, we systematically examine the Gilbert damping parameter of Fe films in contact with a black phosphorus-like bismuth monolayer using first-principles calculations. In these Bi/Fe heterostructures, we obtain a significantly enhanced Gilbert damping owing to strong interfacial spin-orbit couplings (SOCs). Interestingly, we find non-monotonic thickness-dependent Gilbert damping anisotropy and attribute that to the competition between the interfacial SOC and the intrinsically anisotropic SOC of Fe films. We further demonstrate that these SOC effects lead to anisotropic band structures, which are responsible for the anisotropic Gilbert damping. Our work provides a deep understanding of the anisotropic Gilbert damping and opens avenues for exploring it in ferromagnetic heterostructures.

cond-mat.mtrl-sci↗

arXiv2024

Topological Surface State Evolution in Bi$_2$Se$_3$ via Surface Etching

Topological insulators are materials with an insulating bulk interior while maintaining gapless boundary states against back scattering. Bi$_2$Se$_3$ is a prototypical topological insulator with a Dirac-cone surface state around $Γ$. Here, we present a controlled methodology to gradually remove Se atoms from the surface Se-Bi-Se-Bi-Se quintuple layers, eventually forming bilayer-Bi on top of the quintuple bulk. Our method allows us to track the topological surface state and confirm its robustness throughout the surface modification. Importantly, we report a relocation of the topological Dirac cone in both real space and momentum space, as the top surface layer transitions from quintuple Se-Bi-Se-Bi-Se to bilayer-Bi. Additionally, charge transfer among different surface layers is identified. Our study provides a precise method to manipulate surface configurations, allowing for the fine-tuning of the topological surface states in Bi$_2$Se$_3$, which represents a significant advancement towards nano-engineering of topological states.

cond-mat.mtrl-sci↗

arXiv2024

Observation of in-gap states in a two-dimensional CrI2/NbSe2 heterostructure

Low-dimensional magnetic structures coupled with superconductors are promising platforms for realizing Majorana zero modes, which have potential applications in topological quantum computing. Here, we report a two-dimensional (2D) magnetic-superconducting heterostructure consisting of single-layer chromium diiodide (CrI2) on a niobium diselenide (NbSe2) superconductor. Single-layer CrI2 nanosheets, which hold antiferromagnetic (AFM) ground states by our first-principles calculations, were epitaxially grown on the layered NbSe2 substrate. Using scanning tunneling microscopy/spectroscopy, we observed robust in-gap states spatially located at the edge of the nanosheets and defect-induced zero-energy peaks inside the CrI2 nanosheets. Magnetic-flux vortices induced by an external field exhibit broken threefold rotational symmetry of pristine NbSe2 superconductor, implying the efficient modulation of the interfacial superconducting states by the epitaxial CrI2 layer. A phenomenological model suggests the existence of chiral edge states in a 2D AFM-superconducting hybrid system with an even Chern number, providing a qualitatively plausible understanding for our experimental observation.

cond-mat.supr-con↗

arXiv2024

Above room-temperature two-dimensional ferromagnetic half-metals in Mn-based Janus magnets

Two-dimensional (2D) ferromagnets and their heterostructures offer fertile grounds for designing fascinating functionalities in ultra-thin spintronic devices. Here, by first-principles calculations, we report the discovery of energetically and thermodynamically stable 2D ferromagnets with very strong inplane magnetic anisotropy in MnXY (X = S, and Se; Y = Cl, Br and I) monolayers. Remarkably, we find that the Curie temperatures of the ferromagnetic MnSBr, MnSI, MnSeCl, and MnSeI monolayers are as high as 271, 273, 231 and 418 K, respectively. In addition, we demonstrate that these ferromagnetic monolayers are intrinsic half-metals with large spin band gaps ranging from 2.5 eV to 3.2 eV. When spin-orbit coupling is considered in these ferromagnetic monolayers, the nature of their half-metal is almost unaffected. Finally, the strong inplane magnetic anisotropy of MnSY (Y = Br, I) and MnSeY (Y = Cl, I) monolayers originate mainly from halogen and chalcogen atoms, respectively. Our work shows 2D Janus Mn-based ferromagnetic half-metals may have appealing functionalities in high-performance spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Tunable magnetic anisotropy, Curie temperature and band alignment of two-dimensional ferromagnet VSiSnN4 via non-volatile ferroelectrical control

The emergence of multiferroic materials, which possess both ferromagnetic (FM) and ferroelectric (FE) properties, drive advancements in magnetoelectric applications and the next generation of spintronics. Based on first-principles calculations, we investigate an engineered two-dimensional multiferroic van der Waals heterostructures consisting of FM VSiSnN4 monolayer (ML) and fully hydrogenated FE AlN bilayer. We find that the magnetic anisotropy of VSiSnN4 ML is tunable between out-of-plane and in-plane and a phase transition between semiconductor and metal is induced in VSiSnN4/AlN bilayer when the FE polarization direction of AlN bilayer is reversed. Surprisingly, when the FE polarization of AlN bilayer is upward, the Curie temperature of VSiSnN4/AlN bilayer can be significantly increased from 204K to 284K. Such non-volatile and tunable magnetic anisotropy, Curie temperature and band alignment in VSiSnN4/AlN multiferroic heterostructure are highly promising for future low-current operation of data storage and logic devices.

cond-mat.mtrl-sci↗

arXiv2024

The discovery of three-dimensional Van Hove singularity

Arising from the extreme/saddle point in electronic bands, Van Hove singularity (VHS) manifests divergent density of states (DOS) and induces various new states of matter such as unconventional superconductivity. VHS is believed to exist in one and two dimensions, but rarely found in three dimension (3D). Here, we report the discovery of 3D VHS in a topological magnet EuCd2As2 by magneto-infrared spectroscopy. External magnetic fields effectively control the exchange interaction in EuCd2As2, and shift 3D Weyl bands continuously, leading to the modification of Fermi velocity and energy dispersion. Above the critical field, the 3D VHS forms and is evidenced by the abrupt emergence of inter-band transitions, which can be quantitatively described by the minimal model of Weyl semimetals. Three additional optical transitions are further predicted theoretically and verified in magneto-near-infrared spectra. Our results pave the way to exploring VHS in 3D systems and uncovering the coordination between electronic correlation and the topological phase.

cond-mat.mtrl-sci↗

arXiv2024

Switching intrinsic magnetic skyrmions with controllable magnetic anisotropy in van der Waals multiferroic heterostructures

Magnetic skyrmions, topologically nontrivial whirling spin textures at nanometer scales, have emerged as potential information carriers for spintronic devices. The ability to efficiently create and erase magnetic skyrmions is vital yet challenging for such applications. Based on first-principles studies, we find that switching between intrinsic magnetic skyrmion and high-temperature ferromagnetic states can be achieved in two-dimensional van der Waals (vdW) multiferroic heterostructure CrSeI/In2Te3 by reversing the ferroelectric polarization of In2Te3. The core mechanism of this switching is traced to the controllable magnetic anisotropy of CrSeI influenced by the ferroelectric polarization of In2Te3. We propose a useful descriptor linking the presence of magnetic skyrmions to magnetic parameters, and validate this connection through studies of a variety of similar vdW multiferroic heterostructures. Our work demonstrates that manipulating magnetic skyrmions via tunable magnetic anisotropies in vdW multiferroic heterostructures represents a highly promising and energy-efficient strategy for future development of spintronics.

cond-mat.mtrl-sci↗

arXiv2023

Discovery of the high-entropy carbide ceramic topological superconductor candidate (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C

High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements. Material design and property tailoring possibilities emerge from this new class of materials. Here, we report the discovery of superconductivity around 2.35 K and topological properties in the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C high-entropy carbide ceramic (HECC), which has not been observed before in any of the investigated HECC. Density functional theory calculations showed that six type-II Dirac points exist in (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C, which mainly contributed from the t2g orbitals of transition metals and the p orbitals of C. Due to the stability of the structure, we also observed robust superconductivity under pressure in this HEC superconductor. This study expands the physical properties of HECs, which may become a new material platform for superconductivity research, especially for studying the coupling between superconductivity and topological physics.

cond-mat.supr-con↗

arXiv2023

Room-temperature antiferromagnetic CrSe monolayer with tunable metal-insulator transition in ferroelectric heterostructures

Recently, there has been a rapidly growing interest in two-dimensional (2D) transition metal chalcogenide monolayers (MLs) due to their unique magnetic and electronic properties. By using an evolutionary algorithm and first-principles calculations, we report the discovery of a previously unexplored, chemically, energetically, and thermodynamically stable 2D antiferromagnetic (AFM) CrSe ML with a Néel temperature higher than room temperature. Remarkably, we predict an electric field-controllable metal-insulator transition (MIT) in a van der Waals (vdW) heterostructure comprised of CrSe ML and ferroelectric Sc2CO2. This tunable transition in CrSe/Sc2CO2 heterostructure is attributed to the change in the band alignment between CrSe and Sc2CO2 caused by the ferroelectric polarization reversal in Sc2CO2. Our findings suggest that 2D AFM CrSe ML has important potential applications in AFM spintronics, particularly in the gate voltage conducting channel.

cond-mat.mtrl-sci↗

arXiv2023

Electrically tunable Gilbert damping in van der Waals heterostructures of two-dimensional ferromagnetic metals and ferroelectrics

Tuning the Gilbert damping of ferromagnetic (FM) metals via a nonvolatile way is of importance to exploit and design next-generation novel spintronic devices. Through systematical first-principles calculations, we study the magnetic properties of the van der Waals heterostructure of two-dimensional FM metal CrTe2 and ferroelectric (FE) In2Te3 monolayers. The ferromagnetism of CrTe2 is maintained in CrTe2/In2Te3 and its magnetic easy axis can be switched from in-plane to out-of-plane by reversing the FE polarization of In2Te3. Excitingly, we find that the Gilbert damping of CrTe2 is tunable when the FE polarization of In2Te3 is reversed from upward to downward. By analyzing the k-dependent contributions to the Gilbert damping, we unravel that such tunability results from the changed intersections between the bands of CrTe2 and Fermi level on the reversal of the FE polarizations of In2Te3 in CrTe2/In2Te3. Our work provides an appealing way to electrically tailor Gilbert dampings of two-dimensional FM metals by contacting them with ferroelectrics.

cond-mat.mtrl-sci↗