arXiv subjects

Dingfu Shao

Publications and source records attributed to Dingfu Shao.

11 recordsLinked to original sources

arXiv2026

Three-dimensional Ising superconductors designed via inversion-symmetry breaking in intercalated NbSe$_2$ and NbTe$_2$

Ising superconductors exhibit in-plane upper critical fields far exceeding the Pauli paramagnetic limit, a hallmark first established in two-dimensional (2D) monolayer transition-metal dichalcogenides (TMDs). This field resilience requires the coexistence of strong spin-orbit coupling (SOC) and broken inversion symmetry, yet three-dimensional (3D) bulk realizations remain scarce because equilibrium stacking typically restores inversion symmetry. Here we demonstrate that intercalation provides a practical route to break this symmetry, systematically designing 16 NbSe$_2$- and NbTe$_2$-based compounds from four intercalants (In, Sn, Pb, Bi) across two polytypes: non-centrosymmetric $P\bar{6}m2$ and centrosymmetric $P6_3/mmc$. Four compounds in the $P\bar{6}m2$ phase, InNbSe$_2$, SnNbSe$_2$, PbNbSe$_2$, and PbNbTe$_2$, emerge as promising 3D Ising superconductors. They exhibit SOC splittings of 80-100 meV near the Fermi level, dominant out-of-plane spin polarization, and anisotropic superconductivity with $T_c=2.6$-$5.4$ K. Notably, spin-texture analysis reveals that the efficiency of Ising protection is governed not by the magnitude of SOC splitting alone but by the out-of-plane spin purity on the Fermi surface. Bogoliubov-de Gennes (BdG) calculations predict in-plane upper critical fields reaching 4-7 times the Pauli limit. These findings establish intercalation as a promising symmetry-engineering strategy for realizing 3D Ising superconductors in TMDs.

cond-mat.supr-con↗

arXiv2026

Intertwined spin-charge stripe order and polar lattice distortion in La$_{3}$Ni$_{2}$O$_{7}$

The low-temperature density-wave state of La$_3$Ni$_2$O$_7$ hosts pronounced spin-density-wave (SDW) order, while recent experiments further reveal charge redistribution and a concomitant lattice-symmetry lowering. However, the microscopic relationship among spin, charge, and lattice remains unclear. Using first-principles calculations, we investigate the pressure evolution of the electronic structure and static spin susceptibility of La$_3$Ni$_2$O$_7$, together with the energetics and lattice response of representative magnetic configurations. We trace the SDW instability to strong Fermi-surface nesting and find that the high-pressure spin response closely tracks $T_{\mathrm C}$, suggesting spin-fluctuation-mediated pairing. Among the candidate magnetic states considered, the spin-charge-stripe states emerge as energetically favored and dynamically stable, developing pronounced disproportionation of both the local Ni moments and the Ni--O bond lengths. Remarkably, the lowest-energy a-stripe state spontaneously relaxes into the experimentally proposed polar Am2m structure through a polar distortion along the b axis. These results establish a unified picture in which spin, charge, and lattice responses are strongly intertwined in the low-pressure density-wave state, while spin fluctuations remain a plausible ingredient of superconductivity under pressure.

cond-mat.supr-con↗

arXiv2026

Enhanced Curie temperature and room-temperature 50-nm skyrmions achieved in hexagonal ferromagnet Mn5Ge3+x synthesized via a high-pressure method

The development of new high-temperature ultrasmall-size skyrmion materials holds immense significance for the promising applications of topological spintronic devices. In this study, we demonstrate that a high-pressure synthesis technique can significantly elevate the Curie temperature of Mn5Ge3+x crystals, from 294 K to 350 K. This enhancement is attributed to the combined effects of lattice contraction and increased Ge content, the conclusion supported by Density Functional Theory calculations. Additionally, our real-space magnetic imaging reveals the stability of dipolar skyrmions with diameters of approximately 50 nm at room temperature. Our micromagnetic simulations closely replicate the diverse experimental topological magnetic textures observed. Furthermore, magnetotransport measurements indicate the potential for the electrical distinction between various topological magnetic textures in skyrmion-based devices. We also report deterministic manipulations on single dipolar skyrmions in confined nanostructures by using in-plane currents. The observation, electrical manipulation, and electrical detection of room-temperature ultrasmall topological magnetic textures underscore the potential of Mn5Ge3+x as a promising platform for spintronic device applications.

cond-mat.mtrl-sci↗

arXiv2025

Machine learning-accelerated search of superconductors in B-C-N based compounds and R3Ni2O7-type nickelates

Superconductor research has traditionally depended on experiments and theoretical approaches. However, the rapid advancement of data-driven methods and machine learning (ML) has opened avenues for accelerating superconductor discovery. Here, we integrated ML with density functional theory (DFT) calculations to efficiently screen conventional B-C-N based superconductors and identify potential high-TC candidates among R3Ni2O7-type bilayer nickelates. We identified 12 new binary and ternary B-C-N based superconductors with TC >= 10 K, including 3 with TC >= 25 K, such as two structural forms of B2CN (TC = 44.8 K and 41.5 K) and TiNbN2 (TC = 26.2 K). These materials share a common feature of strong {\sigma}-bonds, which is key to achieving relatively high TC. Moreover, we proposed Tb3Ni2O7 (TC = 61.6 K) and Ac3Ni2O7 (TC = 70.3 K) as potential high-TC nickelate superconductors under high pressure. Their electronic structures closely resemble those of La3Ni2O7, especially in the hole-type band dominated by Ni-3dz2 orbital character. We also analyzed feature importance in the ML results for both conventional and high-TC superconductors. These results advance the search for new superconductors and enhance the fundamental understanding of superconducting mechanisms.

cond-mat.supr-con↗

arXiv2025

Orbital-selective two-gap superconductivity in kagome metal CsV3Sb5

Recent experiments have revealed anisotropic multi-gap superconductivity in the kagome metal CsV3Sb5. However, the impact of multi-orbital character and electron-phonon coupling (EPC) on the multiple superconducting gaps remains not fully understood. In this work, we theoretically investigate the multi-orbital electronic structure and superconducting gap properties of CsV3Sb5 by combining first-principles calculations with superconducting density functional theory (SCDFT). Our results demonstrate that orbital-selective pairing drives the observed two-gap superconductivity in CsV3Sb5. Specifically, the two distinct gaps exhibit strong orbital dependence: a large, highly anisotropic gap (average magnitude ~0.64 meV) primarily originates from V-3d orbitals, while a small, isotropic gap (~0.25 meV) is associated with the Sb-5pz orbital. The V-3d orbitals exhibit strong coupling to the in-plane V-V bond-stretching and out-of-plane V-Sb bending phonon modes, whereas the Sb-5pz orbitals show weak coupling to the out-of-plane vibrations of both Cs and the apical Sb atoms. These findings provide fundamental insights into the orbital-selective superconductivity and EPC mechanisms in kagome CsV3Sb5.

cond-mat.supr-con↗

arXiv2025

Phonon anharmonicity-driven charge density wave transition and ultrafast dynamics in 1T-TaS2/TaSe2

Charge density wave (CDW), a symmetry-breaking collective phenomenon in condensed matter systems, exhibits periodic modulations of electron density coupled with lattice distortions, where the lattice plays a critical role via electron-phonon coupling. In transition metal dichalcogenides (TMDs) 1T-TaS2/TaSe2, experiments reveal rich temperature- and pressure-dependent CDW phase behaviors, along with metastable CDW states induced by ultrafast optical excitation. Nevertheless, the underlying mechanisms governing thermal/pressure-driven transitions and particularly the microscopic evolution of CDW phases remain incompletely understood. Here, we perform first-principles anharmonic phonon calculations and machine-learning force-field molecular dynamics at finite temperatures/pressures to investigate the CDW transitions in 1T-TaS2/TaSe2. The calculated CDW transition temperature TCDW and critical pressure Pc are in quantitative agreement with experimental values. Our results demonstrate that the melting of CDW originates from phonon anharmonicity, with ionic fluctuations dominating the transition dynamics. We observe the microscopic evolution of CDW under varying temperature/pressure, revealing an ultrafast nucleation process of CDW (~3 ps). Our results emphasize the essential role of phonon anharmonicity in elucidating CDW transition mechanisms underlying, and advance fundamental understanding of CDW-related phenomena in TMDs.

cond-mat.mtrl-sci↗

arXiv2025

Strain tuning of charge density wave and Mott-insulating states in monolayer VTe2

Monolayer vanadium ditelluride (VTe2) exhibits a 2\sqrt{3}*2\sqrt{3} charge density wave (CDW) order intertwined with a Mott-insulating state. However, the physical mechanisms driving the emergence of CDW order and Mott-insulating state are still not well understood. In this study, we systematically investigate the electronic band structure, phonon dispersion, and electron-phonon coupling (EPC) of monolayer VTe2 under applied biaxial strain. Our results reveal that the CDW phase is metastable in free-standing monolayer VTe2 and becomes stabilized under compressive strain below {\epsilon} = -2%. The formation of CDW order originates dominantly from strong EPC effect, rather than Fermi surface nesting. The narrowing of the bandwidth due to the CDW order, combined with the correlation effect of the V-3d orbital, collectively drives the system into a Mott-insulating state. Furthermore, we find that tensile strain suppresses CDW order and induces a superconducting state above a critical strain threshold ({\epsilon} = 2%). These findings enhance our understanding of correlation physics in monolayer VTe2 and provide a pathway for strain-engineered manipulation of quantum phases in two-dimensional transition metal dichalcogenides.

cond-mat.supr-con↗

arXiv2025

Sign reversal of Berry curvature triple driven by magnetic phase transition in a ferromagnetic polar metal

While the time-reversal-even (T-even) nonlinear Hall effect has been extensively discussed in nonmagnetic materials, the impact of magnetic phase transition on it remains largely overlooked. Here, we report an abrupt enhancement of the T-even nonlinear Hall effect in non-centrosymmetric SrRuO3(111) thin films during the paramagnetic-ferromagnetic transition. Scaling analysis reveals a sign reversal of both the skew scattering and side jump contributions upon the emergence of magnetism, which we attribute to the sign change of Berry curvature triple on the Fermi surface. Density functional theory calculations support this interpretation, ascribing this behavior to distinctive origins of Berry curvature hot spots in paramagnetic and ferromagnetic phases. Our findings unveil the exchange-induced dramatic nonperturbative change of nonlinear Hall effect, and establish SrRuO3(111) thin films as a promising platform for exploring magnetically tunable nonlinear transport effects.

cond-mat.mtrl-sci↗

arXiv2024

Spin-Splitting Magnetoresistance in Altermagnetic RuO2 Thin Films

The recently discovered altermagnets, featured by the exotic correlation of magnetic exchange interaction and alternating crystal environments, have offered exciting cutting-edge opportunities for spintronics. Nevertheless, the altermagnetism of RuO2, one of the earliest-discovered altermagnets, is currently under intense debate. Here we try to resolve this controversy by demonstrating an altermagnetic spin-splitting magnetoresistance (SSMR) effect that is driven by a spin current associated with the giant nonrelativistic spin splitting of an altermagnet. Compared to the spin Hall magnetoresistance induced by a conventional relativistic spin current, the SSMR is characterized by unusual angular dependence with a phase-shift feature underpinned by the Neel-vector orientation and pronounced temperature dependence caused by its susceptibility to electron scattering. Through systematical investigations on the magnetoresistance of (101)-RuO2/Co bilayers, we disentangle a sizable SSMR and hence unveil a Neel vector along [001] direction. Our work not only demonstrates a simple electric avenue to probing the Neel vector of altermagnets, but also indicates long-range magnetic order in thin films of RuO2.

cond-mat.mes-hall↗

arXiv2024

Interlayer ferroelectric polarization modulated anomalous Hall effects in four-layer MnBi2Te4 antiferromagnets

Van der Waals (vdW) assembly could efficiently modulate the symmetry of two-dimensional (2D) materials that ultimately governs their physical properties. Of particular interest is the ferroelectric polarization being introduced by proper vdW assembly that enables the realization of novel electronic, magnetic and transport properties of 2D materials. Four-layer antiferromagnetic MnBi2Te4 (F-MBT) offers an excellent platform to explore ferroelectric polarization effects on magnetic order and topological transport properties of nanomaterials. Here, by applying symmetry analyses and density-functional-theory calculations, the ferroelectric interface effects on magnetic order, anomalous Hall effect (AHE) or even quantum AHE (QAHE) on the F-MBT are analyzed. Interlayer ferroelectric polarization in F-MBT efficiently violates the PT symmetry (the combination symmetry of central inversion (P) and time reverse (T) of the F-MBT by conferring magnetoelectric couplings, and stabilizes a specific antiferromagnetic order encompassing a ferromagnetic interface in the F-MBT. We predict that engineering an interlayer polarization in the top or bottom interface of F-MBT allows converting F-MBT from a trivial insulator to a Chern insulator. The switching of ferroelectric polarization at the middle interfaces results in a direction reversal of the quantum anomalous Hall current. Additionally, the interlayer polarization of the top and bottom interfaces can be aligned in the same direction, and the switching of polarization direction also reverses the direction of anomalous Hall currents. Overall, our work highlights the occurrence of quantum-transport phenomena in 2D vdW four-layer antiferromagnets through vdW assembly. These phenomena are absent in the bulk or thin-film in bulk-like stacking forms of MnBi2Te4.

cond-mat.mtrl-sci↗

arXiv2023

Physical origin of color changes in lutetium hydride under pressure

Recently, near-ambient superconductivity was claimed in nitrogen-doped lutetium hydride (LuH$_{3-δ}$N$_ε$) . Unfortunately, all follow-up research still cannot find superconductivity signs in successfully synthesized lutetium dihydride (LuH$_2$) and N-doped LuH$_{2\pm x}$N$_y$. However, a similar intriguing observation was the pressure-induced color changes (from blue to pink and subsequent red). The physical understanding of its origin and the correlation between the color, crystal structure, and chemical composition of Lu-H-N is still lacking. In this work, we theoretically study the optical properties of LuH$_2$, LuH$_3$, and some potential N-doped compounds using the first-principles calculations by considering both interband and intraband contributions. Our results show that LuH$_2$ has an optical reflectivity peak around blue light up to 10 GPa. Under higher pressure, the reflectivity of red light gradually becomes dominant. This evolution is driven by changes in the direct band gap and the Fermi velocity of free electrons under pressure. In contrast, LuH$_3$ exhibits gray and no color change up to 50 GPa. Furthermore, we considered different types of N-doped LuH$_2$ and LuH$_3$. We find that N-doped LuH$_2$ with the substitution of a hydrogen atom at the tetrahedral position maintains the color change when the N-doping concentration is low. As the doping level increases, this trend becomes less obvious. While other N-doped structures do not show significant color change. Our results can clarify the origin of the experimental observed blue-to-red color change in lutetium hydride and also provide a further understanding of the potential N-doped lutetium dihydride.

cond-mat.supr-con↗