arXiv subjects

Defang Duan

Publications and source records attributed to Defang Duan.

At least 19 recordsLinked to original sources

arXiv2026

Metal hydrides achieve high-Tc superconductivity at low pressure by mimicking high-pressure H3S chemical bonding

Compressed hydrides are promising candidates for high-temperature superconductivity, yet achieving simultaneous structural stability and high-Tc at low pressures remains challenging. Here, we introduce a new mechanism for accomplishing this goal by mimicking the bonding characteristics of high-pressure H3S within metal hydrides. Using Li3CuH4 as an example, its Cu-H covalent interaction effectively mimics the core function of the S-H bonding in H3S. This interaction not only induces a high hydrogen-derived electronic density of states at the Fermi level, but also softens the hydrogen phonon modes, thereby significantly enhancing the electron-phonon coupling. Furthermore, embedding the strongly ionic Li3H lattice into the covalent Cu-H framework stabilizes the structure at significantly low pressures via a chemical-template effect, while maintaining high-Tc. Li3CuH4 exhibits excellent thermodynamic stability at 20 GPa, with a Tc of 39.25 K at 12 GPa. Further comprehensive high-throughput studies on Li3MH4 (M = transition metal) compounds uncover general principles applicable to a broader range of compounds. This work establishes a new paradigm for the simultaneous optimization of the stability and high-temperature superconductivity of metal hydrides through complementary sublattice interactions, thus advancing the search for practical and viable superconducting materials.

cond-mat.supr-con↗

arXiv2025

Theoretical study on the electronic properties and multiorbital models of La$_3$Ni$_2$O$_7$ thin films on SrLaAlO$_4$ (001)

The realization of ambient-pressure superconductivity in La$_3$Ni$_2$O$_7$ thin films raises a fundamental question: is the metallic ground state driven by lattice strain or interfacial charge reconstruction? Using fully self-consistent DFT+$U$ calculations on La$_3$Ni$_2$O$_7$/SrLaAlO$_4$ heterostructures, we identify that intrinsic hole doping via interfacial Sr interdiffusion is the decisive factor in stabilizing the metallic state. Our 1-unit-cell model accurately reproduces the ARPES-observed Fermi surface, particularly the critical Ni-$d_{z^2}$ derived $\gamma$ hole pocket, which originates exclusively from the interface-proximal bilayer. Furthermore, comparative tight-binding analysis suggests that the reduced superconducting transition temperature ($T_c$) in thin films stems from the synergistic suppression of the electronic density of states (DOS) and vertical superexchange coupling ($J \perp Z$). These findings highlight that interface engineering plays a critical role beyond simple strain imposition in modulating nickelate orbital physics.

cond-mat.supr-con↗

arXiv2025

Transforming Acidic Corrosion and Embrittlement into a Hydrogen-Trapping Cage

The vision of a hydrogen economy demands efficient platforms to close the gap between sustainable proton sources and solid-state hydrogen carriers. Metal hydrides serve as key carriers, yet their synthesis remains constrained by the energy-intensive use of high-pressure H2, which fragments the hydrogen chain. Here, we overturn this paradigm by transforming two classic degradation mechanisms, acidic corrosion and hydrogen embrittlement, into a constructive materials-design strategy. We demonstrate that synergistic control of these processes in acid enables the in-situ engineering of a "hydrogen-trapping cage" (HTC) microstructure within metals. Composed of a dense defect network, this cage directly captures and stabilizes protons as hydrides under mild conditions, guided by the universal criterion |DeltaPeq| > DeltaPph. Using this platform, we synthesize over 20 hydrides, including challenging targets such as LiH and NaH, and showcase its functional power with a cage-rich titanium hydride electrocatalyst. This catalyst achieves an exceptional current density of 1.07 A cm-2 for nitrate-to-ammonia conversion, attributed to rapid H- transport within the engineered cage. This work establishes a transformative "failure-to-function" paradigm, delivering an integrated platform that unifies hydrogen capture, stabilization, and conversion.

cond-mat.mtrl-sci↗

arXiv2025

Mechanisms driving robust high-temperature superconductivity in complex metal hydrides under moderate pressure

The discovery of near-room-temperature superconductivity in compressed hydrides has sparked intensive research efforts to identify superconducting hydrides stable at low or even ambient pressures. Herein, we demonstrate a new mechanism for achieving robust superconductivity in complex metal hydrides under moderate pressure, using Li3IrH9 as a paradigmatic example. This compound displays unique electronic structural characteristics where the broadening and overlap between antibonding electronic bands of [IrH8]2- and adjacent H- orbitals not only drive the intrinsic metallicity of the hydrogen sublattice, generating hydrogen-dominated electronic states at the Fermi level, but also soften hydrogen-related optical phonon modes, inducing strong electron-phonon coupling that remains robust even under high-pressures. First-principles calculations predict that Li3IrH9 maintains thermodynamic stability at 100 GPa while exhibiting a consistently high Tc exceeding 100 K across a broad pressure range (8-150 GPa). Through high-throughput computational screening, we have identified a new superconducting family based on this structural prototype, including Li3RhH9 (Tc = 124 K at 20 GPa) and Li3CoH9 (Tc = 80 K at 10 GPa). This work provides a new platform and original theoretical insights for the development of complex metal hydride superconductors that exhibit robust high-temperature superconductivity and promising practical applications.

cond-mat.supr-con↗

arXiv2025

First-principles study on Pr-doped Bilayer Nickelate La3Ni2O7

Recently, the Pr-doped Ruddlesden-Popper phase of bilayer nickelate La3Ni2O7 has been reported to exhibit a superconducting transition temperature (Tc) of 82.5 K and superconducting volume fraction of about 57 % at high pressure. However, the effect of Pr-doping on La3Ni2O7 remains unclear. Here, we studied the crystal structures and electronic properties of Pr-doped La3Ni2O7 at 0 and 15 GPa based on the first-principles calculations to explore the doping effect of Pr. Our findings indicate that the praseodymium atoms prefer to occupy the outer La-O layers site. We then investigated the evolution of crystal structures in both the ambient pressure phase and high pressure phase of La3Ni2O7 as a function of doping concentration, revealing inconsistent trends in their evolution with increasing doping levels. Finally, by fitting the bilayer two-orbital model, we propose that doping Pr may benefit for superconductivity of La3Ni2O7. These results not only can help the further experimental search of RP phase nickelate at lower pressure, but also provide helpful guide for understanding the effect of chemical pressure in isovalent doped RP phase nickelate superconductor.

cond-mat.supr-con↗

arXiv2025

FF7: A Code Package for High-throughput Calculations and Constructing Materials Database

Decades accumulation of theory simulations lead to boom in material database, which combined with machine learning methods has been a valuable driver for the data-intensive material discovery, i.e., the fourth research paradigm. However, construction of segmented databases and data reuse in generic databases with uniform parameters still lack easy-to-use code tools. We herein develop a code package named FF7 (Fast Funnel with 7 modules) to provide command-line based interactive interface for performing customized high-throughput calculations and building your own handy databases. Data correlation studies and material property prediction can progress by built-in installation-free artificial neural network module and various post processing functions are also supported by auxiliary module. This paper shows the usage of FF7 code package and demonstrates its usefulness by example of database driven thermodynamic stability high-throughput calculation and machine learning model for predicting the superconducting critical temperature of clathrate hydrides.

cond-mat.mtrl-sci↗

arXiv2025

The effect of Carrier Doping and Thickness on the Electronic Structures of La$3$Ni$2$O$7$ Thin Films

Recently, the superconductivity of bilayer nickelate La3Ni2O7 has been observed in the thin film at ambient pressure, facilitated by epitaxial strain. Here, we investigate the effects of film thickness and carrier doping on the electronic structure of La3Ni2O7 thin films with thickness of 0.5-3 unit cells (UC) using first-principles calculations. At an optimal doping concentration of 0.4 holes per formula unit for 2UC film, the Ni-"d" _("z" ^"2" ) interlayer bonding state metallizes, leading to the formation of {\gamma} pockets at the Fermi surface, which quantitatively matches the experimental results of angle-resolved photoemission spectroscopy (ARPES). These findings provide theoretical support for recent experimental observations of ambient-pressure superconductivity in La3Ni2O7 thin films and highlight the crucial role of film thickness and carrier doping in modulating electronic properties.

cond-mat.supr-con↗

arXiv2024

High-throughput discovery of robust room-temperature superconductors among complex ternary clathrate hydrides

After the decade-long exhaustive study of binary high-Tc superconducting hydrides, the frontier of this stimulating research field has recently shifted to ternary hydrides with much expanded conformational space in search of coveted room-temperature superconductors. This task, however, presents a formidable challenge due to enormous demands on computational resources. Here, we devise an efficient high-throughput approach using keen material insights and a self-built database to screen for robust ternary hydrides in clathrate structures, which were proven to host highest Tc in binary hydrides, and to estimate Tc by a reliable empirical formula. This approach has made it possible to uncover a diverse set of complex multiple-hydrogen-cage ternary hydrides hosting near or above room-temperature Tc, which are beyond the reach of prevailing structure search methods. This study establishes a distinct paradigm that opens a fresh avenue to enable and accelerate the discovery of promising room-temperature superconductors among unprecedented complex clathrate hydrides.

cond-mat.supr-con↗

arXiv2024

The Critical Metallization of Hydrogen in Pressurized LaBeH8 Hydride

Behaviours of hydrogen, such as fluidity and metallicity, are crucial for our understanding of planetary interiors and the emerging field of high-temperature superconducting hydrides. These behaviours were discovered in complex phase diagrams of hydrogen and hydrides, however, the transition mechanism of behaviours driven by temperature, pressure and chemical compression remain unclear, particularly in the processes of metallization. Until now, a comprehensive theoretical framework to quantify atomization and metallization of hydrogen in phase diagram of hydrides has been lacking. In this study, we address this gap by combining molecular dynamics and electronic structure analysis to propose a theoretical framework, which clarify the content and properties of atomic hydrogen under various temperature and pressure conditions and chemical compression exerted by non-hydrogen elements in hydrides. Applying this framework to the superconducting hydride LaBeH8, we identify three general hydrogen orderings within its phase diagram: molecular, sublattice and warm hydrogens. During the phase transition from molecule to sublattice, hydrogen exhibits different properties from three general hydrogen orderings, such as fast superionicity, metallicity and unusual atomic content response to temperature. These abnormal behaviours were defined as the critical metallization of hydrogen, which not only suggests a potential synthesis route for the metastable phase but also provides valuable insights into the complex synthetic products of superconducting hydrides.

cond-mat.mtrl-sci↗

arXiv2024

High-temperature Superconductivity in Perovskite Hydride below 10 GPa

Hydrogen and hydrides materials have long been considered promising materials for high-temperature superconductivity. But the extreme pressures required for the metallization of hydrogen-based superconductors limit their applications. Here, we have designed a series of high-temperature perovskite hydrides that can be stable within 10 GPa. Our research covered 182 ternary systems and ultimately determined that 9 compounds were stable within 20 GPa, of which 5 exhibited superconducting transition temperatures exceeding 120 K within 10 GPa. Excitingly, KGaH3 and CsInH3 are thermodynamically stable at 50 GPa. Among these perovskite hydrides, alkali metals are responsible for providing a fixed amount of charge and maintaining structural stability, while the cubic framework formed by IIIA group elements and hydrogen is crucial for high-temperature superconductivity. This work will inspire further experimental exploration and take an important step in the exploration of low-pressure stable high-temperature superconductors.

cond-mat.supr-con↗

arXiv2024

Electronic Correlations and Hund's Rule Coupling in Trilayer Nickelate La4Ni3O10

Trilayer Ruddlesden-Popper phase La4Ni3O10 has been observed with Tc of about 30 K at high pressure in recent experiment, which further expanded the family of nickelate superconductors. In this study, we explored the effects of electronic correlations in La4Ni3O10 using density function theory plus dynamical mean-field theory at ambient and high pressures. Our derived spectral functions and Fermi surface of ambient pressure phase are nicely consistent with the experimental results by angle-resolved photoemission spectroscopy, which emphasized the importance of electronic correlations in La4Ni3O10. We also found the electronic correlations in pressured La4Ni3O10 are both orbital-dependent and layer-dependent due to the presence of Hund's rule coupling. There is a competition between the Hund's rule coupling and the crystal-field splitting, and therefore the Ni-O layers with weaker crystal-field splitting energy would have stronger electronic correlations.

cond-mat.str-el↗

arXiv2024

Structures and Superconductivity of Hydrogen and Hydrides under Extreme Pressure

Metallic hydrogen, existing in remarkably extreme environments, was predicted to exhibit long-sought room-temperature superconductivity. Although the superconductivity of metallic hydrogen has not been confirmed experimentally, superconductivity of hydrogen in hydrides was recently discovered with remarkably high critical temperature as theoretically predicted. In recent years, theoretical simulations have become a new paradigm for material science, especially exploration of material at extreme pressure. As the typical high-pressure material, metallic hydrogen has been providing a fertile playground for advanced simulations for long time. Simulations not only provide the substitute of experiments for hydrogen at high-pressure, but also encouraged the discovery of almost all the experimentally discovered superconducting hydrides with the record high superconducting transition temperature. This work reviews recent progress in hydrogen and hydrides under extreme pressure, focusing on phase diagram, structures and the long-sought goal of high-temperature superconductivity. In the end, we highlight structural features of hydrides for realization of hydrogen-driven superconducting hydrides near ambient pressure.

cond-mat.supr-con↗

arXiv2024

Modulation of the Octahedral Structure and Potential Superconductivity of La$_3$Ni$_2$O$_7$ through Strain Engineering

The recent transport measurement of La$_3$Ni$_2$O$_7$ uncover a "right-triangle" shape of the superconducting dome in the pressure-temperature (P-T) phase diagram. Motivated by this, we perform theoretical first-principles studies of La$_3$Ni$_2$O$_7$ with the pressure ranging from 0 to 100 GPa. Notably, we reveal a pressure dependence of the Ni-$d_{z^2}$ electron density at the Fermi energy ($n_z^{EF}$) that highly coincides with such shape. On this basis, we further explore the electronic structure under uniaxial stress. By tracking the stress response of $n_z^{EF}$, we propose that superconductivity can be achieved by applying only about 2 GPa of compression along the c axis. The idea is further exemplified from the perspectives of lattice distortion, band structure, Fermi surface and superconducting phase coherence. We also discuss the possible charge modulation under the stress and provide an insight to the relation between n_z^EF and the superconducting Tc in La$_3$Ni$_2$O$_7$ system. Our study provides a helpful guide to the future experiment.

cond-mat.supr-con↗

arXiv2023

High temperature superconductivity of quaternary hydrides XM3Be4H32 (X, M = Ca, Sr, Ba, Y, La, Ac, Th) under moderate pressure

The compressed hydrogen-rich compounds have received extensive attention as promising candidates for room temperature superconductivity, however, the high pressure required to stabilize such materials hinders their wide practical application. In order to search for potential superconducting hydrides that are stable at low pressures, we have investigated the crystal structures and properties of quaternary hydrides, XM3Be4H32 (X, M = Ca, Sr, Ba, Y, La, Ac, Th) based on the first-principles calculations. We identified nine dynamically stable compounds at moderate pressure of 20 GPa. Strikingly, their superconducting transition temperatures are much higher than that of liquid nitrogen, especially CaTh3Be4H32 (124 K at 5 GPa), ThLa3Be4H32(134 K at 10 GPa), LaAc3Be4H32 (135 K at 20 GPa) and AcLa3Be4H32 (153 K at 20 GPa) exhibit outstanding superconductivity at mild pressures. Metal atoms acting as pre-compressors donate abundant electrons to hydrogen, weakening the H-H covalent bond and thus facilitating the metallization of the hydrogen sublattice. At the same time, the appropriate combination of metal elements with different ionic radius and electronegativity can effectively tune the electronic structure near the Fermi level and improve the superconductivity. These findings fully reveal the great promise of hosting high-temperature superconductivity of quaternary hydrides at moderate pressures and will further promote related exploration.

cond-mat.supr-con↗

arXiv2023

Phase diagrams and superconductivity of ternary Ca-Al-H compounds under high pressure

The search for high-temperature superconductors in hydrides under high pressure has always been a research hotspot. Hydrogen-based superconductors offer an avenue to achieve the long-sought goal of superconductivity at room temperature. We systematically explore the high-pressure phase diagram, electronic properties, lattice dynamics and superconductivity of the ternary Ca-Al-H system using ab initio methods. We found two stable ternary hydrides at 50 GPa: Cmcm-CaAlH5 and Pnnm-CaAl2H8, which both are semiconductors. At 200 GPa, a new phase of P21/m-CaAlH5, P4/mmm-CaAlH7 and a metastable compound Immm-Ca2AlH12 were found. Furthermore, P4/mmm-CaAlH7 has obvious phonon softening of high frequency vibrations along the Z-A direction, point A and point X, which improves the strength of electron-phonon coupling. Therefore, a superconducting transition temperature Tc of 71 K is generated at 50 GPa. In addition, the thermodynamic metastable Immm-Ca2AlH12 exhibits a superconducting transition temperature of 118 K at 250 GPa. These results are very useful for the experimental searching of new high-Tc superconductors in ternary hydrides.

cond-mat.supr-con↗

arXiv2023

First-principles study on the superconductivity of N-doped fcc-LuH3

Recently, room-temperature superconductor has been claimed in a nitrogen-doped lutetium hydride at near-ambient pressure [Nature 615, 244 (2023)]. Using X-ray diffraction (XRD) and Raman spectra analysis, the authors believed that the superconducting properties can most probably be attributed to Fm-3m-LuH3{\delta}N{\epsilon}. Here, we systematic study the phase diagram of Lu-N-H at 1 GPa by using first-principle theory and find that there have no thermodynamically stable ternary compounds. Besides, we analyzed the dynamically stability and superconducting properties of N-doped Fm-3m-LuH3 using virtual crystal approximation (VCA) and supercell method. Our theoretical results show that the Tc of N-doped LuH3 cannot reach the level of room-temperature.

cond-mat.supr-con↗

arXiv2023

Thermodynamically stable room-temperature superconductors in Li-Na hydrides under high pressures

Room-temperature superconductivity has been a long-standing goal for scientific progress and human development. Thermodynamic stability is a prerequisite for material synthesis and application. Here, we perform a combination of high-throughput screening and structural search and uncover two thermodynamically stable room-temperature superconductors, Fd-3m-Li2NaH17 and Pm-3n-LiNa3H23, exhibiting extraordinary critical temperature of 340 K at 300 GPa and 310 K at 350 GPa, respectively. Li2NaH17 possesses the highest Tc among all the thermodynamically stable ternary hydrides hitherto found. The dominated H density of states at the Fermi level and the strong Fermi surface nesting are favorable for the emergence of room-temperature superconductivity. Their excellent superconducting properties help us understand the mechanism of room-temperature superconductivity and find new room-temperature superconductors. Interestingly, the structures of LiNa3H23 and Li2NaH17 equal to the identified type-I and II clathrate geometry. Our results provide a structural reference and theoretical guidance for later experimental structure determination and theoretical search for high temperature superconductors.

cond-mat.supr-con↗

arXiv2023

Prediction of Room-Temperature Superconductivity in Quasi-atomic H2-Type Hydrides at High Pressure

Achieving superconductivity at room temperature (RT) is a holy grail in physics. Recent discoveries on high-Tc superconductivity in binary hydrides H3S and LaH10 at high pressure have directed the search for RT superconductors to compress hydrides with conventional electron-phonon mechanisms. Here, we predict an exceptional family of superhydrides under high pressures, MH12 (M = Mg, Sc, Zr, Hf, Lu), all exhibiting RT superconductivity with calculated Tcs ranging from 313 to 398 K. In contrast to H3S and LaH10, the hydrogen sublattice in MH12 is arranged as quasi-atomic H2 units. This unique configuration is closely associated with high Tc, attributed to the high electronic density of states derived from H2 antibonding states at the Fermi level and the strong electron-phonon coupling related to the bending vibration of H2 and H-M-H. Notably, MgH12 and ScH12 remain dynamically stable even at pressure below 100 GPa. Our findings offer crucial insights into achieving RT superconductivity and pave the way for innovative directions in experimental research.

cond-mat.supr-con↗