arXiv subjects

Pugeng Hou

Publications and source records attributed to Pugeng Hou.

7 recordsLinked to original sources

arXiv2026

Quantum Structural Renormalization and Anharmonic Stabilization of Superconductivity in P4/mmm YScH8

The recent synthesis of P4/mmm-YScH$_{8}$ at 191.7 GPa with a superconducting critical temperature Tc of 113 K has attracted considerable interest in the study of ternary superhydrides. Here we systematically evaluate the effects of quantum and anharmonic motion of ions in P4/mmm-YScH$_{8}$ using the stochastic self-consistent harmonic approximation (SSCHA). We find that these effects renormalize the crystal structure and lower the dynamical stability threshold pressure from $\sim$140 GPa to $\sim$84 GPa, a reduction of about 40%. Furthermore, neglecting these effects causes a significant overestimation of the $T_{c}$, for instance by $\sim$20 K at 190 GPa. Our prediction of $T_{c}$ at 190 GPa is 113 K ($\mu^{*}$= 0.13), close to the experimental observation. Analysis of the phonon density of states and Eliashberg spectral function further reveals site-dependent contributions to superconductivity. These results establish that a consistent treatment of nuclear quantum motion and anharmonicity is essential for accurately predicting superconductivity in compressed ternary hydrides.

cond-mat.supr-con↗

arXiv2026

Structural and Vibrational Properties of D$_3$Se from First Principles: Anharmonic Quantum and Isotope Effects

Hydrogen-rich superconductors have garnered considerable interest following the discovery of hot superconductivity in high pressure H$_3$S, reviving prospects for room temperature superconductors under high-pressures. Using H$_3$Se as a reference system, we investigate the vibrational and superconducting properties of D$_3$Se in the Im\bar{3}m phase across 60-200 GPa by combining first-principles calculations with the stochastic self-consistent harmonic approximation to treat ionic quantum and anharmonic effects. These effects introduce significant renormalization to the phonon spectra and stabilize the lattice down to at least 70 GPa, well below the harmonic prediction of >110 GPa. Ultimately, the phonon renormalizations alter the electron-phonon coupling, introducing a decrease in the superconducting critical temperature by about 3-16 K across the studied pressure range with respect to standard calculations. Including anharmonic phonons within the Migdal-Eliashberg theory yields $T_c \approx 154$ K at 75 GPa (with ${\mu}^* = 0.1$, ${\lambda} = 3.0$), highlighting D3Se as a promising high-Tc superconductor at moderate pressures. Examining the role of anharmonicity in the isotope effect, we find that at 200 GPa it suppresses the isotope coefficient $\alpha$ to 0.29 one third below the harmonic value (0.44) which approaches the BCS limit of 0.5. This dramatic reduction demonstrates that anharmonicity fundamentally governs the isotope effect on this system. The stark discrepancy between anharmonic and harmonic descriptions underscores the need for targeted experimental efforts to resolve the origin of the persistent theory-experiment discrepancy in compressed hydrides.

cond-mat.supr-con↗

arXiv2024

Quantum Anharmonic Effects on the Superconductivity of I-43m CH4-H3S at High Pressures: a First-Principles Study

Making use of first-principles calculations we analyze the effect of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of I-43m CH4-H3S, one of the lowest enthalpy structures in the C-S-H system, in the 150-300 GPa pressure range within the stochastic self-consistent harmonic approximation. We predict a correction to the crystal structure, which is formed by an H3S lattice and CH4 molecules, the phonon spectra, and the pressure-dependent superconducting critical temperatures, which have been estimated in previous calculations without considering ionic fluctuations on the crystal structure and assuming the harmonic approximation for the lattice dynamics. Our results show that quantum ionic fluctuations have an impact on the distance between H atoms and S atoms in the H3S host lattice, pushing it towards more symmetric bonds, while the methane molecules are barely affected. According to our anharmonic phonon spectra, this structure is dynamically stable above 150 GPa, which is 30 GPa lower than the pressure at which the harmonic approximation predicts the emergence of an instability. As a consequence of the strong anharmonic enhancement of the phonon frequencies, the electron-phonon coupling constant is suppressed by 46% at 200 GPa, and even more at lower pressures. As a result, the superconducting critical temperature is overestimated by around 50 K at 200 GPa, such that it falls below 150 K in the whole pressure range studied. Our results underline that ternary hydrides are subject to strong anharmonic effects on their structural, vibrational, and superconducting properties.

cond-mat.mtrl-sci↗

arXiv2024

Significant Impact of Quantum and Anharmonic Effects on the Structural Stability and Superconductivity of NbH3 at High Pressures

First-principles calculations combined with the stochastic self-consistent harmonic approximation reveal significant effects of the quantum ionic fluctuations and lattice anharmonicity on the dynamical stability of NbH3 under high pressures. Previous theoretical predictions, which ignored ionic fluctuations and relied on the harmonic approximation, suggested that the I43d phase is the most thermodynamically favorable structure between 33 and 400 GPa, with the Fm3m phase considered thermodynamically metastable. However, recent experiments at 187 GPa identified the Fm3m phase, conflicting with the prediction. In contrast, the present study indicates that the Fm3m phase remains dynamically stable down to at least 145 GPa, approximately 145 GPa lower than harmonic estimates, while the I43d phase is dynamically unstable at 187 GPa, consistent with the experimental findings. Furthermore, systematic calculations are performed on the structural, vibrational and superconducting properties of Fm3m NbH3 under pressures ranging from 100 to 300 GPa, revealing dramatic modifications due to the quantum and anharmonic effects. The calculated superconducting critical temperature (Tc) from the McMillan equation for Fm3m NbH3 at 187 GPa is 44 K, with mu set at 0.15, close to the measured value. These findings highlight the crucial role of quantum anharmonic effects in stabilizing the Fm3m phase.

cond-mat.mtrl-sci↗

arXiv2024

H3Se in the Im-3m Phase: A High-Pressure Superconductor with Tc Reaching 200 K at 64 GPa Mediated by Anharmonic Phonons

Hydrogen-based compounds have attracted significant attention in recent years due to the discovery of conventional superconductivity with high critical temperature under high pressure, rekindling hopes for searching room temperature superconductor. In this work, we investigated systematically the vibrational and superconducting properties of H3Se in Im-3m phase under pressures ranging from 50 to 200 GPa. Our approach combines the stochastic self-consistent harmonic approximation with first-principles calculations to address effects from the quantum and anharmonic vibrations of ions. It turns out that these effects significantly modify the crystal structure, increasing the inner pressure by about 8 GPa compared to situations where they are ignored. The phonon spectra suggest that with these effects included, the crystal can be stabilized at pressures as low as about 61 GPa, much lower than the previously predicted value of over 100 GPa. Our calculations also highlight the critical role of quantum and anharmonic effects on the electron-phonon coupling properties. Neglecting these factors could result in a substantial overestimation of the superconducting critical temperature Tc, by approximately 25 K at 125 GPa, for example. With anharmonic phonons, the Tc derived from the Migdal-Eliashberg equations, reaches 200 K ($\mu^\star$= 0.1, $\lambda$=4.1) as the pressure decreases to 64 GPa, making the crystal a rare high-Tc superconductor at moderate pressures.

cond-mat.supr-con↗

arXiv2021

Quantum anharmonic enhancement of superconductivity in $P6_3/mmc$ ScH$_6$ at high pressures: a first-principles study

Making use of first-principles calculations, we analyze the effect of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of P63/mmc ScH6 in the 100-160 GPa pressure range within the stochastic self-consistent harmonic approximation. We predict a strong correction to the crystal structure, the phonon spectra, and the superconducting critical temperatures, which have been estimated in previous calculations without considering ionic fluctuations on the crystal structure and assuming the harmonic approximation for the lattice dynamics. Quantum ionic fluctuations have a large impact on the H2 molecular-like units present in the crystal by increasing the hydrogen-hydrogen distance about a 5%. According to our anharmonic phonon spectra, this structure will be dynamically stable at least above 85 GPa, which is 45 GPa lower than the pressure given by the harmonic approximation. Contrary to many superconducting hydrogen-rich compounds, where quantum ionic effects and the consequent anharmonicity tend to lower the superconducting critical temperature, our results show that it can be enhanced in P63/mmc ScH6 by approximately a 15%. We attribute the enhancement of the critical temperature to the stretching of the H$_2$ molecular-like units and the associated increase of the electron-phonon interaction. Our results suggest that quantum ionic effects increase the superconducting critical temperature in hydrogen-rich materials with H2 units by increasing the hydrogen-hydrogen distance and, consequently, the electron-phonon interaction.

cond-mat.supr-con↗

arXiv2021

Strong Anharmonic and Quantum Effects in Pm-3n AlH3 Under High Pressure: A First-Principles Study

Motivated by the absence of experimental superconductivity in the metallic Pm-3n phase of AlH3 despite the predictions, we reanalyze its vibrational and superconducting properties at pressures above 99 GPa making use of first-principles techniques. In our calculations based on the self-consistent harmonic approximation method that treats anharmonicity beyond perturbation theory, we predict a strong anharmonic correction to the phonon spectra and demonstrate that the superconducting critical temperatures predicted in previous calculations based on the harmonic approximation are strongly suppressed by anharmonicity. The electron-phonon coupling concentrates on the lowest-energy hydrogen-character optical modes at the X point of the Brillouin zone. As a consequence of the strong anharmonic enhancement of their frequency, the electron-phonon coupling is suppressed by at least a 30%. The suppression in λ makes Tc smaller than 4.2 K above 120 GPa, which is well consistent with the experimental evidence. Our results underline that metal hydrides with hydrogen atoms in interstitial sites are subject to huge anharmonic effects.

cond-mat.supr-con↗