arXiv subjects

Jakkapat Seeyangnok

Publications and source records attributed to Jakkapat Seeyangnok.

27 records · Page 2Linked to original sources

arXiv2025

Phase Stability and Superconductivity in Hydrogenated and Lithiated Janus GaXS2 (X = Ga, In) Monolayers

Hydrogen and lithium functionalization of two-dimensional (2D) materials offers a promising route to enhance electronic properties and induce superconductivity. Here, we employ first-principles calculations to explore the phase stability and superconducting behavior of hydrogenated and lithiated Janus GaXS2 (X = Ga, In) monolayers. Among Ga2SH, Ga2SLi, GaInSH, and GaInSLi, only the 2H-GaInSLi structure is dynamically, thermally, and mechanically stable, as confirmed by phonon dispersion, ab initio molecular dynamics, and elastic constants. This monolayer adopts a hexagonal lattice, exhibits metallic behavior, and has a negative formation energy, suggesting experimental feasibility. Anisotropic Migdal-Eliashberg analysis reveals phonon-mediated superconductivity with a critical temperature Tc of 4.8 K. Notably, three distinct superconducting gaps emerge, linked to specific atomic orbitals and phonon modes. Electron doping of 0.2 e per cell increases Tc to nearly 6.2 K while maintaining the three-gap character. These results highlight the effectiveness of selective functionalization in engineering superconductivity and identify GaInSLi as a promising platform for next-generation multi-gap 2D superconducting devices.

cond-mat.mtrl-sci↗

arXiv2025

Theoretical prediction of Structural Stability and Superconductivity in Janus Ti2CSH MXene

We present a comprehensive first-principles investigation of the structural stability, vibrational characteristics, and superconducting properties of the Janus Ti2CSH monolayer. Janus MXene (JMXene) materials, such as Ti2CSH, have attracted significant attention due to their intrinsic two-dimensional structure and the absence of out-of-plane symmetry, which give rise to novel physical phenomena. Phonon calculations confirm the dynamical stability of the monolayer, while electronic structure and electron-phonon coupling analyses reveal a strong phonon-mediated pairing mechanism. Anisotropic Migdal-Eliashberg theory predicts a single-gap superconducting state, with gap values between 4.29 and 4.71 meV at 10 K and a critical temperature Tc of 22.6 K. These findings establish Ti2CSH as a promising two-dimensional superconductor with potential applications in quantum and nanoscale technologies.

cond-mat.supr-con↗

arXiv2024

Superconductivity of two-dimensional hydrogenated transition-metal diborides

Since the discovery of MgB2 with Tc=39K, various metal diborides of MB2 have been intensively studied to find possible conventional high-temperature superconductors. A possible 2D structure of the metal diboride has been shown to be in the form of M2B2. Using density functional theory, we investigated phase stability and possible conventional superconductors for non-hydrogenation M2B2, light hydrogenation M2B2H, and heavy hydrogenation M2B2H4 of transition metal borides M2B2 (M=Sc,Y,V,Nb). The light hydrogenation M2B2H show as if they were a perturbed system from the non-hydrogenation in which the electronic structure, the phonon property, and the possible superconducting state are slightly changed. However, the heavy hydrogenation of M2B2H4 give very promising 2D materials with a possible high Tc of up to 84K at ambient pressure. This would fill the gaps for the study of possible conventional high-temperature superconductors at ambient pressure.

cond-mat.supr-con↗

arXiv2024

Half-metallic to ferromagnetic phase transition in CrSH monolayer using DFT+U and BO-MD calculations

We present a comprehensive investigation of the structural, electronic, magnetic, and vibrational properties of CrSH monolayers in the 1T and 2H phases using density functional theory (DFT)+U calculations with a converged Hubbard U value of 5.54 eV and Born-Oppenheimer molecular dynamics (BO-MD) simulations. The ferromagnetic (FM) 1T-CrSH phase is found to be dynamically and thermodynamically stable, exhibiting semiconducting behavior with a band gap of 1.1 eV and a magnetic moment of 3.0 $μ$B per Cr atom. On the other hand, the 2H-CrSH phase is a half-metallic (HM) phase. We found that it is a metastable phase and undergoes a rapid phase transition to the 1T phase under finite temperature at 300 K. Phonon calculations, performed using the finite displacement method and corrected for rotational invariance corrections with Huang and Born-Huang sum rules, resolve spurious imaginary frequencies in the flexural ZA phonon mode near the $Γ$-point, ensuring physical accuracy. These findings establish CrSH monolayers as promising candidates for spintronic and valleytronic applications, with tunable electronic properties enabled by phase engineering.

cond-mat.mtrl-sci↗

arXiv2024

Superconductivity in Janus IV-B transition metal chalcogenide hydrides

Two-dimensional Janus transition-metal chalcogenide -hydrides (2D-JTMCs) feature a three layered structure, with a central layer of transition metal atoms, with chalcogenides below and hydogens above. This asymmetry endows 2D-JTMCs with unique and tunable electronic, optical, and mechanical properties. In this paper, we systematically investigate two-dimensional hexagonal 2H and 1T Janus transition metal chalcogenide (JTMC) hydrides (MXH), with M = Ti, Zr, Hf, and X = S, Se, Te. These JTMCs exhibit metallic behavior with single band crossings at the Fermi level, primarily dominated by transition metal d orbitals and phonon stability, evidenced by DFPT calculations. We estimate Tc using the Allen-Dynes formula and the closing superconducting gap by solving anisotropic gap equations of the Migdal-Eliashberg equations. Calculated Tc values for these materials range from 10 K to 35 K.

cond-mat.supr-con↗

arXiv2024

Organic compounds in metallic hydrogen

Metallic hydrogen is the most common condensed material in the universe, comprising the centre of gas giant planets. However, experimental studies are extremely challenging, and most of our understanding of this material has been led by theory. Chemistry in this environment has not been probed experimentally, so here we examine hydrocarbon chemistry in metallic hydrogen using density functional theory calculations. We find that carbon and oxygen react with metallic hydrogen to produce an entirely new type of hydrocarbon chemistry based on sixfold coordinated carbon with organic-style molecules CH6, C2H8, C3H10 OH3 NH4 and CH4OH. These are charged molecules stabilised by the metallic environment. Their associated electric fields are screened, giving oscillation in the surrounding electron and proton densities. In view of the excess hydrogen we refer to them as hypermethane, hyperethane etc. The relationship to traditional chemistry is that the metallic background acts as an electron donor and stabilizes negatively charged ions. This enables the formation of six covalent bonds per carbon atom, or three per oxygen atom. This demonstrates that organic chemistry may take place in very different environments from those found on earth, and may be common throughout the universe.

cond-mat.mtrl-sci↗

arXiv2024

Solid Solubility in Metallic Hydrogen

Hydrogen in its metallic form is the most common material in our solar system, found under the extreme pressure and temperature conditions found in giant planets. Such conditions are inaccessible to experiment and consequently, theoretical work has typically led experiment. Many remarkable properties are proposed for metallic hydrogen, which is expected to exist in solid form down to low temperatures. Relevant here is that solid metallic hydrogen is not expected to have a close-packed structure, even at extreme pressures. The predicted crystal structure has a packing fraction of only 0.44 compared with 0.74 for fcc. Alloying with other metallic elements can form compounds with atomic hydrogen and much reduced metallization pressure. Here, we investigate the possible solid solubility of a representative range of elements (Be, B, Mg, S, Fe, La) in metallic atomic hydrogen near 500GPa. Zero point energy is highly significant in all cases. The metallic elements Be, Mg, Fe, and La have a well-defined clathrate-style first neighbour shell at 300K, while the non-metallic B and S have more open arrangements. All the elements considered are soluble, in sites substituting for more than one hydrogen atom. The solid solubility of such a wide range of ambient bonding types: simple metals, covalent materials, transition metals, lanthanides, which gives a strong indication that most elements will dissolve in solid metallic hydrogen.

cond-mat.mtrl-sci↗

arXiv2024

Superconductivity and strain-enhanced phase stability of Janus tungsten chalcogenide hydride monolayers

Janus transition metal-dichalcogenide (JTMD) materials have attracted a great deal of attention due to their remarkable physical properties arising from the two-dimensional geometry and the breakdown of the out-of-plane symmetry. Using first-principles density functional theory, we investigated the phase stability, strain-enhanced phase stability, and superconductivity of Janus WSeH and WSH. In addition, we investigated the contribution of the phonon linewidths from the phonon energy spectrum responsible for the superconductivity, and the electron-phonon coupling as a function of phonon wave vectors and modes. Previous work has examined hexagonal 2H and tetragonal 1T structures, but we found that neither is a ground state structure. The metastable 2H phase of WSeH is dynamically stable with Tc around 11.60K, similar to WSH. Compressive biaxial strain - the 2D equivalent of pressure - can stabilize the 1T structures of WSeH and WSH with Tc around 9.23K and 10.52K, respectively.

cond-mat.supr-con↗

arXiv2021

Supersymmetric solutions from N=6 gauged supergravity

We study supersymmetric solutions in four-dimensional $N=6$ gauged supergravity with $SO(6)$ gauge group. There is a unique $N=6$ supersymmetric $AdS_4$ vacuum with $SO(6)$ symmetry dual to an $N=6$ SCFT in three dimensions. We find a number of domain walls interpolating between this $AdS_4$ vacuum and singular geometries in the IR with $SO(2)\times SO(4)$, $U(3)$, $SO(3)$ and $SO(2)\times SO(2)\times SO(2)$ symmetries. The $SO(3)$ case admits $N=6$ or $N=2$ solutions depending on whether the pseudoscalars are present or not. On the other hand, all the remaining solutions preserve $N=6$ supersymmetry. These solutions describe RG flows from the $N=6$ SCFT to non-conformal field theories driven by mass deformations. In particular, the $SO(2)\times SO(4)$ solution is in agreement with the previously known mass deformations of the dual $N=6$ SCFT. We also give a supersymmetric Janus solution with $SO(2)\times SO(4)$ symmetry, describing two-dimensional conformal defects in the $N=6$ SCFT with unbroken $N=(4,2)$ supersymmetry. Finally, we find an $N=2$ supersymmetric $AdS_2\times H^2$ solution with $SO(2)\times SO(4)$ symmetry and the corresponding domain wall interpolating between this fixed point and the $AdS_4$ vacuum. The solution describes an $AdS_4$ black hole with a magnetic charge and is dual to a twisted compactification of the $N=6$ SCFT on a hyperbolic space $H^2$. We also give a domain wall interpolating between a locally supersymmetric $AdS_4$ and a curved domain wall with $SO(2)\times SO(2)\times SO(2)$ symmetry dual to an RG flow across dimensions from the $N=6$ SCFT to a supersymmetric quantum mechanics.

hep-th↗