| 1. |
- Bandyopadhyay, Arka, et al.
(författare)
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8-16-4 graphyne : Square-lattice two-dimensional nodal line semimetal with a nontrivial topological Zak index
- 2021
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 103:7
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Tidskriftsartikel (refereegranskat)abstract
- An unprecedented graphyne allotrope with square symmetry and nodal line semimetallic behavior has been proposed in the two-dimensional (2D) realm. The emergence of the Dirac loop around the high-symmetry points in the presence of both the inversion and time-reversal symmetries is a predominant feature of the electronic band structure of this system. Besides, the structural stability in terms of the dynamic, thermal, and mechanical properties has been critically established for the system. Following the exact analytical model based on the realspace renormalization group scheme and tight-binding approach, we have inferred that the family of 2D nodal line semimetals with square symmetry can be reduced to a universal four-level system in the low-energy limit. This renormalized lattice indeed explains the underlying mechanism responsible for the fascinating emergence of 2D square nodal line semimetals. Besides, the analytical form of the generic dispersion relation of these systems is well supported by our density-functional theory results. Finally, the nontrivial topological properties have been explored for the predicted system without breaking the inversion and time-reversal symmetry of the lattice. We have obtained that the edge states are protected by the nonvanishing topological index, i.e., Zak phase.
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| 2. |
- Gallego-Parra, Samuel, et al.
(författare)
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Pressure-induced order-disorder transitions in beta-In2S3 : an experimental and theoretical study of structural and vibrational properties
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:41, s. 23625-23642
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Tidskriftsartikel (refereegranskat)abstract
- This joint experimental and theoretical study of the structural and vibrational properties of beta-In2S3 upon compression shows that this tetragonal defect spinel undergoes two reversible pressure-induced order-disorder transitions up to 20 GPa. We propose that the first high-pressure phase above 5.0 GPa has the cubic defect spinel structure of alpha-In2S3 and the second high-pressure phase (phi-In2S3) above 10.5 GPa has a defect alpha-NaFeO2-type (R3m) structure. This phase, related to the NaCl structure, has not been previously observed in spinels under compression and is related to both the tetradymite structure of topological insulators and to the defect LiTiO2 phase observed at high pressure in other thiospinels. Structural characterization of the three phases shows that alpha-In2S3 is softer than beta-In2S3 while phi-In2S3 is harder than beta-In2S3. Vibrational characterization of the three phases is also provided, and their Raman-active modes are tentatively assigned. Our work shows that the metastable alpha phase of In2S3 can be accessed not only by high temperature or varying composition, but also by high pressure. On top of that, the pressure-induced beta-alpha-phi sequence of phase transitions evidences that beta-In2S3, a BIII2XV3 compound with an intriguing structure typical of A(II)BIII(2)XVI(4) compounds (intermediate between thiospinels and ordered-vacancy compounds) undergoes: (i) a first phase transition at ambient pressure to a disordered spinel-type structure (alpha-In2S3), isostructural with those found at high pressure and high temperature in other BIII2XV3 compounds; and (ii) a second phase transition to the defect alpha-NaFeO2-type structure (phi-In2S3), a distorted NaCl-type structure that is related to the defect NaCl phase found at high pressure in A(II)BIII(2)XVI(4) ordered-vacancy compounds and to the defect LiTiO2-type phase found at high pressure in A(II)BIII(2)XVI(4) thiospinels. This result shows that In2S3 (with its intrinsic vacancies) has a similar pressure behaviour to thiospinels and ordered-vacancy compounds of the A(II)BIII(2)XVI(4) family, making beta-In2S3 the union link between such families of compounds and showing that group-13 thiospinels have more in common with ordered-vacancy compounds than with oxospinels and thiospinels with transition metals.
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| 3. |
- Majumdar, Arnab, et al.
(författare)
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Drastic reduction of thermal conductivity in hexagonal AX (A = Ga, In & Tl, X = S, Se & Te) monolayers due to alternative atomic configuration
- 2021
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 88
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Tidskriftsartikel (refereegranskat)abstract
- Several two-dimensional chalcogenide materials have been in the limelight in the recent past for their promising thermoelectric properties. It is well established that the thermoelectric performance of materials improves on reducing the physical dimensionality of the system. Two-dimensional hexagonal chalcogen (S, Se and Te) bearing compounds of Ga, In and Tl have already been studied extensively in literature. But in those phases, the group-13 non-chalcogen atoms occupy the two inner planes while the chalcogens occupy the two outer planes of the unit cell. In this work, we have proposed the alternate arrangement in which the chalcogen atoms occupy the two inner planes while the group-13 atoms occupy the two outer planes of the unit cell. Unprecedentedly, this alternate arrangement shows much lower thermal conductivity that leads to superior thermoelectric performance. In this work we have studied in details the thermoelectric properties of hexagonal AX (A = Ga, In & Tl, X = S, Se & Te) monolayers and compare the results having both the atomic arrangements. The very low lattice thermal conductivity of this new arrangement is due to the outermost valence s-orbital lone pair of the chalcogens which leads to enhanced anharmonicity. We have explained these results from the anti-crossing of the phonon branches as well. The electronic, dynamical, thermodynamical and elastic properties have also been studied. We think that these results should have significant impact on the synthesis of high-performance thermoelectric materials based on chalcogenides of gallium, indium and thallium.
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