High pressure induced structural, elastic and electronic properties of Calcium Chalcogenides CaX (X=S, Se and Te) via first-principles calculations

A nuclear clock has been proposed based on the isomeric transition between the ground state and the first excited state of thorium-229. This transition was recognized as a potentially sensitive probe of possible temporal variation of the fine-structure constant, α. The sensitivity to such a variation can be determined from measurements of the mean-square charge radius and quadrupole moment of the different isomers. However, current measurements of the quadrupole moment are yet to achieve accuracy high enough to resolve non-zero sensitivity. Here we determine this sensitivity using existing measurements of the change in mean-square charge radius, coupled with the ansatz of constant nuclear density. The enhancement factor for α-variation is K = −(0.9 ± 0.3) × 10 4 . For the current experimental limit δα/α 10 −17 per year, the corresponding frequency shift is ∼ 200 Hz. This shift is six orders of magnitude larger than the projected accuracy of the nuclear clock, paving the way for increased accuracy for determination of δα and interaction strength with low mass scalar dark matter. We verify that the constant-nuclear-density ansatz is supported by nuclear theory and propose how to verify it experimentally. We also consider a possible effect of the octupole deformation on the sensitivity to α-variation.

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“…This gives a quantitative evaluation of the constant-volume ansatz, which at times is used in the literature, see e.g. [42][43][44].…”

Section: Arxiv:200700408v1 [Physicsatom-ph] 1 Jul 2020mentioning

confidence: 99%

Sensitivity of Th229 nuclear clock transition to variation of the fine-structure constant

2020

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“…[49][50][51][52][53] CaTe undergoes a phase transition from NaCl-type structure at ambient conditions to CsCl-type structure at hydrostatic pressure about 33 GPa. 49,50 The structure of CaTe in CsCl-type is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…As one member of the alkaline-earth chalcogenides, CaTe have attracted tremendous interests because of its technological applications ranging from catalysis to luminescence [38][39][40][41][42]. CaTe undergoes a phase transition from NaCl-type structure at ambient conditions to CsCl-type structure at hydrostatic pressure about 33 GPa [38,39].…”

Section: Crystal Structure and Methodsmentioning

confidence: 99%

CaTe: a new topological node-line and Dirac semimetal

Du¹,

Tang²,

Wang³

et al. 2017

npj Quant Mater

114

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Combining first-principles calculations and effective model analysis, we predict that CaTe is a topological node-line semimetal in the absence of the spin-orbit coupling. Using a slab model, we obtain the nearly flat drumhead surface state near the Fermi level. When the spin-orbit coupling is included, three node lines will evolve into a pair of Dirac points along the M−R line. These Dirac points are robust and protected by the C 4 rotation symmetry. Once this crystal symmetry is broken, the Dirac points will be eliminated, and the system becomes a strong topological insulator.npj Quantum Materials (2017) 2:3 ; doi:10.1038/s41535-016-0005-4 INTRODUCTIONTopological insulator (TI) has attracted broad interest in the past 10 years. [1][2][3][4][5][6][7] The unique property of TI is that it is an insulator in the bulk but has exotic metallic surface states due to the topological order. More recently, the research on topological states has been extended to three-dimensional (3D) semimetal systems. [8][9][10][11][12] These systems could demonstrate many fascinating phenomena, such as Weyl fermion quantum transport and various Hall effects, [13][14][15][16] consequently become the rising stars of the field. Up to now, three kinds of topological semimetals have been discovered, i.e., 3D Dirac semimetal (DSM), 12,[17][18][19][20][21] Weyl semimetal (WSM), 8,9,22,23 and node-line semimetal (NLS). [24][25][26][27][28][29] The 3D DSM has four-fold degeneracy point, which can be viewed as the kiss of two Weyl fermions with opposite chiralities in the Brillouin zone (BZ). Protected by the crystal symmetry and time reversal symmetry, 3D DSMs can be robust against external perturbations. Several materials have been theoretically predicted to be 3D DSMs 12,17-21 and some of them have already been confirmed by experiments. [30][31][32][33] If one breaks the time reversal symmetry 8,22,23,34 or the inversion symmetry, 35-38 the 3D DSM will evolve into WSM. Very recently, the predictions about WSM state in TaAs family 37,38 have been confirmed experimentally. [39][40][41][42] Unlike DSM and WSM whose band crossing points distribute at separate k points in the BZ, for a NLS the crossing points around the Fermi level form a closed loop. Several compounds have been proposed as NLSs, including Mackay-Terrones crystals, 25 Bernal graphite, 43 hyperhoneycomb lattices, 44 and antiperovskite Cu 3 PdN 26,27 and Cu 3 NZn. 27 In the absence of spin-orbit coupling (SOC), time reversal symmetry together with inversion or mirror symmetry will guarantee the occurrence of node line in 3D BZ for systems with band inversion. [25][26][27]37,45,46 Same with TI and WSM, NLS also has a characteristic surface state, namely, drumhead-like state. 24-29 Such a 2D flat band surface state may become a route to achieve high temperature superconductivity. 47,48 As a result, it is of great impetus to search new NLS.In this study, based on first-principles calculations and effective model analysis, we propose that CaTe in CsCl-type structure is a NLS with drumhea...

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“…Under high pressure, alkaline earth chalcogenides such as CaO, CaS, CaSe and CaTe are closed-shell ionic systems that crystallize in B1-type structure at ambient conditions and have technological importance in many applications, from catalysis to microelectronics [1][2][3][4][5]. There are also applications in the field of Luminescent devices [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…Boucenna et al used the pseudo-potential plane-waves (PP-PWs) approach to determine the phase transition from B1 to B2 phase and obtained this transition at 32.7 GPa. They also studied the electronic properties of CaSe and obtained bandgaps of 2.859 eV and 0.407 eV for B1 and B2 phases, respectively [2]. Charifi et al studied the mechanism of transform of CaSe using the scalar relativistic full potential linearized augmented plane-wave (FP-LAPW) method.…”

Section: Introductionmentioning

confidence: 99%

High-pressure structural phase transitions, electronic properties, and intermediate states of CaSe

Kürkçü

2019

Can. J. Phys.

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In this study, ab initio calculations have been carried out to understand the effect of extreme external pressure on the crystal structure of CaSe. The crystal structure of CaSe, a calcium chalcogen, is studied using density functional theory (DFT) with the generalized gradient approximation (GGA) up to 250 GPa under high hydrostatic pressure. Structurally CaSe crystallizes in cubic NaCl-type (B1) structure (space group: [Formula: see text]) at ambient conditions. The results indicated that CaSe undergoes a structural phase transition from this cubic structure to another cubic CsCl-type (B2) structure (space group: [Formula: see text]) at high pressure. This transformation is based on two intermediate states with space group [Formula: see text] and C2/m. Additionally, the electronic band structures and density of states for the obtained B1 and B2 structures of CaSe have been calculated. According to these calculations, obtained band gap values are in good agreement with the values reported in the literature.

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High pressure induced structural, elastic and electronic properties of Calcium Chalcogenides CaX (X=S, Se and Te) via first-principles calculations

Cited by 20 publications

References 47 publications

Sensitivity of Th229 nuclear clock transition to variation of the fine-structure constant

Sensitivity of Th229 nuclear clock transition to variation of the fine-structure constant

CaTe: a new topological node-line and Dirac semimetal

High-pressure structural phase transitions, electronic properties, and intermediate states of CaSe

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