Fermi Surface Properties Research Articles

Electronic Band Structure and Fermi Surface Analysis of Ce2 Ni1-Xcoxge2: A Pseudo Potential Study

This study uses pseudopotential calculations to investigate the electronic band structure and Fermi surface properties of Ce2Ni1-xCoxGe2 alloys. The research problem centers on understanding the effects of Co substitution on the electronic properties of these alloys, particularly regarding potential high-temperature superconducting behavior. The methodology involves density of states (DOS) analysis and Fermi surface calculations for Ce2Ni1-xCoxGe2 alloys with varying Co concentrations. Results reveal a notable increase in DOS around the Fermi level with increasing Co substitution, indicative of enhanced metallic behavior and potential superconducting characteristics. Additionally, band structure analyses demonstrate the significant role of hybridization between Ce 4f, Ni/Co 3d, and Ge 4s/4p orbitals in determining electronic behavior. Fermi surface calculations unveil a transition from near-spherical to complex 2D and 3D shapes with higher Co concentrations, suggesting modifications in Fermi energy surface nestings or electron scattering. This study's conclusions emphasized the intricate electronic structure of Ce2Ni1-xCoxGe2 alloys and highlighted the potential for further exploration in high-temperature super conductivity research.

Superconducting and Fermi Surface Properties of a Valence Fluctuation Compound CeIr2

Superconducting and Fermi Surface Properties of a Valence Fluctuation Compound CeIr₂

Phase and Composition Engineering of Self-Intercalated 2D Metallic Tantalum Sulfide for Second-Harmonic Generation.

Self-intercalation in two-dimensional (2D) materials is significant, as it offers a versatile approach to modify material properties, enabling the creation of interesting functional materials, which is essential in advancing applications across various fields. Here, we define ic-2D materials as covalently bonded compounds that result from the self-intercalation of a metal into layered 2D compounds. However, precisely growing ic-2D materials with controllable phases and self-intercalation concentrations to fully exploit the applications in the ic-2D family remains a great challenge. Herein, we demonstrated the controlled synthesis of self-intercalated H-phase and T-phase Ta1+xS2 via a temperature-driven chemical vapor deposition (CVD) approach with a viable intercalation concentration spanning from 10% to 58%. Atomic-resolution scanning transmission electron microscopy-annular dark field imaging demonstrated that the self-intercalated Ta atoms occupy the octahedral vacancies located at the van der Waals gap. The nonperiodic Ta atoms break the centrosymmetry structure and Fermi surface properties of intrinsic TaS2. Therefore, ic-2D T-phase Ta1+xS2 consistently exhibit a spontaneous nonlinear optical (NLO) effect regardless of the sample thickness and self-intercalation concentrations. Our results propose an approach to activate the NLO response of centrosymmetric 2D materials, achieving the modulation of a wide range of optoelectronic properties via nonperiodic self-intercalation in the ic-2D family.

Characteristic Fermi Surface Properties of Rare Earth and Actinide Compounds

Characteristic Fermi Surface Properties of Rare Earth and Actinide Compounds

Transport properties and doping evolution of the Fermi surface in cuprates

Measured transport properties of three representative cuprates are reproduced within the paradigm of two electron subsystems, itinerant and localized. The localized subsystem evolves continuously from the Cu 3d^9 hole at half-filling and corresponds to the (pseudo)gapped parts of the Fermi surface. The itinerant subsystem is observed as a pure Fermi liquid (FL) with material-independent universal mobility across the doping/temperature phase diagram. The localized subsystem affects the itinerant one in our transport calculations solely by truncating the textbook FL integrals to the observed (doping- and temperature-dependent) Fermi arcs. With this extremely simple picture, we obtain the measured evolution of the resistivity and Hall coefficients in all three cases considered, including LSCO which undergoes a Lifshitz transition in the relevant doping range, a complication which turns out to be superficial. Our results imply that prior to evoking polaronic, quantum critical point, quantum dissipation, or even more exotic scenarios for the evolution of transport properties in cuprates, Fermi-surface properties must be addressed in realistic detail.

Emergent topological quantum orbits in the charge density wave phase of kagome metal CsV3Sb5

The recently discovered kagome materials AV3Sb5 (A = K, Rb, Cs) attract intense research interest in intertwined topology, superconductivity, and charge density waves (CDW). Although the in-plane 2 × 2 CDW is well studied, its out-of-plane structural correlation with the Fermi surface properties is less understood. In this work, we advance the theoretical description of quantum oscillations and investigate the Fermi surface properties in the three-dimensional CDW phase of CsV3Sb5. We derived Fermi-energy-resolved and layer-resolved quantum orbits that agree quantitatively with recent experiments in the fundamental frequency, cyclotron mass, and topology. We reveal a complex Dirac nodal network that would lead to a π Berry phase of a quantum orbit in the spinless case. However, the phase shift of topological quantum orbits is contributed by the orbital moment and Zeeman effect besides the Berry phase in the presence of spin-orbital coupling (SOC). Therefore, we can observe topological quantum orbits with a π phase shift in otherwise trivial orbits without SOC, contrary to common perception. Our work reveals the rich topological nature of kagome materials and paves a path to resolve different topological origins of quantum orbits.

High quantum oscillation frequencies and nontrivial topology in kagome superconductor KV3Sb5 probed by torque magnetometry up to 45 T

Here, we present the Fermi surface properties of the kagome superconductor ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ using torque magnetometry at applied fields up to 45 T and temperatures down to that of liquid $^{3}\mathrm{He}$ (0.32 K). The torque signal shows clear de Haas--van Alphen (dHvA) oscillations with 14 major frequencies ranging from $\ensuremath{\sim}33$ to 2149 T, nine of which are higher frequencies (above 500 T) that have never been reported in ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$. Angular dependence measurements of the dHvA oscillations were carried out to investigate the dimensionality of the Fermi surface. Based on our analysis, several frequencies follow the $1/\mathrm{cos}\phantom{\rule{0.16em}{0ex}}\ensuremath{\theta}$ dependence, where $\ensuremath{\theta}$ is the tilt angle with respect to the applied field direction and oscillations disappear above $\ensuremath{\theta}={60}^{\ensuremath{\circ}}$, which suggest that Fermi surfaces corresponding to these frequencies are quasitwo dimensional. The Berry phase (${\mathrm{\ensuremath{\Phi}}}_{\mathrm{B}}$), determined by constructing a Landau level fan diagram, was found to be ${\mathrm{\ensuremath{\Phi}}}_{\mathrm{B}}\ensuremath{\sim}\ensuremath{\pi}$, which strongly suggests the nontrivial topology of ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$. To explain the experimental results, we carried out band-structure and Fermi-surface calculations using density functional theory (DFT) for both pristine and charge-density wave (CDW) phases. We found that the Fermi surface undergoes severe reconstruction in the CDW phase and, more importantly, our calculation results are in reasonable agreement with the experimentally measured Fermi-surface frequencies. The observation in this paper of very high quantum oscillation frequencies in ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ and the determination of their detailed Fermi-surface properties, along with the analyses of corresponding DFT calculation results, are crucial for understanding CDW order, unconventional superconductivity, and nontrivial topology in $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}\phantom{\rule{0.28em}{0ex}}(A=\mathrm{K},\mathrm{Rb},$ and Cs), as well as the interplay among them.

Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films

Motivated by observations of extreme magnetoresistance (XMR) in bulk crystals of rare-earth monopnictide (RE-V) compounds and emerging applications in novel spintronic and plasmonic devices based on thin-film semimetals, we have investigated the electronic band structure and transport behavior of epitaxial GdSb thin films grown on III-V semiconductor surfaces. The ${\mathrm{Gd}}^{3+}$ ion in GdSb has a high spin $S=7/2$ and no orbital angular momentum, serving as a model system for studying the effects of antiferromagnetic order and strong exchange coupling on the resulting Fermi surface and magnetotransport properties of RE-Vs. We present a surface and structural characterization study mapping the optimal synthesis window of thin epitaxial GdSb films grown on III-V lattice-matched buffer layers via molecular-beam epitaxy. To determine the factors limiting XMR in RE-V thin films and provide a benchmark for band-structure predictions of topological phases of RE-Vs, the electronic band structure of GdSb thin films is studied, comparing carrier densities extracted from magnetotransport, angle-resolved photoemission spectroscopy (ARPES), and density-functional theory (DFT) calculations. ARPES shows a hole-carrier rich, topologically trivial, semimetallic band structure close to complete electron-hole compensation, with quantum confinement effects in the thin films observed through the presence of quantum-well states. DFT-predicted Fermi wave vectors are in excellent agreement with values obtained from quantum oscillations observed in magnetic field-dependent resistivity measurements. An electron-rich Hall coefficient is measured despite the higher hole-carrier density, attributed to the higher electron Hall mobility. The carrier mobilities are limited by surface and interface scattering, resulting in lower magnetoresistance than that measured for bulk crystals.

Effect of the Interlayer Ordering on the Fermi Surface of Kagome Superconductor CsV_{3}Sb_{5} Revealed by Quantum Oscillations.

The connection between unconventional superconductivity and charge density waves (CDWs) has intrigued the condensed matter community and found much interest in the recently discovered superconducting Kagome family of AV_{3}Sb_{5} (A=K, Cs, Rb). X-ray diffraction and Raman spectroscopy measurements established that the CDW order in CsV_{3}Sb_{5} comprises of a 2×2×4 structure with stacking of layers in a star-of-David (SD) and inverse-star-of-David (ISD) pattern along the c-axis direction. Such interlayer ordering will induce a vast normalization of the electronic ground state; however, it has not been observed in Fermi surface measurements. Here we report quantum oscillations of CsV_{3}Sb_{5} using tunnel diode oscillator frequency measurements. We observed a large number of frequencies, many of which were not reported. The number of frequencies cannot be explained by DFT calculations when only SD or ISD distortion is considered. Instead, our results are consistent with calculations when interlayer ordering is taken into account, providing strong evidence that the CDW phase of CsV_{3}Sb_{5} has complicated structure distortion which in turn has dramatic effects on the Fermi surface properties.

Fermiology of the Dirac type-II semimetal candidates (Ni,Zr) Te2 using de Haas–van Alphen oscillations

We have investigated the Fermi surface properties of the Dirac type-II semimetal candidates (Ni,Zr)${\mathrm{Te}}_{2}$ using torque magnetometry with applied fields up to 35 T. Magnetization shows clear de Haas--van Alphen (dHvA) oscillations above 20 T. The dHvA oscillations are smooth and well defined and consist of one distinct frequency (${F}_{\ensuremath{\alpha}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}530$ T) in $\mathrm{Zr}{\mathrm{Te}}_{2}$ and three (${\overline{F}}_{\ensuremath{\alpha}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}72$ T, ${\overline{F}}_{\ensuremath{\beta}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}425$ T, and ${\overline{F}}_{\ensuremath{\gamma}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}630$ T) in $\mathrm{Ni}{\mathrm{Te}}_{2}$. The Berry phase $\ensuremath{\phi}$ was determined by constructing the Landau level fan diagram. It is found that $\ensuremath{\phi}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 0 and $\ensuremath{\pi}$ for ${F}_{\ensuremath{\alpha}}$ and ${\overline{F}}_{\ensuremath{\beta}}$, respectively, for $\mathrm{Zr}{\mathrm{Te}}_{2}$ and $\mathrm{Ni}{\mathrm{Te}}_{2}$. This strongly suggests that the Dirac fermions make a dominant contribution to the transport properties of $\mathrm{Ni}{\mathrm{Te}}_{2}$, whereas topologically trivial fermions dominate those in $\mathrm{Zr}{\mathrm{Te}}_{2}$. The presence of lighter effective mass ${m}^{*}=0.13{m}_{e}$ in $\mathrm{Ni}{\mathrm{Te}}_{2}$ compared to ${m}^{*}=0.26{m}_{e}$ in $\mathrm{Zr}{\mathrm{Te}}_{2}$, where ${m}_{e}$ is an electron's rest mass, further confirms the presence of Dirac fermions in $\mathrm{Ni}{\mathrm{Te}}_{2}$. Our density functional theory calculations find that while both systems host type-II Dirac dispersions along the out-of-plane direction, their relative positions and the natures of the dispersions are different. The Dirac cone is closer to the Fermi energy ${E}_{F}$ ($\ensuremath{\sim}100$ meV above) in $\mathrm{Ni}{\mathrm{Te}}_{2}$, whereas it is far ($\ensuremath{\sim}500$ meV) above ${E}_{F}$ for $\mathrm{Zr}{\mathrm{Te}}_{2}$. This is consistent with our experimental finding of a nontrivial Berry phase and dominant contribution from lighter electrons in the quantum oscillation signal for only $\mathrm{Ni}{\mathrm{Te}}_{2}$. These findings suggest that the proximity of the Dirac cone to ${E}_{F}$ in topological compounds is crucial for observing the effect from Dirac quasiparticles in their electrical transport or magnetic properties.

Lix(C5H5N)yFe2-zSe2: A Defect-Resilient Expanded-Lattice High-Temperature Superconductor.

Two-dimensional iron chalcogenide intercalates display a remarkable correlation of the interlayer spacing with enhancement of the superconducting critical temperature (Tc). In this work, synchrotron X-ray absorption (XAS; at the Fe and Se K-edges) and emission (XES; at the Fe Κβ) spectroscopies allow one to discuss how the important rise of Tc (∼44 K) in the molecule-intercalated Lix(C5H5N)yFe2-zSe2 relates to the electronic and local structural changes felt by the inorganic host upon doping (x). XES shows that widely separated layers of edge-sharing FeSe4 tetrahedra carry low-spin moieties, with a local Fe magnetic moment slightly reduced compared to the parent β-Fe2-zSe2. Pre-edge XAS expresses the progressively reduced mixing of metal 3d-4p states upon lithiation. Doping-mediated local lattice modifications, probed by conventional Tc optimization measures (cf. the anion height and FeSe4 tetrahedra regularity), become less relevant when layers are spaced far away. On the basis of extended X-ray absorption fine structure, such distortions are compensated by a softer Fe network that relates to Fe-site vacancies, alleviating electron-lattice correlations and superconductivity. Density functional theory (DFT) guided modification of the isolated Fe2-zSe2 (z, vacant sites) planes, resembling the host layers, identify that Fe-site deficiency occurs at low energy cost, giving rise to stretched Fe sheets, in accordance with experiments. The robust high-Tc in Lix(C5H5N)yFe2-zSe2, arises from the interplay of electron-donating spacers and the iron selenide layer's tolerance to defect chemistry, a tool to favorably tune its Fermi surface properties.

Distinct signatures of particle-hole symmetry breaking in transport coefficients for generic multi-Weyl semimetals

We propose and study generic multi-Weyl semimetal (mWSM) lattice Hamiltonians that break particle-hole symmetry. These models fall into two categories: model I (model II) where the gap and tilt terms are coupled (decoupled) can host type-I and type-II Weyl nodes simultaneously (separately) in a hybrid phase (type-I and type-II phases, respectively). We concentrate on the question of how anisotropy and non-linearity in the dispersions, gaps and tilt terms influence diffusive second order transport quantities namely, the circular photogalvanic effect (CPGE) and the Berry curvature dipole (BCD) as well as first order Magnus Hall effect (MHE) in the ballistic limit. The signatures of topological charges are clearly imprinted in the quantized CPGE response for the hybrid mWSM phase in model I. Such a quantization is also found in the type-I WSM phase for model II, however, the frequency profiles of the CPGE in these two cases is distinctively different owing to their different band dispersion irrespective of the identical topological properties. The contributions from the vicinity of Weyl nodes and away from the WNs are clearly manifested in the BCD response, respectively, for model I model II. The Fermi surface properties for the activated momentum lead to a few hallmark features on the MHE for both the models. Furthermore, we identify distinguishing signatures of the above responses for type-I, type-II and hybrid phases to provide an experimentally viable probe to differentiate these WSMs phases.

Chiral anomaly in noncentrosymmetric systems induced by spin-orbit coupling

The chiral anomaly may be realized in condensed matter systems with pairs of Weyl points. Here we show that the chiral anomaly can be realized in diverse noncentrosymmetric systems even without Weyl point pairs when spin-orbit coupling induces nonzero Berry curvature flux through Fermi surfaces. This motivates the condensed matter chiral anomaly to be interpreted as a Fermi surface property rather than a Weyl point property. The spin-orbit-coupling-induced anomaly reproduces the well-known charge transport properties of the chiral anomaly such as the negative longitudinal magnetoresistance and the planar Hall effect in Weyl semimetals. Since it is of spin-orbit coupling origin, it also affects the spin transport and gives rise to anomaly-induced longitudinal spin currents and the magnetic spin Hall effect, which are absent in conventional Weyl semimetals.

Nontrivial Fermi surface topology of the kagome superconductor CsV3Sb5 probed by de Haas–van Alphen oscillations

We have investigated the normal state Fermi-surface properties of the kagome superconductor ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ using torque magnetometry with applied fields ($H$) up to 35 T. The torque signal shows clear de Haas--van Alphen (dHvA) oscillations above 15 T. The oscillations are smooth and consist of seven distinct frequencies with values from $\ensuremath{\sim}$ 18 T to 2135 T. The presence of higher frequencies in ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ is further confirmed by carrying out additional measurements using the tunnel diode oscillator technique. All frequencies measured at different tilt angles ($\ensuremath{\theta}$) of the field direction with respect to the c axis show a $1/\mathrm{cos}\ensuremath{\theta}$ dependence, implying that the Fermi surfaces corresponding to these frequencies are two dimensional (2D). The absence of dHvA oscillations at $\ensuremath{\theta}$ = ${90}^{o}$ further supports the presence of 2D Fermi surfaces. The Berry phase ($\ensuremath{\phi}$) determined from the Landau level fan diagram for all frequencies is $\ensuremath{\sim}$ 0.4. This value is close to the theoretical value of $\ensuremath{\phi}$ = 0.5 for a nontrivial system, which strongly supports the nontrivial topology of the Fermi surfaces of these frequencies. Several quantities characterizing the Fermi surface are calculated employing the Lifshitz-Kosevich theory. These findings are crucial for exploring the interplay between nontrivial band topology, charge-density wave, and unconventional superconductivity of ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$.

Intraband Lifshitz transition and Stoner ferromagnetism in Janus PA2As ( A=Si,Ge,Sn , and Pb) monolayers

Using first-principles calculations, a class of Janus two-dimensional materials, $\mathrm{P}{A}_{2}\mathrm{As}$ ($A=\mathrm{Si}$, Ge, Sn, and Pb) monolayers, is predicted to be dynamically and thermally stable. The band gap of $\mathrm{P}{A}_{2}\mathrm{As}$ can be linearly modulated by external strain and electric field. The presence of the peculiar sombrero-type band in strained $\mathrm{P}{A}_{2}\mathrm{As}$ results in the intraband Lifshitz transition near the valence band top when including Rashba spin-orbit coupling. The energy range of intraband Lifshitz transition is linearly dependent on electric field, indicating potential electric control of the Fermi surface properties. In particular, hole doping leads to the ferromagnetic transition in $\mathrm{P}{A}_{2}\mathrm{As}$ due to Van Hove singularity and a divergence with $1/\sqrt{E}$ of the density of states. This ferromagnetism can be understood in terms of the Stoner criterion $D$(${E}_{\mathrm{F}}$)${I}_{\mathrm{S}}>1$. A saturated magnetic moment of $1\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{hole}$ is obtained in hole-doped ${\mathrm{PSn}}_{2}\mathrm{As}$ and ${\mathrm{PPb}}_{2}\mathrm{As}$ with a wide range of hole densities. The highest Curie transition temperature ${T}_{\mathrm{c}}$ is estimated to be 93.5 K at the mean field level. We demonstrate that hole density and tensile strain are two effective approaches to control the Stoner ferromagnetism in practical applications. Moreover, various electronic transitions, such as semiconductor to half-metal, half-metal to metal, and semiconductor to metal, are revealed in hole-doped $\mathrm{P}{A}_{2}\mathrm{As}$. Finally, we explore the feasibility of realizing ferromagnetism by introducing $p$-type dopants and defects. The experimentally controlled intraband Lifshitz transition and Stoner ferromagnetism demonstrate that Janus $\mathrm{P}{A}_{2}\mathrm{As}$ monolayers have a wide application potential in future electronic and spintronic devices.

Fermi surface studies of the topologically nontrivial compound YSi

The Fermi surface properties of a nontrivial system YSi is investigated by de Haas-van Alphen (dHvA) oscillation measurements combined with the first-principle calculations. Three main frequencies ($\alpha$, $\beta$, $\gamma$) are probed up to $14$~T magnetic field in dHvA oscillations. The $\alpha$-branch corresponding to $21$~T frequency possesses non-trivial topological character with $\pi$ Berry phase and a linear dispersion along $\Gamma$ to $Z$ direction with a small effective mass of $0.069~m_e$ with second-lowest Landau-level up to $14$~T. For $B~\parallel$~[010] direction, the 295~T frequency exhibits non-trivial $2D$ character with $1.24\pi$ Berry phase and a high Fermi velocity of $6.7 \times 10^5$~ms$^{-1}$. The band structure calculations reveal multiple nodal crossings in the vicinity of Fermi energy $E_f$ without spin-orbit coupling (SOC). Inclusion of SOC opens a small gap in the nodal crossings and results in nonsymmorphic symmetry enforced Dirac points at some high symmetry points, suggesting YSi to be a symmetry enforced topological metal.

Fermi Surface of the Heavy-fermion Superconductor PrTi2Al20

We have investigated the Fermi surface properties in the Pr-based heavy-fermion superconductor PrTi2Al20 and its reference compound LaTi2Al20 by means of the de Haas–van Alphen effect experiments a...

First Principle’s Prediction of the Electronic and Optical properties of Ca4Bi6O13

Inside a system of DFT made on maximum capacity goals on the Electronic structure, electronic charge thickness, Fermi surface and optical properties we will play out a top to bottom examination of Ca4Bi6O13 compound. With DOS the investigated compound have metallic nature at a Fermi vitality equivalent to 16.4, 16.27 and 14.89 states/eV, and the straightforward direct lowtemperature electronic explicit warmth coefficient (?) for EVGGA, GGA and LDA is start to be 2.84, 2.82 and 2.58 mJ/mol-K2 correspondingly. The fanciful and genuine pieces of the dielectric work were expected by optical scattering. We feature that in the fanciful and genuine pieces of the recurrence subordinate dielectric work the sharp ascent at low energies (underneath 1.0 eV). We can gather the outcomes as: it is appeared by the electronic structure counts that valence band most extreme and the conduction band least happens at ?-point, bringing about an immediate vitality band hole. The conduction band in the higher vitality state comprises of Ca 3d states and the conduction band in the lower vitality locale is essentially made with the admixture of Bi 6p and O 2p.The thickness of states uncover that the conduction groups are generally made out of Cr-d states, though the valence groups are fundamentally overwhelmed by Cr-d, N-p and O-p states. The incomplete thickness of positions shows that there is a solid hybridization between O-p and N-s, Cr-d and C-p and furthermore between N-p and C-p states. The electronic charge thickness investigation shows that there is solid covalent bonds between Cr-d N-p, O-p and Cr-p, N-p and C-p and furthermore between Cr-d and O-p iotas. The TE (thermo-electric) study suggests that this material has potential in thermoelectric side.

First-principles study of electronic structure and fermiology of covellite mineral and its B1, B3 phases

We present the first-principles calculations under the framework of density functional theory to explore the Fermi surface and electronic properties of covellite mineral. The correlation effects are considered applying the +U correction in the density functional theory. Lattice parameters are determined and the possibility of pressure induced phase transitions to the hypothetical B1 and B3 crystals is examined. All calculations show impending B18 → B1 and B3 → B1 phase transitions. Using generalized gradient approximation these are found to occur at 7.4 and 6.48 GPa, respectively. Electronic bands structures of the three crystals highlight metallic properties. Two copper atoms situated at distinct locations in covellite exhibit a distinct role. The Fermi surfaces of all phases are presented. The calculations of B18 map out corrugated cylindrical Fermi surface signifying inter-layer interaction mediated by the S(II)–S(II) bond. The +U correction shows anisotropy in the Fermi surface noted in experiment. It also indicates stronger inter-layer interaction. Applying Debye–Slater and the Debye–Grüneisen models the thermal expansion coefficient, heat capacity and entropy are found and their temperature dependence is discussed.

Structural, elastic, electronic, bonding, and optical properties of topological CaSn3 semimetal

In recent days, topological semimetals have become an active branch of materials research. The topological Weyl semimetal CaSn3, belonging to the AuCu3 type cubic structure, is an important electronic system to investigate both from the point of view of fundamental physics and prospective applications. In this work, we have studied the structural, elastic, mechanical, electronic, bonding, Fermi surface and optical properties of CaSn3 in detail via first-principles method using the density functional theory. A comprehensive study of elastic constants and moduli shows that CaSn3 possesses low level of elastic anisotropy, reasonably good machinability, mixed bonding characteristics with ionic and covalent contributions, brittle nature and relatively high Vickers hardness with a low Debye temperature. The mechanical stability conditions are fulfilled. Analysis of bond population supports the bonding nature as indicated by the elastic parameters. The bulk electronic band structure reveals clear semimetallic features with signature Dirac cone-like dispersions near the Fermi level. A pseudogap in the electronic energy density of states at the Fermi level separating the bonding and the antibonding peaks points towards significant electronic stability of cubic CaSn3. The Fermi surface mostly consists of electron-like sheets with very few small hole pockets. The band structure is fairly isotropic in the k-space. The optical constants show interesting characteristics. The reflectivity spectra show almost non-selective behavior over a wide range of photon energy encompassing infrared to mid-ultraviolet regions. High reflectivity over wide spectral range makes CaSn3 a suitable material for reflecting coating. CaSn3 is an efficient absorber of ultraviolet radiation. The refractive index is very high in the infrared to visible range. All the energy dependent optical parameters exhibit clear metallic signatures and are in complete accord with the underlying bulk electronic density of states calculations.