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A comprehensive investigation of the unexplored mechanical, electronic, Mulliken bond population, vibrational, optical and thermophysical properties of the synthesized compounds NbIn$X_2$ (X = S, Se) have been made for the first time using the density functional theory. The chemical, mechanical and dynamical stabilities of the compounds are established in our calculations. Both compounds are soft, machinable and brittle. The anisotropic nature of the studied compounds is shown by 3D representations of elastic moduli. The density of states and electronic band structure demonstrate that the compounds are metallic. Fermi surfaces of both compounds are almost similar and contain both hole- and electron-like topologies. The characteristics of chemical bonding among different atoms of the compounds are studied via a charge density distribution map and bond population analysis. Both the compounds possess optical anisotropy. Reflectivity is high (above 44%) in the IR–visible–UV region indicating that the phases may be effective in reducing solar heat. Minimum thermal conductivity, $k_{min}$ (used to select appropriate material for thermal barrier coating) and its anisotropy are calculated for the first time. The results show that both compounds have $k_{min}$ much smaller than the reference value of 1.25Wm${}^{-1}$K${}^{-1}$.

For a two-dimensional, weakly coupled system of fermions at temperature zero, one principal ingredient used to control the composition of the associated renormalization group maps is the careful counting of the number of quartets of sectors that are consistent with conservation of momentum. A similar counting argument is made to show that particle–particle ladders are irrelevant in the case of an asymmetric Fermi curve.

We consider many-fermion systems with singular Fermi surfaces, which contain Van Hove points where the gradient of the band function k ↦ e(k) vanishes. In a previous paper, we have treated the case of spatial dimension d ≥ 3. In this paper, we focus on the more singular case d = 2 and establish properties of the fermionic self-energy to all orders in perturbation theory. We show that there is an asymmetry between the spatial and frequency derivatives of the self-energy. The derivative with respect to the Matsubara frequency diverges at the Van Hove points, but, surprisingly, the self-energy is C¹ in the spatial momentum to all orders in perturbation theory, provided the Fermi surface is curved away from the Van Hove points. In a prototypical example, the second spatial derivative behaves similarly to the first frequency derivative. We discuss the physical significance of these findings.

Based on our previous work, we deduce a general formula for pressure of degenerate and relativistic electrons, P_e, which is suitable for superhigh magnetic fields, discuss the quantization of Landau levels of electrons, and consider the quantum electrodynamic (QED) effects on the equations of states (EOSs) for different matter systems. The main conclusions are as follows: P_e is related to the magnetic field B, matter density ρ, and electron fraction Y_e; the stronger the magnetic field, the higher the electron pressure becomes; the high electron pressure could be caused by high Fermi energy of electrons in a superhigh magnetic field; compared with a common radio pulsar, a magnetar could be a more compact oblate spheroid-like deformed neutron star (NS) due to the anisotropic total pressure; and an increase in the maximum mass of a magnetar is expected because of the positive contribution of the magnetic field energy to the EOS of the star.

We measured the angular momentum density distribution of YNi₂B₂C to acquire information about its electronic structure. The measurements were performed using the full-scale utility of the two-dimensional angular correlation of annihilation radiation (2D-ACAR). The measured spectra clarified that Ni (3d) like state, predominantly, affected the Fermi surface of YNi₂B₂C. Further, s- and p-like-states enhanced its superconducting properties. The Fermi surface of YNi₂B₂C. was reconstructed using Fourier transformation followed by the LCW (Loucks, Crisp and West) folding procedure. It showed a large and complex surface similar to that of the high temperature superconductors HTS, with anisotropic properties. It also disclosed the effect of d-like state. Nevertheless, the current Fermi surface could deliver the needed topological information to isolate its features. The general layouts of this Fermi surface are; two large electron surfaces running along Γ–Z direction; as well as an additional large electron surface centered on X point; beside one hole surface centered on 100 point. This Fermi surface was interpreted in view of the earlier results.

We have studied periodic orbit resonances (PORs) in order to probe the topology of the Fermi surface (FS) of the quasi-1D organic conductor (TMTSF)₂ClO₄ and the quasi-2D organic conductors κ-(ET)₂Cu(NCS)₂ and κ-(ET)₂I₃. The FS of (TMTSF)₂ClO₄ consists of a pair of weakly corrugated open sheets, while κ-(ET)₂Cu(NCS)₂ and κ-(ET)₂I₃ additionally possess warped cylindrical FS sections. In this paper, we review the POR technique for the straightforward case of (TMTSF)₂ClO₄. We then report on a detailed study of the FS topology for κ-(ET)₂Cu(NCS)₂.

Electrons, when scattered by static random disorder, form standing waves that can be imaged using scanning tunneling microscopy. Such interference patterns, observable by the recently developed technique of Fourier transform scanning tunneling spectroscopy (FT-STS), are shown to carry unique fingerprints characteristic of the electronic order present in a material. We exploit this feature of the FT-STS technique to propose a test for the nature of the enigmatic pseudogap phase in the high-T_c cuprate superconductors. Through their sensitivity to the quasiparticle spectra and coherence factors, the FT-STS patterns, in principle, carry enough information to unambiguously determine the nature of the condensate responsible for the pseudogap phenomenon. In practice, the absence of a detailed understanding of the scattering mechanism, together with the experimental uncertainties, prevent such an unambiguous determination. We argue, however, that the next generation of FT-STS experiments, currently underway, should be able to distinguish between the pseudogap dominated by the remnants of superconducting order from the pseudogap dominated by some competing order in the particle-hole channel. Using general arguments and detailed numerical calculations, we point to certain fundamental differences between the two scenarios and discuss the prospects for future experiments.

Recent Nernst and interlayer transport experiments in Bi₂Sr₂CaCu₂O_8+y (BSCCO) high temperature superconductors report hugely different limiting magnetic fields. We demonstrate that both fields convert to the same pseudogap energy scale T* upon transformation as orbital and Zeeman critical fields, respectively. We suggest a consistent interpretation of this finding based on separation of spin and charge degrees of freedom residing in different regions of a truncated Fermi surface.

The motion of the guiding center of magnetic circulation generates a charge transport. By applying kinetic theory to the guiding center motion, an expression for the magnetoconductivity σ is obtained: σ = e²n_cτ/M*, where M* is the magnetotransport mass distinct from the cyclotron mass, n_c the density of the conduction electrons, and τ the relaxation time. The density n_c depends on the magnetic field direction relative to copper's fcc lattice, when Cu's Fermi surface is nonspherical with “necks”. The anisotropic magnetoresistance is analyzed based on a one-parameter model, and compared with experiments. A good fit is obtained.

This work investigates a d-p Hubbard model by the n-pole approximation in the hole-doped regime. In particular, the spectral function A(ω, k) is analyzed varying the filling, the local Coulomb interaction and the d-p hybridization. It should be remarked that the original n-pole approximation (Phys. Rev.184, 451 1969) has been improved in order to include adequately the k-dependence of the important correlation function 〈S_j·S_i〉 present in the poles of the Green's functions. It has been verified that the topology of the Fermi surface (defined by A(ω = 0, k)) is deeply affected by the doping, the strength of the Coulomb interaction and also by the hybridization. Particularly, in the underdoped regime, the spectral function A(ω = 0, k) presents very low intensity close to the antinodal points (0, ±π) and (±π, 0). Such a behavior produces an anomalous Fermi surface (pockets) with pseudogaps in the region of the antinodal points. On the other hand, if the d-p hybridization is enhanced sufficiently, such pseudogaps vanish. It is precisely the correlation function 〈S_j·S_i〉, present in the poles of the Green's functions, plays an important role in the underdoped situation. In fact, antiferromagnetic correlations coming from 〈S_j·S_i〉 strongly modify the quasiparticle band structure. This is the ultimate source of anomalies in the Fermi surface in the present approach.

In this paper some structural, magnetic and electronic properties of Zn_1-xV_xO for 0 ≤ x ≤ 0.5, such as optimized lattice constant, cohesive energy, formation enthalpy, density of states, band structure, effective mass and Fermi surface are being investigated. In calculating these properties first principle approach is being used. The calculations performed using DFT theory with full potential linear augmented plane wave (FP-LAPW) and GGA approximation. It is shown that by substituting V instead of Zn, Zn_1-xV_xO compound will gain magnetic properties. The band structure of Zn_1-xV_xO shows that metallic behavior increases with increasing substituted V. This substitution increases extremal area in Fermi surface around Γ point. The results obtained from calculated cohesive energy and formation enthalpy show that substituting V increases the stability of Zn_1-xV_xO. The calculated band gap is in a good agreement with other theoretical results.

We study the transport phenomena in layered conductors with rather general electron energy spectrum placed in a high magnetic field $H$, under conditions when the distance between various sheets of the Fermi surface (FS) may become small under the external effects, such as hydrostatic pressure or impurity atom doping, and electrons can transfer from one sheet of the FS to another due to magnetic breakdown. We calculate the dependence of the in-plane electrical conductivity and magnetoresistance on magnetic field and probability of magnetic breakdown and show that the field-induced quadratic increase of the in-plane resistance in the absence of magnetic breakdown is changed by a linear dependence on $H$. With a further reduction of the energy gap between FS sheets, the in-plane resistance is saturated.

In this paper, we have explored the electronic and magnetic properties of MS₂($\mathrm{\text{M}}=\mathrm{\text{Co}}$, Ni) using first-principles calculations. Our data show rather high tunability of the electronic and magnetic properties of the alloy Co${}_{1-x}$Ni_xS₂$(0.0\le x\le 1.0)$ with the emergence of half-metallicity that persisted up to the intermediate doping concentration. The half-metallic ground state is characterized by large spin polarization at the Fermi level ($E_F$). Beyond the critical doping concentration $x\sim 0.6$, we obtained a metallic solution followed by an antiferromagnetic ground state at a larger doping concentration. This study provides the underlying physics to understand the low-energy Hilbert space and reports the role of the Fermi surface in controlling the electron transport and thus elucidating the anomalous electronic and magnetic behavior of Co${}_{1-x}$Ni_xS₂.

We present a review of our investigations on the increasing specularity of surface scattering of conduction electrons on the W(011), Mo(011), and W(001) surfaces after covering the surfaces with well-ordered (sub)monolayers of adsorbed hydrogen or deuterium. The degree of the specularity of surface scattering was estimated on the base of measurements of magnetoresistance of single-crystalline plates, cooled with liquid He, under ultra-high vacuum conditions, and in a strong magnetic field. The structures of adsorbed hydrogen and deuterium layers were determined from LEED patterns. It is found that the magnetoresistance non-monotonically depends on submonolayer hydrogen coverage and degree of the ordering of adsorbed layers, showing a drastic increase of the specularity (which is higher than for the atomically-clean surfaces!) after the formation of the well-ordered $(1\times 1)$-H structures and a pronounced increase of the specularity after the formation of the well-ordered $(2\times 2)$-2H structure. Changes in the magnetoresistance induced by the ordering of structures of adsorbed H(D) layers are found to corroborate with the adsorption-induced transformation of Fermi contours of surface electronic states obtained in performed DFT calculations. The increase of the specularity of the scattering caused by the ordering of the surface structures is attributed to the decrease of the probability of electronic transitions between the surface and bulk electronic states induced by surface scattering.

A method of building and investigation of the Fermi surfaces for three-dimensional crystals subjected to a uniform magnetic field is presented. The Hamiltonian of a charged particle in the crystal is treated in the framework of the zero-range potential theory. The dispersion relation for the Hamiltonian is obtained in an explicit form.

We have studied periodic orbit resonances (PORs) in order to probe the topology of the Fermi surface (FS) of the quasi-1D organic conductor (TMTSF)₂ClO₄ and the quasi-2D organic conductors κ-(ET)₂Cu(NCS)₂ and κ-(ET)₂I₃. The FS of (TMTSF)₂ClO₄ consists of a pair of weakly corrugated open sheets, while κ-(ET)₂Cu(NCS)₂ and κ-(ET)₂I₃ additionally possess warped cylindrical FS sections. In this paper, we review the POR technique for the straightforward case of (TMTSF)₂ClO₄. We then report on a detailed study of the FS topology for κ-(ET)₂Cu(NCS)₂.

Gapless superconductivity can arise when pairing occurs between fermion species with different Fermi surface sizes, provided there is a sufficiently large mismatch between Fermi surfaces and/or at sufficiently large coupling constant. In gapless states, secondary Fermi surfaces appear where quasiparticle excitation energy vanishes. This work focuses on homogeneous and isotropic superfluids in the s-wave channel, with either zero (conventional superconductor), one, or two spherical Fermi surfaces. The stability conditions for these candidate phases are analyzed. It is found that gapless states with one Fermi surface are stable in the BEC region, while gapless states with two Fermi surfaces are unstable in all parameter space. The results can be applied to ultracold fermionic atom systems.

The motion of the guiding center of magnetic circulation generates a charge transport. By applying kinetic theory to the guiding center motion, an expression for the magnetoconductivity σ is obtained: σ = e²n_cτ/M*, where M* is the magnetotransport mass distinct from the cyclotron mass, n_c the density of the conduction electrons, and τ the relaxation time. The density n_c depends on the magnetic field direction relative to copper's fcc lattice, when Cu's Fermi surface is nonspherical with "necks". The anisotropic magnetoresistance is analyzed based on a one-parameter model, and compared with experiments. A good fit is obtained.