Thermodynamic Properties of a d-Wave Superconductor Near Zero Temperature

On the basis of Fermi liquid theory, we study the thermodynamic properties near zero temperature of a d-wave superconductor assuming the BCS pairing model. The temperature dependence of the order parameter is derived. We then obtain an analytical expression for the free energy difference between the normal and superconducting states in the vicinity of zero temperature from the coupling constant integral. New expressions for the critical field and the specific heat in the superconducting state are given as functions of temperature. We compare our expressions with previous formulas due to others.     

Magnetic Properties of an Antiferromagnetic d-Wave Singlet and π-Triplet Superconductor

In this study we focus on the magnetic properties of a system consisting of Spin Density Wave (SDW) order, d-wave singlet and π-triplet superconductivity (SC) taken on the same footing within a mean-field treatment. The competition and coexistence of these order parameters manifest the H-T phase diagrams of all antiferromagnetic superconductors. An experimental probe to such a multicomponent state can be provided by magnetic measurements such as NMR or magnetization techniques. We have calculated, both analytically and numerically, the static spin susceptibility of our multicomponent system as a function of temperature and external magnetic field under particle–hole asymmetry. Our results can serve as a way to identify these novel multicomponent states. An application to the identification of the high-field low-temperature phase in CeCoIn₅ is discussed.      

Absence of Phase-Fluctuation Contribution to the Low-Frequency Optical Conductivity in d-Wave Superconductors at Zero Temperature

The behavior of the low-frequency optical conductivity _reg() in superconducting cuprates is, at the present, an open and interesting issue. In particular, since the zero-temperature and zero-frequency limit of _reg() attains a value much larger than the universal value expected within a self-consistent T-matrix calculation, an intriguing possibility is that the collective mode can also contribute to _reg(). By taking into account the effect of dissipation on the collective mode in a d-wave superconductor, we evaluate the phase-fluctuation contribution to _reg(0) within the formalism of the phase-only action. We show that even though the collective mode contributes to _reg() at finite frequencies, approaching the zero-temperature and zero-frequency regime the corrections at _reg() due to phase fluctuations vanish.     

Free Energy of a d-Wave Superconductor in the Nearly Antiferromagnetic Fermi Liquid Model

A very general Hamiltonian which describes the coupling of charge carriers via a spin susceptibility is used to derive a formula for the free energy difference between the superconducting and the normal state of a d-wave superconductor. The formula is then specialized to the nearly antiferromagnetic Fermi liquid (NAFL) model and evaluated numerically. The comparison with specific heat data measured for optimally doped YBa₂Cu₃O_6.95 reveals the necessity to include even contributions far away from the Fermi surface to the free energy. The usual restriction to a narrow shell around the Fermi surface in deriving the free energy formula is proved to be inadequate.     

Thermodynamic Properties of Superconductor with Competing Spin-Density Wave and Charge-Density Wave

The mean field Hamiltonian describing the coexistence of the spin-density wave (SDW) and charge-density wave (CDW) for high- T _c superconductor in the underdoped region before the onset of the superconductivity was studied. From self-consistent equations for SDW and CDW gaps derived from Green’s function method, the theromodynamic properties of the superconductor were derived. Our results show the competition between the SDW and CDW state on thermodynamic properties of superconductor that deviate gap-to- T _c ratio, critical temperature, and the specific heat jump from the BCS universal value.     

Temperature Dependence of the Josephson Current in the d-Wave Superconductor Junction Based on the 2-D Extended Hubbard Model

We present a theoretical study of the Josephson current in the d_x ^{2-y 2}-wave superconductor junction. We calculate the current-phase relation and the temperature dependence of the Josephson current for the (100) oriented and the (110) oriented junction using the two-dimensional (2-D) extended Hubbard model. We obtain the anomalous temperature dependence of the current in the (110) oriented junction which has been reported within the quasiclassical theory.     

Cooperative Time-Reversal Symmetry Breaking Induced by a Magnetic Field in a Quasi-2D d-Wave Superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time-reversal symmetry-breaking spin density wave order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity, penetration depth, and zero-bias conduction in cuprates might be ascribed to this effect.     

Anisotropy in Quasiparticle Density of States in the Vortex State of an Orthorhombic d-Wave Superconductor

The quasiparticle density of states is calculated in the vortex state of an orthorhombic d-wave superconductor as a function of the orientation of the external magnetic field (H ) in the CuO ₂ -plane. Because of the existence of chains oriented along the y-axis in YBCO, its in-plane properties are highly anisotropic and in the superconducting state a predominantly order parameter will also contain a subdominant s-wave admixture allowed by the orthorhombic crystal space group. In a simple anisotropic effective mass model for the band structure and a d + s gap we compute the quasiparticle density of states as a function of the orientation () of H with respect to the a-axis in the CuO ₂ plane. As a function of we find a two fold pattern of behavior with minima at the angles where the Fermi velocity at the nodal momentum is in the direction of the external field. For an untwinned single crystal the resulting anisotropy of the specific heat at low temperatures should be measurable. It is greatly reduced in twinned samples     

Modulations of the Local Pairing Interaction Near Magnetic Impurities in d-Wave Superconductors

The spin-fluctuation based pairing mechanism has proven successful in explaining the pairing symmetries due to Fermi surface nesting of both cuprates and iron-based materials. In this work, we study signatures of a spin-fluctuation mediated pairing at the local scale. Specifically, we focus on magnetic impurities and calculate both the local antiferromagnetism and the resulting modulated pairing interaction. The latter gives rise to distinct local enhancements of the superconducting gap in the immediate vicinity of the impurities. Our results show that Coulomb-driven pairing naturally leads to unusual superconducting gap modulations near disorder potentials.     

RETRACTED ARTICLE: Cooperative Time-Reversal Symmetry Breaking Induced by a Magnetic Field in a Quasi-2D d-Wave Superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time-reversal symmetry-breaking spin density wave order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity, penetration depth, and zero-bias conduction in cuprates might be ascribed to this effect.     

Thermophysical Properties of Aqueous Solutions Near the Equilibrium Freezing Temperature

Measurements of the surface tension, viscosity, and thermal conductivity of LiBr and LiSCN aqueous binary solutions have been performed to determine the thermophysical properties near the equilibrium freezing temperature. A differential capillary-rise method for surface tension and the transient hot-wire method for thermal conductivity were employed. Furthermore, a rotational viscometer was utilized for the measurement of viscosity. Correlation equations for the data of the aqueous binary test solutions as a function of temperature and concentration are presented.     

High Frequency Transport Properties of YBCO: Extrinsic Versus Intrinsic d-Wave Properties

In good superconducting YBCO films, the surface impedance Z(T,ω,B)=Z_int(T,ωB)+Z_res(T,ωB) is dominated for T T _c/2 and B～0 by intrinsic properties, which are difficult to improve. Below T _c/2, Z _res usually dominates over Z, and below 0.9 T _c, Z(T,ω,B) increases with field, both are, up till now, explained by extrinsic properties related to extrinsic and intrinsic surfaces. The latter are named weak or strong links (WSL), into which around B _c1J for ω₀ ^J » ω₀ ^A Josephson fluxons (JF) enter, where B_c1J « B_c1 holds with B_c1 the lower critical field of Abrikosov fluxon (AF) with ω₀ ^A ～ MHz their nucleation or pinning frequency. Below fields ?B _C1 and below the pinning or nucleation frequency ω₀ ^J ～ THz hysteresis losses increase Z=R+iX nonlinearly with r(T,ω)=δ X/δ R～2 with the surface resistance R and the surface reactance X. The nonlinearities decrease toward B _c1J to (small) oscillation of JF yielding r(T,ω) δ ω₀ ^J (T)/ω . Those Z nonlinearities yield harmonics or intermodulation products IMD(T). Below B _c1J new types of nonlinearities relate to d-wave properties of HTS. Either nonlinear Meissner effect (NME) and anomalous Meissner effect (AME) at internal or external surfaces are proposed with r ? 1, observed by harmonic generation and by specific IMD(T, B) dependencies being identified recently. New developments in theory and experiment and procedures to separate extrinsic from intrinsic properties will be analyzed.     

Properties of Photonic Band Gaps in Superconductor Multilayer Structure with Periodically Varying Ambient Temperature

The properties of the reflectance for a superconductor multilayer structure with periodically varying ambient temperature have been theoretically investigated by the transfer matrix method (TMM). From the numerical results, it has been shown that such system has the photonic band gap (PBG) properties of photonic crystals (PCs), so it can also be called superconductor photonic crystals (SPCs). It is found that the locations and bandwidths of PBGs can be modulated by the incident angle. The frequency ranges and central frequencies of PBGs can be tuned by the temperature and thickness of superconductor layer A (higher temperature superconductor layer), respectively. The bandwidths of PBGs can be notably enlarged with increasing the temperature of superconductor layer A. The frequency ranges of PBGs can be controlled by increasing the thickness of superconductor layer A, and the more PBGs appear. The damping coefficient of superconductor and the number of periods have little effect on the bandwidths of PBGs under low-temperature conditions. It is shown that this kind of SPCs has potential applications in filters, microcavities, and fibers, etc.     

Magnetic Properties of a Superconductor with no Inversion Symmetry

We study the magnetic properties of a superconductor in a crystal without symmetry, in particular how the lack of this symmetry exhibits itself. We show that, though the penetration depth itself shows no such effect, for suitable orientation of magnetic field, there is a magnetic field discontinuity at the interface which shows this absence of symmetry. The magnetic field profile of a vortex in the x − y plane is shown to be identical to that of an ordinary anisotropic superconductor to second order in a small parameter . For a vortex along z, there is an induced magnetization along the radial direction.     

First-Principles Study the Electronic and Thermodynamic Properties for CoBi<Subscript>3</Subscript> Superconductor

The electronic, elastic, and thermodynamic properties of CoBi₃ superconductor are investigated by means of first-principles calculations along with the quasi-harmonic Debye model. Our results reveal that the calculated lattice constants are in good agreement with the experimental data. The electronic density of states (DOS) in the vicinity of the Fermi level are dominated by Co- 3d and Bi- 6p states, which are crucial for superconductivity. The elastic constants of CoBi₃ superconductor are calculated, and the bulk modulus, shear modulus, and Young’s modulus have been evaluated. In addition, the ductility behavior is also predicted. Finally, using a quasi-harmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter are obtained.     

Transport Properties of a Single Crystal of Pressure-Induced Superconductor CePtSi2

We synthesized single crystals of pressure-induced superconductor CePtSi₂ by an In-flux method, and measured its electrical resistivity ρ under hydrostatic pressure. At ambient pressure, ρ shows two maxima at T ₁=3.7 K and T ₂=33 K, and a downward bend at the Néel temperature T _N. With increasing pressure T _N decreases and disappears above 1.11 GPa, as reported in a polycrystalline sample. On the other hand, the maximum at T ₁ becomes a shoulder above P _v=1.21 GPa, and begins to increase with increasing pressure, indicating the beginning of a valence crossover.     

Thermodynamic Properties of Copper in a Wide Range of Pressure and Temperature Within the Quasi-Harmonic Approximation

A first-principles calculations have been performed based on density functional theory to study the thermal properties of copper. Calculations have been performed using the pseudo-potential method within the generalized gradient approximation (GGA) and local density approximation. Thermodynamic properties including the bulk modulus, thermal expansion coefficient, and heat capacities at constant volume and constant pressure were calculated as a function of pressure and temperature using three different models based on the quasi-harmonic approximation: the Debye–Slater model, the Debye–Grüneisen model, and the full quasi-harmonic model (that requires the phonon density of states at each calculated volume). Also, empirical energy corrections are applied to the results of the three models. The electronic contributions to the specific heat are calculated and discussed, and it was found that they become important at high temperatures. The calculated values are in good agreement with experimental results. It is found that the full quasi-harmonic model with the GGA approximation provides more accurate estimates in comparison with the other models.     

Vacancy Structure of Crystals at High Temperature. Thermodynamic Properties and Melting

A self-consistent statistical method for the calculation of thermodynamic properties for simple crystals is used to study the formation of vacancies in rare gas crystals (RGC) at high temperature near the melting point. We show that the vacancy formation energy drops dramatically as the melting temperature is approached and that the vacancies repel each other. An analysis of the solid state parameters at high temperature leads to the conclusion that at high temperature structural defects, such as vacancies, dislocations, etc., are centers of relaxation for the excessive potential energy of the interatomic interaction.PACS numbers: 61.72 Bb, 61.72 Ji, 64.70 Dv