Polycrystalline samples with a nominal composition of NdFe1-xRhxAsO (0 <= x <= 0.25) were synthesized using a solid state reaction method. Bulk superconductivity with a maximum Tc = 13 K is observed in the x = 0.1 sample. A temperature-composition phase diagram is established for the NdFe1-xRhxAsO system based on the electrical resistivity and magnetization measurements. A first-order-like transition from an antiferromagnetic state to the superconducting state at a critical Rh-doping point xc = 0.045 is observed in the present phase diagram. The value for the upper critical field Hc2(0) is estimated to be about 26 T for the x = 0.10 sample by using the WHH theory.
We report on the electrical resistivity, thermoelectric power and electronic phase diagram of rhodium-doped NdFeAsO. Rhodium doping suppresses the structural phase transition and spin density wave observed in the undoped material, and superconductivity emerges at x close to 0.05, despite the distortion of FeAs4 tetrahedra induced by the large size difference between Rh and Fe elements. The Tc(x) curve is dome-like, and the highest Tc is reached at x = 0.1, with Tconset = 18K. An upturn of the electrical resistivity above Tc has been observed, with a Kondo like behaviour above Tc and a Fermi-li…
We have observed the evolution of phase diagram and vortex pinning using a single ferromagnet/superconductor bilayer of [Co/Pt]8/Nb through a special demagnetization procedure. It induces a continuous and reversible change of the domain width with equal positive/negative domains enabling the observation of the predicted tunable phase diagram. The tunable domain pattern also systematically affects vortex pinning. We have determined the dependence of the activation energy of vortex pinning on domain width, temperature, and magnetic field.
High-entropy alloy (HEA) is an attracting topic raising in materials science and condensed matter physics. Although several types of superconductors have been discovered in HEAs, the critical currents (Jc) of HEA superconductors remain uncharacterized up to now. Here, we systematically study the current-carrying ability of (TaNb)0.7(HfZrTi)0.5 HEA at various heat treatment conditions. We obtained the high upper critical field and large current carrying ability, which point to optimistic applications. Interestingly, the fishtail or second peak effect was found for the first time in HEA supercon…
The recently discovered high-temperature superconductivity in doped quaternary iron oxypnictides correlates experimentally with a magnetic instability. We have used first-principles calculations to determine a magnetic phase diagram of ReO$_{1-δ}$FeAs (Re=La--Dy) as a function of the doping $δ$, of the FeAs in-plane lattice constant $a$, and of the distance between the Fe and As planes, that is qualitatively consistent with recent experimental findings on the doping, internal (chemical) and external pressure dependence. The existence of a tricritical point (TCP) in the phase diagram suggests n…
Polycrystalline samples of RO1-xFxFeAs (0 < x < 0.25) (R = La, Sm, Gd) were investigated by wavelength-dispersive X-ray spectroscopy (WDX) in the electron microscope to determine the composition of the samples, in particular the fluorine content. It was found that the measured fluorine content can deviate considerably from the initial weight. In the lanthanum compound LaO1-xFxFeAs, we found good agreement mainly for x > 0.05, but for x < 0.05 the fluorine hardly goes into the sample. For the samarium compound we measured less than half the fluorine in the sample as initially weighed at all flu…
We investigate the order - disorder transition line from a Bragg glass to an amorphous vortex glass in the H-T phase diagram of three-dimensional type-II superconductors with account of both pinning-caused and thermal fluctuations of the vortex lattice. Our approach is based on the Lindemann criterion and on results of the collective pinning theory and generalizes previous work of other authors. It is shown that the shapes of the order - disorder transition line and the vortex lattice melting curve are determined only by the Ginzburg number, which characterizes thermal fluctuations, and by a p…
Recently emerging two-dimensional (2D) superconductors in atomically thin layers and at heterogeneous interfaces are attracting growing interest in condensed matter physics. Here, we report that ion-gated ZrNCl surface, exhibiting a dome-shaped phase diagram with a maximum critical temperature of 14.8 kelvin, behaves as a superconductor persisting to the 2D limit. The superconducting thickness estimated from the upper critical fields is ~ 1.8 nanometers, which is thinner than one-unit-cell. The majority of the vortex phase diagram down to 2 kelvin is occupied by a metallic state with a finite …
We establish the superconductor-insulator phase diagram for quasi-one dimensional wires by measuring a large set of MoGe nanowires. This diagram is consistent with the Chakravarty-Schmid-Bulgadaev phase boundary, namely with the critical resistance being equal to R_Q = h/4e^2. We find that transport properties of insulating nanowires exhibit a weak Coulomb blockade behavior.
We investigate thermodynamic phases, including the phase of coexistence of superconductivity and ferromagnetism, the possible phase transitions of first and second order, and the shape of the phase diagram in mean-field approximation for a phenomenological model of spin-triplet ferromagnetic superconductors. The results are discussed in view of application to metallic ferromagnets as UGe$_2$, ZrZn$_2$, URhGe, and Fe.
The behavior of clean layered superconductors in the presence of a finite electric current and in zero-magnetic field behavior is addressed. The structure of the current temperature phase diagram and the properties of each of the four regions will be explained. We will discuss the expected current voltage and resistance characteristics of each region as well as the effects of finite size and weak disorder on the phase diagram. In addition, the reason for which a weakly non-ohmic region exists above the transition temperature will be explained.
Mechanism of unconventional superconductivity is still unknown even if more than 25 years have been passed since the discovery of high-Tc cuprate superconductors by J.G. Bednorz and K. A. Muller. Here, we explore the cuprate phase diagram by electronic Raman spectroscopy and shed light on the superconducting state in hole doped cuprates. Namely, how superconductivity and the critical temperature Tc are impacted by the pseudogap.
Anisotropy, thermal and quantum fluctuations and their dependence on dopant concentration appear to be present in all cuprate superconductors, interwoven with the microscopic mechanisms responsible for superconductivity. Here we review anisotropy, in-plane and c-axis penetration depths, isotope effect and conductivity measurements to reassess the universal behavior of cuprates as revealed by the doping dependence of these phenomena and of the transition temperature.
We investigate the behavior of vortices of multi-component superconductivity, realized in $\rm{MgB_2}$ and Fe-based superconductors, within the framework of Ginzburg-Landau (GL) theory in terms of numerical calculations of the time-dependent GL equations and the variational method. It is revealed that close to the critical point of the composite system the inter-component coupling makes the system behave as a single component superconductivity in most cases. However, when the bare mean-field critical points of the two components coincide with each other, and furthermore the inter-band coupling…
We show that a constriction-type Josephson junction realized by an epitactic thin film of a d-wave superconductor with an appropriate boundary geometry exhibits intrinsic phase differences between 0 and pi depending on geometric parameters and temperature. Based on microscopic Eilenberger theory, we provide a general derivation of the relation between the change of the free energy of the junction and the current-phase relation. From the change of the free energy, we calculate phase diagrams and discuss transitions driven by geometric parameters and temperature.
I show that recent theoretical [1,2] and experimental [3] claims about the possibility of the Berezinskii-Kosterlitz-Thouless (BKT) transition of ``fractional vortices'' in thin films of MgB2 are inconsistent with the parameters of the electron-phonon interaction in MgB2.
A general phenomenological theory is presented for the phase behavior of ferromagnetic superconductors with spin-triplet electron Cooper pairing. The theory accounts in detail for the temperature-pressure phase diagram of ZrZn$_2$, while the main features of the diagram for UGe$_2$ are also described. Quantitative criteria are deduced for the U-type (type I) and Zr-type (type II) unconventional ferromagnetic superconductors with spin-triplet Cooper electron pairing. Some basic properties of quantum phase transitions are also elucidated.
Motivated by the recent discovery of iron-based superconductors, with high critical temperatures and multiple bands crossing the Fermi level, we address the conditions for the presence of chiral superconducting phases configurations in the in-plane magnetic field vs. temperature phase diagram of a quasi-2D frustrated three-band superconductor. Due to Zeeman splitting, the coupled superconducting gap equations present a complex set of solutions. For weak interband couplings, chiral configurations are only attained in a narrow strip of the in-plane magnetic field vs. temperature phase diagram. T…
The phase transition to ferromagnetic order in itinerant ferromagnetic superconductor UGe$_2$ as function of pressure shows change of phase transition order. At low temperature and high pressure the transition is of first order and at pressure of about 1.42 GPa the order changes to second. On the basis of Landau expansion of free energy up to the sixth order in magnetization we calculate the phase diagram taking into account the magneto-elastic interaction as the mechanism responsible for this change. We propose a simple Stoner-like dependence of the Curie temperature on the pressure and prese…
We use the two dimensional extended Hubbard Hamiltonian with the position of the attractive potential as a variable parameter with a BCS type approach to study the interplay between the superconductor transition temperature $T_c$ and hole content for high temperature superconductors. This novel method gives some insight on the range and intensity of the Cooper pair interaction and why different compounds have different values for their measured coherence lengths and it describes well the experimental results of the superconducting phase diagram $T_c \times n$. The calculations may also be used…
Experimental evidence suggests that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state may be realized in the unconventional, heavy-fermion superconductor CeCoIn$_5$. We present a self-consistent calculation of the field versus temperature phase diagram and order parameter structures for the FFLO states of quasi-two-dimensional d-wave superconductors. We calculate the spatially nonuniform order parameter, free energy density, and local density of states for magnetic fields parallel to the superconducting planes. We predict that the lower critical magnetic field transition between the spatially …
We study the model of a d-wave superconductor interacting with finite concentration of Anderson impurities at zero temperature. The interaction between impurity and conduction electrons is taken into account within the large-$N$ approximation. We discuss the obtained phase diagram and its dependence on the main energy scales.
The magnetic field (H) - temperature (T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a band-like shape, the critical temperature Tc of the superconductor in zero field is strongly reduced, and the slope of the upper critical field as a function of T is increased by a factor of 2.4 due to the inhomogeneous stray fields of the domains. Field compensation effects can cause an asymmetric phase boundary with respect to H when the ferromagnet contains bubble domains. For…
The complete set of diagrams for conventional fluctuation corrections to the normal state of an ultraclean superconductor is derived using the functional-integral approach. The standard diagrams which characterize the fluctuation phase of a superconductor, namely, Aslamazov-Larkin, Maki-Thompson, and Density of States, are obtained and proved to be insufficient to produce a gauge-invariant electromagnetic response. An additional diagram is derived, and it is found to be essential for resolving a problematic and underappreciated aspect of the conventional fluctuation formalism. It is only with …
The attempt to describe the bell-shape dependence of the critical temperature of high-$T_{c}$ superconductors on charge carriers density is made. Its linear increase in the region of small densities (underdoped regime) is proposed to explain by the role of the order parameter phase 2D fluctuations which become less at this density growth. The critical temperature suppression in the region of large carrier densities (overdoped regime) is connected with the appearance (because of doping) of the essential damping of long-wave bosons which in the frame of the model proposed define the mechanism of…
We present a self-consistent solution for a model of a d-wave superconductor with finite concen- tration of Anderson impurities at zero temperature using the slave boson method. We show how the phase diagram depends on the strength of interaction between impurity and extended states. For fixed impurity level energy $E_0$ in the Kondo limit there is one superconducting-normal state transition for all impurity concentrations $n$. When $E_0$ is close the Fermi energy there are three such transitions for impurity concentration exceeding certain minimum value $n(Γ_0,E_0)$. If hybridization $Γ_0$ is…
The symmetry approach to the description of the (P,T) phase diagram of ferromagnet superconductors with triplet pairing is developed. Taking into account the recent experimental observations made on UCoGe it is considered the case of a crystal with orthorhombic structure and strong spin-orbital coupling. It is shown that formation of ferromagnet superconducting state from a superconducting state is inevitably accompanied by the first order type transition.
The zero temperature vortex phase diagram for uniaxial anisotropic superconductors placed in an external magnetic field tilted with respect to the axis of anisotropy is studied for parameters typical of BSCCO and YBCO. The exact Gibbs free energy in the London approximation, using a self-energy expression with an anisotropic core cutoff, is minimized numerically, assuming only that the equilibrium vortex state is a vortex-line-lattice with a single vortex line per primitive unit cell. The numerical method is based on simulated annealing and uses a fast convergent series to calculate the energy…
A universal phase diagram for weakly pinned low-T$_c$ type-II superconductors is revisited and extended with new proposals. The low-temperature ``Bragg glass'' phase is argued to transform first into a disordered, glassy phase upon heating. This glassy phase, a continuation of the high-field equilibrium vortex glass phase, then melts at higher temperatures into a liquid. This proposal provides an explanation for the anomalies observed in the peak effect regime of 2H-NbSe$_2$ and several other low-T$_c$ materials which is independent of the microscopic mechanisms of superconductivity in these s…
We study topological phase transitions in three-dimensional odd-parity or noncentrosymmetric superconductors with mirror symmetry when time-reversal symmetry is broken. We construct a generic phase diagram for Weyl superconductivity in the mirror-symmetric superconductors. It is shown that Weyl superconductivity generally emerges between the trivial and the topological crystalline superconductor phases. We demonstrate how a trajectory of the Weyl nodes determines the change in mirror Chern numbers in the topological phase transition. We also discuss a relationship between particle-hole symmetr…
High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportion…
A reduction of the density of states near the Fermi energy in the normal state (pseudogap) of high-temperature oxide superconductors is examined on the basis of the two-dimensional tight-binding model with effective interactions due to antiferromagnetic fluctuations. By using antiferromagnetic correlation lengths which are phenomenologically assumed, the doping dependence of the pseudogap is obtained. The superconducting transition temperature decreases and eventually vanishes due to the pseudogap as the hole concentration is reduced.
We present an resonating valence bond (RVB) theory of superconductivity for the Hubbard--Heisenberg model on an anisotropic triangular lattice. We show that these calculations are consistent with the observed phase diagram of the half-filled layered organic superconductors, such as the beta, beta', kappa and lambda phases of (BEDT-TTF)_2X [bis(ethylenedithio)tetrathiafulvalene] and (BETS)_2X [bis(ethylenedithio)tetraselenafulvalene]. We find a first order transition from a Mott insulator to a d_{x^2-y^2} superconductor with a small superfluid stiffness and a pseudogap with d_{x^2-y^2} symmetry…
In this paper we present calculations of the SO(5) quantum rotor theory of high-T$_{c}$ superconductivity in Zeeman magnetic field. We use the spherical approach for five-component quantum rotors in three-dimensional lattice to obtain formulas for critical lines, free energy, entropy and specific heat and present temperature dependences of these quantities for different values of magnetic field. Our results are in qualitative agreement with relevant experiments on high-T$_{c}$ cuprates.
The phase diagram for the vortex states of high-$T_{\rm c}$ superconductors with point defects in $\vec{B} \parallel c$ axis is drawn by large-scale Monte Carlo simulations. The vortex slush (VS) phase is found between the vortex glass (VG) and vortex liquid (VL) phases. The first-order transition between this novel normal phase and the VL phase is characterized by a sharp jump of the density of dislocations. The first-order transition between the Bragg glass (BG) and VG or VS phases is also clarified. These two transitions are compared with the melting transition between the BG and VL phases.
The electronic phase diagram of PrFeAsO$_{1-x}$F$_{x}$ (0$\leq$x$\leq$0.225) has been determined using synchrotron X-ray powder diffraction, magnetization and resistivity measurements. The structural transition temperature is suppressed from 154 K to $\approx$120 K and the magnetic phase transitions of both iron and praseodymium ions are completely suppressed by x$\approx$0.08 fluorine doping, coinciding with the emergence of superconductivity. The optimal doping is x$\approx$0.15 when T$_{C}$=47 K, while the maximum solubility of fluorine in PrFeAsO$_{1-x}$F$_{x}$ is reached around x=0.22. Th…
We apply a method recently derived based on the extended Hubbard Hamiltonian and the BCS approach to obtain the superconducting critical temperature dependence with carrier density for the HgBaCuO compounds. We show that this procedure can be used to study pressure effect with the assumption that pressure changes the supercondutor gap. The results reproduce well the experimental data for the whole doping regime and the high and low pressure dependence.
A general feature of unconventional superconductors is the existence of a superconducting dome in the phase diagram as a function of carrier concentration. For the simplest iron-based superconductor FeSe (with transition temperature Tc ~ 8 K), its Tc can be greatly enhanced by doping electrons via many routes, even up to 65 K in monolayer FeSe/SiTiO3. However, a clear phase diagram with carrier concentration for FeSe-derived superconductors is still lacking. Here, we report the observation of a series of discrete superconducting phases in FeSe thin flakes by continuously tuning carrier concent…
We propose a new magnetic phase diagram of La2-xSrxCuO4 around a quantum critical point x = 1/9 based on field-cooled magnetization measurements and critical fittings. A new phase boundary Tm2(H) is discovered which buries deeply below the first order vortex melting line in the vortex solid phase. The coupling between superconductivity and antiferromagnetism is found to be attractive below Tm2(H) while repulsive above. The attractive coupling between superconducting order and static antiferromagnetic order provides compelling experimental evidence that the antiferromagnetism microscopically co…
We report on a Monte Carlo study of the lowest-Landau-level limit of the Lawrence-Doniach model for a layered superconductor. We have studied order parameter correlation functions for indications of the broken translational symmetry and the off-diagonal long range order present in the mean-field-theory vortex lattice. Our results are consistent with a single first order phase transition between a low temperature 3D vortex solid phase, with both broken translational symmetry and off-diagonal long range order, and a high temperature vortex liquid phase with no broken symmetries. We construct a u…
The magnetic properties of a quasi two-dimensional superconductor, Sn-metal graphite (MG), are studied using DC and AC magnetic susceptibility. Sn-MG has a unique layered structure where Sn metal layer is sandwiched between adjacent graphene sheets. This compound undergoes a superconducting transition at $T_{c}$ = 3.75 K at $H$ = 0. The $H$-$T$ diagram of Sn-MG is similar to that of a quasi two-dimensional superconductors. The phase boundaries of vortex liquid, vortex glass, and vortex lattice phase merge into a multicritical point located at $T^{*}$ = 3.4 K and $H^{*}$ = 40 Oe. There are two …
Possible field-temperature superconducting (SC) phase diagrams in two-band quasi-two-dimensional materials with a strong paramagnetic pair-breaking (PPB) are considered theoretically. Attention is paid to the case under a magnetic field $perpendicular$ to the SC layers and to essential differences from the counterpart in the ordinary single-band material. It is found by examining the $H_{c2}(T)$ curve and the vortex lattices to be realized close to $H_{c2}$ that a PPB-induced SC phase with a spatial modulation parallel to the field tends to occur more easily than in the single-band case, and t…
Multi-band superconductors in which frustrated inter-band couplings yield a time-reversal-symmetry breaking (TRSB) state are investigated. Stability condition for the TRSB state are derived based on the Bardeen-Cooper-Schrieffer (BCS) theory. With the time-dependent Ginzburg-Landau (GL) method, vortex states are investigated first at the vicinity of critical temperature $T_\text{c}$ where the GL theory is valid, and the results are extended to compose the $H$-$T$ phase diagram. When material parameters satisfy the condition that the nucleation field is slightly larger than the thermodynamic fi…
We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. We calculate how this continuous temperature dependent phase separation process occurs in high critical temperature superconductors (HTSC) using the Cahn-Hilliard approach, originally applied to study alloys. Since the level of phase separation varies for different cuprates, it is possible …
We examine the effects of a phenomenological pseudogap on the T=0 K phase diagram of a high temperature superconductor within a self-consistent model which exhibits a d-wave pairing symmetry. At the mean-field level the presence of a pseudogap in the normal phase of the high temperature superconductor is proved to be essential for the existence of a metallic--like state in the density versus interaction phase diagram. In the small density limit, at high attractive interaction, bosonic--like degrees of freedom are likely to emerge. Our result should be relevant for underdoped high temperature s…
Previous experimental results have shown important differences between iron selenide and arsenide superconductors, which seem to suggest that the high temperature superconductivity in these two subgroups of iron-based family may arise from different electronic ground states. Here, we report the complete phase diagram of a newly synthesized superconducting (SC) system (Li1-xFex)OHFeSe with a similar structure to FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ~127 K. This is the first example to demonstrate such an SDW p…
The phase diagram of the cuprate superconductors continues to pose formidable scientific challenges. While these materials are typically viewed as doped Mott insulators, it is well known that they are Fermi liquids at high hole-dopant concentrations. It was recently demonstrated that at moderate doping, in the pseudogap region of the phase diagram, the charge carriers are also best described as Fermi liquid. Nevertheless, the relationship between the two Fermi-liquid regions and the nature of the strange-metal state at intermediate doping have remained unsolved. Here we show in the case of the…
It is demonstrated qualitatively how a unified explanation of the wide variety of different regions in a typical phase diagram of HTSC can be given in terms of the model of negative-U centers superconductivity. Both the existence of four regions (pseudogap, superconducting, non Fermi-liquid and Fermi-liquid), in the phase diagram and all the transitions between these regions were explained by assuming that negative-U centers exist in HTSC and qualitatively taking into account their thermodynamic and direct quantum-mechanical interaction with ordinary electrons from the valence band. It is foun…
We show that an electronic phase transition described by the Cahn-Hilliard equation has important applications to cuprate superconductors. The simulations of the local charge density and free energy reveal two main features: i) The segregation process creates tiny isolated regions with potential wells where the holes can be bound in single-particle levels. ii) The clustering process also gives rise to an effective two-body pairing interactions and superconducting amplitudes $Δ_{sc}(\vec r)$ at low temperatures. The resulting system resembles a granular superconductor with the resistivity trans…
A model for high-temperature superconductors incorporating antiferromagnetism, d-wave superconductivity, and no double lattice-site occupancy can give energy surfaces exquisitely balanced between antiferromagnetic and superconducting order for specific ranges of doping and temperature. The resulting properties can reconcile a universal cuprate phase diagram with rich inhomogeneity, relate that inhomogeneity to pseudogaps, give a fundamental rationale for giant proximity effects and other emergent behavior, and provide an objective framework for separating essential from peripheral in the super…
Recent theoretical understanding of the vortex phase diagram in real layered type II superconductors is briefly described in both cases with fields perpendicular (B \parallel c) and parallel (B \perp c) to the superconducting layers. The description is based on a high field approximation of the Lawrence-Doniach model and on a vortex-glass ordering in each case. It is argued that, generically, the familiar thermal first order transition at B_m(T) occurs between the vortex liquid region and the so-called vortex slush region, and that, in systems with stronger fluctuation, most of the thermal fir…
We comment on a recent work by Nonomura and Hu who simulated the 3D XY model for a type-II superconductor in an applied magnetic field, in the presence of uncorrelated point randomness. We clarify the nature of the "vortex slush" state that they found, and argue that this state is unstable in the thermodynamic limit.
A critical value in the product of the anisotropy parameter and the magnetic field is observed in interlayer Josephson-vortex systems by extensive Monte Carlo simulations. Below/above this critical value the thermodynamic phase transition between the normal and the superconducting states upon temperature sweeping is first/second order. The origin is the intrinsic pinning effect of the layered structure of high-Tc superconductors.
The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of ${\rm V_{3}Si}$ have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However the magnetic moment-magnetic field isotherms are reversible and exhibit features that formally resemble the pressure-volume isotherms of the liquid-gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagra…
We apply a method based on a BCS-type approach to the extended Hubbard model to deal with the YBa_2Cu_3O_{7-δ} superconductor family under pressure. The parameters of the tight-binding band are taken from experiments, and the coupling strength U and V are estimated from the zero pressure phase diagram Tc X n_h, where n_h is the hole content and Tc the critical temperature. With the assumption that the pressure P modifies the magnitude V of the attractive potential besides n_h, we obtain a general expansion of Tc in terms of the pressure P, as Tc(P)=Tc(n_h(P),V(P)). With this we can distinguish…
We investigate the phase diagram of the electron-doped systems in high-Tc cuprates. We calculate the superconducting transition temperature Tc, the antiferromagnetic transition temperature TN, the NMR relaxation rate 1/T1 with the antiferromagnetic fluctuations in the fluctuation-exchange (FLEX) approximation and with the superconducting fluctuations in the self-consistent t-matrix approximation. Obtained phase diagram has common features as those in the hole-doped systems, including the antiferromagnetic state, the superconducting state and the spin gap phenomenon. Doping-dependences of TN, T…
The high field phase diagram and magnetic properties of CeCoIn_5 below H_c2(0) are examined from the picture regarding the high field and low temperature (HFLT) phase as a possible Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) vortex lattice. Crucial roles of antiferromagnetic (AFM) fluctuations enhanced close to H_c2(0) are stressed. The FFLO vortex lattice with a longitudinal modulation parallel to the field is stabilized compared with those with lateral modulations as a consequence of the presence of AFM fluctuations. Further, an unusual field-induced enhancement of the flux distribution is argue…
Although phase diagrams can be leveraged to investigate high transition temperature (high-$T_c$) superconductivity, the issue has not been discussed thoroughly. In this study, we elucidate the phase diagram of the overdoped side of high-$T_c$ cuprates via systematic anisotropic transport measurements for Pb-doped Bi-2212 single crystals. We demonstrate that the characteristic temperatures of the "weak" pseudogap opening and electronic coherence cross each other at a critical doping level, while those of the "strong" pseudogap merges into that of superconducting fluctuations above the critical …
The renormalization group approach to correlated fermions is used to determine the phase diagram of the oxide cuprates modeled by the t-t' Hubbard model at the Van Hove filling. Spin-dependent interactions give rise to instabilities corresponding to ferromagnetic, antiferromagnetic and d-wave superconducting phases. Antiferromagnetism and d-wave superconductivity arise from the same interactions, and compete in the same region of parameter space.
Phase diagrams of as-grown and O2-annealed FeTe1-xSex determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x \geq 0.15, and weak superconductivity appeared when x \geq 0.1. Beginning at x = 0.5, weak superconductivity was found to evolve into bulk superconductivity. Interestingly, for O2-annealed samples, complete suppression of magnetic order and the occurrence of bulk superconductivity were observed when x \geq 0.1. We found that O2-annealing induces bulk superconductivity for FeTe1-xSex.…
The s+- state in which order parameter has different signs in different bands is a leading candidate for the superconducting state in the iron based superconductors. We investigate a Josephson junction between s and s+- superconductors within microscopic theory. Frustration, caused by interaction of the s-wave gap parameter with the opposite-sign gaps of the s+- superconductor, leads to nontrivial phase diagram. When the partial Josephson coupling energy between the s-wave superconductor and one of the s+- bands dominates, s-wave gap parameter aligns with the order parameter in this band. In t…
