The bulk polycrystalline sample FeSe1/2Te1/2 is synthesized by solid state reaction route in an evacuated sealed quartz tube at 750 oC. The presence of superconductivity is confirmed through magnetization/thermoelectric/resistivity studies. It is found that the superconducting transition temperature (Tc) is around 12 K. Heat capacity (Cp) of superconducting FeSe1-xTex exhibited a hump near Tc, instead of well defined Lambda transition. X-ray Photo electron spectroscopy (XPS) studies revealed well defined positions for divalent Fe, Se and Te but with sufficient hybridization of Fe (2p) and Se/Te (3d) core levels. In particular divalent Fe is shifted to higher BE (binding energy) and Se and Te to lower. The situation is similar to that as observed earlier for famous Cu based HTSc (High Tc superconductors), where Cu (3d) orbital hybridizes with O (2p). We also found the satellite peak of Fe at 712.00 eV, which is attributed to charge carrier localization induced by Fe at 2c site.
After an extended introduction, the thesis considers the electronic properties of BSCCO and the recent progress in understanding the electronic structure of this material. The main result of this part of the work is a model of the Green's function that is later used for calculating the two-particle excitation spectrum. Then, the matrix element effects in the photoemission spectra of cuprates are discussed with a focus on the recently discovered anomalous behavior of the ARPES spectra that partially originates from the momentum-dependent photoemission matrix element. The momentum- and excitatio…
We propose a measurement scheme to directly detect odd-frequency superconductivity via time- and angle-resolved photoelectron fluctuation spectroscopy. The scheme includes two consecutive, non-overlapping probe pulses applied to a superconducting sample. The photoemitted electrons are collected in a momentum-resolved fashion. Correlations between signals with opposite momenta are analyzed. Remarkably, these correlations are directly proportional to the absolute square of the time-ordered anomalous Green's function of the superconductor. This setup allows for the direct detection of the "hidden…
In this article, we report magneto-heat capacity analysis of superconducting SnAs, which is characterized through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and magneto-transport measurements. The studied SnAs superconductor evidenced the presence of superconductivity at around 4K, and the same is seen to persist up to an applied field of 250Oe. The bulk nature of superconductivity is determined through AC susceptibility along with heat capacity measurements. Magneto-heat capacity measurements show SnAs to be a fully gapped s wave superconductor. This finding is well supp…
The gap function in unconventional superconductors may vanish at points or lines in momentum space, permitting electronic excitations, termed nodal quasiparticles, to exist at temperatures well below the superconducting transition. In the vortex phase, the presence of nodal quasiparticles should be directly observable through the variation of the heat capacity with the angle between a magnetic field and the location of the zeroes of the gap. The heat capacity of candidate non-magnetic unconventional superconductors Lu(Y)Ni2B2C were found to exhibit fourfold oscillations with field angle, the f…
Recent high-precision measurements employing different experimental techniques have unveiled an anomalous peak in the doping dependence of the London penetration depth which is accompanied by anomalies in the heat capacity in iron-pnictide superconductors at the optimal composition associated with the hidden antiferromagnetic quantum critical point. We argue that finite temperature effects can be a cause of observed features. Specifically we show that quantum critical magnetic fluctuations under superconducting dome can give rise to a nodal-like temperature dependence of both specific heat and…
The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe$_2$. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature $T^{*}$ where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at $T^{*}$ at least under high pressure slightly below…
We consider Aharonov - Bohm effect at normal metal-inhomogeneous LOFF superconducting state transition. It is shown that magnetic flux can increase the transition temperature and AB oscillations can have the double-peak structure at one period. Expressions for fuctuational heat capacity and persistent current are calculated for a thin ring and a cylinder. We also discuss the effect of fluctuations interaction in the nonuniform states in the vicinity of the superconducting transition.
Results of resistivity, Hall effect, magnetoresistance, susceptibility and heat capacity measurements are presented for single crystals of indium-doped tin telluride with compositions Sn$_{.988-x}$In$_x$Te where $0 \leq x \leq 8.4 %$, along with microstructural analysis based on transmission electron microscopy. For small indium concentrations, $x \leq 0.9 %$ the material does not superconduct above 0.3 K, and the transport properties are consistent with simple metallic behavior. For $x \geq 2.7 %$ the material exhibits anomalous low temperature scattering and for $x \geq 6.1 %$ bulk supercond…
Using single crystal neutron and x-ray diffraction, we discovered a charge density wave (CDW) below 320 K, which accounts for the long-sought origin of the heat capacity and resistivity anomalies in UPt2Si2. The modulation wavevector, Qmod, is intriguingly similar to the Fermi surface nesting wavevector of URu2Si2. Qmod shows an unusual temperature dependence, shifting from commensurate to incommensurate position upon cooling and becoming locked at ~ (0.42 0 0) near 180 K. Bulk measurements indicate a cross-over toward a correlated coherent state around the same temperature, suggesting an inte…
A study of the dependence of the heat capacity Cp(alpha) on field angle in LuNi2B2C reveals an anomalous disorder effect. For pure samples, Cp(alpha) exhibits a fourfold variation as the field H < Hc2 is rotated in the [001] plane, with minima along <100> (alpha = 0). A slightly disordered sample, however, develops anomalous secondary minima along <110> for H > 1 T, leading to an 8-fold pattern. The anomalous pattern is discussed in terms of coexisting superconducting gap anisotropy and non-local effects.
Using numerical renormalization group we study thermodynamic properties of a magnetic impurity described by the Anderson impurity model in a superconducting host material described by the BCS Hamiltonian. When the Kondo temperature in the normal state, T_K, is comparable to the critical temperature of the superconducting transition, T_c, the magnetic doublet state may become degenerate with the Kondo singlet state, leading to a ln3 peak in the temperature dependence of the impurity contribution to the entropy. This entropy increase translates into an anomalous feature in the heat capacity whic…
Precise calorimetric measurements have been carried out in the 7 - 300 K temperature range on two ceramic samples of thulium 123 cuprates TmBa2Cu3O6.92 and TmBa2Cu3O6.70. The temperature dependence of the heat capacity was analyzed in the region where the pseudogap state (PGS) takes place. The lattice contribution was subtracted from the experimental data. The PGS component has been obtained by comparing electronic heat capacities of two investigated samples because the PGS contribution for the 6.92 sample is negligible. The anomalous behavior of the electronic heat capacity near the temperatu…
Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Neel temperature rises with small x, and then falls with additional x. Specifically, we find that Neel and structural transitions in BaFe2As2 (TN =Ts= 133 K) increase for x=0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray …
We present a detailed study of the superconducting properties in the beta-phase Mo$_{1-x}$Re$_x$ (x = 0.25 and 0.4) solid solution alloys pursued through magnetization and heat capacity measurements. The temperature dependence of the upper critical field H$_{C2}$(T) in these binary alloys shows a deviation from the prediction of the Werthamer-Helfand-Hohenberg (WHH) theory. The temperature dependence of superfluid density estimated from the variation of lower critical field H$_{C1}$ with temperature, cannot be explained within the framework of a single superconducting energy gap. The heat capa…
We present the evolution of the initial (up to ~ 10 kbar) hydrostatic, pressure dependencies of T_c and of the ambient pressure jump in the heat capacity associated with the superconducting transition as a function of Na - doping in the Ba(1-x)NaxFe2As2 family of iron-based superconductors. For Na concentrations 0.15 <= x <= 0.9, the jump in specific heat at T_c, Delta C_p, follows the Delta C_p ~ T^3 scaling found for most BaFe2As2 - based superconductors. Pressure dependencies are non-monotonic for x = 0.2 and x = 0.24. For other Na concentrations T_c decreases under pressure in almost linea…
The temperature dependence of heat capacity for the samples of 90 K phase of YBa_2Cu_3O_{6+x} with x = 0.85, 0.90 and 0.95 was investigated above T_c. For separating the heat capacity into regular and anomalous contributions the special technique was used. For all the samples the anomalies in intervals 100-200 K (T_{low}), 205-230 K (T_m) and 260-290 K (T_h) were detected. At T = 3T_c the temperature "echo" from superconducting phase transition was discovered. This "echo" is connected with the anomaly T_h, which is believed to mark the rise of pairing carriers of charge without phase coherence…
A perfect topological superconductor can be realized by the simultaneous existence of bulk superconductivity along with topological non-trivial surface states. In this article, we report single crystal growth of superconducting binary compound Pb2Pd. The crystal is well characterized through X-Ray Diffraction (XRD), Selected Area electron diffraction (SAED), Transmission Electron Microscopy (TEM), Field emission Scanning electron Microscopy (FESEM) and X-Ray Photoelectron spectroscopy (XPS). The bulk superconducting nature of the studied crystal is determined through AC susceptibility and magn…
We report the anomalous charge density wave (CDW) state evolution and dome-like superconductivity (SC) in CuIr2Te4-xSex series. Room temperature powder X ray-diffraction (PXRD) results indicate that CuIr2Te4-xSex compounds retain the same structure as the host CuIr2Te4 and the unit cell constants a and c manifest a linear decline with increasing Se content. Magnetization, resistivity and heat capacity results suggest that superconducting transition temperature (Tc) exhibits a weak dome-like variation as substituting Te by Se with the maximum Tc = 2.83 K for x = 0.1 followed by suppression in T…
Single crystals of superconducting OsB_2 [T_c = 2.10(5) K] have been grown using a Cu-B eutectic flux. We confirm that OsB_2 crystallizes in the reported orthorhombic structure (space group Pmmn) at room temperature. Both the normal and superconducting state properties of the crystals are studied using various techniques. Heat capacity versus temperature C(T) measurements yield the normal state electronic specific heat coefficient γ= 1.95(1) mJ/mol K^2 and the Debye temperature Θ_D = 539(2) K. The measured frequencies of Shubnikov-de Haas oscillations are in good agreement with those predicted…
We have carried out high pressure experiment on the pressure-induced superconductor CeIrSi$_3$ without inversion center. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure of the antiferromagnetic state was determined to be $P_{\rm c}$ = 2.25 GPa. The heat capacity $C_{\rm ac}$ shows both antiferromagnetic and superconducting transitions at pressures close to $P_{\rm c}$. The superconducting transition temperature $T_{\rm sc}$ shows a maximum value of 1.6 K around $2.5-2.7$ GPa. At 2.58 GPa, a large heat capacity anomaly was…
