Low temperature specific heat of 12442-type KCa_2Fe_4As_4F_2 single crystals

Low-temperature specific heat(SH) is measured for the 12442-type KCa_2Fe_4As_4F_2 single crystal under different magnetic fields.A clear SH jump with the height of ?C/T|_(T_c)= 130 mJ mol~(-1) K~(-2) is observed at the superconducting transition temperature T_c.It is found that the electronic SH coefficient ?γ(H) quickly increases when the field is in the low-field region below 3T and then considerably slows down the increase with a further increase in the field, which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s). The temperature-dependent SH data indicate the presence of the T~2 term, which supplies further information and supports the picture with a line-nodal gap structure. Moreover, the onset point of the SH transition remains almost unchanged under the field as high as 9 T, which is similar to that observed in cuprates, and places this system in the middle between the BCS limit and the Bose-Einstein condensation.     

Strong Pauli paramagnetic effect in the upper critical field of KCa2Fe4As4F2

Recently, 12442 system of Fe-based superconductors has attracted considerable attention owing to its unique double-Fe As-layer structure. A steep increase in the in-plane upper critical field with cooling has been observed near the superconducting transition temperature, Tc, in KCa2Fe4As4F2 single crystals. Herein, we report a high-field investigation on upper critical field of this material over a wide temperature range, and both out-of-plane(H∥c, Hc2c) and in-plane(H∥ab, Hc2ab ) directions have been measured.A sublinear temperature-dependent behavior is observed for the out-of-plane Hc2c , whereas strong convex curvature with cooling is observed for the in-plane Hc2ab . Such behaviors could not be described by the conventional Werthamer-Helfand-Hohenberg(WHH) model. The data analysis based on the WHH model by considering the spin aspects reveals a large Maki parameter α=9,indicating that the in-plane upper critical field is affected by a very strong Pauli paramagnetic effect.     

Low temperature specific heat in BaFe_(1.9)Ni_(0.1)As_2 single crystals

Low-temperature specific heat was measured on the BaFe1.9Ni0.1As2 single crystals with critical transition temperature Tc = 20.1 K.A clear specific heat jump with the value ΔC/T|Tc ≈ 23 mJ/mol K2 was observed.In addition,a roughly linear magnetic field dependence of the electronic specific heat coefficient Δγ(H) was found in the zero-temperature limit,suggesting that at least one Fermi pocket,probably the hole derivative one,was fully gapped with a small anisotropy in the present sample.A slight curvature of the curve Δγ(H) may suggest a complex gap structure(anisotropic gap or nodes) at other Fermi surfaces.     

Low temperature specific heat of ErAs

The specific heat of a sintered sample of ErAs has been measured from 1.4–6.1 K. A single broad κ-like peak in the data occurs at 3.25K. The entropy associated with the peak is approximately R ln4 suggesting an $\text{S′ =}\text{3}\text{2}$ ground state.     

Low temperature specific heat (zero field and with field) of Fe and Mn-doped MgB2

Polycrystalline samples of MgB₂ superconductor (Mn-doped as well as pristine) were investigated by measurements of the electrical resistivity, magneto-resistance in the temperature range of 4–300 K. All the samples show metallic behaviour. It is observed that the upper critical field slightly decreases with Mn concentration. Specific heat measurements were performed with field as well as without field. For comparison, we also prepared one Fe-doped and specific heat measurements were also carried out on this sample. It is observed that the jump in specific heat decreases with increase in Mn content.     

Low temperature specific heat of Cr-Fe-Si alloys

Low temperature specific heats of Cr-Fe-Si alloys with 3 at. % Si were investigated between 1.4°–4.2°K. The electronic specific heat coefficient γ essentially varies with transition metal electron concentration ( e/a) in the same manner as the Cr-Fe alloys but with the high γ peak slightly shifted to lower e/a. The shift of γ peak suggests transfer of electrons from Si atoms to the 3d magnetic subband of the transition elements.     

Low temperature magnetization of TbAl2 single crystals

Magnetization measurements on TbAl₂ single crystals are reported for 4.2 K in magnetic fields up to 50 kOe applied in the three symmetry directions. We find 〈111〉 as the easy and 〈100〉 as the hard direction of magnetization. No quenching of the magnetic moment is observed. The results are interpreted in terms of the crystalline electric field.     

Phase diagram and transport properties of Sb-doped Ca0.88La0.12Fe2As2 single crystals

The effects of isovalent Sb substitution on the superconducting properties of the Ca_0.88La_0.12Fe₂(As_1-ySb_y)₂ system have been studied through electrical resistivity measurements. It is seen that the antiferromagnetic or structural transition is suppressed with Sb content, and a high-T_c superconducting phase, accompanied by a low-T_c phase, emerges at 0.02 ≤ y ≤ 0.06. In this intermediate-doping regime, normal-state transport shows non-Fermi-liquid-like behaviors with nearly T-linear resistivity above the high-T_c phase. With further Sb doping, this high-T_c phase abruptly vanishes for y > 0.06 and the conventional Fermi liquid is restored, while the low-T_c phase remains robust against Sb impurities. The coincidence of the high-T_c phase and non-Fermi liquid transport behaviors in the intermediate Sb-doping regime suggests that AFM fluctuations play an important role in the observed non-Fermi liquid behaviors, which may be intimately related to the unusual nonbulk high-T_c phase in this system.     

Spectroscopic properties of ZnWO4:Fe single crystals

The incorporation and charge of iron in ZnWO₄:Fecrystals were investigated by absorption spectrometry. The UV bands at 350 nm and the visible band at 460 nm have been found to be related to Fe³⁺ and Fe²⁺ ions respectively. Both ions are mainly in substitutional Zn positions. The infrared absorption at 3445 cm⁻¹ is related to Fe³⁺ OH complexes. The OH⁻ ions compensating the excess charge of Fe³⁺ are probably situated in interstitial positions.     

Low temperature specific heat of Ni-Co and Ni-Fe alloys

Values of the low temperature specific heat of f.c.c. Ni-Co and Ni-Fe alloys have been determined in the 1.2–8 K range with a relative accuracy of 10^-3 and analysed to separate the electron, phonon, magnon and hyperfine terms. Results are in good agreement with former data^5–7 and with theory: Gomes' model⁴ of a d-d tight-binding scattering in the dilute case, Hasegawa's^12,13 CPA calculations are both consistent with experiments.     

Low temperature specific heat of transition metals and alloys

The article reviews experimental results on the low temperature specific heat of the transition metals and their alloys. Particularly discussed are the variations of the electronic part on the basis of a complete compilation of measurements given.     

Low temperature specific heat of Cu3Au

Contrary to a recent letter of Gavignet-Tillard and Hammann, it has been shown that ordering does have a significant effect on the electronic specific heat of Cu₃Au.     

On the anomaly of the specific heat of real KH2PO4 crystals

The splitting of the anomaly revealed in the specific heat of real crystals of potassium dihydrogen phosphate KH₂PO₄ is discussed. It is demonstrated that the observed effect is characteristic of first-order phase transitions occurring near the tricritical point and originates from the specific features inherent in the defect structure of real crystals. A method is proposed for describing the experimentally observed splitting of the specific heat anomaly in the framework of the Landau theory with due regard for the possible formation of metastable states characterized by the polarization aligned antiparallel to the applied electric field in the polar phase.     

Low temperature specific heat of single-domain and polydomain ferroelectric NaNO2

The specific heat of a NaNO₂ sample has been measured between 2 K and 40 K in both single-domain and polydomain states. In this region the specific heat of the single domain sample follows exactly the T³ dependence. A clear excess contribution which in this temperature range has a temperature dependence between T and T² has been detected for the polydomain sample. It is attributed to domain walls.     

Low temperature hysteresis of light reflection from bismuth germanate single crystals

We measured the temperature dependences of light reflection and transmission of bismuth germanate single crystals upon cyclic variation of their temperature in the range of 94–340 K. We revealed an asymmetric temperature hysteresis of reflection, which is accompanied by a change in the Rayleigh scattering. Heating of crystals, in contrast to their cooling, is accompanied by a decrease in the reflection in the range of 100–287 K and near 310 K. We found that reflection minima in the first and second temperature ranges arise as a result of the action of different mechanisms. We assume that temperature changes in the reflection are related to structural phase transitions in the superficial layer.     

Erratum to: Multiple magnetic transitions in single crystals of Ce12Fe57.5As41and La12Fe57.5As41

Commercial computers based on electronic logic devices have brought great changes to the world. However, traditional electronic devices are suffering from numerous technical challenges in their attempts to continue to satisfy Moore's law. Alloptical logic devices, as promising successors to their electronic counterparts, have become a major focus of optics research. In this paper, we provide a review of current all-optical logic devices. The logic gates in these devices, which are described in the first part of the review, are divided into five categories based on the different principles used in their realization. Complex optical devices with various functions and reconfigurable devices are summarized in the next section. In the final part of this paper, we discuss some of the previous works on all-optical integrated chips with specific functions. This review will provide a complete technological roadmap for all-optical devices and aims to be helpful in possible future developments in this growing field.     

Ni-Zr amorphous alloys: Low temperature specific heat and superconductivity

The specific heat (C_p) of the amorphous alloys Ni_100-xZr_x for x = 75, 65, 55 and 35 was measured from 0.8K to 40K and the composition trends of the transition temperature T_c, the enhanced density of states at the Fermi level N_γ(_F) and the Debye temperatures θ_D(0), θ_D(T) established. For the three superconducting compositions (x=75, 65, 55) N_γ(E_F increases rapidly with increasing [Zr] in agreement with the trend in amorphous Cu-Zr alloys. However, for the Zr-Ni alloys the bare density of states $\text{N}{}_0\text{(E}{}_{\mathrm{F}}\text{) =}\text{N}{}_{\mathrm{\gamma }}\text{(E}{}_{\mathrm{F}}\text{)}\text{(1 + λ}{}_{\mathrm{p}}\text{)}$ increases strongly with [Zr] in contrast to the Zr-Cu alloys where it is reported to be almost constant. We conclude that for the Ni-Zr alloys the electron-ion matrix element <I²> decreases with increasing [Zr]. Other results are related to recent photoemission studies of these alloys.     

H+ irradiation effect in Co-doped BaFe2As2 single crystals

We report the suppression of the critical temperature T_c in single crystalline Ba(Fe_1?xCo_x)₂As₂ at under-, optimal-, and over-doping levels by 3 MeV proton irradiation. T_c decreases and residual resistivity increases monotonically with increasing the dose. The low-temperature resistivity does not show the upturn in contrast with the α-particle irradiated NdFeAs(O,F), which suggests that proton irradiation introduces nonmagnetic scattering centers. Critical scattering rates for all samples obtained by three different ways are much higher than that expected in s±-pairing scenario based on inter-band scattering due to antiferro-magnetic spin fluctuations.