Low-temperature Penetration Research Articles

Antitumor effects of plasma‑activated solution on a murine melanoma model in vivo and in vitro.

Melanoma is a common malignant skin tumor with highly invasive features and a high metastasis rate that can be difficult to treat clinically. Large-scale resection of primary cutaneous melanoma is often used to avoid postoperative recurrence. For advanced patients, radiotherapy, targeted therapy and immunotherapy are often needed. Low-temperature plasma has been proved to have significant antitumor effects on a variety of cancer cell lines cultured in vitro. The main limitation of direct low-temperature plasma treatment is that it has weak penetration ability and can only treat superficial lesions. In recent years, research on low-temperature plasma-activated solution has revealed that it also have good antitumor effects and low-temperature plasma penetration depth problems can be solved by local injection. The present study revealed that low-temperature plasma-activated phosphate buffer solution exhibited good antitumor effects and biosafety against melanoma in vitro and in vivo. It demonstrated that low-temperature plasma-activated solution has antitumor effects due to its regulation of intracellular redox, destruction of mitochondrial function and DNA damage. In vivo experiments demonstrated that treatment with low-temperature plasma-activated solution not only exhibited antitumor effects but also caused no significant damage to hematopoietic function or liver and kidney functions in mice. All these results demonstrated that low-temperature plasma-activated solution represent a promising antitumor treatment strategy.

Performance evaluation of lightweight insulating plaster for enhancing the fire endurance of high strength structural concrete

Structural concrete is a widely used building material due to its versatile characteristics including higher compressive strength and longevity. However, when exposed to fire, concrete experiences faster degradation in its mechanical properties and is also susceptible to spalling. To overcome this problem, the possibility of lightweight plaster application on High Strength Concrete (HSC) is explored in the presented investigation. Insulation plasters, namely Sand Plaster (SP), Gypsum Perlite Plaster (GPP), and Gypsum Mineral Wool Plaster (GMP) were developed. This investigation evaluates the compressive strength, bond strength, and shear strength of concrete which is exposed to the standard fire temperature. Varying cooling conditions which involved air and water were adopted to cool the concrete specimens after the elevated temperature test. Further, the damaged concrete and the plaster were examined to analyse the physical changes. Analysis of the study reveals that more number of denser surface cracks and higher mass loss was observed for reference and SP specimens. Temperature penetration at the core of cube, bond, and shear specimens is less for the GPP and GMP specimens when compared with the SP specimens. At higher temperatures (986 °C), the reference and SP specimens show a lower bond and shear strength with higher slip values. Specimens insulated with GPP and GMP exhibited a low-temperature penetration at the core portion. Also, the results of the study reported the higher residual compressive, bond, and shear strength compared to other specimens.

Surface barriers and field direction dependent vortex phase diagrams of YBa2Cu3−xAlxOδ for H c

We report the observation of an unusual field direction dependent second magnetisation peak (SMP) anomaly at very low fields, close to the field of full penetration Hp, in an aluminium-doped single crystal of YBa2Cu3−xAlxOδ, for H c. Such an anomaly is observed at different field values in the field ramp-up direction (H) compared to the field-down direction (H), and it is also found to persist to different temperatures. For the field-up direction, it is observed in the range of 8 K to 30 K (upper range extendible to 40 K depending on the crystal), while for the field-down direction, it is observed between 8 K to 65 K (upper range extendible to 70 K depending on the crystal). The temperature dependence of the fields of full penetration Hp, the onset field of the SMP anomaly, as well as the central magnetisation peak, seem to be affected by surface barriers at low temperatures, where they are seen to rise anomalously. An exponential fit to the low temperature penetration field and central magnetisation peak width, as well as an asymmetric magnetisation towards the irreversibility field, illustrate the effect of surface barriers at low temperatures. At higher temperatures, the onset field of the SMP anomaly is described well by a dislocation mediated order–disorder transition. The temperature dependence of the peak field of the second magnetisation anomaly, however, does not seem to be affected by the surface barrier and is well described by a power law. An oxygen deficient aluminium cluster model is used to explain the differences in the SMP anomalies in the two quadrants. Two vortex phase diagrams, one for each field direction, have been made describing the various phases.

Nodeless superconductivity and time-reversal symmetry breaking in the noncentrosymmetric superconductor Re24Ti5

The noncentrosymmetric superconductor Re$_{24}$Ti$_{5}$, a time-reversal symmetry (TRS) breaking candidate with $T_c = 6$\,K, was studied by means of muon-spin rotation/relaxation ($\mu$SR) and tunnel-diode oscillator (TDO) techniques. At a macroscopic level, its bulk superconductivity was investigated via electrical resistivity, magnetic susceptibility, and heat capacity measurements. The low-temperature penetration depth, superfluid density and electronic heat capacity all evidence an $s$-wave coupling with an enhanced superconducting gap. The spontaneous magnetic fields revealed by zero-field $\mu$SR below $T_c$ indicate a time-reversal symmetry breaking and thus the unconventional nature of superconductivity in Re$_{24}$Ti$_{5}$. The concomitant occurrence of TRS breaking also in the isostructural Re$_6$(Zr,Hf) compounds, hints at its common origin in this superconducting family and that an enhanced spin-orbital coupling does not affect pairing symmetry.

Structure and performance evaluation on aged SBS modified bitumen with bi- or tri-epoxy reactive rejuvenating system

To cater for the concept of global green development, it is of importance, in the bituminous road domain, to achieve the objective of the high-quality rejuvenation of waste bitumen. This paper investigates physical properties, rheological properties, morphology and molecular structure of rejuvenated SBS modified bitumen (SMB) with 1, 4-butanediol diglycidyl ether (BUDGE) or trimethylolpropane triglycidyl ether (TMPGE). The results of physical properties indicate that BUDGE and TMPGE can both improve the low-temperature ductility and penetration of aged SMB, and by contrast, BUDGE can make the aged SMB more flexible at low temperature. From the rheological properties, BUDGE or TMPGE can help restore the crack resistance at low temperature and somewhat decrease the rutting resistance at high temperature, which relies on the reduction of fatigue factor and rutting factor of aged SMB. FTIR spectra and fluorescence images show that the original structure of SBS can be partly rebuilt through the chemical reaction between the terminal groups on BUDGE or TMPGE and the oxygen-containing reactive groups on degraded SBS.

Anomalous scaling of the penetration depth in nodal superconductors

Recent findings of anomalous super-linear scaling of low temperature ($T$) penetration depth (PD) in several nodal superconductors near putative quantum critical points suggest that the low temperature PD can be a useful probe of quantum critical fluctuations in a superconductor. On the other hand, cuprates which are poster child nodal superconductors have not shown any such anomalous scaling of PD, despite growing evidence of quantum critical points. Then it is natural to ask when and how can quantum critical fluctuations cause anomalous scaling of PD? Carrying out the renormalization group calculation for the problem of two dimensional superconductors with point nodes, we show that quantum critical fluctuations associated with point group symmetry reduction result in non-universal logarithmic corrections to the $T$-dependence of the PD. The resulting apparent power law depends on the bare velocity anisotropy ratio. We then compare our results to data sets from two distinct nodal superconductors: YBa$_2$Cu$_3$O$_{6.95}$ and CeCoIn$_5$. Considering all symmetry-lowering possibilities of the point group of interest, $C_{4v}$, we find our results to be remarkably consistent with YBa$_2$Cu$_3$O$_{6.95}$ being near vertical nematic QCP, and CeCoIn$_5$ being near diagonal nematic QCP. Our results motivate search for diagonal nematic fluctuations in CeCoIn$_5$.

Disorder-induced topological change of the superconducting gap structure in iron pnictides.

In superconductors with unconventional pairing mechanisms, the energy gap in the excitation spectrum often has nodes, which allow quasiparticle excitations at low energies. In many cases, such as in d-wave cuprate superconductors, the position and topology of nodes are imposed by the symmetry, and thus the presence of gapless excitations is protected against disorder. Here we report on the observation of distinct changes in the gap structure of iron-pnictide superconductors with increasing impurity scattering. By the successive introduction of nonmagnetic point defects into BaFe2(As(1-x)P(x))(2) crystals via electron irradiation, we find from the low-temperature penetration depth measurements that the nodal state changes to a nodeless state with fully gapped excitations. Moreover, under further irradiation the gapped state evolves into another gapless state, providing bulk evidence of unconventional sign-changing s-wave superconductivity. This demonstrates that the topology of the superconducting gap can be controlled by disorder, which is a strikingly unique feature of iron pnictides.

Superconducting properties of indium-doped topological crystalline insulator SnTe

We report on the superconducting properties of indium-doped SnTe. SnTe has recently been explored as a topological crystalline insulator. Single crystals of Sn0.5In0.5Te have been synthesized by a modified Bridgman method. Resistivity measurement performed in the range 1.6–300 K shows a metallic normal state with onset of superconducting transition at . Bulk superconductivity has also been confirmed by DC magnetization, AC susceptibility and rf penetration depth measurements. Zero-temperature upper critical field, lower critical field, coherence length, and penetration depth are estimated to be 1.6 T, 1 mT, 143.5 Å and 853 nm, respectively. The temperature dependence of the low-temperature penetration depth indicates S-wave fully gapped characteristics with BCS (Bardeen-Cooper-Schrieffer) gap . Hall and Seebeck coefficient measurements confirm the dominance of hole conduction with possible phonon-drag effects around . Resistive transition studied under applied magnetic field shows thermally activated flux flow behaviour.

Anisotropic superconductivity in noncentrosymmetric BiPd

We report measurements of London penetration depth $\lambda(T)$ for the noncentrosymmetric superconductor BiPd by using a tunnel diode oscillator. Pronounced anisotropic behavior is observed in the low-temperature penetration depth; the in-plane penetration depth $\lambda_{ac}(T)$ follows an exponential decrease, but the interplane penetration depth $\lambda_b(T)$ shows power-law-type behavior. The superfluid density $\rho_s(T)$, converted from the penetration depth $\lambda(T)$, is best fitted by an anisotropic two-band BCS model. We argue that such a complex order parameter is attributed to the admixture of spin-singlet and spin-triplet pairing states as a result of antisymmetric spin-orbit coupling in BiPd.

Effect of heavy-ion irradiation on London penetration depth in overdoped Ba(Fe1−xCox)2As2

Irradiation with 1.4 GeV $^{208}$Pb ions was used to induce artificial disorder in single crystals of iron-arsenide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and to study its effect on the temperature-dependent London penetration depth and transport properties. Study was undertaken on overdoped single crystals with $x$=0.108 and $x$=0.127 characterized by notable modulation of the superconducting gap. Irradiation with doses 2.22$\times10^{11}$$\textit{d}$/cm$^2$ and 2.4$\times10^{11}$$\textit{d}$/cm$^2$, corresponding to the matching fields of $B_{\phi} = $6 T and 6.5 T, respectively, suppresses the superconducting $T_c$ by approximately 0.3 to 1 K. The variation of the low-temperature penetration depth in both pristine and irradiated samples is well described by the power-law, $\Delta \lambda (T)=AT^n$. Irradiation increases the magnitude of the pre-factor $A$ and decreases the exponent $n$, similar to the effect of irradiation in optimally doped samples. This finding supports universal $s_{\pm}$ pairing in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ compounds for the whole Co doping range.

A study of London penetration depth for the non-centrosymmetric superconductor LaNiC2

We study the superconducting properties of the polycrystalline LaNiC2 by means of measuring the electrical resistivity ρ(T), magnetization M(T) and London penetration depth Δλ(T). The superconducting order parameter is analyzed in terms of the low temperature penetration depth Δλ(T) and the corresponding superfluid density ρs(T), and the results show strong evidence of two-gap Bardeen-Cooper-Schrieffer (BCS) superconductivity for LaNiC2.

Penetration depth of MgB2 measured using Josephson junctions and SQUIDs

The penetration depth of MgB2 was measured using two methods of different mechanisms. The first method used MgB2 Josephson junctions and the magnetic field dependence of the junction critical current. The second method deduced the penetration depth from the inductance of a MgB2 microstrip used to modulate the voltage of a MgB2 DC SQUID. The two methods showed a consistent value of the low-temperature penetration depth for MgB2 to be about 40 nm. Both the small penetration depth value and its temperature dependence are in agreement with a microscopic theory for MgB2 in the clean limit.

Quasiparticle Scattering Induced by Charge Doping of Iron-Pnictide Superconductors Probed by Collective Vortex Pinning

Charge doping of iron-pnictide superconductors leads to collective pinning of flux vortices, whereas isovalent doping does not. Moreover, flux pinning in the charge-doped compounds is consistently described by the mean-free path fluctuations introduced by the dopant atoms, allowing for the extraction of the elastic quasiparticle scattering rate. The absence of scattering by dopant atoms in isovalently doped BaFe2(As(1-x)P(x))(2) is consistent with the observation of a linear temperature dependence of the low-temperature penetration depth in this material.

Study on the Freeze-to-Crack Test of Asphalt Modified by Waste-PE in Packing

The purposes of this study are to modify asphalt by retrieved waste-PE in packing (WPP) and to investigate the low temperature properties of the modified asphalt. The traditional testing methods such as low temperature ductility, low temperature penetration degree, penetration or Fraass breaking point think that PE can not improve the low temperature properties of asphalt effectively, while this study adopts a new method to test the low temperature properties of WPP modified asphalt through the freeze-to-crack test. The result indicated that, after the modification, the low temperature properties of asphalt are improved, which coincides with the fact. And the improvement of the low temperature properties can be explained by the function of Shear yield and crack pinning.

S-Wave Spin-Triplet Order in Superconductors without Inversion Symmetry:Li2Pd3BandLi2Pt3B

We investigate the order parameter of noncentrosymmetric superconductors Li2Pd3B and Li2Pt3B via the behavior of the penetration depth lambda(T). The low-temperature penetration depth shows BCS-like behavior in Li2Pd3B, while in Li2Pt3B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-singlet and spin-triplet pairing, are responsible for this behavior. The triplet contribution is weak in Li2Pd3B, leading to a wholly open but anisotropic gap. The significantly larger spin-orbit coupling in Li2Pt3B allows the spin-triplet component to be larger in Li2Pt3B, producing line nodes in the energy gap as evidenced by the linear temperature dependence of lambda(T). The experimental data are in quantitative agreement with theory.

Correlation of structural and linear electromagnetic properties ofhigh-Tc thin films with their nonlinear microwave performance

A comprehensive study of the correlation between various structural(Δω°,c-axis),electrical (Tc,ΔT) and linearmicrowave properties (Rs(T0), λ(T0) andσ1(T0)) of epitaxial YBCOthin films on MgO and LaAlO3 substrates, and also their nonlinear microwave properties(Hrf*,d Rs/d Hrf,Hrf _ TOI2,m-slopeand Hrf _ 30 dB2) has been performed. It was found that among the numerous parameters from the first group, thenonlinear microwave properties appear to correlate well only with the low-temperature penetration depthλ(T0), residual quasiparticleconductivity σ1(T0) and the c-axis lattice parameter. Here, among those three parametersthe best correlation of the nonlinear properties is observed withλ(T0). The correlation of the other parameters from the first group with the nonlinear microwaveperformance of the films is either not evident, because of the wide spread of the data, or absent.There is also seen a correlation within the group of linear microwave parameters (such asRs(T0),σ1(T0) and λ(T0)) and partial correlation within the group of the nonlinear parameters (such asHrf*,d Rs/d Hrf and Hrf _ TOI2). However, all the aforementioned correlations seem to be dependent on many conditions(such as film growth technique and substrate), and are by no means quantitative, but onlyqualitative.

Low-energy quasiparticles in high- T c cuprates

The aim of this review is to summarize existing experimental investigations on the nature of the low-energy quasiparticle excitations in high- T c cuprates, and to examine critically recent claims of consistency between the experimentally determined low-temperature thermodynamic and transport properties in certain cuprates and theoretical predictions based on standard perturbation theory for a BCS d-wave superconductor. Measurements of the low-temperature specific heat, thermal conductivity, microwave conductivity, penetration depth and scanning tunnelling microscopy are described, both in the Meissner state and in the mixed state. These results are then compared with the predictions of quasi-classical theory of a d-wave BCS superconductor and the self-consistent T-matrix approximation for both a single impurity and a finite impurity concentration. Detailed inspection reveals that significant discrepancies still exist between experiment and theory, with important implications for the development of a coherent model, perhaps beyond standard perturbation theory. Finally, I discuss how considerations of the possible effects of band structure, anisotropic scattering and low carrier concentration in the underdoped region of the cuprate phase diagram might reconcile some of the discrepancies that have emerged.

Quasiparticles in d-wave superconductors within density functional theory

We present a semiphenomenological approach to calculating thequasiparticle spectra of high-temperature superconductors. It isbased on a particularly efficient parametrization of the effectiveelectron-electron interaction afforded by the density functionaltheory for superconductors and atight-binding linearized-muffin-tin-orbital scheme for solving thecorresponding Kohn-Sham-Bogoliubov-de Gennes equations. We applythis methodology to YBa2Cu3O7-δ (YBCO) andillustrate its potential by investigating a number of site- andorbital-specific, but otherwise phenomenological, models of pairingin quantitative detail. We compare our results for the anisotropyof the gap function on the Fermi surface with those deduced fromphotoemission experiments on single crystals of YBCO. Also, the low-temperature specific heat and penetration depth are calculated andcompared with measurements. We investigate the doping dependence ofthe superconducting gap, transition temperature, Tc, andpenetration depth. We present new evidence that the Van Hove-likescenario is an essential feature of superconductivity in the cupratesuperconductors. Since our description of pairing isphenomenological, we shed new light on the physical mechanism ofpairing only indirectly and conclude, provisionally, that thedominant pairing interaction operates between electrons of oppositespins, on nearest-neighbour Cu sites in dx2-y2 orbitals.

Penetration depth measurements inMgB2:Evidence for unconventional superconductivity

We have measured the magnetic penetration depth of the recently discovered binary superconductor MgB_2 using muon spin rotation and low field $ac$-susceptibility. From the damping of the muon precession signal we find the penetration depth at zero temperature is about 85nm. The low temperature penetration depth shows a quadratic temperature dependence, indicating the presence of nodes in the superconducting energy gap.

Angular dependence of the penetration depth in unconventional superconductors

We examine the Meissner state nonlinear electrodynamic effects on the field and angular dependence of the low-temperature penetration depth \ensuremath{\lambda} of superconductors in several kinds of unconventional pairing states, with nodes or deep minima (``quasinodes'') in the energy gap. Our calculations are prompted by the fact that, for typical unconventional superconducting material parameters, the predicted size of these effects for \ensuremath{\lambda} exceeds the available experimental precision for this quantity by a much larger factor than for others. We obtain expressions for the nonlinear component of the penetration depth \ensuremath{\Delta}\ensuremath{\lambda} for different two- and three-dimensional nodal or quasinodal structures. Each case has a characteristic signature as to its dependence on the size and orientation of the applied magnetic field. This shows that \ensuremath{\Delta}\ensuremath{\lambda} measurements can be used to elucidate the nodal or quasinodal structure of the energy gap. For nodal lines we find that \ensuremath{\Delta}\ensuremath{\lambda} is linear in the applied field, while the dependence is quadratic for point nodes. For layered materials with ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\mathrm{\ensuremath{\delta}}}$ type anisotropy, our results for the angular dependence of \ensuremath{\Delta}\ensuremath{\lambda} differ greatly from those for tetragonal materials and are in agreement with experiment. For the two- and three-dimensional quasinodal cases, \ensuremath{\Delta}\ensuremath{\lambda} is no longer proportional to a power of the field and the field and angular dependences are not separable, with a suppression of the overall signal as the node is filled in.