Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSuperconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga)
206
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin and coworkers 40 years ago, is revisited to investigate the low-energy, local vibrations of the A atoms and their influence on the electronic and superconducting properties of the compound. Polycrystalline samples with A = Al, Ga, Y, and La are studied through resistivity and heat capacity measurements. Weak-coupling BCS superconductivity is observed below Tc = 1.49, 1.66, and 0.69 K for Ax = Al0.3, Ga0.2, and Y, respectively, but not above 0.4 K for Ax = La. Low-energy modes are detected only for A = Al and Ga, which are approximately described by the Einstein model with Einstein temperatures of 24 and 8 K, respectively. A weak but significant coupling between the low-energy modes, which are almost identical to those called rattling in recent study, and conduction electrons manifests itself as anomalous enhancement in resistivity at around low temperatures corresponding to the Einstein temperatures.
rate research
Read More
High-entropy alloys (HEAs) are at the focus of current research for their diverse properties, including superconductivity and structural polymorphism. However, the polymorphic transition has been observed only in nonsuperconducting HEAs and mostly under high pressure. Here we report the discovery of superconductivity and temperature-driven polymorphism in the (V$_{0.5}$Nb$_{0.5}$)$_{3-x}$Mo$_{x}$Al$_{0.5}$Ga$_{0.5}$ (0.2 $leq$ $x$ $leq$ 1.4) HEAs. It is found that the as-cast HEA is of a single body-centered cubic (bcc) structure for $x$ = 0.2 and a mixture of the bcc and A15 structures for higher $x$ values. Upon annealing, the bcc structure undergoes a polymorphic transformation to the A15 one and all HEAs exhibits bulk superconductivity. For $x$ = 0.2, whereas the bcc polymorph is not superconducting down to 1.8 K, the A15 polymorph has a superconducting transition temperature $T_{rm c}$ of 10.2 K and an estimated zero-temperature upper critical field $B_{rm c2}$(0) of 20.1 T, both of which are the highest among HEA superconductors. With increasing Mo content $x$, both $T_{rm c}$ and $B_{rm c2}$(0) of the A15-type HEAs decrease, yet the large ratio of $B_{rm c2}$(0)/$T_{rm c}$ signifies a disorder-induced enhancement of the upper critical field over a wide $x$ range. The decrease in $T_{rm c}$ is attributed to the decrease in both the electronic specific-heat coefficient and electron-phonon coupling strength. Furthermore, the valence electron count dependence of $T_{rm c}$, which is different from both the binary A15 and other structurally different HEA superconductors, suggests that $T_{rm c}$ may be increased further by reducing the number of valence electrons. Our results not only uncover HEA superconductors of a new structural type, but also provide the first example of polymorphism dependent superconductivity in HEAs.
Ni/Ga bilayers are a versatile playground for exploring the competition of the strongly antagonistic ferromagnetic and superconducting phases. Systematically characterizing this competitions impact on highly ballistic Al/Al$_2 $O$_3 $/Ni/Ga junctions transport properties from both the experimental and theoretical viewpoints, we identify novel conductance peak structures, which are caused by superconducting triplet pairings at the Ni/Ga interface, and which are widely adjustable through the Ni-Ga thickness ratio. We demonstrate that these conductance anomalies persist even in the presence of an in-plane magnetic field, which provides -- together with the detection of the paramagnetic Meissner effect in Ga -- the clear experimental evidence that the observed conductance features serve indeed as the triplet pairings unique transport fingerprints. Our work demonstrates that Ni/Ga bilayers have a strong potential for superconducting spintronics applications, in particular for triplet-pairing engineering.
In this paper, potential two-gap superconductivity in Mo$_8$Ga$_{41}$ is addressed in detail by means of thermodynamic and spectroscopic measurements. Combination of highly sensitive ac-calorimetry and scanning tunneling spectroscopy (STS), as bulk and surface sensitive probes, utilized on the same piece of crystal reveals that there is only one intrinsic gap in the system featuring strong electron-phonon coupling. Traces of multiple superconducting phases seen by STS and also in the heat capacity measured in high magnetic fields on a high-quality and seemingly single-phase crystal might mimic the multigap superconductivity of Mo$_8$Ga$_{41}$ suggested recently in several studies.
We report a $^{71}$Ga nuclear-quadrupole-resonance (NQR) study on the characteristics of superconductivity in noncentrosymmetric Ir$_2$Ga$_9$ at zero field (H=0). The $^{71}$Ga-NQR measurements have revealed that $1/T_1$ has the clear coherence peak just below $T_{rm c}$, and decreases exponentially upon further cooling in Ir$_2$Ga$_9$. From these results, Ir$_2$Ga$_9$ is concluded to be the conventional s-wave superconductor. Despite the lack of spatial centrosymmetry, there are no evidence for unconventional superconducting state ascribed to ASOC in Ir$_2$Ga$_9$.
(Abridged abstract) Alloyed MgB2 differs from pure forms in that diffusion is needed to distribute the alloying elements homogeneously. Williamson-Hall analyses of x-ray diffraction peaks showed that Mg1-xAlxB2 samples made by a typical reaction A had higher crystalline strain than when thoroughly annealed by reaction B. The strain and other analyses indicate that reaction A produced substantial Al gradients across the individual grains while reaction B did not. The gredients skew the apparent superconducting behavior: properties appeared to be distinct when plotted vs. x (e.g. two Tc(x) curves), but all of the data merged when analyzed in terms of the unit cell volume v (e.g. one Tc(v) curve). Since v is derived from x-ray diffraction, it captures the average Al content actually present inside the grains and better reflects the behavior intrinsic to the addition of Al. These analyses show that it is important to coordinate structural and property characterizations to remove artifacts of composition gradients and uncover the intrinsic trends. Because the standard characterizations of the superconducting properties above gave no clear indication that the two sample sets had different homogeneity, the structural information was vital to make a correct assessment of the effects of Al doping on superconductivity.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
