Raising the superconducting Tc of gallium: In situ characterization of the transformation of α -Ga into β -Ga

Abstract

Gallium (Ga) displays several metastable phases. Superconductivity is strongly enhanced in the metastable β-Ga with a critical temperature Tc = 6.04(5) K, while stable α-Ga has a much lower Tc < 1.2 K. Here we use a membrane-based nanocalorimeter to initiate the transition from α-Ga to β-Ga on demand, as well as study the specific heat of the two phases on one and the same sample. The in-situ transformation is initiated by bringing the temperature to about 10 K above the melting temperature of α-Ga. After such treatment, the liquid supercools down to 232 K, where β-Ga solidifies. We find that β-Ga is a strong-coupling type-I superconductor with ∆(0)/kBTc = 2.00(5) and a Sommerfeld coefficient γn = 1.53(4) mJ/molK 2 , 2.55 times higher than that in the α phase. The results allow a detailed comparison of fundamental thermodynamic properties between the two phases.

A perspective on conventional high-temperature superconductors at high pressure: Methods and materials

“…• Metastability: An ample number of examples have been recently reported, in which metastability adds an extra dimension in the phase diagram of several systems: elemental phosphorus [74]; barium [91] and gallium under pressure [496]; tinnitrides under pressure [497]; PdH [442]; PH 2 [168]; LaH x [3,181]; metastable charge-density-wave superconductors [498] as well as oxides [499,500]. These works showed that controlled heating and cooling cycles or pressure-hysteresis cycles permit to selectively stabilize different metastable phases.…”

A bound on the superconducting transition temperature

“…At ambient pressure, the highest temperature superconductivity of a clearly conventional sort (with w 1) is MgB 2 , which does not appear in the figure because it has such a high Θ D = 884 K, and thus has T c /Θ D = 0.04 [11]. This suggests that if a way can be found to increase the value of λ in this material, it Data on the various materials were obtained from the following references: elements from [3,4]; A-15s from [5], Skutterudites from [6,7,8]; CaC 6 from [9]; BKBO from [10]. In most cases estimates of Θ D were obtained from low-temperature specific-heat measurements, in others it was estimated from e.g.…”

Thermal Effects on the Crystallization Kinetics, and Interfacial Adhesion of Single‐Crystal Phase‐Change Gallium

“…Because of its cost effectiveness and accessibility, Ga is an interesting material in phase transition (PT) studies. Ga also shows a promising potential in monatomic PC memory devices for data storage, superconductivity, metamaterial, and reversible adhesion . To reverse the supercooling of liquid Ga, external perturbations are applied to induce nucleation and subsequent crystal growth .…”

“…Ga also shows a promising potential in monatomic PC memory devices for data storage, superconductivity, metamaterial, and reversible adhesion . To reverse the supercooling of liquid Ga, external perturbations are applied to induce nucleation and subsequent crystal growth . Even though molecular liquids are promising candidates to study phase transformation at ambient pressures and moderate temperatures, it is rather difficult to practically monitor the exact site of nucleation, since nucleation is a stochastic process …”

“…The crystallization was only achieved by seeded growth. The driving force of crystallization (the Gibbs free energy difference between the crystalline phase and the supercooled liquid, Δ G ) is related to the latent heat of melting Δ H m and the melting temperature T m by the equation: Δ where Δ T is the supercooling temperature ( T m − T ) and Δ H m = 5585 J mol −1 for Ga . The used seeding Ga crystal had surface irregularities and sharp wedges of the lamella morphology (Figure S4, Supporting Information).…”