Magnetic flux trapping in hydrogen-rich high-temperature superconductors

Abstract

Recent discoveries of superconductivity in various hydrides at high pressures have shown that a critical temperature of superconductivity can reach near-room-temperature values. However, experimental studies are limited by high-pressure conditions, and electrical transport measurements have been the primary technique for detecting superconductivity in hydrides. Here we implement a non-conventional protocol for the magnetic measurements of superconductors in a SQUID magnetometer and probe the trapped magnetic flux in two near-room-temperature superconductors H3S and LaH10 at high pressures. Contrary to traditional magnetic susceptibility measurements, the magnetic response from the trapped flux is almost unaffected by the background signal of the diamond anvil cell due to the absence of external magnetic fields. The behaviour of the trapped flux generated under zero-field-cooled and field-cooled conditions proves the existence of superconductivity in these materials. We reveal that the absence of a pronounced Meissner effect is associated with the very strong pinning of vortices inside the samples. This approach can also be a tool for studying multiphase samples or samples that have a low superconducting fraction at ambient pressure.

Trapped flux in pure and Mn-substituted CaKFe4As4and MgB2superconducting single crystals

“…To summarize, in agreement with the statements in [14], trapped flux measurements are indeed a very powerful experimental approach to evaluate basic superconducting properties, in particular for the case of small samples or samples contained in a pressure cell or non-superconducting matrix, since the measurements are performed in nominally zero applied field, thus almost canceling the background signal associated with the pressure cell or the matrix.…”

“…Last but not least, in many aspects our results for these known, single crystalline, superconductors that were well shaped and measured at ambient pressure are similar to those for superhydrides at megabar pressures [14] and as such hopefully serve as a baseline and help to clear the doubts in the interpretation of the measurements in [14].…”

“…In the discussion surrounding superconductivity in hydrides, it was suggested that the measurement of trapped magnetic flux '...should establish definitively that these materials are indeed high temperature superconductors' [13]. Indeed, such measurements were performed and confirmed high temperature superconductivity in H 3 S and LaH 10 [14], even if facing subsequent comments [15] and revised expectations from the authors of [13]. Moreover, the trapped flux measurements were shown to have a great advantage for a small superconducting sample enclosed in a bulky pressure cell, given that the large addenda signal from the cell is minimized by use of zero applied field measurements.…”

Vortex Phase Dynamics in Yttrium Superhydride YH6 at Megabar Pressures

“…It should be noted that the critical current data result in higher London penetration depths λ L for superhydrides than the SQUID method. , Both methods are not ideal. The use of current–voltage characteristics requires accurate knowledge of the thickness of hydride samples in DACs as well as the geometry of electrodes.…”

Hints of granular superconductivity in natural graphite verified by trapped flux transport measurements

“…One of the main examples of a granular superconductor is the very first report on the high-temperature superconducting oxides, where no zero resistance was achieved added to very broad transitions in temperature [6]. However, even in the case of sharp transitions in the temperature dependence of the resistance, the phenomenology of granular superconductors should be always considered, as the recently discussion on the interpretation of the available experimental data on the apparent superconductivity in some hydrides under pressure demonstrates [7][8][9][10][11].…”