搬運

First video of LK-99 Full Levitation, aka flux-pinning

This video was just posted to the Chinese video-sharing site BiliBili and claims to be a highly pure synthesized sample of LK-99.

What is the physical phenomenon behind this and what does it mean?

Levitation of superconducting materials is a phenomenon unique to what is called Type-II superconductors, and is an effect whereby magnetic field lines becomes 'trapped' as it passes through the material, providing the force needed to levitate. These are the popular images and videos of cryogenically-cooled discs floating above a magnet frequently seen online and in the pinned post on my profile.

You can think of this like strands of hair being caught in gum - the gum is suspended in mid-air by adhering strongly to the hair as the hair passes through it. The hair in this case is magnetic field lines and the gum is the Type-II superconductor. Just like hair comes in individual strands, or in other words hair is 'quantized' or 'discrete', so is the flux trapped at the 'pinning centers' quantized in what are called 'magnetic vortices' - the quantization of pinned flux lines is a key property and distinguishing characteristic of Type-II superconductors (although technically can occur in Type-I superconductors if the material thickness is smaller than the London penetration depth, which is indeed very small - specifics for the physics nerds out there).

Flux-pinning is entirely unique to superconductors and is also wholly distinct from the Meissner effect. It is not a property of diamagnets or diamagnetism.

At @TRIUMFLab I contributed to flux-pinning studies in Niobium crystal superconducting radio-frequency cavities used for particle acceleration. In that application, trapped flux poses an issue by increasing the remnant surface resistivity of the cavity, which has the effect of decreasing its effective quality factor or Q-factor, which is a measurement of a resonators efficiency. SRF cavities typically have Q-factors of 10E10 and trapped flux at pinning centers reduces the maximum effective accelerating electric field used to drive charged particle bunches close to the speed of light.

Flux pinning is thought to arise in some Type-II superconductors by small imperfections in the crystal, also called volume defects, that enable flux to penetrate the material. In SRF cavities an issue that arises is any magnetic field that is passing through the material, e.g. by the Earth's background field, can become pinned or trapped inside the cavity as it transitions into a superconducting state. See some attached plots in the comments from a study showing how the surface resistivity of SRF cavities increases the more there is a background field as the cavity transitions into superconducting state.

This is the first video I am aware of that claims to show the flux-pinned levitation of a LK-99 sample. If this is in fact what is happening, then it is a very unique and promising finding of this new materials properties and potential for future study.

If this is real then it is truly ground-breaking

LK-99 全懸?。ㄓ置酷斣┑牡谝粋€視頻

該視頻剛剛發(fā)布在中國視頻分享網(wǎng)站嗶哩嗶哩上，聲稱是LK-99的高純度合成樣品。

這背后的物理現(xiàn)象是什么？這意味著什么？

超導(dǎo)材料的懸浮是一種所謂的 II 型超導(dǎo)體特有的現(xiàn)象，是一種磁力線在穿過材料時被“捕獲”的效應(yīng)，從而提供懸浮所需的力。這些是漂浮在磁鐵上方的低溫冷卻圓盤的流行圖像和視頻，這些圖像和視頻經(jīng)常在網(wǎng)上和我個人資料的固定帖子中看到。

你可以把這想象成一縷頭發(fā)被口香糖夾住——當(dāng)頭發(fā)穿過口香糖時，口香糖牢固地粘附在頭發(fā)上，懸浮在半空中。在這種情況下，頭發(fā)是磁力線，牙齦是 II 型超導(dǎo)體。就像頭發(fā)是單根的一樣，或者換句話說，頭發(fā)是“量子化的”或“離散的”，被困在“釘扎中心”的通量也在所謂的“磁渦流”中被量子化——釘扎磁通線的量子化是II 型超導(dǎo)體的關(guān)鍵屬性和顯著特征（盡管從技術(shù)上講，如果材料厚度小于倫敦穿透深度，則可以在 I 型超導(dǎo)體中出現(xiàn)，倫敦穿透深度確實非常小 - 對于物理迷來說是特定的）。

磁通釘扎對于超導(dǎo)體來說是完全獨特的，也與邁斯納效應(yīng)完全不同。它不是抗磁體或抗磁性的特性。

在@TRIUMFLab ，我參與了用于粒子加速的鈮晶體超導(dǎo)射頻腔的通量釘扎研究。在該應(yīng)用中，被捕獲的磁通通過增加腔體的殘余表面電阻率而產(chǎn)生問題，這會降低其有效品質(zhì)因數(shù)或 Q 因數(shù)，而 Q 因數(shù)是諧振器效率的度量。 SRF 腔的 Q 因子通常為 10E10，釘扎中心處的俘獲通量會降低用于驅(qū)動帶電粒子束接近光速的最大有效加速電場。

磁通釘扎被認為是在某些 II 型超導(dǎo)體中由晶體中的小缺陷（也稱為體積缺陷）引起的，這些缺陷使磁通能夠穿透材料。在SRF空腔中出現(xiàn)的一個問題是，當(dāng)材料轉(zhuǎn)變?yōu)槌瑢?dǎo)狀態(tài)時，任何穿過材料的磁場（例如地球的背景場）都可能被釘扎或捕獲在空腔內(nèi)。請參閱一項研究評論中的一些附圖，該研究顯示了當(dāng)空腔轉(zhuǎn)變?yōu)槌瑢?dǎo)狀態(tài)時，背景場越多，SRF 空腔的表面電阻率如何增加。

這是我所知道的第一個聲稱展示 LK-99 樣本磁通釘懸浮的視頻。如果這確實是正在發(fā)生的事情，那么對于這種新材料的特性和未來研究的潛力來說，這是一個非常獨特且有前途的發(fā)現(xiàn)。

如果這是真的，那么這確實是開創(chuàng)性的