圖1. 該光學裝置，被用來產生共振激發樣品的低頻雷射脈衝。
The optical setup used to generate the low frequency laser pulses that resonantly excited the sample.
An organic material in a metastable phase behaves a little like a room-temperature superconductor when excited with laser light. Though this behaviour fades almost as quickly as the laser pulse that induces it, the team behind the discovery say that with the right light source, it might be possible to keep the material in its superconducting-like state continuously.
當被使用雷射激發時，一種處於亞穩態的有機材料，表現有點像室溫超導體。雖然此種表現，幾乎與引發它的雷射脈衝，一樣快速消失。該項發現背後的團隊表示，以最適宜的光源，這或許可能持續使該種材料，保持類似超導的狀態。
Scientists have known for a while that shining light at terahertz and mid-infrared frequencies on certain materials is a good way to manipulate their properties. In some cases, this method can even be used to create non-equilibrium material phases that have no analogue under normal conditions.
科學家們知曉，以兆赫茲及中紅外線頻率的光，照射於某些材料上，是一種操縱其屬性的好方法，已經達一段時間。在某些情況下，此方法甚至能被用來，於正常條件下，產生無類似物之非平衡的材料相。
“Our group has been studying how to use coherent light fields to amplify or otherwise enhance superconductivity – a state that is generally obtained from the spontaneous formation of electronic coherence (the pairing up electron pairs),” explains Andrea Cavalleri, a physicist at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg, Germany who led the research effort. “In the past, we found that in a number of materials (the cuprates [copper oxides] and some organic materials like K3C60), this effect appears to be possible.”
於德國漢堡市，馬克斯普朗克物質結構暨動力學研究所(MPSD)，領導該項研究全部工作的物理學家，Andrea Cavalleri解釋：「我們的團隊一直在研究，如何使用相干的光場，來放大或以其他方式增強超導性。這是一種，通常從電子相干性，自然發生之形成方式(配對電子對)獲得的。於過去，我們發現了，在許多材料(銅酸鹽[銅氧化物]，及一些如K3C60的有機材料)中，這種效應顯然是可能的。」
In the new work, which is described in Nature Physics, Cavalleri and colleagues showed that photoexciting the material with a light source tuned to 10 THz is much more efficient at producing the effect in K3C60 than previous techniques.
在該項，於《自然•物理學》雜誌上，被記述的新研究中，Cavalleri及其同僚們證實，使用調諧至10兆赫茲(THz)的光源，來光激發K3C60 ，在該種材料中，於產生上述效應上，比先前的諸多技術，更有效率得多。
Indeed, the researchers found they could generate the same superconducting state as in earlier studies with a 100-fold lower laser fluence. This non-equilibrium superconducting state lasts for nanoseconds and appears at room temperature, making the discovery “especially significant”, Cavalleri says.
實際上，此些研究人員發現，使用低100倍的雷射能量密度，他們能產生與早期諸多研究中，相同的超導態。此種非平衡的超導態，持續達幾奈秒且於室溫中出現。Cavalleri表示，使得此發現“特別有意義”。
Frequencies in the few-terahertz range are particularly difficult for ultrashort pulsed lasers to produce, and the latest result was made possible by developing a new optical source.
對超短脈衝的雷射而言，於幾兆赫茲範圍內的頻率，特別難以產生。而該最新的結果，是藉由開發新光源使之可能的。
This source is based on chirped pulses, and the MPSD researchers fabricated it using a combination of techniques. In a follow-up work published in Nature Communications, they additionally showed that they could integrate the source onto a chip, which they say could lead to a wider range of opto-electronic applications.
此光源是以啁啾脈衝(波長於脈衝持續時間內發生變化的脈衝)為基礎。因此，MPSD的研究人員們使用多種技術創造了它。在發表於《自然•通訊》期刊的一項後續研究中，他們額外證實了，他們能將光源整合到，他們表示，可能導致更廣泛之光電應用的晶片上。
圖2. 測量裝置，於其中的中紅外線及可見光束，聚焦到光電器件上。插圖：這是於此裝置被發射、傳輸及偵測之皮秒電流脈衝的影像。
Measurement setup, in which mid-infrared and visible beams are focused onto the optoelectronic device. Inset: Image of the device on which picosecond current pulses are launched, transported and detected.
According to the researchers, a light source with a higher repetition rate – that is, a shorter duration between consecutive laser pulses – could allow the metastable superconducting state to last longer. “If we could deliver each new pulse before the sample returns to its non-superconducting equilibrium state, it may be possible to sustain the superconducting-like state continuously,” explains team member Edward Rowe.
根據此些研究人員的說法，一種具有較高重複率(即，在連續雷射脈衝之間，持續較短時間)的光源，可能使亞穩超導態，得以持續較長時間。團隊成員，Edward Rowe解釋：「倘若能在樣品返回其非超導的平衡態之前，傳遞每一新脈衝。這或許可能持續維持，類超導的狀態。」
Cavalleri is even more optimistic. “We are reaching a regime that is not far off from one in which you could imagine driving superconductors with continuous wave sources to obtain steady state room temperature operation,” he tells Physics World. “We could envisage driving this effect in steady state with only a few watts of power.”
Cavalleri甚至更為樂觀。他告訴Physics World：「我們正在達到一種，離能想像使用連續波源驅動超導體，來獲得穩態室溫運作，不遠的狀況。我們能展望，僅用幾瓦的功率，於穩態中，驅動此效應。」
The main bottleneck, he adds, is the shortage of continuous-wave light sources available at 10 THz.
他附言，主要瓶頸是，缺乏可獲得之10 THz的連續波光源。
The MPSD team now plans to characterize the metastable superconducting-like state to the same level of precision that is possible at equilibrium, with the aim of better understanding the microscopic mechanisms behind photoinduced superconductivity.
具有更深入瞭解光致超導性，背後之諸多微觀機制的目的。目前，該MPSD團隊計劃，使該種亞穩之類超導的狀態表現出，達到於平衡時，可能的相同精確水平。
Among other quantities, they hope to measure the state’s magnetic and electrical properties, atomic structure and perhaps quantum phenomena such as electron tunnelling, proximity effects and other related phenomena. “It will also be interesting to think of new potential applications for such system in quantum optoelectronics,” Cavalleri says.
於其他量中，他們希望測量此態之磁與電的屬性、原子結構及或許諸如，電子穿隧、鄰近效應與其他相關現象等量子現象。Cavalleri宣稱：「思考此類系統，於量子光電子學中的新潛在應用，這也會是引人感興趣的。」
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翻譯：許東榮
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