- The research team has broken the speed limit of superconductors to explore the de-pairing phenomenon of electron entangled pairs.
- The de-pairing phenomenon causes disturbances within a billionth of a second, affecting superconductivity.
- The team conducted experiments using niobium nitride and yttrium barium copper oxide materials, demonstrating different superconducting behaviors.
- The findings contribute to future research on superconducting properties in new ways.
The research team from the Max Planck Institute for the Structure and Dynamics of Matter in Germany, the Shanghai Institute of Microsystem and Information Technology in China, ETH Zurich in Switzerland, and the University of Oxford in the UK has achieved a significant breakthrough in exploring the de-pairing phenomenon of electron entangled pairs (i.e., Cooper pairs) by breaking the "speed limit" of superconductors. Superconductors are materials that can conduct electricity without resistance and generate a magnetic field when cooled below a certain temperature. These unique properties have enabled technologies such as particle colliders and magnetic resonance imaging (MRI) devices, which would have seemed like science fiction a century ago.
While we have successfully achieved superconducting states in various materials, scientists are well aware of the fragility of these systems. Increases in temperature or changes in current and magnetic fields are sufficient to cause materials to lose their superconducting state.
Challenges of the De-pairing Phenomenon
The de-pairing phenomenon, while magnetic fields and currents can be measured, presents another limit that is difficult to quantify, as it can induce disturbances within a billionth of a second. This is known as the de-pairing limit, where electron entangled pairs (i.e., Cooper pairs) are torn apart, leading to an immediate loss of superconductivity. Due to the extremely rapid disturbances caused by crossing the de-pairing limit, scientists need to investigate more quickly to determine if this limit has been surpassed. The research team found a novel method, akin to breaking the speed limit when crossing this threshold. Type-II superconductors are widely used in various applications and represent a physical compromise.
Unlike type-I superconductors, which have fragile magnetic limits, type-II superconductors possess a higher threshold due to their internal magnetic fields (i.e., quantum vortices), allowing current to flow and maintain superconductivity even under extreme conditions.
Superconducting Behaviors of Different Materials
Strong currents can tear apart these quantum vortices, generating resistance within the material and thus terminating its superconductivity. Consequently, the research team decided to leverage this information to gain further insights into the de-pairing limit. Breaking the speed limit, the team utilized two different types of superconducting materials, niobium nitride (NbN) and a member of the yttrium barium copper oxide (YBCO) family, both of which exhibit high-temperature superconductivity. NbN has an s-wave gap symmetry, while YBCO has a d-wave gap symmetry, which determines the ease of tearing its superconductivity.
To surpass the quantum processes occurring within a billionth of a second, the team established a photonic circuit with speeds several orders of magnitude greater than the movement of quantum vortices, exceeding tens of kilometers per second. The researchers found that NbN maintained its superconductivity until the applied current reached a critical value, after which it suddenly lost its superconductivity. In contrast, the YBCO material gradually lost its superconductivity. The team attributed this difference to the gap symmetry of the two materials, where NbN's energy gap is uniform in all directions, while YBCO's energy gap varies significantly, making it impossible to extinguish all at once.
The behavioral differences between the two materials provided researchers with fundamental insights into superconductivity, ultimately relating to Cooper pairs and their stability. Surpassing the speed limit of superconducting material transitions enables researchers to study and acquire these properties in new ways. The findings have been published in the journal Nature Physics.
New Directions in Superconductor Research
The research team's breakthrough in the field of superconductors not only reveals the fragility of electron entangled pairs but also provides new perspectives for future research on superconducting materials. The rapid disturbances of the de-pairing phenomenon make the stability of materials crucial, which is vital for the development of practical applications such as particle colliders and medical devices. Through in-depth studies of different materials, scientists can better understand superconducting properties, thereby driving innovation and application in related technologies.