23: Chapter 23 Room Temperature Superconductivity: The Gap Between Theory and Materials

Deep inside the underground information fortress, time seemed to have lost its usual flow.

Only the scrolling data on the screens, the constantly refreshing simulation results, and the nutritional supplements delivered through special tubes signaled the passage of time.

Lin Shen felt as if he were steering three ships toward different unknown seas simultaneously.

One was the Topological Quantum Computing ship of the "Xuance Group," cautiously sailing toward the reef area of high magnetic field experimental verification; another was the photon chip ship of the "Chasing Light" project, searching for a stable route amidst the turbulence of "on-chip light sources"; and the latest one he had taken over was the massive, fog-shrouded giant: Controlled Nuclear Fusion, especially its compact miniaturization path.

He was not crushed by this triple pressure; instead, in a state of near-limit focus, he found a peculiar balance.

Knowledge, thinking patterns, and even sparks of inspiration from different fields collided and merged in his mind, occasionally sparking "non-traditional" connections that surprised even him.

High-temperature superconducting (HTS) high magnetic field technology became his first entry point into solving the fusion problem.

Through the "Star Sea" library and expert resources coordinated in an emergency, he was able to glimpse the cutting-edge progress and the most profound dilemmas in this field.

The latest second-generation high-temperature superconducting tapes, based on Rare Earth Barium Copper Oxide (REBCO) coated conductor technology, have already demonstrated excellent current-carrying capacity in the liquid nitrogen temperature zone (77K, -196 degrees Celsius) and moderate magnetic fields.

However, to apply them to the extremely high magnetic fields (>20T, or even over 30T) and relatively high operating temperatures (possibly aiming for 30-50K to reduce cooling power) required by Compact Fusion devices, the performance of existing materials is still stretched thin.

The key bottleneck lies in "flux pinning"—those nanoscale defects embedded inside the superconductor, responsible for "pinning" the flux lines attempting to penetrate the material to maintain the superconducting state.

Under super-strong magnetic fields, the density of flux lines is extremely high, and the resulting "Lorentz force" is also extremely strong, requiring denser and stronger "pinning centers" to resist it.

Existing processes, whether introducing nanoparticles (such as BaZrO₃) or creating columnar defects through ion irradiation, see their pinning force decay sharply in magnetic fields exceeding 20T, leading to a substantial drop in critical current density (Jc), which may cause the magnet to quench (lose superconductivity) or even be damaged.

Lin Shen was immersed in those complex phase diagrams, defect distribution images under transmission electron microscopy, and various pinning force theoretical models.

He needed to understand how to design and control the morphology, size, distribution, and coupling strength of these "pinning centers" with the superconducting matrix from the atomic scale to achieve stable operation under extreme conditions.

This is a classic problem of the microscopic determining the macroscopic, and its complexity is no less than designing an entirely new alloy.

Massive computational simulations and experimental trial-and-error are inevitable.

Meanwhile, the storm of global energy and geopolitics was continuously sending shockwaves into this underground studio through encrypted news briefings.

After breaking through $160, oil prices finally experienced violent, wide-ranging fluctuations accompanied by huge trading volumes, which is usually a sign of extreme market panic and white-hot competition.

The currencies of several emerging market countries plummeted, and the risk of debt default surged.

Major developed economies, while releasing strategic petroleum reserves to try to stabilize oil prices, continued to implement policies with obvious protectionist colors in key minerals, chips, and other fields, and the cracks in the global supply chain continued to widen.

The tension in the Xingzhou Strait had become public.

Ships from the Federation and its allies had several "dangerous approach" incidents with coast guard and naval vessels from the Dragon Kingdom, and the diplomatic rhetoric from both sides was becoming increasingly fierce.

A local, controllable friction seemed to be sliding from "possible" to "very likely."

International observers generally believed that any substantive armed conflict would drag the world into an unpredictable abyss.

The tone of internal briefings from the highest level was becoming increasingly severe, requiring all strategic technology projects to accelerate their progress and prepare for the worst-case scenario (including the interruption of some international cooperation and the escalation of embargoes on key technical equipment).

Pressure was no longer a sword hanging over his head, but the air filled with rust and gunpowder smoke that permeated his breathing.

That evening, while reviewing a simulation report on "Spheromak plasma self-organization magnetic field startup and maintenance," Lin Shen's thoughts were once again stirred by that peculiar, cross-disciplinary "sense of resonance" on the technology tree.

Spheromak is a theoretically very elegant Compact Fusion concept.

It does not require complex external coils to generate a confining magnetic field but relies on the magnetic field generated by the plasma's own current to self-organize into a stable toroidal structure (similar to a twisted "donut").

However, its biggest problem is extremely poor stability; tiny disturbances can lead to the collapse of the magnetic field structure and the failure of plasma confinement.

Solving the stability problem requires a deep understanding of the complex nonlinear interactions between current, magnetic field, and fluid motion in plasma; it is essentially a highly complex "many-body problem" involving electromagnetic fields and fluid dynamics.

Many-body problem... Topological Quantum Computing... Tensor networks...

A thought struck Lin Shen's mind like lightning!

In the theoretical research of Topological Quantum Computing, Topologist and his team often use a method called "Matrix Product States (MPS)" or more generally "Tensor Networks" to approximate, describe, and analyze quantum many-body systems with complex entanglement structures.

The core idea of this method is to use a set of low-dimensional tensors (which can be understood as multi-dimensional arrays) contraction (specific operations) to efficiently represent the wave function of high-dimensional quantum states, thereby capturing the system's core correlations and topological properties while greatly reducing computational complexity.

So, could this mathematical tool of "tensor networks," used to describe complex quantum correlations, be used to describe and simulate the "correlation structures" and "stability patterns" in classical (but highly nonlinear) many-body systems like plasma?

Could the turbulence, magnetic islands, and various instability modes in plasma also be viewed as a kind of abstract "topological structure" or "correlation pattern"?

Could we learn from or adapt tools from quantum many-body theory to more deeply understand and predict plasma behavior, or even find a "topological handle" to actively control its stability and suppress unfavorable modes?

This idea was extremely bold, crossing the seemingly solid disciplinary barrier between quantum physics and classical plasma physics.

But the more Lin Shen thought about it, the more he felt that it might contain some profound, not yet fully recognized possibilities.

Both deal with complex systems with a large number of degrees of freedom and strong interactions; one just follows the laws of quantum mechanics, and the other follows the laws of classical electrodynamics and fluid dynamics.

In terms of mathematical description and the search for system "robustness," there might be something to learn.

He immediately recorded this idea and labeled it as a "high-risk, high-potential-reward cross-disciplinary theoretical exploration direction," preparing to discuss it with experts in fusion physics and theoretical physics at the appropriate time.

Just as he finished recording this spark of inspiration, an urgent communication request from Sun Qiming came through the "firefly" channel.

After connecting, Sun Qiming's face looked unusually grim in the encrypted video.

"Engineer Lin, two things, both very urgent."

Sun Qiming spoke very fast, "First, regarding the 'Xuance Group,' the first batch of bismuth sulfide-niobium nitride heterojunction samples from Professor Wu Qingquan's team, the preliminary electrical transport test results are out."

Lin Shen's spirits lifted: "How are they?"

Sun Qiming did not answer immediately but pulled up a set of data charts.

"The test was done on the base's small cryogenic platform. The lowest temperature only reached 4.2 K (liquid helium), and there was no strong magnetic field."

"Preliminary data shows that the sample showed some signs of superconductivity at low temperatures, but the transition temperature (Tc) was only about 5K, far lower than our theoretical model predictions and process optimization goals (above 17K)."

"Moreover, the resistance did not completely drop to zero after the transition; there was residual resistance, indicating that there might be problems with sample quality, interfaces, or uniformity."

"Professor Wu's team is analyzing the cause; it might be a deviation in the stoichiometric ratio control of the bismuth sulfide in the initial growth layer, or the stress state of the niobium nitride layer is not ideal."

[part:gemini-3.0-flash]

Lin Shen's heart sank slightly. Although this was only the first round of attempts and failure was expected, seeing the specific unsatisfactory data still brought pressure. The theoretical predictions of Topological Quantum Computing are extremely sensitive to material parameters; if Tc does not meet the standard, the experimental difficulty of finding subsequent topological edge states will increase drastically.

"Understood. Have Researcher Lu re-examine the parameter sensitivity of the theoretical model based on this preliminary data to see if any fine-tuning is needed. On Engineer Shen's side, maintain close communication with Professor Wu's team and launch the second round of growth optimization as soon as possible. We cannot stagnate in the face of the first failure," Lin Shen instructed quickly.

"Understood." Sun Qiming nodded, and then his tone became even heavier. "The second matter is a top-secret briefing from Director Zhao's office at the Energy Security Commission."

He paused for a moment, as if confirming the security of the communication. "An important but extremely secretive overseas supply channel for rare elements has just been cut off. Citing 'end-user verification' as the reason, the other party has indefinitely suspended the supply of a special rare earth oxide used in the synthesis of key precursors for new high-temperature superconducting materials under the contract."

Lin Shen's pupils contracted suddenly!

High-temperature superconducting materials! One of the key raw materials for REBCO tape!

"Is it... a response to our recent increase in investment in the direction of fusion?" Lin Shen's voice was a bit dry.

"It's highly likely," Sun Qiming said in a low voice. "The other party's intelligence network is very sharp. Although our restart of Fusion Miniaturization research is top secret, expert consultations, data reviews in related fields, and especially the concentrated focus on performance data for high-temperature superconducting materials may have alerted them. Cutting off the supply of this special raw material has a very clear intent—to choke the 'neck' of our high-performance Compact Fusion magnets. Without this high-purity precursor with a specific crystal phase, our progress in independently preparing the next generation of high-performance REBCO tape could be delayed by at least a year, or even longer."

One year! In the current climate of an escalating global energy crisis and geopolitical conflict risks, one year could mean a world of difference!

"What about domestic reserves and alternative solutions?" Lin Shen pressed.

"There are some in the national strategic reserves, but they are only enough to support the short-term needs of existing research projects, far from enough to support future possible engineering scale-up production. Finding alternative elements or developing entirely new superconducting material systems that do not rely on this raw material... takes time, and whether the performance can meet the standards is unknown." Sun Qiming's tone was heavy. "Director Zhao requested that we immediately assess the impact of this event on the feasibility of the Compact Fusion technology route and do everything possible to find solutions to break the blockade, including... unconventional technical paths."

Unconventional technical paths...

Lin Shen's gaze involuntarily turned once again to the technology tree in his mind.

Beside the prerequisite path of [High-Performance High-Temperature Superconducting Magnet System], under the [Controlled Nuclear Fusion] node, there seemed to be another extremely faint branch, almost completely hidden in the shadows. Previously, his attention had been mainly drawn to the relatively 'mainstream' path of High-Temperature Superconductivity, and he hadn't paid much attention to it.

Now, under the immense pressure of the raw material supply being 'choked,' he focused his consciousness there.

The end of that dim branch pointed to a name—[Room-Temperature Superconducting Material Exploration (Theoretical Deduction)].

Room-Temperature Superconductivity! This is one of the ultimate dreams of condensed matter physics! If a superconductor existed that could work at room temperature and pressure (or at least above the liquid nitrogen temperature of 77K or above, without the need for complex and expensive cooling systems), then not only fusion energy, but the entire power transmission, transportation, medical imaging, precision instruments... almost all industrial fields would undergo a revolutionary change!

But at present, this is considered 'science fiction' or a 'distant future' by almost all mainstream physicists. Although laboratories occasionally claim signs of Room-Temperature Superconductivity under extreme high pressure (millions of atmospheres), it is far from practical application. To many, exploring Room-Temperature Superconductivity seems even more elusive than achieving Controlled Nuclear Fusion.

The technology tree marked this direction as 'Theoretical Deduction,' and its status was even dimmer than Topological Quantum Computing. The prerequisites were vague, seemingly requiring a breakthrough in more fundamental physical theories.

However, facing the reality of high-performance high-temperature superconducting materials being 'choked,' this seemingly ethereal path was like a tiny, extremely faint firefly from a completely different direction in the dark abyss, catching Lin Shen's eye.

What if... what if there was a way to bypass the dependence on specific rare elements and, starting from a completely different material design concept, deduce a new substance structure or mechanism with room-temperature superconducting potential based on more common elements, even if only theoretically?

It sounded like a fantasy.

But the existence of the technology tree itself was the greatest fantasy. Since it pointed in this direction, no matter how dim it was, did it mean that in its beyond-the-era knowledge map, there truly were unusual clues or ideas regarding Room-Temperature Superconductivity, even if only a glimpse?

Lin Shen felt a wave of dizziness. On one hand, there was the real pressure of the initial setback in the topological quantum experiment and the cut-off of key fusion materials; on the other hand, there was the faint call from the deepest part of the technology tree, from a seemingly impossible direction.

"Engineer Sun," Lin Shen spoke slowly, his voice carrying a hint of resolve. "Reply to Director Zhao: The interruption of the supply of high-performance high-temperature superconducting materials will indeed pose a serious constraint on our Compact Fusion research and development based on the current technology path. We must immediately launch research into backup plans and alternative materials."

He paused and continued, "At the same time, in my own name, submit a supplementary application to Director Zhao and Academician Qin: Requesting authorization to use a small amount of computing and literature resources outside of existing research work to concurrently conduct a top-secret theoretical exploration project code-named 'Deep Blue.' This project aims to attempt a rapid, forward-looking theoretical deduction and screening of the possibilities and potential implementation paths of 'Room-Temperature Superconductivity' based on the latest interdisciplinary theoretical progress and unconventional material design ideas. The goal is not to obtain the material immediately, but to find new ideas and directions that could overturn existing perceptions and break the blockade. The risk is extremely high, and the probability of success is extremely low, but... I believe it is necessary to try."

On the other end of the video, Sun Qiming was clearly shocked by this sudden, bold, almost crazy suggestion, and he remained silent for several seconds.

"...Engineer Lin, are you sure? Room-Temperature Superconductivity... this is much more... distant than anything we are doing now." Sun Qiming's voice was full of uncertainty.

"I'm sure." Lin Shen's gaze was exceptionally firm. "Precisely because it is distant, precisely because it is blocked, we need someone to take a look and see if there truly isn't even a single crack in that seemingly impossible path. Even if it just proves that the path is currently impassable, it will allow us to more firmly concentrate our efforts on overcoming other difficulties. But what if... I mean what if, we find a bit of a different 'light'?"

Another silence.

"...I will forward the original text of your application," Sun Qiming finally said. "But before getting approval, please do not perform any related operations. Additionally, the work of the 'Xuance Group' and the alternative fusion material solutions must not stop."

"Of course." Lin Shen nodded.

The communication ended.

The studio fell back into silence. Only the low hum of the server cooling fans and the simulation program for high-temperature superconducting magnets still calculating on the screen remained.

Lin Shen leaned back in his chair and closed his eyes.

Room-Temperature Superconductivity... the chasm from theory to material is deeper than the Mariana Trench and higher than the Himalayas. This is almost challenging the cognitive boundaries of modern physics.

But in that endless darkness and impossibility, the faint direction of the technology tree and the stubbornness deep in his heart not to be locked down drove him to want to go to the base of that cliff and cast the first stone to find the way.

Even if it was just to hear an echo.