A diamond can look flawless under every conventional measurement and still be hiding something unexpected in its electronic interior.
The findings suggest that atomic-scale disorder can organize itself into a type of electronic order that scientists can control with temperature and magnetic fields.
Superconductivity occurs only for very high levels of boron doping (≥ 4 × 10²⁰ atoms per cm³) and cannot occur in pure diamond.
New 2D material could store quantum information at room temperatureThis tunability has implications not just in the fundamental physics of diamond.
Understanding the relationship between disorder and this three-phase electronic structure could provide a way to achieve higher transition temperatures.
A diamond can look flawless under every conventional measurement and still be hiding something unexpected in its electronic interior.
Now, researchers at Penn State University and the University of Chicago have shown that when a boron-doped single-crystal diamond film, just above a critical dopant concentration, undergoes a transition from an insulating state to a superconducting state, it spontaneously forms a 3-phase electronic landscape hidden in time.
The findings suggest that atomic-scale disorder can organize itself into a type of electronic order that scientists can control with temperature and magnetic fields.
That result goes against a widely held assumption in material science. Theoretically, as the long-range-ordered properties of a single-crystal material free of grain boundaries and structural defects, together with uniform doping verified on length scales greater than nine micrometers, then uniform electronic behavior is expected.
As the authors note directly in the paper, “doping induced disorder can lead to inhomogeneity in the superconducting order parameter even in structurally homogeneous samples.” In simple words, even a perfect crystal can have electrical turbulence when its chemistry sits at a tipping point.
Superconductivity occurs only for very high levels of boron doping (≥ 4 × 10²⁰ atoms per cm³) and cannot occur in pure diamond. At this concentration, boron atoms replace carbon in the lattice; it is therefore soluble, which causes a phase transition from insulating to metallic behavior, and, if the conditions are right, with more boron, superconductivity also occurs.
First-ever triple bond between Boron and Carbon formed
Superconducting diamond has been known since 2004, but the effects of disorder right at this chemical cutoff have remained elusive.
To investigate this transition in detail, the researchers created ultrathin diamond films via microwave plasma chemical vapor deposition, using boron trichloride as a dopant source rather than the more common diborane-based chemistry.
Their main sample was around 0.5 microns thick and had boron concentrations marginally above the critical threshold. The team used techniques such as Raman spectroscopy and X-ray diffraction to confirm a clean, single-crystal structure with no trace of polycrystalline growth or amorphous carbon.
Next, they cooled the film to cryogenic temperatures, then applied a magnetic field whose axis was gradually rotated in 5 ° increments, measuring electrical resistance at each orientation. The resulting dataset captured more than 50 maps of how the material responds across temperature and field conditions.
Further analysis uncovered three different electronic phases. At about 3.3 Kelvin, where superconductivity begins, the electrons behaved like a conventional metal, and scattering was not dispersionless.
Lower temperatures lead to the formation of small patches of electron pairs before superconductivity fully develops. A more extensive superconducting state emerged below 2.8 K; yet, a residual electrical resistance remained, indicative of isolated superconducting islands embedded in a metallic matrix.
The researchers further reported a self-generated transverse voltage across the sample even without applying a magnetic field. This Hall anomaly was about an order of magnitude greater than the conventional Hall effect, which could be expected under these conditions. This indicates the variably disordered electronic environment in which different portions of the film alternatively carry electrical current via fundamentally disparate mechanisms.
“Boron doping in diamond induces fluctuations and inhomogeneity in the superconducting phase, even in highly ordered, crystalline HBDD,” the authors write, noting that the anisotropic order emerging within this electronic disorder can be tuned by both temperature and magnetic field.
New 2D material could store quantum information at room temperature
This tunability has implications not just in the fundamental physics of diamond. Diamond already hosts a class of spin-based quantum bits called nitrogen-vacancy centers, which are being explored for quantum sensing and information processing.
The authors suggest that this tunable superconducting patchwork could be used to route quantum information within a single chip, noting that “a magnetic field could control whether the NVs interact with fermionic or bosonic patches.”
Boron‑doped diamond becomes a superconductor at about 10 Kelvin, which is the highest temperature seen for this material so far. But this is still more than five times lower than what scientists expect if the boron atoms were arranged in a more orderly way.
Understanding the relationship between disorder and this three-phase electronic structure could provide a way to achieve higher transition temperatures. This might help build quantum devices from a finite, continuous block of diamond.
Journal Reference
