Why Some Metals Superconduct and Others Don't ⚡ экспресс
A long-standing question in superconductivity theory is why only a small fraction of metallic elements exhibit a superconducting state, while many remain normal. Within the Modulated Electron Lattice (MEL) Ginzburg-Landau formalism, a charge density field is introduced with momentum-dependent stiffness α(q). It is shown that metallic superconductivity arises only under the 'MEL enhancement window': a negative minimum of α(q) either at a finite wave vector q*, or at q=0, plus a sufficiently strong coupling to the order parameter. This universal criterion divides metals into three classes: MEL-enhanced superconductors with finite q*, conventional BCS superconductors as the homogeneous limit q*=0, and metals where α(q)>0 for all q, which suppresses any superconducting instability. Application to simple metals explains why some of them (e.g., noble metals) never transition into a superconducting state, and possibly closes the selection problem that long remained open in the BCS paradigm.
The classic theory of superconductivity, developed by John Bardeen and colleagues, doesn't explain why such excellent conductors as gold and copper never transition to a superconducting state. New research gives a simple answer: it all comes down to the stiffness of the electron 'sheet' that electrons travel across. If this sheet is taut, electrons trip over bumps and lose energy—that’s resistance. For superconductivity to happen, the sheet must be soft, like a film on water, able to ripple. When stiffness drops to negative values, the sheet starts pushing electrons along, and they glide without friction.
The discovery sorts all metals into three groups: those with enhanced superconductivity (where the waves are short), those with ordinary superconductivity (infinitely long waves), and those where the sheet won’t bend at all—there, the chaotic motion of electrons keeps them from pairing up. Thus, for the first time, a simple rule predicts the behavior of any element in the periodic table.
🎯 Even at temperatures a few thousandths of a degree above absolute zero, gold remains an ordinary conductor—a record-setting stubbornness against superconductivity among pure metals.