Why superconducting Ta qubits have fewer tunneling two-level systems at the vacuum-oxide interface than Nb qubits

Superconducting qubits are a key contender for quantum computing elements, but they often face challenges like noise and decoherence from two-level systems (TLSs). Tantalum (Ta) qubits are notable for their long T1 coherence times, nearing milliseconds, presumably due to fewer TLSs, though the cause