Quantum Phase Transitions in Superconducting Systems

Quantum phase transitions (QPTs) in superconducting systems arise when a fundamental change in ground state is driven by quantum rather than thermal fluctuations. In low-dimensional materials such as thin films, interfaces and nanowires, the competition between superconducting order and disorder or external tuning parameters (magnetic field, carrier density, pressure) yields a rich variety of emergent phases. Beneath the superconducting dome, critical fluctuations can give rise to anomalous metallic regimes or broadened critical states, while on the insulating side one finds superinsulation or charge Berezinskii–Kosterlitz–Thouless behaviour. Central to these transitions is the existence of a zero-temperature quantum critical point (QCP), where characteristic energy scales vanish and new scaling laws emerge. Recent advances in measurement techniques—particularly in sensitive probes of fluctuation phenomena—have revealed ghost-temperature and ghost-field lines that delineate thermal-to-quantum crossovers. At the same time, theoretical developments in effective field theories and topological descriptions have expanded the conceptual framework beyond conventional Ginzburg–Landau approaches. Understanding these QPTs not only illuminates the interplay of coherence, disorder and dimensionality, but also has implications for designing robust quantum devices and exploring analogous critical phenomena in other fields.

Research from Nature Portfolio

In disordered two-dimensional superconducting films, precise mapping of the Nernst effect across the magnetic-field–temperature plane has uncovered a thermal-to-quantum crossover of superconducting fluctuations. A ghost-temperature line emerging within an anomalous metallic regime intercepts the zero-temperature axis, pinpointing the QCP and demonstrating that the intervening metallic state corresponds to a broadened critical region of the superconductor–insulator transition. Earlier work on highly crystalline two-dimensional systems has revealed a generic evolution from a quantum metallic state at low fields to a quantum Griffiths state at higher fields, characterised by a diverging dynamical exponent and the formation of superconducting puddles. These studies collectively establish that quantum fluctuations in low-disorder, high-quality superconductors manifest distinct scaling behaviour and intermediate metallic phases not captured by conventional theories.

Quantum Phase Transitions in Superconducting Systems publication trend

The graph below shows the total number of articles in quantum phase transitions in superconducting systems across all publications each year (not limited to Nature Index journals).

Technical terms

Quantum phase transition: Transition at zero temperature driven by quantum fluctuations rather than thermal energy.

Superconductor–insulator transition: Quantum phase transition between a zero-resistance superconducting state and an insulating state.

Quantum critical point: Singularity at zero temperature where characteristic energy scales vanish and new scaling laws emerge.

Quantum Griffiths singularity: Disorder-induced phenomenon in which rare regions cause a diverging dynamical exponent near a quantum critical point.

Nernst effect: Transverse electric field generated by a temperature gradient in a magnetic field, highly sensitive to superconducting fluctuations.

References

1. Broadened quantum critical ground state in a disordered superconducting thin film. Nature Communications (2024).
2. Quantum phase transitions in highly crystalline two-dimensional superconductors. Nature Communications (2018).
3. Three-dimensional quantum Griffiths singularity in bulk iron-pnictide superconductors. National Science Review (2024).
4. Dynamical Conductivity across the Disorder-Tuned Superconductor-Insulator Transition. Physical Review X (2014).
5. Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films. Scientific Reports (2018).