Quantum

NTHU Researchers Identify Quantum Critical Point in Cuprate Superconductors

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Briefings

NTHU researchers using resonant inelastic X-ray scattering (RIXS) identified a quantum critical point in lanthanum strontium copper oxide (LSCO), a high-temperature cuprate superconductor. This landmark discovery reveals that charge density waves, superconductivity, and pair density waves coexist on one side of the critical point, while a distinct superconducting state exists beyond it. The findings, published in Nature Communications, clarify the complex phase diagram that had previously been obscured by the superconducting dome, offering a benchmark for future theoretical models. The study was led by Chung-Yu Mou, Dean of the College of Science at NTHU, with international collaboration involving the National Synchrotron Radiation Research Center.

Key points

• Researchers from National Tsing Hua University and the National Synchrotron Radiation Research Center used resonant inelastic X-ray scattering (RIXS) to observe quantum critical scaling in lanthanum strontium copper oxide (LSCO).
• The analysis revealed that charge density waves, superconductivity, and pair density waves coexist on one side of the quantum critical point, while a separate superconducting state exists beyond it.

Context

This research addresses the long-standing unsolved problem of high-temperature superconductivity in cuprates, which exhibit multiple competing orders. The findings provide a definitive benchmark for testing theoretical models and clarify the material's quantum state transitions, marking a significant milestone in condensed matter physics.

Limitations

Evidence is limited to the specific case of lanthanum strontium copper oxide (LSCO) and does not generalize to other cuprate materials. The study relies on experimental data from the Taiwan Photon Source, and while the quantum critical law is confirmed, the exact physical mechanisms driving the transition remain subject to further theoretical development.

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