[NCTS Physics Research Highlights] Chung-Hou Chung 'A mechanism for quantum-critical Planckian metal phase in high-temperature cuprate superconductors' Rep. Prog. Phys. 88 048001 (2025)

• 2025-04-29
• Chen, Jhan Yu 陳詹喻
• Strongly correlated condensed matter and cold atom systems Condensed Matter

A mechanism for quantum-critical Planckian metal phase in high-temperature cuprate superconductors
銅酸鹽高溫超導體「普朗克奇異金屬量子臨界相」之形成機制理論研究

Yung-Yeh Chang, Khoe Van Nguyen, Kim Remund and Chung-Hou Chung*
Reports on Progress in Physics 88 048001 (2025)
DOI: https://doi.org/10.1088/1361-6633/adc330

The mysterious metallic phase showing T-linear resistivity and a universal scattering rate 1/τ = 2 p αP kB T/h with a universal prefactor αP ~ 1 and logarithmic-in-temperature singular specific heat coefficient, the so-called ‘Planckian metal phase’ was observed in various overdoped high-Tc cuprate superconductors over a finite range in doping. Here, we propose a generic microscopic mechanism for this state based on quantum-critical local bosonic charge Kondo fluctuations coupled to both spinon and a heavy conduction-electron Fermi surface within the heavy-fermion formulation of the slave-boson t–J model. By a controlled perturbative renormalization group analysis, we examine the competition between the pseudogap phase, characterized by Anderson’s Resonating-Valence-Bond spin-liquid, and the Fermi-liquid state, modeled by the electron hopping (effective charge Kondo effect). We find a quantum-critical metallic phase with a universal Planckian ω/T scaling in scattering rate near an extended localized-delocalized (pseudogap-to-Fermi liquid) charge-Kondo breakdown transition. The d-wave superconducting ground state emerges near the transition. Unprecedented qualitative and quantitative agreements are reached between our theoretical predictions and various transport and thermodynamic experiments. The mechanism we propose here offers a promising route for understanding how d-wave superconductivity emerges from such a strange metal phase in cuprates–one of the long-standing open problems in condensed matter physics since 1990s.

神秘而令人費解之「普朗克奇異金屬量子態」—其電子散射率與溫度呈現普遍統一之奇特線性關係，而其比熱係數與溫度呈現對數發散—已經在有限範圍電洞參雜之銅酸鹽高溫超導體之實驗中被發現。因為奇異金屬態是高溫超導態尚未形成的高溫「前身狀態」，科學家因此長久以來都認為揭開奇異金屬的奧秘是理解高溫超導體超導機制的最重要關鍵。本論文以最尖端之理論架構對高溫超導體之普朗克奇異金屬態提供了微觀描述。此一理論聚焦於在量子臨界點附近之局部電荷擾動在形成此一量子態中所扮演之關鍵角色。我們從描述高溫超導之t-J模型之計算得出普朗克金屬態為侷域電荷擾動之「量子臨界基態」。此為高溫超導體之「贗能隙態」與「費米液體普通金屬態」相互競爭下之「量子臨界相」，其電子傳輸具有「頻率除以溫度」之量子臨界統一標度律。本文之理論預測與各種於銅酸鹽高溫超導體之傳輸與熱力學實驗觀察結果史無前例地吻合。因此，這項研究工作使我們更接近理解「於高溫超導體銅酸鹽中出現之超導性是如何從奇異金屬狀態演變而來」──這個自1990年代至今長期懸而未解之物理難題！