[论文解读] Quasiparticle to local moment crossover in bad metals

A. Chen, F. B. Kugler+5 more|arXiv (Cornell University)|Jan 14, 2026

Organic and Molecular Conductors Research被引用 0

一句话总结

paper 将从费米液体输运的偏离起始点与在κ-(BEDT-STF) x (BEDT-TTF)1−x 2 Cu2(CN)3 的马特转变附近逐渐的准粒子破坏与局部磁矩的出现联系起来，利用 NMR 与 DMFT 将输运、光谱权重与自旋动力学联系起来。

ABSTRACT

Non-Fermi-liquid charge transport in the vicinity of electronic instabilities has been intensely studied for decades. Deviations from $ρ_{ m FL}=ρ_0+AT^2$ in bad and strange metals are commonly ascribed to a breakdown of Landau's quasiparticle (QP) concept. Yet, it remains unclear what mechanism drives the temperature dependence of $ρ(T)$ beyond $ρ_{ m FL}$. Here, we examine the bad metal upon approaching the Mott metal-insulator transition via chemical pressure in $κ$-[(BEDT-STF)$_x$(BEDT-TTF)$_{1-x}$]$ m _2 Cu_2 (CN)_3$. Through nuclear magnetic resonance (NMR) and transport experiments on the same single crystals, we directly link the onset of deviations from Korringa law $(T_1T)^{-1} = \mathrm{const.}$ with the rise of $ρ(T)$ beyond $ρ_{ m FL}$. From the NMR relaxation rate, we can identify the gradual crossover between the QP-dominated regime at low $T$ to predominant local moments at higher $T$. By comparing our experimental findings with dynamical mean-field theory calculations, which accurately reproduce the transport data, we reveal how this crossover is reflected in $T$-dependent changes of the QP spectrum. Near the Mott insulator, where $dρ/dT<0$ at high $T$, an Einstein-relation analysis shows that bad-metal behavior with $dρ/dT>0$ is driven by the temperature dependence of the electronic compressibility rather than the diffusion constant.

研究动机与目标

• Investigate non-Fermi-liquid transport near a Mott metal-insulator transition in κ-(BEDT-STF) x (BEDT-TTF)1−x)2Cu2(CN)3.
• Directly connect deviations from Korringa behavior in NMR (T1−1) to deviations from ρFL(T) in resistivity.
• Determine how quasiparticle coherence evolves with temperature and correlation strength across the MIT.
• Elucidate how DMFT captures the QP spectrum, transport, and the onset of local moments in this system.

提出的方法

• Perform four-point dc transport and 1H/13C NMR on the same κ-STF x single crystals across 2–200 K.
• Identify the insulating master curve in T1−1(T) indicative of local-moment relaxation in the insulating regime.
• Use dynamical mean-field theory (DMFT) on a half-filled Bethe lattice to compute ρ(T) and the spectral function A(ω,T) and compare with experiments.
• Decompose DMFT conductivity via the Einstein relation σ=Dκ and via a Drude-like expression σ/σMIR=τtr Ekin to interpret transport mechanisms.
• Relate the QP peak height A(0,T) in A(ω) to transport and T1−1 to illustrate QP coherence loss with temperature.

实验结果

研究问题

• RQ1 How does resistivity evolve with temperature as a function of correlation strength near the Mott MIT in κ-STF x?
• RQ2 When and how do quasiparticles lose coherence, and how does this reflect in NMR relaxation (T1−1) and Korringa behavior?
• RQ3 Can DMFT correctly reproduce the observed ρ(T) and the QP peak’s temperature dependence in A(ω)?
• RQ4 What is the relative role of electronic compressibility and diffusion in driving bad-metal transport near the MIR limit?
• RQ5 How does the crossover from quasiparticle-dominated transport to local-moment transport manifest in combined transport and NMR data?

主要发现

• A direct link is established between the breakdown of Korringa law (T1T)−1 and the rise of ρ(T) beyond ρFL in the bad-metal regime.
• NMR reveals a gradual crossover from quasiparticle-dominated transport at low T to local-moment dominance at higher T, with a maximum in (T1T)−1 near the bad-metal crossover.
• DMFT quantitatively reproduces ρ(T) and shows the quasiparticle peak in A(ω) fading with T, leaving a thermally filled pseudogap above Tmax.
• In the bad-metal regime, diffusion constant D changes little while the compressibility κ drives the drastic drop in σ, consistent with an Einstein relation viewpoint.
• The FL regime exhibits a T−2 resistivity with a relatively constant (T1T)−1, while beyond FL the transport is controlled by the evolving QP weight Zω and the bandwidth effects.