More Like this

1. Electronic Band Structure of a Superconducting Nickelate Probed by the Seebeck Coefficient in the Disordered Limit

   https://doi.org/10.1103/PhysRevX.14.041021  

   Grissonnanche, G; Pan, G A; LaBollita, H; Segedin, D Ferenc; Song, Q; Paik, H; Brooks, C M; Beauchesne-Blanchet, E; Santana_González, J L; Botana, A S; et al (October 2024, Physical Review X)

   Superconducting nickelates are a new family of strongly correlated electron materials with a phase diagram closely resembling that of superconducting cuprates. While analogy with the cuprates is natural, very little is known about the metallic state of the nickelates, making these comparisons difficult. We probe the electronic dispersion of thin-film superconducting five-layer ( $n=5$) and metallic three-layer ( $n=3$) nickelates by measuring the Seebeck coefficient $S$. We find a temperature-independent and negative $S/T$for both $n=5$and $n=3$nickelates. These results are in stark contrast to the strongly temperature-dependent $S/T$measured at similar electron filling in the cuprate ${\mathrm{La}}_{1.36}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{0.24}{\mathrm{CuO}}_4$. The electronic structure calculated from density-functional theory can reproduce the temperature dependence, sign, and amplitude of $S/T$in the nickelates using Boltzmann transport theory. This demonstrates that the electronic structure obtained from first-principles calculations provides a reliable description of the fermiology of superconducting nickelates and suggests that, despite indications of strong electronic correlations, there are well-defined quasiparticles in the metallic state. Finally, we explain the differences in the Seebeck coefficient between nickelates and cuprates as originating in strong dissimilarities in impurity concentrations. Our study demonstrates that the high elastic scattering limit of the Seebeck coefficient reflects only the underlying band structure of a metal, analogous to the high magnetic field limit of the Hall coefficient. This opens a new avenue for Seebeck measurements to probe the electronic band structures of relatively disordered quantum materials. Published by the American Physical Society2024 

   more » « less
2. Lattice-Charge Coupling in a Trilayer Nickelate with Intertwined Density Wave Order

   https://doi.org/10.1103/s5j9-cbg7  

   Jia, Xun; Shen, Yao; LaBollita, Harrison; Chen, Xinglong; Zhang, Junjie; Li, Yu; Zhao, Hengdi; Kanatzidis, Mercouri G; Krogstad, Matthew; Zheng, Hong; et al (January 2026, Physical Review X)

   Intertwined charge and spin correlations are ubiquitous in a wide range of transition metal oxides and are often perceived as intimately related to unconventional superconductivity. Theoretically envisioned as driven by strong electronic correlations, the intertwined order is usually found to be strongly coupled to the lattice as signaled by pronounced phonon softening. Recently, both charge and spin density waves (CDW and SDW) and superconductivity have been discovered in several Ruddlesden-Popper (RP) nickelates, in particular trilayer nickelates $R{E}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$( $RE=\mathrm{Pr}$, La). The nature of the intertwined order and the role of lattice-charge coupling are at the heart of the debate about these materials. Using inelastic x-ray scattering, we mapped the low-energy phonon dispersions in $R{E}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$and found no evidence of softening near the CDW wave vector over a wide temperature range, which contrasts with the pronounced anomalies frequently observed in cuprate superconductors. Calculations of the electronic susceptibility revealed a peak at the observed SDW ordering vector but not at the CDW wave vector. Our experimental and theoretical findings highlight the crucial role of the spin degree of freedom and establish a foundation for understanding the interplay between superconductivity and density-wave transitions in RP nickelate superconductors and beyond. 

   more » « less
3. Measurement of the dynamic charge susceptibility near the charge density wave transition in ErTe ₃

   https://doi.org/10.1073/pnas.2424430122  

   Chaudhuri, Dipanjan; Jiang, Qianni; Guo, Xuefei; Chen, Jin; Kengle, Caitlin S; Hoveyda-Marashi, Farzaneh; Bernal-Choban, Camille; de_Vries, Niels; Chiang, Tai-Chang; Fradkin, Eduardo; et al (June 2025, Proceedings of the National Academy of Sciences)

   A charge density wave (CDW) is a phase of matter characterized by a periodic modulation of valence electron density coupled with lattice distortion. Its formation is closely tied to the dynamical charge susceptibility, $\chi (q,\omega )$, which reflects the collective electron dynamics of the material. Despite decades of study, $\chi (q,\omega )$near a CDW transition has never been measured at nonzero momentum, $q$, with meV energy resolution. Here, we investigate the canonical CDW transition in ErTe ${}_3$using momentum-resolved electron energy loss spectroscopy, a technique uniquely sensitive to valence band charge excitations. Unlike phonons, which soften via the Kohn anomaly, we find the electronic excitations exhibit purely relaxational dynamics well described by a diffusive model, with the diffusivity peaking just below the critical temperature, $T_{C1}$. Additionally, we report for the first time a divergence in the real part of $\chi (q,\omega )$in the static limit ( $\omega \to 0$), a long-predicted hallmark of CDWs. Unexpectedly, this divergence occurs as $T\to 0$, with only a weak thermodynamic signature at $T=T_{C1}$. Our study necessitates a reexamination of the traditional description of CDW formation in quantum materials. 

   more » « less
4. Thermodynamic Evidence of Fermionic Behavior in the Vicinity of One-Ninth Plateau in a Kagome Antiferromagnet

   https://doi.org/10.1103/PhysRevX.15.021076  

   Zheng, Guoxin; Zhang, Dechen; Zhu, Yuan; Chen, Kuan-Wen; Chan, Aaron; Jenkins, Kaila; Kang, Byungmin; Zeng, Zhenyuan; Xu, Aini; Ratkovski, D; et al (May 2025, Physical Review X)

   The spin- $1/2$kagome Heisenberg antiferromagnets are believed to host exotic quantum entangled states. Recently, the reports of $1/9$magnetization plateau and magnetic oscillations in a kagome antiferromagnet ${\mathrm{YCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Br}}_2\left[{\text{Br}}_x{\left(\mathrm{OH}\right)}_{1-x}\right]$(YCOB) have made this material a promising candidate for experimentally realizing quantum spin liquid states. Here, we present measurements of the specific heat $C_p$in YCOB in high magnetic fields (up to 41.5 T) down to 0.46 K, and the $1/9$plateau feature has been confirmed. Moreover, the temperature dependence of $C_p/T$in the vicinity of $1/9$plateau region can be fitted by a linear in $T$term which indicates the presence of a Dirac spectrum, together with a constant term, which indicates a finite density of states contributed by other spinon Fermi surfaces. Surprisingly, the constant term is highly anisotropic in the direction of the magnetic field. Additionally, we observe a double-peak feature near 30 T above the $1/9$plateau which is another hallmark of fermionic excitations in the specific heat. This combination of gapless behavior and the double-peak structure strongly suggests that the $1/9$plateau in YCOB is nontrivial and hosts fermionic quasiparticles. 

   more » « less
5. Probing Gluon Fluctuations in Nuclei with the First Energy-Dependent Measurement of Incoherent $J/\psi$ Photoproduction in Ultraperipheral PbPb Collisions

   https://doi.org/10.1103/w9kp-f8xr  

   Chekhovsky, V; Hayrapetyan, A; Makarenko, V; Tumasyan, A; Adam, W; Andrejkovic, J W; Benato, L; Bergauer, T; Chatterjee, S; Damanakis, K; et al (September 2025, Physical Review Letters)

   Incoherent $J/\psi$photoproduction in heavy ion ultraperipheral collisions (UPCs) provides a sensitive probe of localized, fluctuating gluonic structures within heavy nuclei. This Letter reports the first measurement of the photon-nucleon center-of-mass energy ( $W_{\gamma \mathrm{N}}$) dependence of this process in PbPb UPCs at a nucleon-nucleon center-of-mass energy of 5.02 TeV, using $1.52{\mathrm{nb}}^{-1}$of data recorded by the CMS experiment. The measurement covers a wide $W_{\gamma \mathrm{N}}$range of $\approx 40–400\mathrm{GeV}$, probing gluons carrying a fraction $x$of nucleon momentum down to an unexplored regime of $6.5\times {10}^{-5}$. Compared to baseline predictions neglecting nuclear effects, the measured cross sections exhibit significantly greater suppression at lower $x$. Additionally, the ratio of incoherent to coherent photoproduction is found to be constant across the probed $W_{\gamma \mathrm{N}}$and $x$range, disfavoring the establishment of the black disk limit. This Letter provides critical insights into the $x$-dependent evolution of fluctuating gluonic structures within nuclei and calls for further advancements in theoretical models incorporating nuclear shadowing and gluon saturation. 

   more » « less