The specific heat $C$ of the cuprate superconductors ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ and ${\mathrm{Bi}}_{2+y}{\mathrm{Sr}}_{2-x-y}{\mathrm{La}}_x{\mathrm{CuO}}_{6+\delta }$ was measured at low temperatures (down to 0.5 K) for dopings $p$ close to $p^{★}$, the critical doping for the onset of the pseudogap phase. A magnetic field up to 35 T was applied to suppress superconductivity, giving direct access to the normal state at low temperatures, and enabling a determination of $C_{\mathrm{e}}$, the electronic contribution to the normal-state specific heat at $T\to 0$. In ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ at $x=p=0.22$, 0.24 and 0.25, $C_{\mathrm{e}}/T=15\mathrm{to}16\mathrm{mJ}{\mathrm{mol}}^{-1}{\mathrm{K}}^{-2}$ at $T=2\mathrm{K}$, values that are twice as large as those measured at higher doping ($p>0.3$) and lower doping ($p<0.15$). This confirms the presence of a broad peak in the doping dependence of $C_{\mathrm{e}}$ at $p^{★}\simeq 0.19$ as previously reported for samples in which superconductivity was destroyed by Zn impurities. Moreover, at those three dopings, we find a logarithmic growth as $T\to 0$ such that $C_{\mathrm{e}}/T\sim Bln(T_0/T)$. The peak versus $p$ and the logarithmic dependence versus $T$ are the two typical thermodynamic signatures of quantum criticality. In the very different cuprate ${\mathrm{Bi}}_{2+y}{\mathrm{Sr}}_{2-x-y}{\mathrm{La}}_x{\mathrm{CuO}}_{6+\delta }$, we again find that $C_{\mathrm{e}}/T\sim Bln(T_0/T)$ at $p\simeq p^{★}$, strong evidence that this $ln(1/T)$ dependence of the electronic specific heat—first discovered in the cuprates ${\mathrm{La}}_{1.8-x}{\mathrm{Eu}}_{0.2}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ and ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$—is a universal property of the pseudogap critical point.

We have performed magnetic torque and resistivity measurements on the centrosymmetric skyrmion host ${\mathrm{GdRu}}_2{\mathrm{Si}}_2$, in which the dominant magnetic interaction leading to skyrmion formation is under debate. We observe both the de Haas–van Alphen and Shubnikov–de Haas oscillations in the forced ferromagnetic phase. The angular dependence of the quantum oscillation frequencies can be reproduced by an ab initio calculation. The de Haas–van Alphen oscillation is also observed in the double-$\mathbf{Q}$ phase with a frequency different from that in the forced ferromagnetic phase, indicating a Fermi surface reconstruction due to the coupling between localized spins and conduction electrons. Based on these experimental findings, the magnetic interactions in this system are discussed.

The quest for high-temperature superconductivity at ambient pressure is a central issue in physics. In this regard, the relationship between unconventional superconductivity and the quantum critical point (QCP) associated with the suppression of some form of symmetry-breaking order to zero temperature has received particular attention. The key question is how the strength of the electron pairs changes near the QCP, and this can be verified by high-field experiments. However, such studies are limited mainly to superconductors with magnetic QCPs, and the possibility of unconventional mechanisms by which nonmagnetic QCP promotes strong pairing remains a nontrivial issue. Here, we report systematic measurements of the upper critical field $H_{c2}$ in nonmagnetic ${\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$ superconductors, which exhibit a pure QCP of electronic nematicity characterized by spontaneous rotational-symmetry breaking. As the magnetic field increases, the superconducting phase of ${\mathrm{FeSe}}_{1-x}{\mathrm{Te}}_x$ shrinks to a narrower dome surrounding the nematic QCP. The analysis of $H_{c2}$ reveals that the Pauli-limiting field is enhanced toward the QCP, implying that the pairing interaction is significantly strengthened via nematic fluctuations emanating from the QCP. Remarkably, this nematic QCP is not accompanied by a divergent effective mass, distinct from the magnetically mediated pairing. Our observation opens up a nematic route to high-temperature superconductivity.

Quantum spin liquids (QSLs), in which spins are highly entangled, have been considered a groundwork for generating exotic superconductivity. Despite numerous efforts, superconductivity emerging from QSLs has been unrealized in actual materials due to the difficulties in stabilizing QSL states with metallic conductivity. Recently, an organic compound, $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_4{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_8$, with a nearly regular triangular lattice of molecular dimers was recognized as a candidate for doped QSLs. In this study, we report an unusual superconducting phase of $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_4{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_8$: unexpectedly large ratios of the upper critical field to the critical temperature $H_{\mathrm{c}2}/T_{\mathrm{c}}$ in fields not only parallel but also perpendicular to the two-dimensional conducting layers and a very wide region of fluctuating superconductivity above $T_{\mathrm{c}}$. Our results reveal that these peculiarities arise from strong electron correlations and possible quantum criticality unique to the doped QSL state, leading to a heavy mass of itinerant carriers and a large superconducting energy gap.

Magnetically intercalated transition metal dichalcogenides (TMDs) provide a versatile three-dimensional (3D) material platform to explore quantum phenomena and functionalities that emerge from an intricate interplay among magnetism, band structure, and electronic correlations. Here, we report the observation of a nearly magnetization-free anomalous Hall effect (AHE) accompanied by non-Fermi liquid (NFL) behavior and collinear antiferromagnetism (AFM) in V_1/3NbS₂. Our single-crystal neutron diffraction measurements identify a commensurate, collinear AFM order formed by intercalated V moments. In the magnetically ordered state, the spontaneous AHE is tenfold greater than expected from empirical scaling with magnetization, and this strongly enhanced AHE arises in the NFL regime that violates the quasiparticle picture. V_1/3NbS₂ challenges the existing single-particle framework for understanding AHEs based on one-body Berry curvature and highlights the potential of magnetically intercalated TMDs to unveil new electronic functionalities where many-body correlations play a critical role.