Hui Qiu Yuan

Magnetic anisotropy encodes key information about the angular dependence of the magnetic free energy, but its quantitative characterization often requires probes beyond conventional magnetometry. Magnetotropic susceptibility offers a thermodynamic route to this problem. Here we use quartz tuning-fork resonators to establish the ferromagnet Cr ₂ Ge ₂ Te ₆ as a controlled benchmark for spin-derived magnetic anisotropy and compare it with the kagome metal CsV ₃ Sb ₅ . Although both systems exhibit pronounced magnetic anisotropy at low temperature and low field, their field evolution is qualitatively distinct. In Cr ₂ Ge ₂ Te ₆ , the full angular and field-dependent response is quantitatively captured by an easy-axis ferromagnetic model. In CsV ₃ Sb ₅ , by contrast, the anisotropic response persists and strengthens to high magnetic fields, indicating a moment that is not simply spin-ferromagnetic in origin but is instead consistent with the proposed loop-current magnetism. This work indicates high-field magnetotropic susceptibility as a thermodynamic criterion for distinguishing rotatable spin magnetism from possible lattice-locked orbital-current magnetism in correlated quantum materials.

The recently discovered heavy-fermion spin-triplet superconductor candidate UTe₂ provides a rich platform for unconventional pairing and topological phenomena. However, limited has been known about its superconducting order parameters and their evolution with control parameters, largely due to the lack of appropriate symmetry-sensitive detection methods. Here, we report comprehensive point-contact spectroscopy measurements of pressurized UTe₂ on the (0 0 1) surface. The observation of Andreev bound states strongly suggests the presence of a p_z component in the superconducting order parameters. Quantitative analysis based on an extended Blonder-Tinkham-Klapwijk model unveils the superconducting order parameters with a finite odd-k_z component (e.g., B_2u or B_3u) for both ambient and pressurized UTe₂. Remarkably, the multiple superconducting phases can be distinguished by a single parameter 〈Δ_z〉/〈Δ_x(y)〉, the relative weight between the p_z-wave and p_x(y)-wave pairings. These findings place stringent constraints on the pairing symmetry and provide essential spectroscopic signatures for distinguishing pressure-induced multiple superconducting phases in UTe₂.

Nonreciprocal responses transform broken symmetries into direction-dependent functionality, while a nonreciprocal response encoded directly in static magnetic response of an ordered magnet has not been realized. Here we reveal an intrinsic transverse magnetic nonreciprocity in the noncollinear antiferromagnet Mn3Ge. Using torque magnetometry, we observe a pronounced transverse torque that is odd under magnetic-field reversal, in sharp contrast to the reciprocal response of conventional magnets. A concomitant even-in-field planar Hall response emerges at the same low temperature around 210~K, well below the Neel temperature. Together, these measurements reveal a field-reversal-even transverse magnetic response in which opposite fields select symmetry-related, rather than time-reversed, noncollinear antiferromagnetic states. We attribute this behavior to spin-orbit-coupling-induced breaking of spin space group symmetry, which locks the noncollinear spin texture and its net magnetization to the lattice. These results establish a nonreciprocal magnetic response as a distinct collective response of chiral antiferromagnets, extending nonreciprocal phenomena beyond charge-current-based transport.

Kagome metals are prone to charge-density wave (CDW), magnetic, and superconducting phases, with their flat electronic band conducive for correlated physics. In contrast to the weakly correlated AV3Sb5 (A = K, Rb, Cs) kagome metals with a 2 × 2 CDW, CsCr3Sb5 is a correlated metal with a flat band close to the Fermi level, and exhibits a 4 × 1 CDW intertwined with magnetic order. Under pressure, the intertwined orders are suppressed and give way to a dome of superconductivity that emerges from a non-Fermi liquid normal state. Here, we solve the crystal structure of the 4×1 CDW state in CsCr3Sb5, and show it consists of Cr dimers separated by Cr chains. First-principles calculations show the dominant exchange interaction is antiferromagnetic within the dimers, while the intra-chain and dimer-chain couplings are much weaker. The CDW transition of CsCr3Sb5 is found to be more strongly first-order than those in AV3Sb5, without significant soft phonons or diffuse scattering above the CDW transition temperature. These findings suggest that fluctuating antiferromagnetic dimers may play a major role in the electron pairing of superconducting CsCr3Sb5.

Quantum phase transitions are an established setting for emergent phenomena driven by strong electronic correlations, including strange metals and unconventional superconductivity. These have been explored extensively in Kondo lattice materials tuned to an antiferromagnetic quantum critical point (QCP), but superconductivity emerging near ferromagnetic quantum criticality is not yet observed, and the conditions under which it occurs in proximity to ferromagnetism are undetermined. Here, we report a new setting for superconductivity in the ferromagnetic Kondo-lattice material Ce₅CoGe₂, where there is a ferromagnetic ground state at ambient pressure, which evolves to antiferromagnetism under applied pressures. The antiferromagnetic transition is suppressed to a zero-temperature QCP, which is accompanied by strange-metal behavior. Superconductivity does not occur at the QCP, but instead appears at pressures beyond the magnetic instability. These findings suggest that Ce₅CoGe₂ represents a distinct class of correlated materials exhibiting a unique scenario for the emergence of superconductivity, likely associated with unconventional pairing mechanisms beyond spin-fluctuations.

Quantum phase transitions are an established setting for emergent phenomena driven by strong electronic correlations, including strange metals and unconventional superconductivity. These have been explored extensively in Kondo lattice materials tuned to an antiferromagnetic quantum critical point (QCP), but superconductivity emerging near ferromagnetic quantum criticality is not yet observed, and the conditions under which it occurs in proximity to ferromagnetism are undetermined. Here, we report a new setting for superconductivity in the ferromagnetic Kondo-lattice material Ce5CoGe2, where there is a ferromagnetic ground state at ambient pressure, which evolves to antiferromagnetism under applied pressures. The antiferromagnetic transition is suppressed to a zero-temperature QCP, which is accompanied by strange-metal behavior. Superconductivity does not occur at the QCP, but instead appears at pressures beyond the magnetic instability. These findings suggest that Ce5CoGe2 represents a distinct class of correlated materials exhibiting a unique scenario for the emergence of superconductivity, likely associated with unconventional pairing mechanisms beyond spin-fluctuations.