Altermagnets are a class of materials with compensated magnetic moments, in which spin sublattices are related by specific rotational symmetries other than inversion or translation. This allows time-reversal symmetry to be broken without a net magnetization. Cr-doped FeSb2 has been theoretically proposed as a candidate d-wave altermagnetic system, yet its magnetic ground state has remained unresolved. Here, we synthesize single crystals of Fe1-xCrxSb2 and investigate their electrical transport and magnetic properties, with a focus on Fe0.85Cr0.15Sb2. Magnetization measurements suggest spin-compensated ordering below 3.5 K, where magnetic moments align along the crystallographic b-direction. Transport measurements reveal a crossover from large positive to negative magnetoresistance, while an anomalous Hall response emerges below 5 K, indicating time-reversal symmetry breaking. Muon spin relaxation measurements confirm that the magnetic ordering below 3.5 K is bulk in nature. The absence of coherent oscillations in zero-field μSR spectra and of magnetic Bragg intensity in single-crystal neutron diffraction establishes that the magnetically ordered state is short-range or disordered, rather than collinear altermagnetic order. These results demonstrate that Cr-doping alone breaks time-reversal symmetry without stabilizing long-range altermagnetic order in FeSb2.

Extreme magnetoresistance (XMR) is a phenomenon characterized by an increase in resistance by factors of 10 4 –10 7 % when a magnetic field is applied. This phenomenon is found in a number of semimetals such as WTe 2 , PtSn 4 , Cd 3 As 2 , and LaSb. The origin of XMR is still hotly debated, possibly with different materials having different (or multiple) explanations. Extreme transverse magnetoresistance of up to 8000% at 14 T and 1.8 K is measured in TiZn 16 , a semimetal with a multitude of bands crossing the Fermi energy, akin to PtSn 4 . The magnetoresistance is suppressed when the magnetic field is rotated to be parallel to the applied current, similar to PtSn 4 and PdSn 4 . The resistance of TiZn 16 follows Kohler's rule, but displays different behavior under an applied transverse field and under a longitudinal magnetic field, suggesting distinct electrical phases. Also present are Shubnikov‐de Haas and de Haas‐van Alphen oscillations with a transverse magnetic field up to 43 T, showing that despite an insulator‐like temperature‐resistance curve, charge carriers are still present. This positions TiZn 16 as an interesting addition to the investigation of XMR materials as a multi‐band metal with complex Fermi surface geometries.

Moiré semiconductors built on angle-aligned transition metal dichalcogenide (TMD) heterobilayers provide a physical realization of the Kondo lattice model, in which one TMD layer is prepared in a Mott insulating state supporting a lattice of local magnetic moments and the other layer in a metallic state supporting itinerant carriers. The artificial Kondo lattice enables the exploration of exotic states of matter near a continuously tunable Kondo breakdown. Here we report the emergence of a symmetry-broken Chern insulator at a moiré hole filling factor 4/3 in angle-aligned MoTe2/WSe2 moiré bilayers, which realize a chiral Kondo lattice. The symmetry-broken Chern insulator, which exhibits integer quantized Hall conductance at a fractional moiré filling, breaks the translational symmetry of the lattice spontaneously; it also appears only near a magnetic field-induced Kondo breakdown in the mixed-valence regime of the material. We further demonstrate that the magnetic field required to induce the Kondo breakdown and to stabilize the symmetry-broken Chern insulator is twist angle dependent. The results present new opportunities for exploring the subtle interplay between topology and Kondo interactions in moiré semiconductors.

Reducing magnetic domain size to the nanoscale can generate unconventional with short-range magnetic phases, such as spin-glass states, Griffiths phase, and superparamagnetism. Here, we report the synthesis of a two-dimensional magnet, CrxPt1−xTe2, using the self-flux method. Magnetization and anomalous Hall effect (AHE) measurements reveal a canonical temperature-dependent evolution from a blocked superparamagnetic state at low temperature to a superparamagnetic state at intermediate temperature and a paramagnetic state at high temperature. Scanning transmission electron microscopy with magnetization analyses based on the Langevin function demonstrates that the superparamagnetism arises from the formation of magnetic nanoclusters induced by Cr doping within the PtTe2 lattice. Importantly, the AHE cannot be well described by conventional scaling laws developed for long-range ordered magnetic systems. This motivates a phenomenological framework based on multiple competing scattering mechanisms, where the blocking dynamics of magnetic nanoclusters governs the AHE. These findings enhance our understanding of superparamagnetism in CrxPt1−xTe2 and motivate the development of theoretical models for short-range ordered magnetism. Reducing magnetic domain size to the nanoscale can lead to unconventional short-range magnetic phases. Here, the authors synthesize a two-dimensional magnet, CrxPt1-xTe2, revealing a temperature-dependent evolution of superparamagnetism and a unique anomalous Hall effect, advancing our understanding of short-range ordered magnetism and inspiring new theoretical models.

We perform a differential resistance study in the hydrodynamic regime of an electron liquid in GaAs/AlGaAs quantum wells. At zero magnetic field (B) a Lorentzian profile occurs in the nonlinear transport driven by a U-turn (ac) current loop, in (ac+dc) measurements a minimum deepens with the external dc current bias (j(dc)). Our analysis shows that the observed electronic transport valley induced by jdc is attributed to the Joule heating effect on the electron temperature (T-e) of the electron liquid. Quantitatively, we demonstrate that the viscosity resistivity (Delta rho) is proportional to T-2 and is consistent with the dc-current-induced electronic Gurzhi effect in various configurations of measurement.

Extreme magnetoresistance (XMR) is a phenomenon characterized by an increase in resistance by factors of 104-107% when a magnetic field is applied. This phenomenon is found in a number of semimetals such as WTe2, PtSn4, Cd3As2, and LaSb. The origin of XMR is still hotly debated, possibly with different materials having different (or multiple) explanations. Extreme transverse magnetoresistance of up to 8000% at 14 T and 1.8 K is measured in TiZn16, a semimetal with a multitude of bands crossing the Fermi energy, akin to PtSn4. The magnetoresistance is suppressed when the magnetic field is rotated to be parallel to the applied current, similar to PtSn4 and PdSn4. The resistance of TiZn16 follows Kohler's rule, but displays different behavior under an applied transverse field and under a longitudinal magnetic field, suggesting distinct electrical phases. Also present are Shubnikov-de Haas and de Haas-van Alphen oscillations with a transverse magnetic field up to 43 T, showing that despite an insulator-like temperature-resistance curve, charge carriers are still present. This positions TiZn16 as an interesting addition to the investigation of XMR materials as a multi-band metal with complex Fermi surface geometries.

Kagome metals provide a material platform for probing new correlated quantum phenomena due to the naturally incorporated linear dispersions, flat bands, and Van Hove singularities in their electronic structures. Among these quantum phenomena is the charge density wave (CDW), or the distortion of the lattice structure due to the motion of correlated electrons through the material. CDWs lower the energy of the compound, creating an energy gap that facilitates behaviors akin to superconductivity, nonlinear transport, or other quantum correlated phenomena. The kagome metal FeGe has been shown to host a CDW transition at approximately 100 K, and its occurrence is strongly influenced by the sample annealing conditions. However, a notable gap in the literature is the lack of clear thermoelectric transport evidence for electronic structure changes associated with this CDW transition. Here, we present evidence of electron behavior modification due to annealing disorder via thermoelectric measurements on FeGe crystals presenting a CDW transition and those without a CDW. The observed Nernst effect and Seebeck effects demonstrate pronounced modifications of electrical transport properties associated with CDW formation and its suppression by annealing-induced disorder, including a change in the thermopower sign and a strong enhancement of the Nernst response in the CDW state. Our results provide evidence of multiple phase transitions, which confirms the influence of CDW on the thermal properties of FeGe and demonstrates the suppression of CDW with sufficient disordering.

Understanding if low-energy excitations can remain itinerant in the presence of strong disorder remains a central challenge in frustrated quantum magnets, where disorder is generally expected to localize excitations through Anderson-like mechanisms. Here we report the emergence of charge-neutral itinerant excitations in a van der Waals compound Cr_3Se_2Br_5, a strongly disordered S = 3/2 Mott insulator with a frustrated triangular lattice. Structural analysis reveals substantial intrinsic disorder arising from Cr-site deficiency and Se/Br-site mixing, which appear to be fixed and cannot be readily tuned. No long-range magnetic order or conventional glassy behavior is observed. In addition to its highly insulating nature, the magnetic specific heat C_mag/T and thermal conductivity ąp̨p̨ą_xx/T both exhibit linear temperature dependencies with substantial finite intercepts. In particular, a sizeable field-independent residual term κ/T ≈ 0.03 W m^-1 K^-2 is observed, providing compelling evidence of itinerant low-energy excitations that carry entropy without charge. These findings conceptually advance our understanding of quantum matter by demonstrating a rare regime where the interplay of disorder, frustration, and electronic correlations actively reshapes the nature of low-energy excitations, allowing itinerant neutral excitations to coexist with strong intrinsic disorder.

Electro-optics, the tuning of optical properties of materials with electric fields, is key to a multitude of quantum and classical photonics applications. However, a major obstacle preventing many emerging use cases is inefficient modulation in cryogenic environments, as traditional tuning mechanisms degrade at low temperatures. Guided by the connection between phase transitions and nonlinearity, we identify the quantum paraelectric perovskite SrTiO_3 (STO) as the strongest cryogenic electro-optic photonic material. As a result of the unique quantum paraelectric phase of STO, we demonstrate a dynamically tunable linear Pockels coefficient (r_33) exceeding 500 pm/V at T=5 K, and study its full temperature and bias dependence. We also measure an enhanced piezo-electric coefficient (d_33) above 90 pC/N. Both of these coefficients exceed all previously reported values for cryogenic materials, including lithium niobate (r_33≈24 pm/V) and barium titanate (r_42≈170 pm/V). Furthermore, by tuning STO towards quantum criticality with oxygen isotope substitution we more than double the optical and piezo-electric nonlinearities, demonstrating a linear Pockels coefficient above 1100 pm/V. Our results probe the link between quantum phase transitions, dielectric susceptibility, and optical nonlinearities, unlocking opportunities in cryogenic optical and mechanical systems, and provide a framework for discovering new nonlinear materials.

Quantum magnetism is one of the most active fields for exploring exotic phases and phase transitions. The recently synthesized Na2BaCo(PO4)2 (NBCP) is an ideal material incarnation of the spin-1/2 easy axis triangular lattice antiferromagnet (TLAF). Experimental evidence shows that NBCP hosts the spin supersolid state with a giant magnetocaloric effect. It was also proposed that the applied magnetic field B can drive the system through Berezinskii-Kosterlitz-Thouless (BKT) and other richer quantum phase transitions. However, the detection of these transitions is challenging because they onset at extremely low temperature T at around 60 mK, and the measurement of the magnetic susceptibility of these transitions requires high sensitivity. With the help of our newly developed gradient force magnetometer in a dilution refrigerator, we constructed the contour diagram of the magnetic susceptibility in the B-T phase diagram in T as cold as 30 mK. These results provide a more comprehensive and accurate understanding of the several field-tunable quantum phase transitions and BKT melting of the spin supersolidity, which are especially significant when their giant magnetocaloric effects highlight potential applications for sub-Kelvin refrigeration under concerns about global helium shortages.

In metals, electrons in a magnetic field undergo cyclotron motion, leading to oscillations in physical properties called quantum oscillations. This phenomenon has never been seen in a robust insulator because there are no mobile electrons. We report an exception to this rule. We study a Mott insulator on a kagome lattice which does not order magnetically down to milli-Kelvin temperatures despite antiferromagnetic interactions. We observe a plateau at magnetization equal to 1 9 Bohr magneton per magnetic ion, accompanied by oscillations in the magnetic torque, reminiscent of quantum oscillations in metals. The temperature dependence obeys Fermi distribution. These phenomena are consistent with a quantum spin liquid state whose excitations are fermionic spinons with a Dirac-like spectrum coupled to an emergent gauge field.

Although electro-optic (EO) nonlinearities are essential for many quantum and classical photonics applications, a major challenge is inefficient modulation in cryogenic environments. Guided by the connection between phase transitions and nonlinearity, we identify the quantum paraelectric perovskite SrTiO3 as a strong cryogenic EO [>500 picometers per volt (pm/V)] and piezo-electric material (>90 picocoulombs per newton) at T = 5 K, at frequencies to at least 1 megahertz. Furthermore, by tuning SrTiO3 toward quantum criticality, we more than double the EO and piezo-electric effects, demonstrating a linear Pockels coefficient above 1000 pm/V. Our results probe the link between quantum phase transitions, dielectric susceptibility, and nonlinearity, unlocking opportunities in cryogenic optical and mechanical systems and providing a framework for discovering new nonlinear materials.

We observe magnetic quantum oscillations in the heat capacity of the Kondo insulator YbB_{12}. The frequency of these oscillations, F=700  T, agrees with that from magnetoresistance and torque magnetometry experiments for μ_{0}H>35  T in the Kondo insulating phase. Remarkably, the quantum-oscillation amplitudes in the heat capacity are substantial, with ΔC[over ˜]/T≈0.5  mJ mol^{-1} K^{-2} at 0.8 K, accounting for 13% of the known linear heat-capacity coefficient γ. Double-peak structures of quantum-oscillation amplitudes due to the distribution function of fermions were identified and used to determine the value of the effective mass from the heat capacity, which agrees well with that from torque magnetometry. These observations support bulk charge-neutral fermions contributing to the quantum oscillations in YbB_{12}.

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 YCu_{3}(OH)_{6}Br_{2}[Br_{x}(OH)_{1-x}] (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.

While the spin-ice state of bulk pyrochlores such as Dy_{2}Ti_{2}O_{7} and Ho_{2}Ti_{2}O_{7} has been extensively studied in the past several decades due to its unique degenerate ground state and emergent monopole excitation, whether it survives in the thin-film form remains a mystery. The limited volume of the thin-film sample makes it challenging to study the intrinsic magnetic properties. Here, we synthesized 18-nm-thick Dy_{2}Ti_{2}O_{7} thin film on yttria-stabilized zirconia with 9.5  mol% Y_{2}O_{3} substrate and capped it by a thin conductive Bi_{2}Ir_{2}O_{7} layer and performed the proximitized magnetoresistance measurements. Our Letter found that the ice-rule-breaking phase transition survives but with a modified effective nearest-neighbor interaction (J_{eff}=1.054  K) and distorted Ising spin axes (ε=+0.051) compared to the bulk crystal. The results are supported by the simultaneously measured capacitive torque magnetometry. Our Letter demonstrates that proximitized transport is an effective tool for thin films of insulating frustrated magnets.

The anomalous Hall effect describes the generation of a transverse voltage by a longitudinal current even in the absence of an external magnetic field. While typically observed in ferromagnets, it has also been predicted to arise in altermagnets, materials characterized by rotational symmetries that enable broken time reversal symmetry despite compensated collinear magnetic ordering. These symmetries enforce band (anti)crossings that can generate significant contributions to the Berry curvature that drives the anomalous Hall effect. This Berry curvature is predicted to exhibit a characteristic multipolar order, resulting in a symmetry-enforced distribution at or near net compensation which is highly sensitive to perturbations that distort this balance. However, exploring the predicted multipolar Berry curvature of altermagnets and its reversible manipulation remains challenging. Here, we demonstrate evidence for the multipolar nature of the altermagnetic Berry curvature in MnTe by tuning the anomalous Hall effect via uniaxial stress. Upon straining, the magnitude of the anomalous Hall conductivity changes and, at a critical strain of 0.14

The correlation of topology and disorder has attracted great intention due to appropriate disorder could induce the phase transition between trivial and nontrivial topological states. While it is widely recognized that strong disorder can produce rich phase diagrams in topological nontrivial states, moderate disorder has been proposed to induce transitions into topologically nontrivial phases counter-intuitively, leading to the concept of topological Anderson insulators. This phenomenon has been theoretically explored and simulated in various systems, yet experimental realization in solid state systems has remained elusive due to challenges in controlling disorder. Here, we report the experimental observation of Chern insulator state signed by the coexistence of quantized Hall plateau and zero longitudinal resistance in monolayer MnBi_4Te_7 Hall bar device, which originally hosts a trivial insulating state with Chern number C = 0 in clean limit. We demonstrate that the observed trivial to nontrivial transition in this monolayer device can be attributed to disorder, evidenced by universal conductance fluctuations. Our findings substantiate the existence of a long-sought topological Anderson Chern insulator in real materials, a unique variant of the topological Anderson insulator characterized by broken time-reversal-symmetry.

Ferro-rotational magnet RbFe(SO4)2has attracted attention for its stable ferro-rotational phase and electric-field-controlled magnetic chirality. This work presents the multiferroic properties andH-Tphase diagram of RbFe(SO4)2, which have been underexplored. Our measurements of magnetic susceptibility, ferroelectric polarization, and dielectric constant under various magnetic fields reveal four distinct phases: (I) a ferroelectric and helical magnetic phase below 4 K and 6 T, (II) a paraelectric and collinear magnetic phase below 4 K and above 6 T, (III) a paraelectric and non-collinear magnetic phase below 4 K and above 9 T, and (IV) a paraelectric and paramagnetic above 4 K. This study clarifies the multiferroic behavior andH-Tphase diagram of RbFe(SO4)2, providing valuable insights into ferro-rotational magnets.

Quantum magnetism is one of the most active fields for exploring exotic phases and phase transitions. The recently synthesized Na2BaCo(PO4)2 (NBCP) is an ideal material incarnation of the spin-12 easy-axis triangular lattice antiferromagnet (TLAF). Experimental evidence shows that NBCP hosts the spin supersolid state with a giant magnetocaloric effect. Theory further predicts that magnetic fields can drive NBCP through Berezinskii-Kosterlitz-Thouless (BKT) and other richer quantum phase transitions. However, detecting these transitions is challenging, as they onset at ultralow temperatures near 60 mK and require high magnetization sensitivity. Using a newly developed gradient force magnetometer in a dilution refrigerator, we mapped the magnetic susceptibility phase diagram down to 30 mK. Our results provide a more comprehensive and accurate understanding of BKT melting of spin supersolidity and several field-tunable quantum phase transitions, which establish NBCP as a model platform for frustrated magnetism and highlight potential applications of its giant magnetocaloric effects.

Metals with kagome lattice provide bulk materials to host both the flat-band and Dirac electronic dispersions. A new family of kagome metals is recently discovered inAV6Sn6. The Dirac electronic structures of this material needs more experimental evidence to confirm. In the manuscript, we investigate this problem by resolving the quantum oscillations in both electrical transport and magnetization in ScV6Sn6. The revealed orbits are consistent with the electronic band structure models. Furthermore, the Berry phase of a dominating orbit is revealed to be aroundπ, providing direct evidence for the topological band structure, which is consistent with calculations. Our results demonstrate a rich physics and shed light on the correlated topological ground state of this kagome metal.