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Abstract The Sangre de Cristo Range in southern Colorado exposes some of the deepest Cenozoic structural levels in the Rocky Mountain region, including mylonitic shear zones associated with both the Laramide orogeny and Rio Grande rift. We investigated the relation between Laramide contraction and Rio Grande rift extension with detailed geologic mapping, kinematic analysis, and geochronometry in a 50 km2 area centered on the Independence Mine shear zone (IMSZ). The 15–100-m-thick IMSZ is one of several shallowly to moderately (~45° ± 20°) W-SW–dipping brittle-plastic shear zones along the western flank of the range. These shear zones display microstructural evidence of initiation as top-NE contractional mylonite zones, consistent with regional Laramide kinematics, which have been pervasively overprinted by shear fabrics indicating top-SW extensional reactivation. Both top-NE and top-SW shear fabrics involve cataclasis and quartz dislocation creep, although top-SW shear is more commonly localized along phyllosilicate-lined shear bands. Shear zones are hosted predominately within Proterozoic gneiss, and contain abundant chlorite and white mica derived from alteration of hornblende and feldspar, which indicates that weakening driven by fluid reactions played an important role in localizing strain. Extensional overprinting appears to be most pervasive along more steeply dipping portions of shear zones and where secondary phyllosilicates form an interconnected weak phase, which suggests that reactivation was primarily controlled by geometry and rheological contrasts inherited from contraction. One top-SW shear zone adjacent to the IMSZ cuts a late Oligocene gabbro stock, and monazite grains synkinematic with top-SW shear in the IMSZ yielded late Oligocene to Early Miocene U-Th-Pb dates that correspond with initiation of the Rio Grande rift. Reactivation of weak reverse faults may represent an important structural control during initial extension in the middle crust, prior to slip along the high-angle Sangre de Cristo normal fault system. 

The magnetic properties and phase diagrams of S = 1/2 quasi-one-dimensional Heisenberg antiferromagnets are well established with copper-containing coordination polymers as the platform of choice due to their low energy scales and ease of chemical substitution. The inability to uncover orbitally resolved components of the magnetization has, however, been a longstanding barrier to greater understanding of high field spin state transitions. In this work, we combine pulsed field magnetization, optical spectroscopy, and magnetic circular dichroism with complementary electronic structure calculations to unravel orbital-specific contributions to the magnetism in the linear chain quantum magnet [CuL2(H2O)2(pyz)](ClO4)2 [L = 5-methyl-2-pyridone; pyz = pyrazine]. In addition to revealing a spin flop and field-driven transition to the fully saturated spin state, we untangle the green → teal color change across the 185 K structural phase transition and employ what we learn about the different Cu2+ → pyrazine charge transfer excitations to decompose the magnetic circular dichroism. Analysis reveals that both eg-derived Cu2+ 3d orbitals play a role in the field-driven transition to the fully saturated state, not just those formally hosting unpaired electrons. We attribute the surprisingly strong dichroic signature at room temperature to the presence of uncorrelated spin. 

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. 

Abstract Reentrant superconductivity is an uncommon phenomenon in which the destructive effects of magnetic field on superconductivity are mitigated, allowing a zero-resistance state to survive under conditions that would otherwise destroy it. Typically, the reentrant superconducting region derives from a zero-field parent superconducting phase. Here, we show that in UTe₂crystals extreme applied magnetic fields give rise to an unprecedented high-field superconductor that lacks a zero-field antecedent. This high-field orphan superconductivity exists at angles offset between 29^oand 42^ofrom the crystallographicbtocaxes with applied fields between 37 T and 52 T. The stability of field-induced orphan superconductivity presented in this work defies both empirical precedent and theoretical explanation and demonstrates that high-field superconductivity can exist in an otherwise non-superconducting material. 

Abstract Proposed mechanisms for large intrinsic anomalous Hall effect (AHE) in magnetic topological semimetals include diverging Berry curvatures of Weyl nodes, anticrossing nodal rings or points of non-trivial bands. Here we demonstrate that a half-topological semimetal (HTS) state near a topological critical point can provide an alternative mechanism for a large AHE via systematic studies on an antiferromagnetic (AFM) half-Heusler compound TbPdBi. We not only observe a large AHE with tanΘ^H≈ 2 in its field-driven ferromagnetic (FM) phase, but also find a distinct Hall resistivity peak in its canted AFM phase. Moreover, we observe a large negative magnetoresistance with a value of ~98%. Our in-depth theoretical modelling indicates that these exotic transport properties originate from the HTS state which exhibits Berry curvature cancellation between the trivial spin-up and nontrivial spin-down bands. Our study offers alternative strategies for improved materials design for spintronics and other applications. 

Abstract In the recently discovered kagome metal CsV₃Sb₅, an intriguing proposal invoking a doped Chern insulator state suggests the presence of small Chern Fermi pockets hosting spontaneous orbital-currents and large orbital magnetic moments. While the net thermodynamic magnetization is nearly insensitive to these moments, due to their antiferromagnetic alignment, their presence can be revealed by the Zeeman effect, which shifts electron energies in magnetic fields with a proportionality given by the effectiveg−factor. Here, we determine theg-factor using the spin-zero effect in magnetic quantum oscillations. A largeg-factor enhancement is visible only in magnetic breakdown orbits between conventional and concentrated Berry curvature Fermi pockets that host large orbital moments. Such Berry-curvature-generated large orbital moments are almost always concealed by other effects. In this system, however, magnetic breakdown orbits due to the proximity to a conventional Fermi-surface section allow them to be visibly manifested in magnetic quantum oscillations. Our results provide a remarkable example of the interplay between electronic correlations and more conventional electronic bands in quantum materials.