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Abstract Under magnetic fields, quantum magnets often undergo exotic phase transitions with various kinds of order. The discovery of a sequence of fractional magnetization plateaus in the Shastry-Sutherland compound SrCu2(BO3)2 has played a central role in the high-field research on quantum materials, but so far this system could only be probed up to half the saturation value of the magnetization. Here, we report the first experimental and theoretical investigation of this compound up to the saturation magnetic field of 140 T and beyond. Using ultrasound and magnetostriction techniques combined with extensive tensor-network calculations (iPEPS), several spin-supersolid phases are revealed between the 1/2 plateau and saturation (1/1 plateau). Quite remarkably, the sound velocity of the 1/2 plateau exhibits a drastic decrease of -50%, related to the tetragonal-to-orthorhombic instability of the checkerboard-type magnon crystal. The unveiled nature of this paradigmatic quantum system is a new milestone for exploring exotic quantum states of matter emerging in extreme conditions.

Frustration-induced dimensional reduction is manifested in lower dimensionality of magnetic correlations compared to that of the magnetic structure. Here the authors demonstrate the role of the uniform Dzyaloshinskii-Moriya interaction in the recently synthesized material Ca3ReO5Cl2 exhibiting dimensional reduction.

Frustrated magnets with a strong spin-lattice coupling can show rich magnetic phases and the associated fascinating phenomena. A promising platform is the breathing pyrochlore magnet CuInCr_{4}S_{8} with localized S=3/2Cr^{3+} ions, which is proposed to be effectively viewed as an S=6 Heisenberg antiferromagnet on the face-centered-cubic lattice. Here we unveil that CuInCr_{4}S_{8} exhibits a complex magnetic phase diagram with a small phase pocket (A phase) by means of magnetization, magnetostriction, magnetocapacitance, and magnetocaloric-effect measurements in pulsed high magnetic fields of up to 60 T. Remarkably, the appearance of A phase is accompanied by anomalous magnetostrictive and magnetocapacitive responses, suggesting the emergence of helimagnetism in contrast to the neighboring commensurate magnetic phases. Besides, the high-entropy nature is confirmed in the high-temperature side of A phase. These features are potentially related to a thermal fluctuation-driven multiple-q state caused by the magnetic frustration, which has been theoretically predicted but yet experimentally undiscovered in insulating magnets.

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, κ-(BEDT-TTF)_{4}Hg_{2.89}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 κ-(BEDT-TTF)_{4}Hg_{2.89}Br_{8}: unexpectedly large ratios of the upper critical field to the critical temperature H_{c2}/T_{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_{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.

We report on the magnetocaloric effect and ultrasound studies of the frustrated quasi-one-dimensional spin-1/2 compound LiCuVO_{4}, evidencing a spin-nematic state. The magnetic Grüneisen parameter diverges at the transition to the spin-nematic phase, μ_{0}H_{c3}≈40 T, showing quantum criticality accompanied by entropy accumulation. The observed high-field anomalies in the acoustic properties clearly evidence a strong involvement of the lattice in the spin dynamics. The theoretical approach, based on exchange-striction coupling with dipolar and quadrupolar contributions, suggests that the spin-dipole-strain and quadrupole-strain interactions govern the spin-nematicity in LiCuVO_{4}.

The electric resistivity of single crystalline Fe-based superconductors FeSe and FeSeTe was measured in pulsed magnetic fields up to 55 T. Te-doped iron selenide, FeSeTe, shows rather isotropic behavior in both magnetoresistance (MR) and upper critical fields ((0)/(0) = 48 T/ 42 T ∼ 1.14), when an external magnetic field is applied parallel and perpendicular to the crystallographic c-axis. These isotropic behaviors are frequently observed in an iron-based superconductor, and the isotropy in Hc2 can likely be described by the Pauli effect. In contrast, our measurements elucidate that the undoped iron selenide, FeSe, exhibits a clear anisotropy in both MR and Hc2 ((0)/(0) = 27 T/ 15 T ∼ 1.8). This behavior occurs because the clean in-plane conduction (RRR = 35) allows to form a closed electron orbit within the two-dimensional Fermi sheets only for the magnetic field parallel to the c-axis, which results in an appearance of an intrinsic (orbital-effect limited) upper critical field for the undoped FeSe. Doping of Te breaks the clean in-plane conduction and leads to a crossover from an orbital limit dominating behavior to a Pauli limit dominating one. [ABSTRACT FROM AUTHOR]

The article discusses research that resulted in the detection of a nontrivial pi geometric quantum phase, also known as a pi Berry's phase, in the bulk Rashba semiconductor BiTel via analysis of a Shubnikov-de Haas effect. Topics include phase shifts, Fermi surfaces, oscillations, and wave functions.