Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several kagome magnets have appeared as the most promising platforms. Here, ...we explore magnetic correlations in the kagome magnet Co
Sn
S
. Using muon spin-rotation, we present evidence for competing magnetic orders in the kagome lattice of this compound. Our results show that while the sample exhibits an out-of-plane ferromagnetic ground state, an in-plane antiferromagnetic state appears at temperatures above 90 K, eventually attaining a volume fraction of 80% around 170 K, before reaching a non-magnetic state. Strikingly, the reduction of the anomalous Hall conductivity (AHC) above 90 K linearly follows the disappearance of the volume fraction of the ferromagnetic state. We further show that the competition of these magnetic phases is tunable through applying either an external magnetic field or hydrostatic pressure. Our results taken together suggest the thermal and quantum tuning of Berry curvature induced AHC via external tuning of magnetic order.
Abstract
Charge ordered kagome lattices have been demonstrated to be intriguing platforms for studying the intertwining of topology, correlation, and magnetism. The recently discovered charge ordered ...kagome material ScV
6
Sn
6
does not feature a magnetic groundstate or excitations, thus it is often regarded as a conventional paramagnet. Here, using advanced muon-spin rotation spectroscopy, we uncover an unexpected hidden magnetism of the charge order. We observe an enhancement of the internal field width sensed by the muon ensemble, which takes place within the charge ordered state. More importantly, the muon spin relaxation rate below the charge ordering temperature is substantially enhanced by applying an external magnetic field. Taken together with the hidden magnetism found in
A
V
3
Sb
5
(
A
= K, Rb, Cs) and FeGe kagome systems, our results suggest ubiqitous time-reversal symmetry-breaking in charge ordered kagome lattices.
To trace the origin of time-reversal symmetry breaking (TRSB) in Re-based superconductors, we performed comparative muon-spin rotation and relaxation (μSR) studies of superconducting ...noncentrosymmetric Re_{0.82}Nb_{0.18} (T_{c}=8.8 K) and centrosymmetric Re (T_{c}=2.7 K). In Re_{0.82}Nb_{0.18}, the low-temperature superfluid density and the electronic specific heat evidence a fully gapped superconducting state, whose enhanced gap magnitude and specific-heat discontinuity suggest a moderately strong electron-phonon coupling. In both Re_{0.82}Nb_{0.18} and pure Re, the spontaneous magnetic fields revealed by zero-field μSR below T_{c} indicate time-reversal symmetry breaking and thus unconventional superconductivity. The concomitant occurrence of TRSB in centrosymmetric Re and noncentrosymmetric ReT (T=transition metal), yet its preservation in the isostructural noncentrosymmetric superconductors Mg_{10}Ir_{19}B_{16} and Nb_{0.5}Os_{0.5}, strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re and ReT. We discuss the superconducting order parameter symmetries that are compatible with the experimental observations.
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•The spin reorientation effect can be induced by applied hydrostatic pressure and/or a magnetic field.•Both TSRT and magnetization tend to decrease under hydrostatic pressure.•The shift of TSRT is ...related to changes in the crystal lattice constants and anisotropy parameter.•Entropy change attains large values a wide range of temperatures.•The application of hydrostatic pressure induces a strong BCE.
The effect of hydrostatic pressure on magnetic entropy change in a magnetic field, ΔSm, in Fe7Se8 single crystals is determined. The application of hydrostatic pressure shifts the spin–reorientation transition temperature, TSRT, to lower temperatures, similar to the action of a magnetic field applied perpendicularly to the c-axis. The magnetization of Fe7Se8 in a field parallel to the c-axis monotonically decreases under increasing pressure. ΔSm and the refrigeration capacity of investigated crystals strongly depend on TSRT and thus on hydrostatic pressure. Experimental results are described in the frame of a one-ion model of magnetic anisotropy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report the observation of anomalous Hall resistivity in single crystals of EuAl4 , a centrosymmetric tetragonal compound, which exhibits coexisting antiferromagnetic (AFM) and charge-density-wave ...(CDW) orders with onset at T N ∼ 15.6 K and T CDW ∼ 140 K , respectively. In the AFM state, when the magnetic field is applied along the c -axis direction, EuAl4 undergoes a series of metamagnetic transitions. Within this field range, we observe a clear humplike anomaly in the Hall resistivity, representing part of the anomalous Hall resistivity. By considering different scenarios, we conclude that such a humplike feature is most likely a manifestation of the topological Hall effect, normally occurring in noncentrosymmetric materials known to host nontrivial topological spin textures. In view of this, EuAl4 would represent a rare case where the topological Hall effect not only arises in a centrosymmetric structure, but it also coexists with CDW order.
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The tetragonal Mo5PB2 compound was recently reported to show superconductivity with a critical temperature up to 9.2 K. In search of evidence for multiple superconducting gaps in Mo5PB2, ...comprehensive measurements, including magnetic susceptibility, electrical resistivity, heat capacity, and muon-spin rotation and relaxation measurements were carried out. Data from both low-temperature superfluid density and electronic specific heat suggest a nodeless superconducting ground state in Mo5PB2. Two superconducting energy gaps Δ0 = 1.02 meV (25%) and 1.49 meV (75%) are required to describe the low-T electronic specific-heat data. The multigap features are clearly evidenced by the field dependence of the electronic specific-heat coefficient and the Gaussian relaxation rate in the superconducting state (i.e., superfluid density), as well as by the temperature dependence of the upper critical field. By combining our extensive experimental results with numerical band-structure calculations, we provide compelling evidence of multigap superconductivity in Mo5PB2.
Superconducting materials with a nontrivial band structure are potential candidates for topological superconductivity. Here, by combining muon-spin rotation and relaxation (μSR) methods with ...theoretical calculations, we investigate the superconducting and topological properties of the rocksalt-type compounds NbC and TaC (with Tc = 11.5 and 10.3 K, respectively). At a macroscopic level, the magnetization and heat-capacity measurements under applied magnetic field provide an upper critical field of 1.93 and 0.65 T for NbC and TaC, respectively. The low-temperature superfluid density, determined by transverse-field μ SR and electronic specific-heat data, suggest a fully gapped superconducting state in both NbC and TaC, with a zero-temperature gap Δ0 = 1.90 and 1.45 meV, and a magnetic penetration depth λ0 = 141 and 77 nm, respectively. Band-structure calculations suggest that the density of states at the Fermi level are dominated by the Nb 4d (or Ta 5d ) orbitals, which are strongly hybridized with the Cp orbitals to produce large cylinderlike Fermi surfaces, similar to those of high- Tc iron-based superconductors. Without considering the spin-orbit coupling (SOC) effect, the first Brillouin zone contains three closed node lines in the bulk band structure, protected by time-reversal and space-inversion symmetry. When considering SOC, its effects in the NbC case appear rather modest. Therefore, the node lines may be preserved in NbC, hence proposing it as a potential topological superconductor.
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We report a comprehensive study of the centrosymmetric Re3 B and noncentrosymmetric Re7 B3 superconductors. At a macroscopic level, their bulk superconductivity (SC), with Tc = 5.1 K(Re3 B) and 3.3 ...K(Re7 B3), was characterized via electrical-resistivity, magnetization, and heat-capacity measurements, while their microscopic superconducting properties were investigated by means of muon-spin rotation and relaxation (μ SR). In both Re3 B and Re7 B3 the low-T zero-field electronic specific heat and the superfluid density (determined via transverse-field μ SR) suggest a nodeless SC. Both compounds exhibit some features of multigap SC, as evidenced by the temperature-dependent upper critical fields Hc2 (T), as well as by electronic band-structure calculations. The absence of spontaneous magnetic fields below the onset of SC, as determined from zero-field μ SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of both Re3 B and Re7 B3. Our results suggest that a lack of inversion symmetry and the accompanying antisymmetric spin-orbit coupling effects are not essential for the occurrence of multigap SC in these rhenium-boron compounds.
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