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We perform magnetic susceptibility and magnetic torque measurements on the organic $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br, which is recently suggested to host an exotic quantum dipole-liquid in its low-temperature insulating phase. Below the metal-insulator transition temperature, the magnetic susceptibility follows a Curie-Weiss law with a positive Curie-Weiss temperature, and a particular $M\propto \sqrt{H}$ curve is observed. The emergent ferromagnetically interacting spins amount to about 1/6 of the full spin moment of localized charges. Taking account of the possible inhomogeneous quasi-charge-order that forms a dipole-liquid, we construct a model of antiferromagnetically interacting spin chains in two adjacent charge-ordered domains, which are coupled via fluctuating charges on a Mott-dimer at the boundary. We find that the charge fluctuations can draw a weak ferromagnetic moment out of the spin singlet domains., Comment: 9 pages, 5 figures, Supplementary Material attached

Both cuprates and iron-based superconductors demonstrate nematicity, defined as the spontaneous breaking of rotational symmetry in electron systems. The nematic state can play a role in the high-transition-temperature superconductivity of these compounds. However, the microscopic mechanism responsible for the transport anisotropy in iron-based compounds remains debatable. Here, we investigate the electronic anisotropy of CaFeAsF by measuring its interlayer resistivity under magnetic fields with varying field directions. Counterintuitively, the interlayer resistivity was larger in the longitudinal configuration ($B \parallel I \parallel c$) than in the transverse one ($B \perp I \parallel c$). The interlayer resistivity exhibited a so-called coherence peak under in-plane fields and was highly anisotropic with respect to the in-plane field direction. At $T$ = 4 K and $B$ = 14 T, the magnetoresistance $\Delta\rho/\rho_0$ was seven times larger in the $B \parallel b_o$ than in the $B \parallel a_o$ configuration. Our theoretical calculations of the conductivity based on the first-principles electronic band structure qualitatively reproduced the above observations but underestimated the magnitudes of the observed features. The proposed methodology can be a powerful tool for probing the nematic electronic state in various materials., Comment: 25 pages, 5 figures

In this study, we succeeded in synthesizing new antiperovskite phosphides MPd3P (M = Ca, Sr, Ba) and discovered the appearance of a superconducting phase (0.17 ≤ x ≤ 0.55) in a solid solution (Ca1-xSrx)Pd3P. Three perovskite-related crystal structures were identified in (Ca1-xSrx)Pd3P, and a phase diagram was built on the basis of experimental results. The first phase transition from centrosymmetric (Pnma) to noncentrosymmetric orthorhombic (Aba2) occurred in CaPd3P near room temperature. The phase transition temperature decreased as Ca2+ was replaced with a larger-sized isovalent Sr2+. Bulk superconductivity at a critical temperature (Tc) of approximately 3.5 K was observed in a range of x = 0.17-0.55; this was associated with the centrosymmetric orthorhombic phase. Thereafter, a noncentrosymmetric tetragonal phase (I41md) remained stable for 0.6 ≤ x ≤ 1.0, and superconductivity was significantly suppressed as samples with x = 0.75 and 1.0 showed Tc values as low as 0.32 K and 57 mK, respectively. For further substitution with a larger-sized isovalent Ba2+, namely, (Sr1-yBay)Pd3P, the tetragonal phase continued throughout the composition range. BaPd3P no longer showed superconductivity down to 20 mK. Since the inversion symmetry of structure and superconductivity can be precisely controlled in (Ca1-xSrx)Pd3P, this material may offer a unique opportunity to study the relationship between inversion symmetry and superconductivity.

Antiperovskites are a promising candidate structure for the exploration of new materials. We discovered an antiperovskite phosphide, LaPd

Magnetic susceptibility and torque measurements have been performed for neutral BEDT-TTF crystals to investigate the diamagnetic properties. The diamagnetic susceptibility is found to be anisotropi...

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, $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{4}{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_{8}$, 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 $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{4}{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_{8}$: unexpectedly large ratios of the upper critical field to the critical temperature ${H}_{\mathrm{c}2}/{T}_{\mathrm{c}}$ in fields not only parallel but also perpendicular to the two-dimensional conducting layers and a very wide region of fluctuating superconductivity above ${T}_{\mathrm{c}}$. 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.

Resistivity measurements for a layered transition metal dichalcogenide 2H-NbSe2 were performed to investigate the in-plane anisotropy of the upper critical field (Hc2) for magnetic fields up to 14.5 T at temperatures down to 2.0 K. For fields rotated within the basal plane, the in-plane anisotropy of a characteristic field H∗ (defined as the field strength at which the resistivity reaches zero) showed twofold symmetry at low temperatures. On the basis of this result, the in-plane anisotropy of Hc2 and the superconducting gap structure in 2H-NbSe2 are discussed.

Unconventional superconductivity and magnetism are intertwined on a microscopic level in a wide class of materials, including high-$T_c$ cuprates, iron pnictides, and heavy-fermion compounds. A new approach to this most fundamental and hotly debated subject focuses on the role of interactions between superconducting electrons and bosonic fluctuations at the interface between adjacent layers in heterostructures. A recent state-of-the-art molecular-beam-epitaxy technique has enabled us to fabricate superlattices consisting of different heavy-fermion compounds with atomic thickness. These Kondo superlattices provide a unique opportunity to study the mutual interaction between unconventional superconductivity and magnetic order through the atomic interface. Here, we design and fabricate hybrid Kondo superlattices consisting of alternating layers of superconducting CeCoIn$_5$ with $d$-wave pairing symmetry and nonmagnetic metal YbCoIn$_5$ or antiferromagnetic heavy fermion metals, such as CeRhIn$_5$ and CeIn$_3$. In these Kondo superlattices, superconducting heavy electrons are confined within the two-dimensional CeCoIn$_5$ block layers and interact with the neighboring nonmagnetic or magnetic layers through the interface. In CeCoIn$_5$/YbCoIn$_5$ superlattices, the superconductivity is strongly influenced by the local inversion symmetry breaking at the interface. In CeCoIn$_5$/CeRhIn$_5$ and CeCoIn$_5$/CeIn$_3$ superlattices, the superconducting and antiferromagnetic states coexist in spatially separated layers, but their mutual coupling via the interface significantly modifies the superconducting and magnetic properties. The fabrication of a wide variety of hybrid superlattices paves a new way to study the relationship between unconventional superconductivity and magnetism in strongly correlated materials., Comment: 18 pages, 17 figures. arXiv admin note: text overlap with arXiv:1904.06937

Antiperovskites are a promising candidate structure for the exploration of new materials. We discovered an antiperovskite phosphide, LaPd$_{3}$P, following our recent synthesis of $A$Pd$_{3}$P ($A$ = Ca, Sr, Ba). While $A$Pd$_{3}$P and (Ca,Sr)Pd$_{3}$P were found to be tetragonal or orthorhombic systems, LaPd$_{3}$P is a new prototype cubic system ($a$ = 9.0317(1) A) with a noncentrosymmetric space group ($I-43m$). LaPd$_{3}$P exhibited superconductivity with a transition temperature ($T_\mathrm{c}$) of 0.28 K. The upper critical field, Debye temperature, and Sommerfeld constant ($\gamma$) were determined as 0.305(8) kOe, 267(1) K, 6.06(4) mJ mol-1 K-2 f.u.-1, respectively. We performed first-principles electronic band structure calculations for LaPd$_{3}$P and compared the theoretical and experimental results. The calculated Sommerfeld constant (2.24 mJ mol-1 K-2 f.u.-1) was much smaller than the experimental value of $\gamma$ because the Fermi energy ($E_\mathrm{F}$) was located slightly below the density of states (DOS) pseudogap. This difference was explained by the increase in the DOS at $E_\mathrm{F}$ due to the approximately 5 at.% La deficiency (hole doping) in the sample. The observed Tc value was much lower than that estimated using the Bardeen-Cooper-Schrieffer equation. To explain the discrepancy, we examined the possibility of an unconventional superconductivity in LaPd$_{3}$P arising from the lack of space inversion symmetry., Comment: 13 pages, 5 figures, 4 tables

In the recently discovered antiperovskite phosphide (Ca,Sr)Pd$_3$P, centrosymmetric (CS) and non-centrosymmetric (NCS) superconducting phases appear depending on the Sr concentration, and their transition temperatures ($T_\mathrm{c}$) differ by as much as one order of magnitude. In this study, we investigated the superconducting properties and electronic band structures of CS orthorhombic (CSo) (Ca$_{0.6}$Sr$_{0.4}$)Pd$_3$P ($T_\mathrm{c}$ = 3.5 K) and NCS tetragonal (NCSt) (Ca$_{0.25}$Sr$_{0.75}$)Pd$_3$P ($T_\mathrm{c}$ = 0.32 K) samples with a focus on explaining their large $T_\mathrm{c}$ difference. Specific heat measurements indicated that CSo (Ca$_{0.6}$Sr$_{0.4}$)Pd$_3$P was an s-wave superconductor in a moderate-coupling regime with a 2$\Delta$$_0$/k$_B$$T_\mathrm{c}$ value of 4.0. Low-lying phonons leading to the strong coupling in the structurally analogous SrPt$_3$P were unlikely to be present in CSo (Ca$_{0.6}$Sr$_{0.4}$)Pd$_3$P. Given that CSo (Ca$_{0.6}$Sr$_{0.4}$)Pd$_3$P and NCSt (Ca$_{0.25}$Sr$_{0.75}$)Pd$_3$P exhibited similar Debye temperatures ($\Theta$$_D$) of approximately 200 K, the large $T_\mathrm{c}$ difference could not be attributed to $\Theta$$_D$.$T_\mathrm{c}$ of each phase was accurately reproduced based on the Bardeen-Cooper-Schrieffer (BCS) theory using experimental data and the density of states of the Fermi level $N$(0) calculated from their band structures. We concluded that the considerable suppression of $T_\mathrm{c}$ in NCSt (Ca$_{0.25}$Sr$_{0.75}$)Pd$_3$P can be primarily attributed to the decrease in $N$(0) associated with the structural phase transition without considering the lack of inversion symmetry., Comment: 14 pages, 8 figures

Magnetic torque measurements in the spin-orbit coupled metal ${\mathrm{Cd}}_{2}{\mathrm{Re}}_{2}{\mathrm{O}}_{7}$ have been performed to investigate unique multipole orders associated with inversion symmetry breaking. The torque curves as a function of field angle are decomposed into two terms, a fourfold symmetry term (${\ensuremath{\tau}}_{4}\ensuremath{\propto}{H}^{4}$), corresponding to an electric quadrupole order, and a twofold symmetry term (${\ensuremath{\tau}}_{2}\ensuremath{\propto}{H}^{2}$), likely corresponding to an electric toroidal quadrupole order at low temperatures. Below 20 K, a strong enhancement of the fourfold symmetry term following a large phase change is observed toward the superconducting transition whereas no such behavior is evident in the twofold symmetry term. The results show anomalous changes of the electric quadrupole order at the low temperatures.

We report resistance and elastoresistance measurements on $({\mathrm{Ba}}_{0.5}{\mathrm{K}}_{0.5}){\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$, ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, and ${\mathrm{KCa}}_{2}{\mathrm{Fe}}_{4}{\mathrm{As}}_{4}{\mathrm{F}}_{2}$. The Fe-site symmetry is ${D}_{2d}$ in the first compound but ${C}_{2v}$ in the latter two, which lifts the degeneracy of the Fe ${d}_{xz}$ and ${d}_{yz}$ orbitals. The temperature dependence of the resistance and elastoresistance is similar between the three compounds. Especially, the [110] elastoresistance is enhanced with decreasing temperature irrespective of the Fe-site symmetry. This appears to be in conflict with recent Raman scattering studies on ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, which suggest the absence of nematic fluctuations. We consider possible ways of reconciliation and suggest that the present result is important in elucidating the origin of in-plane resistivity anisotropy in iron-based superconductors.

The cubic Kondo lattice ${\mathrm{YbCo}}_{2}{\mathrm{Zn}}_{20}$ is one of the heaviest known Fermi liquids. We have measured the low-temperature electrical resistivity $\ensuremath{\rho}(T)$, magnetic susceptibility $\ensuremath{\chi}(T)$, and heat capacity $C(T)$ in single crystals of $\mathrm{Yb}{({\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{2}{\mathrm{Zn}}_{20}$ ($x\ensuremath{\le}0.126$) and $\mathrm{Yb}{({\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{y})}_{2}{\mathrm{Zn}}_{20}$ ($y\ensuremath{\le}0.07$). While pure ${\mathrm{YbCo}}_{2}{\mathrm{Zn}}_{20}$ displays maxima in $\ensuremath{\rho}(T)$ and $\ensuremath{\chi}(T)$, ascribed to an enhanced crystal electric field (CEF) degeneracy, the maxima are suppressed by small amounts ($\ensuremath{\approx}6$ at.%) of substitutions of the Co atoms. This goes along with a suppression of superheavy Fermi liquid behavior as manifested in the divergence of $C/T$. We ascribe the observations to local distortions at the Yb site due to the chemical disorder in the environment, rather than to a chemical pressure effect. This fragileness to the local distortion indicates that superheavy Fermion behavior in ${\mathrm{YbCo}}_{2}{\mathrm{Zn}}_{20}$ is closely linked to an enhanced CEF degeneracy.

Magnetic torque measurements have been performed to investigate the phase transitions of the metallic pyrochlore compound $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$, in which a spin-orbit (SO) interaction leads to unique multipole orders associated with an inversion symmetry breaking. We find that the magnetic torque signals with a fourfold symmetry (${\ensuremath{\tau}}_{4}\ensuremath{\propto}{H}^{4}$) as well as a twofold symmetry (${\ensuremath{\tau}}_{2}\ensuremath{\propto}{H}^{2}$) are significantly enhanced at low temperatures below a structural phase transition temperature (\ensuremath{\sim}200 K). The analyses of the torque curve symmetries show that the ${\ensuremath{\tau}}_{4}$ term arises from an even-parity order parameter (OP) with the irreducible representation ${E}_{\mathrm{g}}$, whereas the ${\ensuremath{\tau}}_{2}$ term from an odd-parity OP with ${E}_{\mathrm{u}}$, ${T}_{1\mathrm{u}}$ or ${T}_{2\mathrm{u}}$. The parity mixing of the primary OPs shows a peculiar phase transition in the SO coupled $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{e}}_{2}{\mathrm{O}}_{7}$. The coexistence of the two OPs provides important insights into the origin of the multipole orders induced by the SO interaction.

We present the topology of spin-split Fermi surface of CaAgAs as determined by de Haas-van Alphen (dHvA) effect measurements combined with ab initio calculations. We have determined the torus-shaped nodal-line Fermi surface from the dHvA oscillations of $\beta$ and $\gamma$ orbits. The former orbit encircles the nodal-line, while the latter does not. Nevertheless, a nontrivial Berry phase is found for both orbits. The nontrivial phase of $\beta$ arises from the orbital characters, which can be expressed as a pseudospin rotating around the nodal-line. On the other hand, the phase of $\gamma$ is attributed to the vortex of real spin texture induced by an antisymmetric spin-orbit interaction. Our result demonstrates that both the real- and pseudo-spin textures are indispensable in interpreting the electronic topology in noncentrosymmetric nodal-line semimetals., Comment: 11 pages, 7 figures

Diamond has attracted attention as a next-generation semiconductor because of its various exceptional properties such as a wide bandgap and high breakdown electric field. Diamond field effect transistors, for example, have been extensively investigated for high-power and high-frequency electronic applications. The quality of their charge transport (i.e., mobility), however, has been limited due to charged impurities near the diamond surface. Here, we fabricate diamond field effect transistors by using a monocrystalline hexagonal boron nitride as a gate dielectric. The resulting high mobility of charge carriers allows us to observe quantum oscillations in both the longitudinal and Hall resistivities. The oscillations provide important information on the fundamental properties of the charge carriers, such as effective mass, lifetime, and dimensionality. Our results indicate the presence of a high-quality two-dimensional hole gas at the diamond surface and thus pave the way for studies of quantum transport in diamond and the development of low-loss and high-speed devices.

A quantum spin liquid (QSL) is an exotic state of matter in condensed-matter systems, where the electron spins are strongly correlated, but conventional magnetic orders are suppressed down to zero temperature because of strong quantum fluctuations. One of the most prominent features of a QSL is the presence of fractionalized spin excitations, called spinons. Despite extensive studies, the nature of the spinons is still highly controversial. Here we report magnetocaloric-effect measurements on an organic spin-1/2 triangular-lattice antiferromagnet, showing that electron spins are decoupled from a lattice in a QSL state. The decoupling phenomena support the gapless nature of spin excitations. We further find that as a magnetic field is applied away from a quantum critical point, the number of spin states that interact with lattice vibrations is strongly reduced, leading to weak spin–lattice coupling. The results are compared with a model of a strongly correlated QSL near a quantum critical point., A number of materials have been proposed as realizations of exotic quantum spin liquids but many important properties are difficult to establish. Isono et al. show evidence for spin-lattice decoupling in an organic material, which may help resolve conflicting results about the existence of a spin-excitation gap.

Magnetocaloric effect for a layered organic superconductor β′′-(BEDT-TTF)2SF5CH2CF2SO3 has been investigated. At low magnetic fields, a sinusoidal quantum oscillation, arising from a closed Fermi s...

A spin–orbit coupled metal Cd2Re2O7 is known to show two structural phase transitions at Ts1 ≈ 200 K and Ts2 ≈ 115 K, which are likely of an electronic origin. The magnetic torque curves have been ...

The authors would like to acknowledge the financial support from the Max-Planck Society. E.H. and M.N. acknowledge support from Deutsche Forschungsgemeinschaft (DFG) through the Project No. 107745057 (TRR80: From Electronic Correlations to Functionality). This work is also supported by JSPS KAKENHI (No. 18K04715). A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreements No. DMR-1157490 and No. DMR-1644779 and the State of Florida. The delafossite series of layered oxides includes some of the highest conductivity metals ever discovered. Of these, PtCoO2, with a room-temperature resistivity of 1.8 μΩcm for in-plane transport, is the most conducting of all. The high conduction takes place in triangular lattice Pt layers, separated by layers of Co-O octahedra, and the electronic structure is determined by the interplay of the two types of layers. We present a detailed study of quantum oscillations in PtCoO2, at temperatures down to 35 mK and magnetic fields up to 30 T. As for PdCoO2 and PdRhO2, the Fermi surface consists of a single cylinder with mainly Pt character and an effective mass close to the free-electron value. Due to Fermi-surface warping, two close-lying high frequencies are observed. Additionally, a pronounced difference frequency appears. By analyzing the detailed angular dependence of the quantum-oscillation frequencies, we establish the warping parameters of the Fermi surface. We compare these results to the predictions of first-principles electronic-structure calculations including spin-orbit coupling on Pt and Co and on-site correlation U on Co, and hence demonstrate that electronic correlations in the Co-O layers play an important role in determining characteristic features of the electronic structure of PtCoO2. Publisher PDF

Interlayer resistance is reported in a layered organic superconductor ${\ensuremath{\beta}}^{\ensuremath{''}}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{SF}}_{5}{\mathrm{CH}}_{2}{\mathrm{CF}}_{2}{\mathrm{SO}}_{3}$ with ${T}_{\mathrm{c}}\ensuremath{\approx}5$ K. At 0.7 K in parallel magnetic fields, the interlayer resistance has nonzero values in a wide field region from 2 T to the upper critical field $(\ensuremath{\sim}13\phantom{\rule{0.16em}{0ex}}\mathrm{T})$, which can be ascribed to the Josephson vortex (JV) dynamics. Significant hysteresis between 2 T and 8 T and a steplike structure between 4 T and 8 T are found, both of which become less evident with increasing temperature. In the second field-derivative curves, successive small dips are observed between 10 T and 12 T, which are ascribed to the commensurability (CM) effect between the JV lattice and the wavelength ${\ensuremath{\lambda}}_{\mathrm{FFLO}}$ of the order parameter oscillation in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. The CM effect is observed only in nearly parallel fields, showing that the FFLO phase is stabilized only in a limited field angle region. The temperature-field phase diagram and ${\ensuremath{\lambda}}_{\mathrm{FFLO}}$ values are obtained.

We perform de Haas-van Alphen measurements and quasiparticle self-consistent \textit{GW} (QS\textit{GW}) calculations on FeS. The calculated Fermi surface (FS) consists of two hole and two electron cylinders. We observe all the eight predicted FS cross sections experimentally. With momentum-independent band-energy adjustments of less than 0.1 eV, the maximum deviation between the calculated and observed cross sections is less than 0.2\% of the Brillouin zone area for $B \parallel c$. The carrier density is $\sim$0.5 carriers/Fe. The mass enhancements are nearly uniform across the FS cylinders and moderate, $\sim$2. The absence of a third hole cylinder with $d_{xy}$ character is favorable for the formation of a nodal superconducting gap., 7 pages, 3 figures

Recently the metastable 1T'-type VIB-group transition metal dichalcogenides (TMDs) have attracted extensive attention due to their rich and intriguing physical properties, including superconductivity, valleytronics physics, and topological physics. Here, a new layered WS

We report magnetic torque measurements on iron-pnictide superconductors ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ ($x\ensuremath{\approx}$ 0.69 and 0.76) to an applied field of ${B}_{a}=45$ T. The peak effect is observed in torque-vs-field curves below the irreversibility field. It is enhanced and becomes asymmetric as the field is tilted from the $c$ axis. For field directions close to the $ab$ plane, increasing- and decreasing-field curves peak at markedly different fields and exhibit a sharp jump, suggestive of a first-order phase transition, on the high- and the low-field sides of the peak, respectively. Complicated history dependence of the torque is observed in the peak-effect region. We construct and discuss the temperature-- ($T$) applied-magnetic-field (${B}_{a}$) phase diagram. Since the upper critical field for the $ab$-plane direction is comparable to the Pauli limit, we also consider possible influence of the spin paramagnetic effect on the anomalous peak effect.

Three independent components of critical current density, one for the $H//c$ axis and the other two for the $H//ab$ plane, have been studied in ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$ single crystals. When the magnetic field is applied along the $c$ axis, we observed fish-tail-like peaks in the $M\ensuremath{-}H$ hysteresis loop, and the magnetization at higher temperatures exceeds that at lower temperatures at high fields. When the field is applied parallel to the $ab$ plane, a dip structure is observed in the $M\ensuremath{-}H$ hysteresis loop near the self-field. In addition, for the $H//ab$ plane, we succeeded in separately evaluating the large and significantly anisotropic in-plane and out-of-plane ${J}_{\mathrm{c}}$. Transmission electron microscopy revealed the presence of planar defects parallel to the $ab$ plane in ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$, which have not been observed in any other iron-based superconductors. We discuss the possible relationship between the anomalous ${J}_{\mathrm{c}}$ behavior and the planar defects.

We report on the first observation of the de Haas–van Alphen (dHvA) effect in CrAs under hydrostatic pressures of up to 2.2 GPa, exceeding the critical pressure Pc ∼ 0.7 GPa, where the antiferromag...

To investigate the electronic state of CeRu2Al10, which exhibits an unusual antiferromagnetic order below TN = 27 K, we measured the electrical resistivity ρ, the transverse magnetoresistance (TMR)...

Magnetic properties of an Yb-based semiconductor YbCuS2 with a zigzag chain of Yb3+ ions were studied. The Curie–Weiss behavior of the magnetic susceptibility χ(T) indicates antiferromagnetic inter...

We report the observation of an anomalously large in-plane upper critical field, exceeding at least 2.5 times the Pauli paramagnetic limit, in a thin superconducting W film grown on a topological insulator (Bi,Sb)2Te3. This can be accounted for by setting the spin–orbit scattering length of superconducting W to a value ranging from 1 to 2 nm, which is comparable to the spin diffusion length of normal state W. The coupling between the topological surface states of (Bi,Sb)2Te3 and the wave functions of superconducting W may also contribute to the observed giant critical field. Our results suggest the universality of the spin–orbit scattering formalism for describing the transport involving the diffusive carriers as well as the Cooper pairs in systems with strong spin–orbit coupling.

The Ce atoms in CeIrSn form a quasikagome lattice in the hexagonal $c$ plane. Our single-crystal x-ray diffraction analysis has confirmed the absence of superstructure in the ZrNiAl-type structure. Motivated by the recent observation of quantum critical behaviors in the isostructural and isoelectronic compound CeRhSn, we have studied low-temperature properties of single-crystalline samples of CeIrSn by measuring the electrical resistivity, magnetic susceptibility $\ensuremath{\chi}$, magnetization $M$, and specific heat $C$ down to 0.05 K. Our study does not show evidence of a long-range magnetic ordering down to the lowest temperature. The $\ensuremath{\chi}(T)$ data show an Ising character, ${\ensuremath{\chi}}_{c}\ensuremath{\gg}{\ensuremath{\chi}}_{a}$, and power-law behaviors at low temperatures: ${\ensuremath{\chi}}_{c}\ensuremath{\propto}{T}^{\ensuremath{-}0.8}$ and ${\ensuremath{\chi}}_{a}\ensuremath{\propto}{T}^{\ensuremath{-}0.6}$. When external field $B$ is applied along the $a$ axis, both $M(B)$ and $C(B)/T$ exhibit metamagnetic anomalies at 5.5 T, which resemble those observed in CeRhSn at 3.5 T. We attribute the metamagnetic crossover under in-plane magnetic fields to the alleviation of magnetic frustration inherent in the quasikagome Ising Kondo lattice.

Despite the fact that 1111-type iron arsenides hold the record transition temperature of iron-based superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study, we completely determine the Fermi surface in the antiferromagnetic state of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum oscillation measurements and band-structure calculations. The determined Fermi surface consists of a symmetry-related pair of Dirac electron cylinders and a normal hole cylinder. From analyses of quantum-oscillation phases, we demonstrate that the electron cylinders carry a nontrivial Berry phase $��$. The carrier density is of the order of 10$^{-3}$ per Fe. This unusual metallic state with the extremely small carrier density is a consequence of the previously discussed topological feature of the band structure which prevents the antiferromagnetic gap from being a full gap. We also report a nearly linear-in-$B$ magnetoresistance and an anomalous resistivity increase above about 30 T for $B \parallel c$, the latter of which is likely related to the quantum limit of the electron orbit. Intriguingly, the electrical resistivity exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal phase ($T >$ 118 K), which may suggest an incoherent state. Our study provides a detailed knowledge of the Fermi surface in the antiferromagnetic state of 1111 parent compounds and moreover opens up a new possibility to explore Dirac-fermion physics in those compounds., 11 pages, 7 figures, 1 table