The electronic structure of the spin-ladder cuprate Sr14Cu24O41 challenges the presumed universality of the Zhang-Rice singlet (ZRS) framework and models based exclusively on Cu-O hybridized orbitals. Combining polarization-dependent resonant soft X-ray scattering at the O K-edge with inelastic neutron scattering, we show that doped holes in the Cu2O3 ladders localize predominantly in planar non-bonding O 2pz (pπ) orbitals of rung oxygen sites rather than forming conventional ZRS states. Polarization-resolved RSXS uniquely identifies this orbital assignment, while lattice and magnetic excitations reveal its coupled consequences, establishing a unified microscopic picture that excludes the conventional σ-bonded singlet. This oxygen-sublattice charge order produces an anomalous diagonal stretching phonon and explains the absence of incommensurate magnetic fluctuations and anomalous magnon splitting. These findings motivate a reassessment of hole pairing in ladder cuprates and the sufficiency of copper-centric models for cuprate superconductors.

The intermetallic compound Fe1−xCoxSi exhibits helical magnetic order for 0.05

Recent observations of unconventional superconductivity (SC) in thin films of LaNiO2 (critical temperature Tc approximate to 10 K) and in bulk single crystals of La3Ni2O7 under pressure T-c approximate to 80 K have cemented a long sought-after class of SC nickelates. In La1-xSrxNiO2, SC appears only in films for reasons not understood. We perform a combination of experiments to probe the crystal structure and magnetic order in bulk LaNiO2 together with ab initio calculations of the electronic structure. We find that the infinite layers are naturally buckled out-of-plane. The electronic bands are largely unaffected by the buckling, but uniaxial compression along the c axis may lead to a Lifshitz transition.

The B20 type chiral magnet FeGe exhibits the formation of skyrmion-lattice (SkL) phases in the vicinity of the magnetic ordering temperature. The SkL is a magnetic superlattice composed of vortex-type topological spin objects, and it has experimentally been known that its formation requires the existence of an intermediate (IM) phase between SkL and the paramagnetic (PM) phases. We take interest in how the crystal lattice experiences the formation of these topological spin texture. In this study, we observed the so-called spin-orbit coupling induced magnetostriction related to these topological spin texture formation, in addition to the ac magnetization anomalies. The temperature and magnetic field dependences of the lattice parameter reflected the transformation of phases, such as helimagnetic (HM), SkL, IM, conical (CM), and PM phases. In the PM region, a phase characterized as gaseous skyrmions was detected similarly to the case of the same B20 type MnSi. Furthermore, the HM, CM, and IM phases were also divided into two regions. Thus, the precise phase diagram near T c was reconstructed from the prospect of the magnetostriction such that we demonstrated that the stabilization of skyrmions needs a finite magnetic field.

MnNb3S6 is a monoaxial chiral magnet and stabilizes magnetic solitons in the presence of a magnetic field (H). The number of solitons can be controlled by varying H. Furthermore, MnNb3S6 exhibits magnetization relaxation due to soliton annihilation, that is, a nonequilibrium chiral soliton lattice (CSL) state. In this study, we observed soliton locking phenomena in a CSL state on bulk MnNb3S6 crystal, as on micro-processed crystals of CrNb3S6. Thus, we could create nonequilibrium and equilibrium CSL states and switch between them. A numerical simulation revealed that the soliton number was preserved in the soliton locking region; thus, magnetization relaxation was not observed.

A graphite-like material boron carbide (BCx) was synthesized under various heat treatment conditions and extensively characterized. First, we synthesized the BCx precursor phase by a single-step reaction using a mixed solution of BBr3 and C6H6. We confirmed that the precursor phase had a graphite-like structure with B-C chemical bonds, but its crystallinity was poor. To improve their crystallinity, we annealed the precursor sample at high temperature using a high-frequency furnace and determined the annealing condition. We also investigated the magnetic properties of BCx. The high-temperature annealing for the precursor phase yields the highest Pauli paramagnetic susceptibility χPauli, indicating the highest density of states at the Fermi level. Accordingly, the high-temperature treatment for the precursor phase is significant to improve its crystallinity and physical properties. In addition, we synthesized a Ti-intercalated material TiBC by using the same procedure as that for making the BCx precursor phase. The crystal structure can be indexed by the AlB2 structure, indicating that Ti atoms are intercalated between the BC layers. The χPauli value of TiBC is obtained to be 1 order of magnitude smaller than that of BCx, suggesting the compensation of hole carriers by electron doping through Ti intercalation into the BCx system.

This section introduces superconductors with “hyperordered structures.” Recent rapid advancements in the physics and chemistry of superconductors have yielded diverse superconductors with intriguing and unique structures. Important superconducting materials were recently generated in two-dimensional (2D) layered compoundsTwo-dimensional (2D) layered compounds intercalated with various elements and molecules in which superconducting and insulating layers often coexist, that is, other ordered structures were created within the superconducting layers. Such a structure can be regarded as a “hyperordered structure.” This chapter outlines recent topical 2D layered compounds recognized as “hyperordered structures.” Moreover, other types of superconductors consisting of “hyperordered structures” are also introduced. For example, C60 is a typical hyperordered structure of carbon, that is, a carbon cluster. The superconductivity of materials consisting of clusters is also discussed in this chapter. The superconductivity in non-periodic structured materials, such as quasicrystals, which is considered as “superconductivity induced in an incomplete-ordered system (or non-periodic arrangement)” is introduced. Finally, the superconductivity discovered in graphite and graphene is described. In particular, the slight-twisted connection of two graphene sheets leads to the “Moiré super-lattice structure,” which explicitly modifies the electronic structure. Throughout this chapter, superconductivitySuperconductivity is discussed by considering the characteristic properties of “hyperordered structures.”

The reason for the absence of superconductivity in Sr2IrO4 was estimated by photoelectron spectra and photoelectron holograms. The analysis of the La photoelectron hologram concluded that La atoms are substituted to Sr sites. Two O 1s peaks were observed and were identified as the oxygens in the IrO2 and SrO planes by photoelectron holography and density functional theory (DFT) calculations. In the Ir 4f spectrum of Sr2IrO4, an unexpected Ir3+ peak was observed as much as 50% of all of the Ir. The photoelectron hologram of Ir3+ showed a displacement of about 0.15 Å. This displacement is thought to be due to the oxygen vacancies in the IrO2 plane. These oxygen vacancies and the associated local displacement of the atoms might inhibit superconductivity in spite of sufficient electron doping.

The local structure around Ag atoms in Ag-doped Bi2Se3 (AgxBi2−ySe3) was investigated by photoelectron diffraction and X-ray fluorescence holography to understand the manner of Ag atom doping. At a low Ag concentration (x=0.05), photoelectron diffraction indicated that Ag atoms occupied Bi substitution sites. However, a mere accumulation of holes via Ag substitution for Bi fails to explain the observed variation previously reported in the transport properties of Ag-doped Bi2Se3 with different x values. In particular, simple Ag substitution for Bi fails to explain the pinning of the Fermi level at the bottom of conduction band, as suggested by the observed transport properties. In the case of a high Ag concentration (x=0.2), photoelectron diffraction suggested that the Ag atoms occupied not only the substitutional Bi site but also multiple interstitial sites, namely, the octahedral site in the van der Waals interlayer and the interstitial site in the Se layer. Ag 3d photoelectron spectra revealed that the Ag atoms had the same oxidation state, +1, regardless of the type of occupied site. Furthermore, X-ray fluorescence holography was employed for a model-free local structural analysis that refined the exact locations of Ag atoms in the Bi2Se3 crystal lattice. The behavioral crossover documented herein from hole doping at the substitutional site to electron doping at multiple sites reasonably explains the dependence of electronic structures and transport properties of Ag-doped Bi2Se3 on dopant concentration.

In a magnetic superlattice composed of kinks in a ferromagnetic spin array, the change in the kink number requires the movement of the kinks to and from the crystal surface. Namely, the kinks must have a velocity, and the superlattice must be nonequilibrium. Evidence of the nonequilibrium state has never been observed in previous model compounds. In MnNb3S6 , a long magnetization relaxation was observed, and the nature of the nonequilibrium state was more pronounced in the kink annihilation process rather than the kink creation process. The annihilation process can be phenomenologically reproduced using the unfrustrated magnetic clusters model. The nonequilibrium state in the annihilation process has a longer relaxation time than that in the nucleation process, since an energy barrier exists only in the latter.

We report that the magnetostriction (MS) effects occur in a paramagnetic state of a chiral magnet CrNb3S6. Through a series of experimental tests at room temperature, structural changes were observed at the level of a unit cell. The structural parameters are dependent of the strength and direction of magnetic field (H) even at temperature excessively higher than the magnetic ordering temperature T-c of 127 K. The present paramagnetic MS prominently appeared under H parallel to the ab plane (easy plane) as opposed to under H parallel to the c axis. Features observed in the paramagnetic MS effect significantly differ from those of the spontaneous MS in the vicinity of T-c [Phys. Rev. B 102, 014446 (2020)]. In this material, the orbital angular momentum L of Cr originates from the hybridization between Cr and Nb, and L is strongly coupled with the crystal structure [Phys. Rev. B 99, 174439 (2019)]. The present study clarified that the symmetry of the CrS6 octahedron is sensitive to H even at room temperature. The paramagnetic spin-orbit coupling should induce the distortion of CrS(6)( )octahedron, resulting in the changes in Cr-Nb(4f) distance via the change in the hybridization between Cr-a(1g) and Nb-4d(z)2 orbitals.

A synthesis of single crystals of chiral dichalcogenides TM3X6 (T: 3d transition metal, M: Nb or Ta, X: S or Se) remains an intriguing issue for the investigation of emergent quantum properties such as chiral helimagnetism. In this study, we investigated a correlation between the quantity of Cr intercalation x and the magnetic property in single crystals of a chromium (Cr) intercalated chiral disulfide CrxNb3S6 in order to optimize the synthesis condition for the intercalation-controlled single crystals. The magnetic properties, including a magnetic transition temperature Tc, take different values depending on the samples. We systematically grew single crystals of CrxNb3S6 with x ranged from 0.89 to 1.03 and found that the amount of the Cr intercalation x is an essential factor in controlling the magnetic properties of the grown crystals. The magnetization anomaly, which appears in the temperature dependence as evidence of the formation of chiral magnetic soliton lattice (CSL), was observed only in a narrow region of x from 0.98 to 1.03. The single crystals with x being 0.98 and 0.99 showed the CSL behavior with the highest Tc of 133 K. These results indicate that the small number of defects on the sites for T ions dramatically affects the quality of the single crystals in the synthesis of TM3S6. We also discuss the importance of synthesizing enantiopure single crystals of chiral dichalcogenides in order to observe chiral physical properties unique to chiral compounds such as magneto-chiral effect and chiral-induced spin selectivity.

It is well known that the archetype chiral magnet MnSi stabilizes a skyrmion lattice, termed “A-phase,” in a narrow temperature range in the vicinity of the paramagnetic boundary around Tc ∼ 29 K and Hc ∼ 2 kOe. Recently, it has been predicted that at much lower temperatures below Tc, the conical helicoid and the forced ferromagnetic (FFM) states could be separated by a new “unknown state.” In order to detect this “unknown state,” we explored the phase diagram of MnSi oriented single crystals as a function of the d.c. magnetic field (H⃗dc) and the temperature (T) by using a.c. magnetization measurements. For H⃗dc∥ 〈111〉, we observed a new region, termed “B-phase,” in the magnetic phase diagram, characterized by a flat-valley-like anomaly on the in-phase component of the a.c. magnetization (m′), over 3.5 ≤ Hdc ≤ 6.2 kOe just below the low temperature (T < 6 K) FFM boundary. The observed frequency independence over 0.3–1000 Hz and the absence of any measurable absorption in the a.c. magnetization (m″) in the “B-phase” suggest a static nature. The “B-phase” was not observed for either H⃗dc∥ 〈100〉 or 〈110〉, revealing that the magnetic anisotropy could play a role in the stabilization of the phase. The “B-phase” could be compatible with the theoretical predictions if the new magnetic state is supposedly related with a relative reorientation of the four helices in MnSi.

The intermetallic compound Fe1-xCoxSi has a helical magnetic order for 0.05 < x < 0.8, whereas its orbital angular momentum contributing to the occurrence of a Dzyaloshinskii-Moriya interaction has not yet been verified. We applied soft x-ray magnetic circular dichroism spectroscopy on the Fe L-2,L- 3 and Co L-2,L- 3 edges below T-c for Fe0.75Co0.25Si such that their orbital magnetic moments m orb were evaluated independently. The dichroic signals provide direct experimental evidence that m orb for both Fe and Co is coupled in a parallel manner with each spin counterpart m(spin). The ratio of m(orb) to m(spin) is independently estimated as m(orb)/m(spin) similar to 3% for Fe and 9% for Co. By comparing the average of the two m(spin) values with the saturated magnetization using a commercial superconducting quantum interference device (SQUID) magnetometer, the hole number in the d bands for both Fe and Co is roughly estimated as approximately 1.5. This suggests that Fe and Co should be arranged closely for stabilizing the ferromagnetic moments. Published under an exclusive license by AIP Publishing,

We performed a crystal growth to obtain chirality-controlled enantiopure crystals using a laser-diode-heated floating zone (LDFZ) method with a composition-gradient feed rod. It has been argued that the crystal handedness of TSi (T : transition metal) is fixed depending on T in the case of the ones grown by the conventional methods. We found that right-handed single crystals of CoSi and MnSi were grown from the composition-gradient feed rods that consist of FeSi–CoSi and FeSi–MnSi, respectively. The obtained CoSi and MnSi crystals inherit the chirality from the seed part of FeSi, which grows in a right-handed structure, and thus has the chirality opposite to that for the crystals in the literature. The LDFZ method with the feed rods with various combinations of TSi compounds enables flexible control of the chirality of TSi and will be useful for clarifying the interplay between crystalline chirality and chirality-induced physical responses.

A. Wang,1 Z. Y. Nie,1 F. Du ,1 G. M. Pang ,1 N. Kase,2 J. Akimitsu,3 Y. Chen,1 M. J. Gutmann,4 D. T. Adroja,4,5 R. S. Perry,4,6 C. Cao,7,1 M. Smidman ,1,8,* and H. Q. Yuan1,8,9,10,† 1Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China 2Department of Applied Physics, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan 3Research Institute for Interdisciplinary Science, Okayama University, 3-1-1 Tsushima-naka, Kitaku, Okayama 700-8530, Japan 4ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxon OX11 0QX, United Kingdom 5Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa 6Centre for Materials Discovery and London Centre for Nanotechnology, University College London, London WC1E 6BT, United Kingdom 7Condensed Matter Group, Department of Physics, Hangzhou Normal University, Hangzhou 311121, China 8Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310058, China 9State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310058, China 10Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China

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The ladder-chain compound ${(\mathrm{Sr}, \mathrm{Ca})}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ is a semiconductor at ambient pressure, but becomes a bulk superconductor above the pressure of about 3 GPa. Since the compound is at the verge of the metal-insulator transition, it is reasonable to make tunnel measurements to probe the electronic density of states in its subtleties. We present the results of such measurements carried out at ambient pressure. The break junction (BJ) tunneling gives evidence for the apparent typical gap $2\mathrm{\ensuremath{\Sigma}}$ of about 140 meV at temperature $T$, equal to 4 K. The gap is smeared out at ${T}^{*}\ensuremath{\approx}90--100$ K. We interpret the gap as that induced by the charge density wave (CDW) formation, although its $T$-dependence differs from the usually observed CDW-like mean-field behavior. Quite unexpectedly, BJ spectra also exhibit distinct zero-bias peak accompanied by the low-energy gaps of $2\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}4--8$ meV immediately after BJ are formed at 4 K. The thermally driven disappearance of this apparently superconducting structure at ${T}_{c}\ensuremath{\approx}7--13$ K is consistent with the conventional properties of superconducting tunnel junctions. The resultant ratio $\mathrm{\ensuremath{\Delta}}/{T}_{c}$ is consistent with similar observed values for a high-${T}_{c}$ cuprate superconductor. Therefore, we attribute this feature as well as the Josephson-like zero-bias conductance peak to the superconductivity induced at the freshly created BJ surface of the ${(\mathrm{Sr}, \mathrm{Ca})}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$, which is semiconducting in the sample bulk. Our additional scanning tunneling microscopy data testify that the cracked atomic surface of this compound is substantially modified, which might be the reason for the superconductivity appearance.