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• The X 2 N (X = Ca,Sr) can change from non-magnetic metal into the ferromagnetic semiconductors by oxygen termination. • The Ca 2 NO 2 and Sr 2 NO 2 monolayers become half metals under carrier doping. • The spin polarized direction of Ca 2 NO 2 monolayer is depended on the carrier doping type. Two-dimensional (2D) ferromagnetic semiconductors with robust magnetism are urgently desired for nanoscale spintronics applications. However, it remains a challenge to realize them experimentally. In this work, we proposed intriguing 2D p-orbital ferromagnetic semiconductors X 2 NO 2 (X = Ca , Sr) monolayer with 3 μ B magnet per unit under O surface termination using first-principles calculations. The Ca 2 NO 2 monolayer is bipolar magnetic material (BMS) with spin-flip gap 0.24 eV, and the Sr 2 NO 2 is half-semiconductor (HSC) with spin-flip gap 0.31 eV, which is large enough to prevent the spin-flip transition. The Curie temperature can reach to 206 and 239 K, respectively, due to the superexchange interaction between N - ions. The values are much higher than the boiling point of liquid nitrogen (77 K) and comparable to that of the reported ScCl monolayer. Moreover, the half metals are obtained via carrier doping for both the Ca 2 NO 2 and Sr 2 NO 2 monolayers. In addition, the half-metallic completely spin-polarized direction of BMS Ca 2 NO 2 monolayer can be controlled by carrier doping type. Furthermore, the magnetism of X 2 NO 2 monolayer is derived from p orbital, without the involvement of conventional transition metals or rare earth atoms. This is advantageous for high-speed and long-distance spin-polarization transport. These results suggest that the X 2 NO 2 monolayer can develop spin field effect transistor for information processing and storage, and open opportunities for designing new ferromagnetic semiconductors. [ABSTRACT FROM AUTHOR]

Majorana Josephson junctions in nanowire systems exhibit a pseudo-4 π period current-phase relation in the clean limit. In this work, we study how this current-phase relation responds to a tilted magnetic field in a disordered Majorana Josephson junction within the Bogoliubov-de Gennes approach. We show that the tilted magnetic field induces a ϕ 0 phase shift to the current-phase relation. Most importantly, we find that this ϕ 0 -junction behavior is robust even in the presence of disorders. [ABSTRACT FROM AUTHOR]

Understanding the interplay between superconductivity and magnetism has been a longstanding challenge in condensed matter physics. Here we report high pressure studies on the C-type antiferromagnetic semiconductor EuTe2 up to 36.0 GPa. A structural transition from the I4/mcm to the C2/m space group is identified at ~16 GPa. Superconductivity is observed above ~5 GPa in both structures. In the low-pressure phase, magnetoresistance measurements reveal strong couplings between the local moments of Eu2+ and the conduction electrons of Te 5p orbits. The upper critical field of superconductivity is well above the Pauli limit. While EuTe2 becomes nonmagnetic in the high-pressure phase and the upper critical field drops below the Pauli limit. Our results demonstrate that the high upper critical field of EuTe2 in the low-pressure phase is due to the exchange field compensation effect of Eu2+ and the superconductivity in both structures may arise in the framework of the Bardeen-Cooper-Schrieffer theory. Understanding the interplay between superconductivity and magnetism has been a longstanding challenge in condensed matter physics. Here, the authors uncover a sensitive coupling between the two within the pressure-tuned phase diagram of EuTe2 and find that certain magnetic orders can stabilize conventional superconductivity far exceeding the Pauli limit. [ABSTRACT FROM AUTHOR]

We report a systematic investigation on the evolution of the structural and physical properties, including the charge density wave (CDW) and superconductivity of the polycrystalline CuIr2Te4−xIx for 0.0 ≤ x ≤ 1.0. X-ray diffraction results indicate that both of a and c lattice parameters increase linearly when 0.0 ≤ x ≤ 1.0. The resistivity measurements indicate that the CDW is destabilized with slight x but reappears at x ≥ 0.9 with very high TCDW. Meanwhile, the superconducting transition temperature Tc enhances as x increases and reaches a maximum value of around 2.95 K for the optimal composition CuIr2Te1.9I0.1 followed by a slight decrease with higher iodine doping content. The specific heat jump (ΔC/γTc) for the optimal composition CuIr2Te3.9I0.1 is approximately 1.46, which is close to the Bardeen–Cooper–Schrieffer value of 1.43, indicating that it is a bulk superconductor. The results of thermodynamic heat capacity measurements under different magnetic fields [Cp(T, H)], magnetization M(T, H) and magneto-transport ρ(T, H) measurements further suggest that CuIr2Te4−xIx bulks are type-II superconductors. Finally, an electronic phase diagram for this CuIr2Te4−xIx system has been constructed. The present study provides a suitable material platform for further investigation of the interplay of the CDW and superconductivity. [ABSTRACT FROM AUTHOR]

Graphene was predicted to have a long spin relaxation time in the range of microseconds to milliseconds due to its weak spin-orbit coupling and hyperfine interaction. However, very short spin relaxation times were measured experimentally on the order of nanoseconds. Magnetic proximity effect from spin valves were considered strongly to influence the electronic and spin properties in graphene. Here, a graphene/nonmagnetic semiconductor CdX heterostructure is proposed to eliminate the magnetic effect and to fulfill optical injection of spin polarization. Based on the first-principles calculation within the density functional theory, we perform a systematic study on the structural, electronic properties and band structures of the heterostructures, and find that graphene on CdX (X = S, Se and Te) slabs preserves its linear Dirac band structure within the bandgap of CdX, and a built-in electric field occurs near the interface. The built-in electric field drives spin polarized electrons into graphene preferably. An optical detection scheme of spin relaxation time of graphene is proposed based on Faraday and Hanle effects. [Display omitted] • A graphene/nonmagnetic semiconductor heterostructure constructed to eliminate strong magnetic effects on spin relaxation time of electrons in graphene. • First-principles calculations reveal Graphene on CdX (X = S, Se and Te) slabs preserves its linear Dirac band structure which locates within the bandgap of CdX. • A built-in electric field exists within interface, which favor spin polarized electrons transported into graphene. • A new scheme of all-optical injection and detection of electron spin is proposed to measure true long spin relaxation time of graphene. [ABSTRACT FROM AUTHOR]

In this study, we determined the effect of doping with the noble metal Ag on CuIr 2 Te 4 superconductors. Based on the resistivity, magnetization, and heat capacity, we explored the changes in the superconductivity (SC) and charge density wave (CDW) for Cu 1- x Ag x Ir 2 Te 4 (0 ≤ x ≤ 1) as a function of isoelectric substitution (Cu/Ag). We assessed a complete set of competing states from suppressed CDW in the low doping region to superconductor in the middle doping region and re-entrant CDW in the high doping region, thereby obtaining an electronic phase diagram, where the superconducting dome was near bipartite CDW regions with a maximum superconducting temperature (T c) of about 2.93 K at an Ag doping level of 12%. The lower H c 1 and upper H c 2 critical magnetic fields were determined for some representative samples in the Cu 1- x Ag x Ir 2 Te 4 series based on magnetization and resistivity measurements, respectively. We showed that H c 1 decreased whereas H c 2 increased as the doping content increased. The specific heat anomalies at the superconducting transitions Δ C el / γT c for representative samples comprising Cu 0.92 Ag 0.08 Ir 2 Te 4 , Cu 0.88 Ag 0.12 Ir 2 Te 4 , and Cu 0.85 Ag 0.15 Ir 2 Te 4 were approximately 1.40, 1.44, and 1.42, respectively, which are all near the Bardeen-Cooper-Schrieffer (BCS) value of 1.43 and they indicate bulk SC in these compounds. • Series of new Cu 1- x Ag x Ir 2 Te 4 superconductors investigated. • Dome-like superconductivity established. • Possible re-appearance of charge density wave states observed. [ABSTRACT FROM AUTHOR]

Low-dimensional magnetic structures coupled with superconductors are promising platforms for realizing Majorana zero modes, which have potential applications in topological quantum computing. Here, we report a two-dimensional (2D) magnetic-superconducting heterostructure consisting of single-layer chromium diiodide (CrI 2 ) on a niobium diselenide (NbSe 2 ) superconductor. Single-layer CrI 2 nanosheets, which hold antiferromagnetic (AFM) ground states by our first-principles calculations, were epitaxially grown on the layered NbSe 2 substrate. Using scanning tunneling microscopy/spectroscopy, we observed robust in-gap states spatially located at the edge of the nanosheets and defect-induced zero-energy peaks inside the CrI 2 nanosheets. Magnetic-flux vortices induced by an external field exhibit broken 3-fold rotational symmetry of the pristine NbSe 2 superconductor, implying the efficient modulation of the interfacial superconducting states by the epitaxial CrI 2 layer. A phenomenological model suggests the existence of chiral edge states in a 2D AFM-superconducting hybrid system with an even Chern number, providing a qualitatively plausible understanding for our experimental observation.

The intricate correlation between lattice geometry, topological behavior and charge degrees of freedom plays a key role in determining the physical and chemical properties of a quantum-magnetic system. Herein, we investigate the introduction of the unusual oxidation state as an alternative pathway to modulate the magnetic ground state in the well-known S = 1 Haldane system nickelate Y 2 BaNiO 5 (YBNO). YBNO is topologically reduced to incorporate d 9 -Ni + ( S = 1/2) in the one-dimensional Haldane chain system. The random distribution of Ni + for the first time results in the emergence of a one-dimensional ferromagnetic phase with a transition temperature far above room temperature. Theoretical calculations reveal that the antiferromagnetic interplay can evolve into ferromagnetic interactions with the presence of oxygen vacancies, which promotes the formation of ferromagnetic order within one-dimensional nickel chains. The unusual electronic instabilities in the nickel-based Haldane system may offer new possibilities towards unconventional physical and chemical properties from quantum interactions.

The latest discovery of high temperature superconductivity near 80 K in La 3 Ni 2 O 7 under high pressure has attracted much attention. Many proposals are put forth to understand the origin of superconductivity. The determination of electronic structures is a prerequisite to establish theories to understand superconductivity in nickelates but is still lacking. Here we report our direct measurement of the electronic structures of La 3 Ni 2 O 7 by high-resolution angle-resolved photoemission spectroscopy. The Fermi surface and band structures of La 3 Ni 2 O 7 are observed and compared with the band structure calculations. Strong electron correlations are revealed which are orbital- and momentum-dependent. A flat band is formed from the Ni-3d z 2 orbitals around the zone corner which is ~ 50 meV below the Fermi level and exhibits the strongest electron correlation. In many theoretical proposals, this band is expected to play the dominant role in generating superconductivity in La 3 Ni 2 O 7 . Our observations provide key experimental information to understand the electronic structure and origin of high temperature superconductivity in La 3 Ni 2 O 7 ., (© 2024. The Author(s).)

The disorder operator is often designed to reveal the conformal field theory (CFT) information in quantum many-body systems. By using large-scale quantum Monte Carlo simulation, we study the scaling behavior of disorder operators on the boundary in the two-dimensional Heisenberg model on the square-octagon lattice with gapless topological edge state. In the Affleck-Kennedy-Lieb-Tasaki phase, the disorder operator is shown to hold the perimeter scaling with a logarithmic term associated with the Luttinger liquid parameter K. This effective Luttinger liquid parameter K reflects the low-energy physics and CFT for (1+1)D boundary. At bulk critical point, the effective K is suppressed but it keeps finite value, indicating the coupling between the gapless edge state and bulk fluctuation. The logarithmic term numerically captures this coupling picture, which reveals the (1+1)D SU(2)_{1} CFT and (2+1)D O(3) CFT at boundary criticality. Our Letter paves a new way to study the exotic boundary state and boundary criticality.

Topological superconductors have drawn significant interest from the scientific community due to the accompanying Majorana fermions. Here, the discovery of electronic structure and superconductivity (SC) in high-entropy ceramics Ti 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Ta 0.2 C x (x = 1 and 0.8) combined with experiments and first-principles calculations is reported. The Ti 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Ta 0.2 C x high-entropy ceramics show bulk type-II SC with T c ≈ 4.00 K (x = 1) and 2.65 K (x = 0.8), respectively. The specific heat jump (∆C/γT c ) is equal to 1.45 (x = 1) and 1.52 (x = 0.8), close to the expected value of 1.43 for the BCS superconductor in the weak coupling limit. The high-pressure resistance measurements show a robust SC against high physical pressure in Ti 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Ta 0.2 C, with a slight T c variation of 0.3 K within 82.5 GPa. Furthermore, the first-principles calculations indicate that the Dirac-like point exists in the electronic band structures of Ti 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Ta 0.2 C, which is potentially a topological superconductor. The Dirac-like point is mainly contributed by the d orbitals of transition metals M and the p orbitals of C. The high-entropy ceramics provide an excellent platform for the fabrication of novel quantum devices, and the study may spark significant future physics investigations in this intriguing material., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

We report the crystal structure, charge-density-wave (CDW), superconductivity (SC), and ferromagnetism (FM) in CuIr 2- x Cr x Te 4 (0 ≤ x ≤ 2) chalcogenides. Powder x-ray diffraction (PXRD) results reveal that the CuIr 2- x Cr x Te 4 series are distinguished between two structural types and three different regions: (i) layered trigonal structure region, (ii) mixed phase regions, and (iii) spinel structure region. Besides, Cr substitution for Ir site results in rich physical properties including the collapse of CDW, the formation of dome-shaped like SC, and the emergence of magnetism. Cr doping slightly elevates the superconducting critical temperature ( T sc ) to its highest T sc = 2.9 K around x = 0.06. As x increases from 0.3 to 0.4, the ferromagnetic Curie temperature ( T c ) increases from 175 to 260 K. However, the T c remains unchanged in the spinel range of 1.9 ≤ x ≤ 2. This finding provides a comprehensive material platform for investigating the interplay between CDW, SC, and FM multipartite quantum states.

Understanding the electric dipole switching in multiferroic materials requires deep insight of the atomic-scale local structure evolution to reveal the ferroelectric mechanism, which remains unclear and lacks a solid experimental indicator in high-pressure prepared LiNbO 3 -type polar magnets. Here, we report the discovery of Zn-ion splitting in LiNbO 3 -type Zn 2 FeNbO 6 established by multiple diffraction techniques. The coexistence of a high-temperature paraelectric-like phase in the polar Zn 2 FeNbO 6 lattice motivated us to revisit other high-pressure prepared LiNbO 3 -type A 2 BB'O 6 compounds. The A-site atomic splitting (∼1.0-1.2 Å between the split-atom pair) in B/B'-mixed Zn 2 FeTaO 6 and O/N-mixed ZnTaO 2 N is verified by both powder X-ray diffraction structural refinements and high angle annular dark field scanning transmission electron microscopy images, but is absent in single-B-site ZnSnO 3 . Theoretical calculations are in good agreement with experimental results and suggest that this kind of A-site splitting also exists in the B-site mixed Mn-analogues, Mn 2 FeMO 6 (M = Nb, Ta) and anion-mixed MnTaO 2 N, where the smaller A-site splitting (∼0.2 Å atomic displacement) is attributed to magnetic interactions and bonding between A and B cations. These findings reveal universal A-site splitting in LiNbO 3 -type structures with mixed multivalent B/B', or anionic sites, and the splitting-atomic displacement can be strongly suppressed by magnetic interactions and/or hybridization of valence bands between d electrons of the A- and B-site cations.

We report pressure-dependent neutron diffraction and muon spin relaxation/rotation measurements combined with first-principles calculations to investigate the structural, magnetic, and electronic properties of BaFe 2 S 3 under pressure. The experimental results reveal a gradual enhancement of the stripe-type ordering temperature with increasing pressure up to 2.6 GPa and no observable change in the size of the ordered moment. The ab initio calculations suggest that the magnetism is highly sensitive to the Fe-S bond lengths and angles, clarifying discrepancies with previously published results. In contrast to our experimental observations, the calculations predict a monotonic reduction of the ordered moment with pressure. We suggest that the robustness of the stripe-type antiferromagnetism is due to strong electron correlations not fully considered in the calculations.

We calculate the K-edge indirect bimagnon resonant inelastic x-ray scattering (RIXS) intensity spectra of the bicollinear antiferromagnetic order known to occur in the α-FeTe chalcogenide system. Utilizing linear spin wave theory for this large-S spin system we find that the bimagnon spectrum contains four scattering channels (two intraband and two interband). We find from our calculations that for suitable energy-momentum combination the RIXS spectra can exhibit a one-, two- or three- peak structure. The number of peaks provides a clue on the various bimagnon excitation processes that can be supported both in and within the acoustic and optical magnon branches of the bicollinear antiferromagnet. Unlike the RIXS response of the antiferromagnetic or the collinear antiferromagnetic spin ordering, the RIXS intensity spectrum of the bicollinear antiferromagnet does not vanish at the magnetic ordering wave vector [Formula: see text]. It is also sensitive to next-next nearest neighbor and biquadratic coupling interactions. Our predicted RIXS spectrum can be utilized to understand the role of multi-channel bimagnon spin excitations present in the α-FeTe chalcogenide.

Linear alkanes undergo different C-C bond chemistry (coupling or dissociation) thermally activated on anisotropic metal surfaces depending on the choice of the substrate material. Owing to the one-dimensional geometrical constraint, selective dehydrogenation and C-C coupling (polymerization) of linear alkanes take place on Au(110) surfaces with missing-row reconstruction. However, the case is dramatically different on Pt(110) surfaces, which exhibit similar reconstruction as Au(110). Instead of dehydrogenative polymerization, alkanes tend to dehydrogenative pyrolysis, resulting in hydrocarbon fragments. Density functional theory calculations reveal that dehydrogenation of alkanes on Au(110) surfaces is an endothermic process, but further C-C coupling between alkyl intermediates is exothermic. On the contrary, due to the much stronger C-Pt bonds, dehydrogenation on Pt(110) surfaces is energetically favorable, resulting in multiple hydrogen loss followed by C-C bond dissociation., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)