The novel nickelate superconductors of infinite-layer type feature challenging electronic pecularities in the normal-state phase diagram with doping. Distinct many-body behavior and different dispersion regimes of the entangled $\{$Ni-$d_{z^2}$, Ni-$d_{x^2-y^2}$$\}$ orbital sector give rise to highly rich physics, which is here studied for the case of the NdNiO$_2$ system. An analysis based on advanced realistic dynamical mean-field theory unveils that the superconducting hole-doped region is the meeting place of a (self-)doped Mott insulator from the underdoped side, and a bad Hund metal from the overdoped side. Fermi-level crossing of the Ni-$d_{z^2}$ flat-band ties both regimes together to form a singular arena for unconventional superconductivity. We furthermore shed light on the intriguing problem of elusive magnetism in infinite-layer nickelates. Antiferromagnetic (AFM) order with small Ni moments is shown to be a vital competitor at low temperature. At stoichiometry, C-AFM order with ferromagnetic spin-alignment along the $c$-axis benefits from a conceivable coexistence with Kondo(-lattice) screening.
We investigate the electronic structure of nickelate superconductor NdNiO2 upon hole doping, by means of density-functional theory and dynamical mean-field theory. We demonstrate the strong intrinsic hybridization between strongly correlated states formed by Ni-3dx2-y2 orbital and itinerant electrons due to Nd-5d and Ni-3dz2 orbitals, producing a valence-fluctuating correlated metal as the normal state of hole-doped NdNiO2. The Hund's rule appears to play a dominating role on multi-orbital physics in the lightly doped compound, while its effect is gradually reduced by increasing the doping lev…
Soft x-ray resonant scattering at the Ni L2,3 edges is used to test models of magnetic and orbital-ordering below the metal-insulator transition in NdNiO3. The large branching ratio of the L3 to L2 intensities of the (1/2,0,1/2) reflection and the observed azimuthal angle and polarization dependence originates from a non collinear magnetic structure. The absence of an orbital signal and the non collinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition.
We perform a comparative $2 \times 2$ real space cluster DMFT study on minimal models for NdNiO$_2$ and CaCuO$_2$ obtained from downfolding DFT states, using a Nambu formalism that allows for both superconducting and antiferromagnetic order. We produce a phase diagram in temperature and doping. We find that for the nickelate, like the cuprate, the stoichiometric compound is antiferromagnetic. We find superconductivity in a doping range bounded, with a small coexistence region, by the onset of antiferromagnetism at low doping and with transition temperature becoming immeasurably small at high d…
Motivated by the recent discovery of superconductivity in the infinite-layer (Sr,Nd)NiO$_2$ films with Sr content $x \simeq0.2$ [Li et al., Nature (London) \textbf{572}, 624 (2019)], we examine the effects of electron correlations and Sr-doping on the electronic structure, Fermi surface topology, and magnetic correlations in (Nd,Sr)NiO$_2$ using a combination of dynamical mean-field theory of correlated electrons and band-structure methods. Our results reveal a remarkable orbital selective renormalization of the Ni $3d$ bands, with $m$*/$m\sim 3$ and 1.3 for the $d_{x^2-y^2}$ and $d_{3z^2-r^2}…
Recent discovery of superconductivity in the doped infinite-layer nickelates has renewed interest in understanding the nature of high-temperature superconductivity more generally. The low-energy electronic structure of the parent compound NdNiO$_{2}$, the role of electronic correlations in driving superconductivity, and the possible relationship betweeen the cuprates and the nickelates are still open questions. Here, by comparing LaNiO$_2$ and NdNiO$_2$ systematically within a parameter-free density functional framework, all-electron first-principles framework, we reveal the role Nd 4$f$ elect…
We report detailed magnetization measurements on the perovskite oxide NdNiO$_3$. This system has a first order metal-insulator (M-I) transition at about 200 K which is associated with charge ordering. There is also a concurrent paramagnetic to antiferromagnetic spin ordering transition in the system. We show that the antiferromagnetic state of the nickel sublattice is spin canted. We also show that the concurrency of the charge ordering and spin ordering transitions is seen only while warming up the system from low temperature. The transitions are not concurrent while cooling the system throug…
Using density functional based LDA+U method and linear-response theory, we study the magnetic exchange interactions of the superconductor Nd{1-x}Sr{x}NiO2. Our calculated nearest-neighbor exchange constant J1=82 meV is large, weakly affected by doping and is only slightly smaller than that found in the sister compound CaCuO2. We however find that the hole doping significantly enhances the inter--layer exchange coupling as it affects the magnetic moment of the Ni-3d{3z2-r2} orbital. This can be understood in terms of small hybridization of Ni-3d{3z2-r2} within the NiO2 plane which results in a …
The recent observation of superconductivity in infinite-layer nickelates has brought intense debate on the established knowledge of unconventional superconductivity based on the cuprates. Despite many similarities, the nickelates differ from the cuprates in many characteristics, the most notable one among which is the magnetism. Instead of a canonical antiferromagnetic Mott insulator as the undoped cuprates, from which the superconductivity is generally believed to arise upon doping, the undoped nickelates show no sign of magnetic ordering in experiments. Through a combined density functional …
Superconductivity with $T_c \approx 15K$ was recently found in doped NdNiO$_2$. The Ni$^{1+}$O$_2$ layers are expected to be Mott insulators so hole doping should produce Ni$^{2+}$ with $S=1$, incompatible with robust superconductivity. We show that the NiO$_2$ layers fall inside a ``critical'' region where the large $pd$ hybridization favors a singlet $^1\!A_1$ hole-doped state like in CuO$_2$. However, we find that the superexchange is about one order smaller than in cuprates, thus a magnon ``glue'' is very unlikely and another mechanism needs to be found.
The combination of charge and spin degrees of freedom with electronic correlations in condensed matter systems leads to a rich array of phenomena, such as magnetism, superconductivity, and novel conduction mechanisms. While such phenomena are observed in bulk materials, a richer array of behaviors becomes possible when these degrees of freedom are controlled in atomically layered heterostructures, where one can constrain dimensionality and impose interfacial boundary conditions. Here, we unlock a host of unique, hidden electronic and magnetic phase transitions in NdNiO$_3$ while approaching th…
The recent discovery of Sr-doped infinite-layer nickelate $\textrm{NdNiO}_2$ [D. Li et al. Nature 572, 624 (2019)] offers an exciting platform for investigating unconventional superconductivity in nickelatebased compounds. In this work, we present a first-principles calculations for the electronic and magnetic properties of undoped parent $\textrm{NdNiO}_2$. Intriguingly, we found that: 1) the paramagnetic phase has complex Fermi pockets with 3D characters near the Fermi level; 2) by including electronelectron interactions, 3d-electrons of Ni tend to form $(π, π, π)$ antiferromagnetic ordering…
We study the many-body electronic structure of the stoichiometric and electron-doped trilayer nickelate Pr$_4$Ni$_3$O$_8$ in comparison to that of the stoichiometric and hole-doped infinite layer nickelate NdNiO$_2$ within the framework of density functional plus dynamical mean field theory, noting that Pr$_4$Ni$_3$O$_8$ has the same nominal carrier concentration as NdNiO$_2$ doped to a level of 1/3 holes/Ni. We find that the correlated Ni-$3d$ shells of both of these low valence nickelates have similar many-body configurations with correlations dominated by the $d_{x^2-y^2}$ orbital. Addition…
Motivated by recent core-level x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) experiments for the newly-discovered superconducting infinite-layer nickelate, we investigate the core-level spectra of the parent compounds NdNiO$_2$ and LaNiO$_2$ using the combination of local density approximation and dynamical mean-field theory (LDA+DMFT). Adjusting a charge-transfer energy to match the experimental spectra, we determine the optimal model parameters and discuss the nature of the NdNiO$_2$ ground state. We find that self-…
Motivated by the recent discovery of superconductivity in the Sr-doped layered nickelate NdNiO$_2$, we perform a systematic computational materials design of layered nickelates that are dynamically stable and whose electronic structure better mimics the electronic structure of high-$T_c$ cuprates than NdNiO$_2$. While the Ni $3d$ orbitals are self-doped from the $d^9$ configuration in NdNiO$_2$ and the Nd-layer states form Fermi pockets, we find more than 10 promising compounds for which the self-doping is almost or even completely suppressed. We derive effective single-band models for those m…
The discovery of superconductivity in hole-doped infinite-layer NdNiO$_2$ -- a transition metal (TM) oxide that is both isostructural and isoelectronic to cuprate superconductors -- has lead to renewed enthusiasm in the hope of understanding the origin of unconventional superconductivity. Here, we investigate the electron-removal states in infinite-layered Ni$^{1+}$ oxide, NdNiO$_2$, which mimics hole-doping, with the state-of-the-art many-body multireference quantum chemistry methods. From the analysis of the many-body wavefunction, we find that the hole-doped $d^8$ ground state of NdNiO$_2$ …
In materials science, much effort has been devoted to reproduce superconductivity in chemical compositions analogous to cuprate superconductors since their discovery over thirty years ago. This approach was recently successful in realising superconductivity in infinite-layer nickelates. Although differing from cuprates in electronic and magnetic properties, strong Coulomb interactions suggest infinite-layer nickelates have a propensity to various symmetry-breaking orders that populate the cuprates. Here we report the observation of charge density waves (CDWs) in infinite-layer NdNiO$_2$ films …
The large antiferromagnetic exchange coupling in the parent high-$T_{\rm c}$ cuprate superconductors is believed to play a crucial role in pairing the superconducting carriers. The recent observation of superconductivity in hole-doped infinite-layer (IL-) NdNiO$_2$ brings to the fore the relevance of magnetic coupling in high-$T_{\rm c}$ superconductors, particularly because no magnetic ordering is observed in the undoped IL-NdNiO$_2$ unlike in parent copper oxides. Here, we investigate the electronic structure and the nature of magnetic exchange in IL-NdNiO$_2$ using state-of-the-art many-bod…
Electronic structure of NdNiO3 and YNiO3 are calculated by using LSDA+U method with rotational invariance. No orbital order on Ni sites is observed in both systems but different charge orderings. In a small distorting system NdNiO3, all Ni ions are trivalent and oxygen sites have a particular ordering, both in charge and orbital. In a large distorting system YNiO3, the charge disproportionation occurs. The charge ordering stabilizes the asymmetry of the arrangement of the local magnetic moments around each nickel site without the Jahn-Teller distortion in both systems. The charge compensation …
Motivated by the recent discovery of superconductivity in doped NdNiO$_2$, we study the magnetic exchange interaction $J$ in layered $d^9$ nickelates from first principles. The mother compounds of the high-$T_{\rm c}$ cuprates belong to the charge-transfer regime in the Zaanen-Sawatzky-Allen diagram and have $J$ larger than 100 meV. While this feature makes the cuprates very different from other transition metal oxides, it is of great interest whether layered $d^9$ nickelates can also have such a large $J$. However, one complexity is that NdNiO$_2$ is not a Mott insulator due to carrier doping…
We present a theoretical study of the effect of electron-electron interactions and Sr doping on the electronic structure of infinite-layer (Nd,Sr)NiO$_2$ using the density functional+dynamical mean-field theory approach. In particular, we explore the impact of epitaxial compressive strain that experience (Nd,Sr)NiO$_2$ films on the electronic properties, magnetic correlations, and exchange couplings. Our results reveal the crucial importance of orbital-dependent correlation effects in the Ni $3d$ shell of Sr-doped NdNiO$_2$. Upon doping with Sr, it undergoes a Lifshitz transition which is acco…
Employing first-principles density functional theory calculations and Wannierization of the low energy band structure, we analyze the electronic structure of undoped, infinite-layer nickelate compounds, NdNiO$_2$, PrNiO$_2$ and LaNiO$_2$. Our study reveals important role of non-zero $f$-ness of Nd and Pr atoms, as opposed to $f^{0}$ occupancy of La. The non-zero $f$-ness becomes effective in lowering the energy of the rare-earth 5$d$ hybridized axial orbital, thereby enhancing the electron pockets and influencing the Fermi surface topology. The Fermi surface topology of NdNiO$_2$ and PrNiO$_2$…
The recent discovery of superconductivity in Sr-doped NdNiO$_2$, with a critical temperature of $10-15$ K suggests the possibility of a new family of nickel-based high-temperature superconductors (HTS). NdNiO$_{2}$ is the $n=\infty$ member of a larger series of layered nickelates with chemical formula R$_{n+1}$Ni$_{n}$O$_{2n+2}$ (R $=$ La, Nd, Pr; $n = 2, 3, \dots, \infty$). The $n=3$ member has been experimentally and theoretically shown to be cuprate-like and a promising HTS candidate if electron doping could be achieved. The higher-order $n=4,5,$ and $6$ members of the series fall directly …
The correlated electronic structure of the infinite-layer compounds NdNiO$_2$ and SrCuO$_2$ at stoichiometry and with finite hole doping is compared. Key differences are elucidated from an advanced first-principles many-body perspective. Contrary to the charge-transfer insulating cuprate, the self-doped nickelate remains non-insulating even for large interaction strength, though the Ni-$d_{x^2-y^2}$ spectral weight is also gapped in that limit. Hybridization between Ni$(3d)$ and Nd$(5d)$ is crucial for the appearance of the self-doping band. Upon realistic hole doping, Sr$_{1-y}$CuO$_2$ shows …
To understand the superconductivity recently discovered in Nd$_{0.8}$Sr$_{0.2}$NiO$_2$, we carried out LDA+DMFT (local density approximation plus dynamical mean-field theory) and magnetic force response calculations. The on-site correlation in Ni-$3d$ orbitals causes notable changes in the electronic structure. The calculated temperature-dependent susceptibility exhibits the Curie-Weiss behavior, indicating the localized character of its moment. From the low-frequency behavior of self-energy, we conclude that the undoped phase of this nickelate is Fermi-liquid-like contrary to cuprates. Intere…
We have investigated possible spin and charge ordered states in 3d transition-metal oxides with small or negative charge-transfer energy, which can be regarded as self-doped Mott insulators, using Hartree-Fock calculations on d-p-type lattice models. It was found that an antiferromagnetic state with charge ordering in oxygen 2p orbitals is favored for relatively large charge-transfer energy and may be relevant for PrNiO$_3$ and NdNiO$_3$. On the other hand, an antiferromagnetic state with charge ordering in transition-metal 3$d$ orbitals tends to be stable for highly negative charge-transfer e…
Strongly correlated quantum solids are characterized by an inherently granular electronic fabric, with spatial patterns that can span multiple length scales in proximity to a critical point. Here, we used a resonant magnetic X-ray scattering nanoprobe with sub-100 nm spatial resolution to directly visualize the texture of antiferromagnetic domains in NdNiO$_3$. Surprisingly, our measurements revealed a highly textured magnetic fabric, which is shown to be robust and nonvolatile even after thermal erasure across its ordering ($T_{N\acute{e}el}$) temperature. The scale-free distribution of antif…
Atomic $4f$ states have been found to be essential players in the physical behavior of lanthanide compounds, at the Fermi level $E_F$ as in the proposed topological Kondo insulator SmB$_6$, or further away as in the magnetic superconductor system ${\cal R}$Ni$_2$B$_2$C (${\cal R}$=rare earth ion) and in Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_7$, where the $4f$ shell of Pr has a devastating effect on superconductivity. In hole-doped ${\cal R}$NiO$_2$, the ${\cal R}$=Nd member is found to be superconducting while ${\cal R}$=La is not, in spite of the calculated electronic structures being nearly identica…
The superconductivity in Na0.3Co1-xMxO2.1.3H2O and the charge ordering in Na0.5Co1-xMxO2 have been investigated for M = Mn and Ti substituting for Co. We have first successfully synthesized the single-phase Na0.7Co1-xMxO2(M= Mn and Ti) materials with 0 < = x < = 0.1, then we obtained Na0.5Co1-xMxO2 (0 < = x < = 0.1, M = Mn and Ti) by Na deintercalation and Na0.3Co1-xMxO2.1.3H2O (0 < = x < = 0.1, M = Mn and Ti) by an additional water intercalations. X-ray diffraction measurements revealed that all samples are single-phase materials, their lattice parameters depend systematically on the Ti and M…
Impurity effects on the stability of a ferromagnetic metallic state in a bicritical-state manganite, (La0.7Pr0.3)0.65Ca0.35MnO3, on the verge of metal-insulator transition have been investigated by substituting a variety of transition-metal atoms for Mn ones. Among them, Fe doping exhibits the exceptional ability to dramatically decrease the ferromagnetic transition temperature. Systematic studies on the magnetotransport properties and x-ray diffraction for the Fe-doped crystals have revealed that charge-orbital ordering evolves down to low temperatures, which strongly suppresses the ferromagn…
Alkali-doped fullerides exhibit a wealth of unusual phases that remain controversial by nature. Here we report a cryogenic scanning tunneling microscopy study of the sub-molecular structural and electronic properties of expanded fullerene C60 films with various cesium (Cs) doping. By varying the discrete charge states and film thicknesses, we reveal a large tunability of orientational ordering of C60 anions, yet the tunneling conductance spectra are all robustly characteristic of energy gaps, hallmarks of Jahn-Teller instability and electronic correlations. The Fermi level lies halfway within …
The roles of crystal-field splitting and Jahn-Teller distortions on the orbital ordering transition are investigated in the single-layer manganites near half doping. Crystal-field splitting of energy levels favoring the $d_{3z^2-r^2}$ occupancy provides not only the correct Fermi surface topology for La$_{0.5}$Sr$_{1.5}$MnO$_4$ having a circular electron pocket around the $Γ$ point, but also enhances the flatness of the hole pocket around the M point thereby improving the nesting. In the presence of the circular electron pocket, Jahn-Teller distortions are found to be crucial for the transitio…
We have studied the chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ and the charge ordering transition in La$_{1.67}$Sr$_{0.33}$NiO$_4$ by photoemission spectroscopy. The result shows a large ($\sim$ 1 eV/hole) downward shift of the chemical potential with hole doping in the high-doping regime ($δ\gtrsim$ 0.33) while the shift is suppressed in the low-doping regime ($δ\lesssim$ 0.33). This suppression is attributed to a segregation of doped holes on a microscopic scale when the hole concentration is lower than $δ\simeq 1/3$. In the $δ= 1/3$ sample, the photoemission intensity at the chemic…
We present a mean-field theory of charge, orbital, and spin ordering in manganites at 50% and 0% dopings by considering Jahn-Teller interaction, nearest-neighbor repulsion, and no single-site double occupancy. For spinless fermions, we show that Jahn-Teller distortion and charge-orbital ordering occur simultaneously. In our two-dimensional model at 50% doping, for small nearest-neighbor repulsion the system is orbitally polarized while for larger repulsion the system undergoes CE type ordering. As for the 0% doping case, the ground state is orbitally antiferromagnetic. Upon including spin degr…
The effects of nonmagnetic Zn and magnetic Ni substitution for Cu site on magnetism are studied by measurements of uniform magnetic susceptibility for lightly doped La_{2-x}Sr_xCu_{1-z}M_zO_4 (M=Zn or Ni) polycrystalline samples. For the parent x=0, Zn doping suppresses the Néel temperature T_N whereas Ni doping hardly changes T_N up to z=0.3. For the lightly doped samples with T_N~0, the Ni doping recovers T_N. For the superconducting samples, the Ni doping induces the superconductivity-to-antiferromagnetic transition (or crossover). All the heavily Ni doped samples indicate a spin glass beha…
A systematic LSDA+U study of doping effects on the electronic and structural properties of single layer CoO2 is presented. Undoped CoO2 is a charge transfer insulator within LSDA+U and a metal with a high density of states (DOS) at the Fermi level within LSDA. (CoO2)$^{1.0-}$, on the other hand, is a band insulator with a gap of 2.2 eV. Systems with fractional doping are metals if no charge orderings are present. Due to the strong interaction between the doped electron and other correlated Co d electrons, the calculated electronic structure of (CoO2)$^{x-}$ depends sensitively on the doping le…
The recently discovered superconductivity in Nd$_{1-x}$Sr$_x$NiO$_2$ provides a new opportunity for studying strongly correlated unconventional superconductivity. The single-hole Ni$^+$ ($3d^9$) configuration in the parent compound NdNiO$_2$ is similar to that of Cu$^{2+}$ in cuprates. We suggest that after doping, the intra-orbital spin-singlet and inter-orbital spin-triplet double-hole (doublon) configurations of Ni$^{2+}$ are competing, and we construct a two-band Hubbard model by including both the $3d_{x^2-y^2}$ and $3d_{xy}$-orbitals. The effective spin-orbital super-exchange model in th…
We report hole-doping dependence of the in-plane resistivity ρ_{ab} in a cuprate superconductor La_{2-x}Sr_{x}CuO_{4}, carefully examined using a series of high-quality single crystals. Our detailed measurements find a tendency towards charge ordering at particular rational hole doping fractions of 1/16, 3/32, 1/8, and 3/16. This observation appears to suggest a specific form of charge order and is most consistent with the recent theoretical prediction of the checkerboard-type ordering of the Cooper pairs at rational doping fractions x = (2m+1)/2^n, with integers m and n.
Graphene phonons are measured as a function of electron doping via the addition of potassium adatoms. In the low doping regime, the in-plane carbon G-peak hardens and narrows with increasing doping, analogous to the trend seen in graphene doped via the field-effect. At high dopings, beyond those accessible by the field-effect, the G-peak strongly softens and broadens. This is interpreted as a dynamic, non-adiabatic renormalization of the phonon self-energy. At dopings between the light and heavily doped regimes, we find a robust inhomogeneous phase where the potassium coverage is segregated in…
We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.
The cuprate superconductors exhibit ubiquitous instabilities toward charge-ordered states. These unusual electronic states break the spatial symmetries of the host crystal, and have been widely appreciated as essential ingredients for constructing a theory for high-temperature superconductivity in cuprates. Here we report real-space imaging of the doping-dependent charge orders in the epitaxial thin films of a canonical cuprate compound La2-xSrxCuO4 using scanning tunneling microscopy. As the films are moderately doped, we observe a crossover from incommensurate to commensurate (4a0, where a0 …
We perform a thorough study of an extended Hubbard model featuring local and nearest-neighbor Coulomb repulsion. Using dynamical mean-field theory we investigated the zero temperature phase-diagram of this model as a function of the chemical doping. The interplay between local and non-local interaction drives a variety of phase-transitions connecting two distinct charge-ordered insulators, i.e., half-filled and quarter-filled, a charge-ordered metal and a Mott insulating phase. We characterize these transitions and the relative stability of the solutions and we show that the two interactions c…
The layered perovskite cobaltite RBaCo$_2$O$_{5.5}$ (R: rare-earth elements or Yttrium) exhibits an abrupt temperature-induced metal$-$insulator transition (MIT) and has been attributed to spin-state ordering (SSO) of Co$^{3+}$ ions. Here we investigated the hole doping member of PrBaCo$_2$O$_{5.5+x}$ ($0 \le x \le 0.24$) with multiple techniques. The analysis on crystal and magnetic structures by electron and neutron diffraction confirm the SSO in the insulating phase of undoped PrBaCo$_2$O$_{5.5}$, which is melted by increasing the temperature across the MIT. In addition, we discovered that …
The in-plane oxygen vibrations in La2NiO4 are investigated for several hole-doping concentrations both theoretically and experimentally via inelastic neutron scattering. Using an inhomogeneous Hartree-Fock plus RPA numerical method in a two-dimensional Peierls-Hubbard model, it is found that the doping induces stripe ordering of localized charges, and that the strong electron-lattice coupling causes the in-plane oxygen modes to split into two subbands. This result agrees with the phonon band splitting observed by inelastic neutron scattering in La2-xSrxNiO4. Predictions of strong electron-latt…
We demonstrated experimentally a direct way to probe a hidden propensity to the formation of spin density wave (SDW) in a non-magnetic metal with strong Fermi surface nesting. Substituting Fe for a tiny amount of Cu (1%) induced an incommensurate magnetic order below 20 K in heavily-overdoped La2-xSrxCuO4 (LSCO). Elastic neutron scattering suggested that this order cannot be ascribed to the localized spins on Cu or doped Fe. Angle-resolved photoemission spectroscopy (ARPES), combined with numerical calculations, revealed a strong Fermi surface nesting inherent in the pristine LSCO that likely …
The effect of Ni-doping on the magnetism and superconductivity in Eu0.5K0.5Fe2As2 has been studied through a systematic investigation of magnetic and superconducting properties of Eu0.5K0.5(Fe1-xNix)2As2 (x = 0, 0.03, 0.05, 0.08 and 0.12) compounds by means of dc and ac magnetic susceptibilities, electrical resistivity and specific heat measurements. Eu0.5K0.5Fe2As2 is known to exhibit superconductivity with superconducting transition temperature Tc as high as 33 K. The Ni-doping leads to a rapid decrease in Tc; Tc is reduced to 23 K with 3% Ni-doping, and 8% Ni-doping suppresses the supercond…
Since the discovery of high-temperature superconductivity in the copper oxide materials, there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconducting materials. One prime materials platform has been the rare-earth nickelates and indeed superconductivity was recently discovered in the doped compound Nd$_{0.8}$Sr$_{0.2}$NiO$_2$. Undoped NdNiO$_2$ belongs to a series of layered square-planar nickelates with chemical formula Nd$_{n+1}$Ni$_n$O$_{2n+2}$ and is known as the 'infinite-layer' ($n = \infty$) nickelate. Here, we report the s…
The layered 5d transition metal oxide Sr2IrO4 has been shown to host a novel Jeff=1/2 Mott spin orbit insulating state with antiferromagnetic ordering, leading to comparisons with the layered cuprates. Here we study the effect of substituting Mn for Ir in single crystals of Sr2Ir0.9Mn0.1O4 through an investigation involving bulk measurements and resonant x-ray and neutron scattering. We observe a new long range magnetic structure emerge upon doping through a reordering of the spins from the basal plane to the c-axis with a reduced ordering temperature compared to Sr2IrO4. The strong enhancemen…
A study of an impurity driven phase-transition into a magnetically ordered state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both, macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR) measurements reveal that the spin nature of dopants has a crucial role in determining the stability of the induced long-range magnetic order. In the case of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition is observed in relatively low magnetic fields. On the other hand, the magnetic order in magnetically (Co2+) doped compounds survives at muc…
We have used resonant x-ray diffraction to develop a detailed description of antiferromagnetic ordering in epitaxial superlattices based on two-unit-cell thick layers of the strongly correlated metal LaNiO3. We also report reference experiments on thin films of PrNiO3 and NdNiO3. The resulting data indicate a spiral state whose polarization plane can be controlled by adjusting the Ni d-orbital occupation via two independent mechanisms: epitaxial strain and quantum confinement of the valence electrons. The data are discussed in the light of recent theoretical predictions.
The magnetic ground state of the Eu$^{2+}$ moments in a series of Eu(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ single crystals grown from the Sn flux has been investigated in detail by neutron diffraction measurements. Combined with the results from the macroscopic properties (resistivity, magnetic susceptibility and specific heat) measurements, a phase diagram describing how the Eu magnetic order evolves with Co doping in Eu(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ is established. The ground-state magnetic structure of the Eu$^{2+}$ spins is found to develop from the A-type antiferromagnetic (AFM) order in …
