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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Random-exchange Heisenberg behavior in the electron-doped quasi-one-dimensional spin-1 chain compound AgVP 2 ⁢S 6

Recent theoretical work suggests that a pair-density wave superconducting state can be realized by doping a one-dimensional spin-1 chain. Here, we report the physical properties of single crystals of Mg x Ag 1–x VP 2 S 6 [x = 0, x = 0.017(6), x = 0.067(8), and 0.098(11)] prepared by solid-state synthesis. Single-crystal x-ray-diffraction measurements confirm that Mg 2+ is substituting for Ag + to electron dope the V 3+ zigzag chains. Magnetization measurements reveal that electron doping breaks up the V 3+ chains, resulting in unpaired spins at the chain ends. The Mg x Ag 1–x VP 2 S 6 series is consistent with random-exchange Heisenberg antiferromagnetic chain behavior and can be well described by the exchange-coupled pair model at low temperatures. As a result, transport measurements show Mg x Ag 1–x VP 2 S 6 remains insulating in the range 0 ≤ x ≤ 0.098(11), with the band gap decreasing to ~ 0.2 eV at x = 0.098(11).

1-dimensional spin chains↗
DOE OSTI2018

Anisotropy of the Hall Effect in a Quasi-Two-Dimensional Electron-Doped Nd{sub 2 –} {sub x}Ce{sub x}CuO{sub 4 + δ} Superconductor

Abstract—The temperature dependences of the Hall effect of an electron-doped Nd{sub 2 –} {sub x}Ce{sub x}CuO{sub 4 + δ} superconductor have been studied at the antiferromagnet–superconductor quantum phase transition boundary (0.135 ≤ x ≤ 0.15) in conducting CuO{sub 2} planes and in the direction perpendicular to the CuO{sub 2} plane. The hall coefficient between the conducting planes has been found be two orders higher than that in the conducting planes over entire temperature range, which is due to the incoherent character of the charge carrier transfer in the direction of axis c.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Quantized Electronic Doping towards Atomically Controlled “Charge-Engineered” Semiconductor Nanocrystals

“Charge engineering” of semiconductor nanocrystals (NCs) through so-called electronic impurity doping is a long-standing challenge in colloidal chemistry and holds promise for ground-breaking advancements in many optoelectronic, photonic, and spin-based nanotechnologies. To date, our knowledge is limited to a few paradigmatic studies on a small number of model compounds and doping conditions, with important electronic dopants still unexplored in nanoscale systems. Equally importantly, fine-tuning of charge engineered NCs is hampered by the statistical limitations of traditional approaches. The resulting intrinsic doping inhomogeneity restricts fundamental studies to statistically averaged behaviors and complicates the realization of advanced device concepts based on their advantageous functionalities. We aim to address these issues by realizing the first example of II–VI NCs electronically doped with an exact number of heterovalent gold atoms, a known p-type acceptor impurity in bulk chalcogenides. Single-dopant accuracy across entire NC ensembles is obtained through a novel non-injection synthesis employing ligand-exchanged gold clusters as “quantized” dopant sources to seed the nucleation of CdSe NCs in organic media. Structural, spectroscopic, and magneto-optical investigations trace a comprehensive picture of the physical processes resulting from the exact doping level of the NCs. Gold atoms, doped here for the first time into II–VI NCs, are found to incorporate as nonmagnetic Au + species activating intense size-tunable intragap photoluminescence and artificially offsetting the hole occupancy of valence band states. Fundamentally, the transient conversion of Au + to paramagnetic Au 2+ (5d 9 configuration) under optical excitation results in strong photoinduced magnetism and diluted magnetic semiconductor behavior revealing the contribution of individual paramagnetic impurities to the macroscopic magnetism of the NCs. Altogether, our results demonstrate a new chemical approach toward NCs with physical functionalities tailored to the single impurity level and offer a versatile platform for future investigations and device exploitation of individual and collective impurity processes in quantum confined structures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Evolution of the Magnetic Excitations in Electron-Doped La 2 - x Ce x CuO 4

Here we investigated the high energy spin excitations in electron-doped La 2-x Ce x CuO 4 , a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at Q ∥ =(0.6π,0) and (0.9π,0) along the (1 0) direction. Our results show that, for doping level x from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Three-dimensional collective charge excitations in electron-doped copper oxide superconductors

High-temperature copper oxide superconductors consist of stacked CuO 2 planes, with electronic band structures and magnetic excitations that are primarily two-dimensional1,2, but with superconducting coherence that is three-dimensional. This dichotomy highlights the importance of out-of-plane charge dynamics, which has been found to be incoherent in the normal state within the limited range of momenta accessible by optics. Here in this study, we use resonant inelastic X-ray scattering to explore the charge dynamics across all three dimensions of the Brillouin zone. Polarization analysis of recently discovered collective excitations (modes) in electron-doped copper oxides reveals their charge origin, that is, without mixing with magnetic components. The excitations disperse along both the in-plane and out-of-plane directions, revealing its three-dimensional nature. The periodicity of the out-of-plane dispersion corresponds to the distance between neighbouring CuO 2 planes rather than to the crystallographic c-axis lattice constant, suggesting that the interplane Coulomb interaction is responsible for the coherent out-of-plane charge dynamics. The observed properties are hallmarks of the long-sought ‘acoustic plasmon’, which is a branch of distinct charge collective modes predicted for layered systems and argued to play a substantial part in mediating high-temperature superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis and Superconductivity of Electron-Doped β-ZrNCl with Partial Substitution of Ti on Zr Site

Highly crystallized α-TiNCl and ZrNCl with orthogonal network of [M{sub 2}N{sub 2}] (M: Ti and Zr) were used to synthesize the solid-solution phase α-Ti{sub y}Zr{sub 1−y}NCl, which was irreversibly transformed into its β-form polymorph with honeycomb network upon a heat treatment. The intercalation of lithium (Li) into the obtained powder samples was carried out to realize the electron doping in β-form compound. The measurements of magnetic susceptibility and electrical resistivity suggest that the intercalated compound β-Li{sub 0.43}Ti{sub 0.09}Zr{sub 0.91}NCl shows superconductivity with transition temperature (T{sub c}) of 15.0 K. Upon the cointercalation of solvent molecule of tetrahydrofuran (THF), two transitions were observed at 14.1 and ∼21 K, corresponding to the main phase of β-Li{sub x}(THF){sub y}ZrNCl and a THF-cointercalated phase of β-Ti{sub y}Zr{sub 1−y}NCl, respectively. We consider that such a tiny substitution of Ti on Zr site in β-form structure play an important role in the increase of T{sub c}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Prediction of s ± -Wave Superconductivity Enhanced by Electronic Doping in Trilayer Nickelates La 4 Ni 3 O 10 under Pressure

Motivated by the recently reported signatures of superconductivity in trilayer La 4 ⁢Ni 3 ⁢O 10 under pressure, here we comprehensively study this system using ab initio and random-phase approximation techniques. Without electronic interactions, the Ni d 3z 2 –r 2 orbitals show a bonding-antibonding and nonbonding splitting behavior via the O p z orbitals inducing a “trimer” lattice in La 4⁢ Ni 3 ⁢O 10 , analogous to the dimers of La 3 ⁢Ni 2 ⁢O 7 . The Fermi surface consists of three electron sheets with mixed e g orbitals, and a hole and an electron pocket made up of the d 3⁢z 2 –r 2 orbital, suggesting a Ni two-orbital minimum model. In addition, we find that superconducting pairing is induced in the s ± -wave channel due to partial nesting between the M = (π,π) centered pockets and portions of the Fermi surface centered at the Γ = (0,0) point. With changing electronic density n, the s ± instability remains leading and its pairing strength shows a domelike behavior with a maximum around n = 4.2 ( ~6.7% electron doping). The superconducting instability disappears at the same electronic density as that in the new 1313 stacking La 3 ⁢Ni 2 ⁢O 7 , correlated with the vanishing of the hole pocket that arises from the trilayer sublattice, suggesting that the high-T c superconductivity of La 3⁢ Ni 2 ⁢O 7 does not originate from a trilayer and monolayer structure. Furthermore, we confirm the experimentally proposed spin state in La 4 ⁢Ni 3 ⁢O 10 with an in-plane (π, π) order and antiferromagnetic coupling between the top and bottom Ni layers, and spin zero in the middle layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Stabilization of s -wave superconductivity through arsenic p -orbital hybridization in electron-doped BaFe 2 As 2

In this paper, using random-phase approximation spin-fluctuation theory, we study the influence of the hybridization between iron $d$ orbitals and pnictide $p$ orbitals on the superconducting pairing state in iron-based superconductors. The calculations are performed for a 16-orbital Hubbard-Hund tight-binding model of ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ that includes the As-$p$ orbital degrees of freedom in addition to the Fe-$d$ orbitals and compared to calculations for a 10-orbital Fe-$d$ only model. In both models we find a leading ${s}^{±{}}$ pairing state and a subleading ${d}_{{x}^{2}{-}{y}^{2}}$-wave state in the parent compound. Upon doping, we find that the ${s}^{±{}}$ state remains the leading state in the 16-orbital model up to a doping level of 0.475 electrons per unit cell, at which the hole Fermi-surface pockets at the zone center start to disappear. This is in contrast to the 10-orbital model, where the $d$-wave state becomes the leading state at a doping of less than 0.2 electrons. This improved stability of ${s}^{±{}}$ pairing is found to arise from a decrease of ${d}_{xy}$ orbital weight on the electron pockets due to hybridization with the As-$p$ orbitals and the resulting reduction of near $({\pi},{\pi})$ spin-fluctuation scattering which favors the competing $d$-wave state. Finally, these results show that the orbital dependent hybridization of Fermi-surface Bloch states with the usually neglected $p$-orbital states is an important ingredient in an improved itinerant pairing theory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Antiferromagnetic metal phase in an electron-doped rare-earth nickelate

Long viewed as passive elements, antiferromagnetic materials have emerged as promising candidates for spintronic devices due to their insensitivity to external fields and potential for high-speed switching. Recent work exploiting spin and orbital effects has identified ways to electrically control and probe the spins in metallic antiferromagnets, especially in non-collinear or non-centrosymmetric spin structures. The rare-earth nickelate NdNiO 3 is known to be a non-collinear antiferromagnet in which the onset of antiferromagnetic ordering is concomitant with a transition to an insulating state. In this work, we find that for low electron doping, the magnetic order on the nickel site is preserved, whereas electronically, a new metallic phase is induced. We show that this metallic phase has a Fermi surface that is mostly gapped by an electronic reconstruction driven by bond disproportionation. Furthermore, we demonstrate the ability to write to and read from the spin structure via a large zero-field planar Hall effect. Our results expand the already rich phase diagram of rare-earth nickelates and may enable spintronics applications in this family of correlated oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Pressure tuning of structure, superconductivity, and novel magnetic order in the Ce-underdoped electron-doped cuprate T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 )

High-pressure neutron powder diffraction, muon-spin rotation, and magnetization studies of the structural, magnetic, and the superconducting properties of the Ce-underdoped superconducting (SC) electron-doped cuprate system with the Nd 2 CuO 4 (the so-called T ' ) structure T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 with x = 0.1 are reported. A strong reduction of the in-plane and out-of-plane lattice constants is observed under pressure. However, no indication of any pressure-induced phase transition from T' to the K 2 NiF 4 (the so-called T) structure is observed up to the maximum applied pressure of p = 11 GPa. Large and nonlinear increase of the short-range magnetic order temperature T so in T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1) was observed under pressure. Simultaneous pressure causes a nonlinear decrease of the SC transition temperature T c . All these experiments establish the short-range magnetic order as an intrinsic and competing phase in SC T' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 ). The observed pressure effects may be interpreted in terms of the improved nesting conditions through the reduction of the in-plane and out-of-plane lattice constants upon hydrostatic pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electron Doping of Proposed Kagome Quantum Spin Liquid Produces Localized States in the Band Gap

Carrier doping of quantum spin liquids is a long-proposed route to the emergence of high-temperature superconductivity. Electrochemical intercalation in kagome hydroxyl halide materials shows that samples remain insulating across a wide range of electron counts. In this work, we demonstrate through first-principles density-functional calculations, corrected for self-interaction, the mechanism by which electrons remain localized in various Zn-Cu hydroxyl halides, independent of the chemical identity of the dopant - the formation of polaronic states with attendant lattice displacements and a dramatic narrowing of bandwidth upon electron addition. The same theoretical method applied to electron doping in cuprate Nd 2 CuO 4 correctly produces a metallic state when the initially formed polaron dissolves into an extended state. In conclusion, our general findings explain the insulating behavior in a wide range of 'doped' quantum magnets and demonstrate that new quantum spin liquid host materials are needed to realize metallicity borne of a spin liquid.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Emergence of low-energy spin waves in superconducting electron-doped cuprates

In order to fully utilize the technological potential of unconventional superconductors, an enhanced understanding of the superconducting mechanism is necessary. In the best performing superconductors, the cuprates, superconductivity is intimately linked with magnetism, although the details of this coupling remain elusive. Here, we address this gap by studying the electron-doped cuprate Nd 1.85 Ce 0.15 CuO 4−δ that has an antiferromagnetic ground state when synthesized and only becomes superconducting after a reductive annealing process. Using neutron spectroscopy, we show that the as-grown crystal exhibits a large spin pseudogap in the magnetic fluctuation spectrum. Annealing removes defects introduced by the commonly employed synthesis method and significantly reduces the spin pseudogap. While the spin pseudogap in the annealed sample likely arises from superconductivity, in the as-grown sample it results from the absence of long-wavelength spin waves. These results reveal a direct connection between defects, magnetism, and superconductivity, offering new insight into the mechanisms underlying high-temperature superconductivity and guiding the design of improved superconducting materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

From the Ternary Phase Ca 14 Zn 1+δ Sb 11 (δ ≈ 0.4) to the Quaternary Solid Solutions Ca 14– x RE x ZnSb 11 (RE = La–Nd, Sm, Gd, x ≈ 0.9). A Tale of Electron Doping via Rare-Earth Metal Substitutions and the Concomitant Structural Transformations

In this work, the ternary compound Ca 14 Zn 1.37(1) Sb 11 and its six rare-earth metal substituted derivatives Ca 14–x RE x ZnSb 11 (RE = La–Nd, Sm, Gd; x ≈ 0.90±0.06) have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. All com-pounds formally crystallize in the tetragonal Ca 14 AlSb 11 structure type (space group $I$4 1 $/ acd$, No. 142, $Z$ = 8). The crystal structure of Ca 14 Zn 1.37(1) Sb 11 subtly differs from the structure of the remaining six, as well as from the structure of the archetype, due to the presence of a partially occupied interstitial Zn position. The extra zinc atom is needed in this structure to alleviate the unfavorable number of valence electrons in the imaginary Ca 14 ZnSb 11 . Electron doping, via substitution of RE 3+ ions on Ca 2+ sites is shown as an alternative route to achieve electron balance in these Zn-based analogs of the Ca 14 AlSb 11 structure, which does not require the in-corporation of interstitial atoms. Electrical resistivity measurements done on single-crystalline samples are in agreement with the notion that Ca 14–x RE x ZnSb 11 behave as either bad metals or heavily-doped semi-conductors. Magnetization measurements show Curie-Weiss paramagnetic behavior related to the local-moment magnetism of the RE 3+ ions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Correlation between scale-invariant normal-state resistivity and superconductivity in an electron-doped cuprate

An understanding of the normal state in the high-temperature superconducting cuprates is crucial to the ultimate understanding of the long-standing problem of the origin of the superconductivity itself. This so-called “strange metal” state is thought to be associated with a quantum critical point (QCP) hidden beneath the superconductivity. In electron-doped cuprates—in contrast to hole-doped cuprates—it is possible to access the normal state at very low temperatures and low magnetic fields to study this putative QCP and to probe the T → 0 K state of these materials. We report measurements of the low-temperature normal-state magnetoresistance (MR) of the n-type cuprate system La 2– x Ce x CuO 4 and find that it is characterized by a linear-in-field behavior, which follows a scaling relation with applied field and temperature, for doping ( x ) above the putative QCP ( x = 0.14). The magnitude of the unconventional linear MR decreases as T c decreases and goes to zero at the end of the superconducting dome ( x ~ 0.175) above which a conventional quadratic MR is found. These results show that there is a strong correlation between the quantum critical excitations of the strange metal state and the high- T c superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Hidden strange metallic state in underdoped electron-doped cuprates

The low-temperature linear-in-T resistivity of “strange metals,” such as the metallic state of the cuprate high-temperature superconductors, has long been thought to be associated with a quantum critical point. However, recent transport studies of the cuprates have found this behavior persists over a finite range of overdoping. Here, in this work, we report magnetoresistance and Hall effect results for electron-doped films of the cuprate superconductor La 2-x ⁢ Ce x CuO 4 (LCCO) for temperatures from 0.7 to 45 K and magnetic fields up to 65 T. For x = 0.12 and 0.13, just below the Fermi surface reconstruction (FSR) at x = 0.14, the normal state in-plane resistivity exhibits a well-known upturn at low temperature. Our new results show that this resistivity upturn is eliminated at high magnetic field and the resistivity becomes linear-in-temperature from ~40 K down to 0.7 K. The magnitude of the linear coefficient scales with Tc and doping, as found previously for dopings above the FSR. This striking observation suggests that the strange metal is not confined to a single “critical point” in the phase diagram, but rather is a robust universal feature of the metallic ground state of the cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Cobalt on the Crystal Structure and Magnetism of Electron-Doped Sr{sub 0.8}Ce{sub 0.2}MnO{sub 3} Oxide

The Sr{sub 0.8}Ce{sub 0.2}Mn{sub 1 –} {sub y}Co{sub y}O{sub 3 – δ} (y = 0.2, 0.3, 0.4, 0.5, and 0.6) complex oxides with the perovskite structure obtained from simple oxides by the solid–state reaction technique have been examined using structural analysis and magnetic measurements. Substitution of Co for Mn in the dilute Sr{sub 0.8}Ce{sub 0.2}MnO{sub 3} antiferromagnet with a Néel temperature of T{sub N} = 210 K leads to a decrease in the degree of tetragonal distortion of the crystal structure and transition to the cubic cell. The degeneracy of the antiferromagnetic interaction (T{sub N} = 138 K at y = 0.2) observed at the first stage of the substitution of Co for Mn changes for its gradual enhancement with an increase in the magnetic transformation temperature up to 239 K at y = 0.6. An increase in the Co content weakens the competition between the ferromagnetic and antiferromagnetic couplings and reduces the temperature of the transition to the spin-glass-like state. The magnetic inhomogeneity and formation of Co{sup 2+}–Mn{sup 4+} ferromagnetic clusters in Sr{sub 0.8}Ce{sub 0.2}Mn{sub 0.4}Co{sub 0.6}O{sub 2.69} at 140 K have been observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Quantum fluctuations lead to glassy electron dynamics in the good metal regime of electron doped KTaO 3

One of the central challenges in condensed matter physics is to comprehend systems that have strong disorder and strong interactions. In the strongly localized regime, their subtle competition leads to glassy electron dynamics which ceases to exist well before the insulator-to-metal transition is approached as a function of doping. Here, we report on the discovery of glassy electron dynamics deep inside the good metal regime of an electron-doped quantum paraelectric system: KTaO 3 . We reveal that upon excitation of electrons from defect states to the conduction band, the excess injected carriers in the conduction band relax in a stretched exponential manner with a large relaxation time, and the system evinces simple aging phenomena—a telltale sign of glassy dynamics. Most significantly, we observe a critical slowing down of carrier dynamics below 35 K, concomitant with the onset of quantum paraelectricity in the undoped KTaO 3 . Our combined investigation using second harmonic generation technique, density functional theory and phenomenological modeling demonstrates quantum fluctuation-stabilized soft polar modes as the impetus for the glassy behavior. This study addresses one of the most fundamental questions regarding the potential promotion of glassiness by quantum fluctuations and opens a route for exploring glassy dynamics of electrons in a well-delocalized regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Momentum-resolved lattice dynamics of parent and electron-doped Sr2IrO4

The mixing of orbital and spin character in the wavefunctions of the 5d iridates has led to predictions of strong couplings between their lattice, electronic and magnetic degrees of freedom. As well as realising a novel spin-orbit assisted Mott-insulating ground state, the perovskite iridate Sr 2 IrO 4 has strong similarities with the cuprate La 2 CuO 4 , which on doping hosts a charge density wave that appears intimately connected to high-temperature superconductivity. These phenomena can be sensitively probed through momentum-resolved measurements of the lattice dynamics, made possible by meV-resolution inelastic x-ray scattering. Here we report the rst such measurements for both parent and electron-doped Sr2IrO4. We nd that the low-energy phonon dispersions and intensities in both compounds are well described by the same non-magnetic DFT calculation. In the parent compound, no changes of the phonons upon magnetic ordering are discernible within the experimental resolution, and in the doped compound no anomalies are apparent due to charge density waves. These measurements extend our knowledge of the lattice properties of (Sr 1-x La x ) 2 IrO 4 , and constrain the couplings of the phonons to magnetic and charge order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗