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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Multidimensional coherent spectroscopy of light-driven states and their collective modes in multiband superconductors

We present a comprehensive theory of light-controlled multiband superconductivity, and apply it to predict distinctive signatures of light-driven superconducting (SC) states in terahertz multidimensional coherent spectroscopy (THz-MDCS) experiments. We first derive gauge-invariant Maxwell-Bloch equations for multiband BCS superconductors with spatial fluctuations. We consider driving electromagnetic fields determined self-consistently by Maxwell's equations. By calculating the THz-MDCS spectra measured experimentally in the clean SC limit, we identify unique signatures of finite-momentum Cooper-pairing states that live longer than the laser pulse. They are controlled by a pair of THz laser pulses with well-defined relative phase (pulse pair). The pseudospin oscillators that describe the properties of these SC states are parametrically driven by both finite-momentum Cooper pairing and by time oscillations of the order-parameter relative phase. We show that such strong parametric driving leads to drastic changes in the THz-MDCS spectral shape from the predictions of third-order nonlinear susceptibility calculations. These spectral changes strongly depend on the interband-to-intraband interaction ratio and on the collective modes of the light-driven state. For negligible interband interaction, the spectra show a transition with increasing field, from traditional pump-probe, four-wave-mixing, and third-harmonic generation peaks determined by the laser frequency to sidebands determined by the excitations of the driven system. These sidebands emerge from difference-frequency Raman processes in the nonequilibrium SC state. For interband couplings weaker than the intraband pairing, we show that the Leggett phase collective mode leads to harmonic sidebands around the traditional pump-probe peaks. Additional Higgs collective mode peaks result from light-induced inversion-symmetry breaking in a thin-film geometry. For strong interband coupling, we find a transition from a nonequilibrium finite Cooper-pair momentum state characterized by hybrid-Higgs amplitude mode peaks in THz-MDCS spectra to a driven state identified experimentally by the emergence of Floquet-type sidebands at bi-Higgs frequencies. Those dominant bi-Higgs-frequency satellites are manifestations of a new order parameter relative phase collective mode that characterizes the nonequilibrium SC state. The predicted interaction- and field-dependent transitions in the spectral profile allow us to propose THz-MDCS experiments for quantum tomography of light-driven superconductivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

DNA-assembled superconducting 3D nanoscale architectures

Studies of nanoscale superconducting structures have revealed various physical phenomena and led to the development of a wide range of applications. Most of these studies concentrated on one- and two-dimensional structures due to the lack of approaches for creation of fully engineered three-dimensional (3D) nanostructures. Here, we present a ‘bottom-up’ method to create 3D superconducting nanostructures with prescribed multiscale organization using DNA-based self-assembly methods. We assemble 3D DNA superlattices from octahedral DNA frames with incorporated nanoparticles, through connecting frames at their vertices, which result in cubic superlattices with a 48 nm unit cell. The superconductive superlattice is formed by converting a DNA superlattice first into highly-structured 3D silica scaffold, to turn it from a soft and liquid-environment dependent macromolecular construction into a solid structure, following by its coating with superconducting niobium (Nb). Through low-temperature electrical characterization we demonstrate that this process creates 3D arrays of Josephson junctions. This approach may be utilized in development of a variety of applications such as 3D Superconducting Quantum interference Devices (SQUIDs) for measurement of the magnetic field vector, highly sensitive Superconducting Quantum Interference Filters (SQIFs), and parametric amplifiers for quantum information systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Disorder-robust $\textit{p}$-wave pairing with odd-frequency dependence in normal metal–conventional superconductor junctions [plus supplemental information]

We investigate the induced superconducting pair correlations in junctions between a conventional spin-singlet s-wave superconductor and a disordered normal metal. Decomposing the pair amplitude based on its symmetries in the time domain, we demonstrate that the odd-time, or equivalently odd-frequency, spin-singlet p-wave correlations are both significant in size and entirely robust against random nonmagnetic disorder. We find that these odd-frequency correlations can even be generated by disorder. Our results show that anisotropic odd-frequency pairing represent an important fraction of the proximity-induced correlations in disordered superconducting hybrid structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Orbital and spin character of doped carriers in infinite-layer nickelates

The recent discovery of superconductivity in Nd1-xSrxNiO2 has drawn significant attention in the field. A key open question regards the evolution of the electronic structure with respect to hole doping. Here we exploit x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the doping-dependent electronic structure of Nd1-xSrxNiO2. Upon doping, a high-energy feature in Ni L3-edge XAS develops in addition to the main absorption peak, while XAS at the O K-, Nd M3- and Nd M5-edge exhibits a much weaker response. This implies that doped holes are mainly introduced into Ni 3d states. By comparing our data to atomic multiplet calculations including D4h crystal field, the doping-induced feature in Ni L3-edge XAS is consistent with a d8 spin-singlet state in which doped holes reside in the 3dx2-y2 orbitals. This is further supported by the softening of RIXS orbital excitations due to doping, corroborating with the Fermi level shift associated with increasing holes in the Ni 3dx2-y2 orbital.

2-dimensional systems↗
DOE OSTI2022

Gapless Higgs mode in the Fulde-Ferrell-Larkin-Ovchinnikov state of a superconductor

We report the Higgs mode associated with amplitude fluctuations of the superconducting gap in uniform superconductors is usually heavy, which makes its excitation and detection difficult. We report on the existence of a gapless Higgs mode in the Fulde-Ferrell-Larkin-Ovchinnikov states. This feature originates from the Goldstone mode associated with translation-symmetry breaking. The existence of the gapless Higgs mode is demonstrated by using both a phenomenological model and microscopic Bardeen-Cooper-Schrieffer (BCS) theory. The gapless Higgs mode can avoid the decay into other low-energy excitations, which renders it stable and detectable.

36 MATERIALS SCIENCE↗
DOE OSTI2024

ARPES detection of superconducting gap sign in unconventional superconductors

The superconducting gap symmetry is crucial in understanding the underlying superconductivity mechanism. Angle-resolved photoemission spectroscopy (ARPES) has played a key role in determining the gap symmetry in unconventional superconductors. However, it has been considered so far that ARPES can only measure the magnitude of the superconducting gap but not its phase; the phase has to be detected by other phase-sensitive techniques. Here we propose a method to directly detect the superconducting gap sign by ARPES. This method is successfully validated in a cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ with a well-known d-wave gap symmetry. When two bands have a strong interband interaction, the resulted electronic structures in the superconducting state are sensitive to the relative gap sign between the two bands. Our present work provides an approach to detect the gap sign and can be applied to various superconductors, particularly those with multiple orbitals like the iron-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Superconducting Nd 1- x Eu x NiO 2 thin films using in situ synthesis

We report on superconductivity in Nd 1-x Eu x NiO 2 using Eu as a 4f dopant of the parent NdNiO 2 infinite-layer compound. We use an all–in situ molecular beam epitaxy reduction process to achieve the superconducting phase, providing an alternate method to the ex situ CaH 2 reduction process to induce superconductivity in the infinite-layer nickelates. The Nd 1-x Eu x NiO 2 samples exhibit a step-terrace structure on their surfaces, have a T c onset of 21 K at x = 0.25, and have a large upper critical field that may be related to Eu 4f doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Entangling remote superconducting qubits via transducer-generated multi-time-bin states

Recent studies have shown long-distance entanglement using NV centers, atoms, and quantum dots with single-photon time-bin encoding. We propose a method to entangle remote superconducting qubits via microwave-optical transduction using multi-time-bin states. By adapting conventional entanglement swapping techniques, fidelity improves from 0.75 to $0.98$ in transduction systems, and 0.66 to 0.89 in noisy channels. The protocol mitigates thermal noise without relying on purification and offers a practical path toward scalable, heterogeneous quantum systems.

Wu, Jing [Fermilab]↗
DOE OSTI2020

Pairing glue in cuprate superconductors from the self-energy revealed via machine learning

Recently, machine learning was applied to extract both the normal and the anomalous components of the self-energy from photoemission data at the antinodal points in Bi– based cuprate high-temperature superconductors. It was argued that both components do show prominent peaks near 50 meV, which hold information about the pairing glue, but the peaks are hidden in the actual data, which measure only the total self-energy. We analyze the self-energy within an effective fermion-boson theory. We show that soft thermal fluctuations give rise to peaks in both components of the self-energy at a frequency comparable to the superconducting gap, while they cancel in the total self-energy, all irrespective of the nature of the pairing boson. Furthermore, in the quantum limit T → 0 prominent peaks survive only for a very restricted subclass of pairing interactions. We argue that the way to potentially nail down the pairing boson is to determine the thermal evolution of the peaks.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Oxidation in Ca/K-1144 iron-based superconductors polycrystalline compounds

Iron-based superconductors (IBSCs) are a class of material under investigation for the development of superconducting wires in the low-temperature-high magnetic fields power application. Among the various families of IBSCs, the 1144 CaKFe$_4$As$_4$ compound is a promising material able to achieve outstanding superconducting properties with a cheap and simple chemical composition. Oxidation, in these compounds, is considered an obstacle for high intergranular critical current density, J c,GB . A study devoted to the evaluation of oxidation phenomena and their effects on the superconducting properties is thus needed in order to fully understand the involved mechanisms. From the evaluation of polycrystalline samples obtained by a mechanochemically assisted synthesis route, a degradation of the critical temperature and critical currents has been observed concurrently with oxygen accumulation at grain boundaries in open porosities. However, the crystalline structure at an atomic level seems not affected, as well as intragranular superconducting properties assessed by means of calorimetric methods. These results suggest that loss of superconducting properties in Ca/K-1144 compounds following oxidation is significantly associated with the worsening of grain connectivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Distinguishing finite-momentum superconducting pairing states with two-electron photoemission spectroscopy

Here, we show theoretically that double photoemission (2e-ARPES) may be used to identify the pairing state in superconductors in which the Cooper pairs have a nonzero center-of-mass momentum, q cm . We theoretically evaluate the 2e-ARPES counting rate P (2) for the cases of a d x 2 -y 2 -wave superconductor, a pair-density-wave (PDW) phase, and a Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase. We show that P (2) provides direct insight into the center-of-mass momentum and spin state of the superconducting condensate, and thus can distinguish between these three different superconducting pairing states. In addition, P (2) can be used to map out the momentum dependence of the superconducting order parameter. Our results identify 2e-ARPES as an ideal tool for identifying and probing q cm ≠ 0 superconducting pairing states in superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Multiband superconductivity in strongly hybridized 1 T ' - WTe 2 / NbSe 2 heterostructures

The interplay of topology and superconductivity has become a subject of intense research in condensed-matter physics for the pursuit of topologically nontrivial forms of superconducting pairing. An intrinsically normal-conducting material can inherit superconductivity via electrical contact to a parent superconductor via the proximity effect, usually understood as Andreev reflection at the interface between the distinct electronic structures of two separate conductors. However, at high interface transparency, strong coupling inevitably leads to changes in the band structure, locally, owing to hybridization of electronic states. Here, we investigate such strongly proximity-coupled heterostructures of monolayer $1T$' - $\mathrm{WTe_2}$ grown on NbSe 2 by van der Waals epitaxy. The superconducting local density of states, resolved in scanning tunneling spectroscopy down to 500 mK, reflects a hybrid electronic structure well described by a multiband framework based on the McMillan equations which captures the multiband superconductivity inherent to the NbSe 2 substrate and that is induced by proximity to $\mathrm{WTe_2}$ self-consistently. Our material-specific tight-binding model captures the hybridized heterostructure quantitatively and confirms that strong interlayer hopping gives rise to a semimetallic density of states in the two-dimensional $\mathrm{WTe_2}$ bulk, even for nominally band-insulating crystals. The model further accurately predicts the measured order parameter Δ ≅ 0.6 meV induced in the $\mathrm{WTe_2}$ monolayer bulk, stable beyond a 2 T magnetic field. So we believe that our detailed multiband analysis of the hybrid electronic structure provides a useful tool for sensitive spatial mapping of induced order parameters in proximitized atomically thin topological materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Phonon-Mediated Long-Range Attractive Interaction in One-Dimensional Cuprates

Establishing a minimal microscopic model for cuprates is a key step towards the elucidation of a high-T c mechanism. By a quantitative comparison with a recent in situ angle-resolved photoemission spectroscopy measurement in doped 1D cuprate chains, our simulation identifies a crucial contribution from long-range electron-phonon coupling beyond standard Hubbard models. Using reasonable ranges of coupling strengths and phonon energies, we obtain a strong attractive interaction between neighboring electrons, whose strength is comparable to experimental observations. Additionally, nonlocal couplings play a significant role in the mediation of neighboring interactions. Considering the structural and chemical similarity between 1D and 2D cuprate materials, this minimal model with long-range electron-phonon coupling will provide important new insights on cuprate high-T c superconductivity and related quantum phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Quasiparticle Scattering in a Superconductor near a Nematic Critical Point: Resonance Mode and Multiple Attractive Channels

We analyze the scattering rate for 2D fermions interacting via soft nematic fluctuations. The ground state is an s-wave superconductor, but other pairing channels are almost equally attractive. This strongly alters the scattering rate: At energies beyond the pairing gap Δ, it is renormalized by contributions from all pairing channels. At energies of order Δ, it is determined by the competition between scattering into a gapped continuum and dispersing nematic resonance. The outcome is a “peak-peak-dip-hump” spectrum, similar, but not identical, to the “peak-dip-hump” structure in the cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Inelastic Scattering of a Photon by a Quantum Phase Slip

Spontaneous decay of a single photon is a notoriously inefficient process in nature irrespective of the frequency range. We report that a quantum phase-slip fluctuation in high-impedance superconducting waveguides can split a single incident microwave photon into a large number of lower-energy photons with a near unit probability. The underlying inelastic photon-photon interaction has no analogs in non-linear optics. Instead, the measured decay rates are explained without adjustable parameters in the framework of a new model of a quantum impurity in a Luttinger liquid. Our result connects circuit quantum electrodynamics to critical phenomena in two-dimensional boundary quantum field theories, important in the physics of strongly-correlated systems. Here, the photon lifetime data represents a rare example of verified and useful quantum many-body simulation.

1-dimensional systems↗
DOE OSTI2022

Effects of spin-orbit interaction and electron correlations in strontium titanate

Here, we show that the Bloch states in the conduction band of SrTiO 3 arise from the interplay between highly anisotropic hopping in subbands derived from the Ti t2g orbitals and spin-orbit coupling that mixes these orbitals. Because of the nearly flat-band characteristics for one of the principal axes, at sufficiently high doping these Bloch states become unstable with respect to electron interactions, resulting in Mott-like singlet correlations. These findings may be relevant to the anomalous electronic properties of SrTiO 3 , including its unusual superconductivity.

36 MATERIALS SCIENCE↗