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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Multimodal synchrotron x-ray diffraction across the superconducting transition of Sr 0.1 Bi 2 Se 3

Here, in the doped topological insulator Sr x Bi 2 ⁢Se 3 , a pronounced in-plane twofold symmetry is observed in electronic properties below the superconducting transition temperature T c ~ 3 K, despite the threefold symmetry of the observed $R\overline{3}m$ space group. The axis of twofold symmetry is nominally pinned to one of three rotationally equivalent crystallographic directions and crystallographic strain has been proposed to be the origin of this pinning. We carried out multimodal synchrotron diffraction and resistivity measurements down to and in magnetic fields up to 45 kG on a single crystal of to probe the effect of superconductivity on the crystallographic distortion. Our results indicate that there is no in-plane crystallographic distortion at the level of 1 x 10 -5 associated with the superconducting transition. These results further support the model that the large twofold in-plane anisotropy of superconducting properties of Sr x Bi 2 ⁢Se 3 is not structural in origin, but electronic, namely, it is caused by a nematic superconducting order parameter of E u symmetry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La 1.85 Sr 0.15 CuO 4 / La 2 / 3 Ca 1 / 3 MnO 3 superlattices on (001)-oriented LaSrAlO 4 substrates

Epitaxial La 1.85 Sr 0.15 CuO 4 / La 2 / 3 Ca 1 / 3 MnO 3 (LSCO/LCMO) superlattices (SL) on (001)- oriented LaSrAlO 4 substrates have been grown with pulsed laser deposition (PLD) technique. Their structural, magnetic and superconducting properties have been determined with in-situ reflection high energy electron diffraction (RHEED), x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy (STEM), electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a = 0.3779 nm) and LCMO (a = 0.387 nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the LSAO substrate, a sizeable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of T c onset ≈ 36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H ∥ ab and a sizeable paramagnetic shift for H ∥ c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of T Curie ≈ 190 K and a large low-temperature saturation moment of about 3.5 (1) μ B . These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on YBCO/LCMO superlattices, may allow one to identify the relevant mechanisms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal K x Fe 2-y Se 2

Here, we report how the superconducting phase forms in pseudo-single-crystal K x Fe 2-y Se 2 . In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition. It should be emphasized that the phase separation in pseudo-single-crystal K x Fe 2-y Se 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Superconducting energy gap of 2 H - NbS e 2 in phonon spectroscopy

We present a high-energy-resolution inelastic x-ray scattering data investigation of the charge-density-wave (CDW) soft phonon mode upon entering the superconducting state in 2 H –NbSe 2 . Measurements were done close to the CDW ordering wave vector qCDW at q=q CDW + (0,0,l), 0.15 ≤ l ≤ 0.5, for T = 10K (CDW order) and 3.8K (CDW order+superconductivity). We observe changes of the phonon line shape that are characteristic for systems with strong electron-phonon coupling in the presence of a superconducting energy gap 2Δ c and from which we can demonstrate an l dependence of the superconducting gap. Reversely, our data imply that the CDW energy gap is strongly localized along the c* direction. The confinement of the CDW gap to a very small momentum region explains the rather low competition and easy coexistence of CDW order and superconductivity in 2 H –NbSe 2 . Furthermore, the energy gained by opening Δ CDW seems to be too small to be the driving force of the phase transition at T CDW = 33K, which is better described as an electron-phonon coupling driven structural phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Superconductivity and hybrid soft modes in Ti Se 2

The interplay between superconductivity and charge-density-wave (CDW) order plays a central role in the layered transition-metal dichalcogenides. 1 T -TiSe 2 forms a prime example, featuring superconducting domes on intercalation as well as under applied pressure. Here, we present high energy-resolution inelastic x-ray scattering measurements of the CDW soft phonon mode in intercalated Cu x TiSe 2 and pressurized 1 T -TiSe 2 along with detailed ab-initio calculations for the lattice dynamical properties and phonon-mediated superconductivity. We find that the intercalation-induced superconductivity can be explained by a solely phonon-mediated pairing mechanism, while this is not possible for the superconducting phase under pressure. We argue that a hybridization of phonon and exciton modes in the pairing mechanism is necessary to explain the full observed temperature-pressure-intercalation phase diagram. Finally, these results indicate that 1 T -TiSe 2 under pressure is close to the elusive state of the excitonic insulator.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Pressure-tuned superconductivity and normal-state behavior in Ba ( Fe 0.943 Co 0.057 ) 2 As 2 near the antiferromagnetic boundary

Superconductivity in iron pnictides is unconventional and pairing may be mediated by magnetic fluctuations in the Fe sublattice. Pressure is a clean method to explore superconductivity in iron based superconductors by tuning the ground state continuously without introducing disorder. Here we present a systematic high pressure transport study in Ba (Fe 1 - x Co x ) 2 As 2 single crystals with x = 0.057, which is near the antiferromagnetic instability. Resistivity ρ = ρ 0 + AT n was studied under applied pressure up to 7.90 GPa. The parameter n approaches a minimum value of n ≈ 1 at a critical pressure P c = 3.65 GPa. Near P c , the superconducting transition temperature T c reaches a maximum value of 25.8 K. In addition, the superconducting diamagnetism at 2 K shows a sudden change around the same critical pressure. Finally, these results may be associated with a possible quantum critical point hidden inside the superconducting dome, near optimum T c .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Multiple phases with intertwined magnetic and superconducting orders in Nd-doped CeCoIn 5

In this study, the thermal conductivity of heavy-fermion superconductor Ce 0.95 Nd 0.05 CoIn 5 was measured with a magnetic field rotating in the tetragonal a-b plane. The thermal conductivity exhibits a step within the high-field low-temperature (HFLT) phase, which exists above 8 Tesla within the superconducting state, when field is rotated through the antinodal [100] direction of the superconducting d-wave order parameter. This anomaly indicates the presence of a third order parameter within the HFLT phase, similar to that of pure CeCoIn 5 . Therefore, the HFLT state with triply intertwined orders, i.e., superconducting d-wave, magnetic spin-density wave (SDW), and a putative superconducting p-wave pair-density wave (PDW), is robust against 5% Nd doping. The second magnetic phase within the superconducting state below 8 Tesla, a low-field SDW, displays a hysteresis in thermal conductivity as a function of field magnitude, which is also revealing the existence of a third order consistent with a p-wave PDW. Lastly, given different origins and properties of the HFLT and low-field SDW states, the presence of three intertwined orders in both phases is remarkable and of far-reaching consequences.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Coexistence of superconductivity and magnetism in CaK(Fe 1–x Ni x ) 4 As 4 as probed by 57 Fe Mössbauer spectroscopy

Temperature dependent 57 Fe Mössbauer spectroscopy and specific heat measurements for CaK(Fe 1–x Ni x ) 4 As 4 with x = 0, 0.017, 0.033, and 0.049 are presented. No magnetic hyperfine field (i.e., no static magnetic order) down to 5.5 K was detected for x = 0 and 0.017 in agreement with the absence of any additional feature below superconducting transition temperature T c in the specific heat data. The evolution of magnetic hyperfine field with temperature was studied for x = 0.033 and 0.049. The long-range magnetic order in these two compounds coexists with superconductivity. The magnetic hyperfine field B hf (ordered magnetic moment) below T c in CaK(Fe 0.967 Ni 0.033 ) 4 As 4 is continuously suppressed with the developing superconducting order parameter. The B hf ( T ) data for CaK(Fe 0.967 Ni 0.033 ) 4 As 4 and CaK(Fe 0.951 Ni 0.049 ) 4 As 4 can be described reasonably well by Machida's model for coexistence of itinerant spin density wave magnetism and superconductivity. Furthermore, we demonstrate directly that superconductivity suppresses the spin density wave order parameter if the conditions are right, in agreement with the theoretical analysis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Superconductivity Above the Paramagnetic Limit

We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor. kappa-(BEDT-TTF)(2) Cu(NCS)(2) as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field superconducting state displays the bulk paramagnetic ordering of spin domains required of the FFLO state. These results rule out the alternate possibility of spin-density wave ordering in the high-field superconducting phase. The phase diagram determined from our measurements-including the observation of a phase transition into the FFLO phase at Hp-is in good agreement with recent NMR results and our own earlier tunnel-diode magnetic penetration depth experiments but is in disagreement with the only previous calorimetric report.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Majorana Superconducting Qubit

In this paper, we propose a platform for universal quantum computation that uses conventional $s$-wave superconducting leads to address a topological qubit stored in spatially separated Majorana bound states in a multiterminal topological superconductor island. Both the manipulation and readout of this “Majorana superconducting qubit” are realized by tunnel couplings between Majorana bound states and the superconducting leads. The ability of turning on and off tunnel couplings on demand by local gates enables individual qubit addressability while avoiding cross-talk errors. By combining the scalability of superconducting qubit and the robustness of topological qubits, the Majorana superconducting qubit may provide a promising and realistic route towards quantum computation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Using uniaxial stress to probe the relationship between competing superconducting states in a cuprate with spin-stripe order

In this work, we report muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system La 2-x Ba x CuO 4 with x = 0.115. An extremely low uniaxial stress of ~0.1 GPa induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from ~10 to 32 K; however,the onset of at-least-2D superconductivity is much less sensitive to stress. These results show not only that large-volume-fraction spin-stripe order is anti-correlated with 3D superconducting (SC) coherence, but also that these states are energetically very finely balanced. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. Furthermore, these results strongly suggest a similar pairing mechanism for spin-stripe order, the spatially-modulated 2D and uniform 3D SC orders, imposing an important constraint on theoretical models.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Superconductivity in the Nb-Ru-Ge σ phase

Here, we show that the previously unreported ternary σ-phase material Nb 20.4 Ru 5.7 Ge 3.9 (Nb 0.68 Ru 0.19 Ge 0.13 ) is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for Nb 20.4 Ru 5.7 Ge 3.9 is 91 mJ mol-f.u. -1 K -2 (~3 mJ mol-atom -1 K -2 ) and the specific heat anomaly at the superconducting transition, ΔC/γT c , is approximately 1.38. The zero-temperature upper critical field (µ 0 Hc 2 (0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated µ 0 Hc 1 (0) to be 5.5 mT. Thus, the characterization shows Nb 20.4 Ru 5.7 Ge 3.9 to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge σ-phases shows that all three elements are necessary to stabilize the material. An analogous σ-phase in the Ta-Ru-Ge system did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting σ-phase in the Nb-Ru-Ga system is also reported.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Superconducting contact and quantum interference between two-dimensional van der Waals and three-dimensional conventional superconductors

Atomically thin two-dimensional (2D) transition-metal dichalcogenide (TMD) superconductors enable uniform, flat, and clean van der Waals tunneling interfaces, motivating their integration into conventional superconducting circuits. However, fully superconducting contact must be made between the 2D material and three-dimensional (3D) superconductors to employ the standard microwave drive and readout of qubits in such circuits. We present a method for creating zero-resistance contacts between 2D NbSe 2 and 3D aluminum that behave as Josephson junctions (JJs) with large effective areas compared to 3D-3D JJs. The devices formed from 2D TMD superconductors are strongly influenced by the geometry of the flakes themselves as well as the placement of the contacts to bulk 3D superconducting leads. We present a model for the supercurrent flow in a 2D-3D superconducting structure by a numerical solution of the Ginzburg-Landau equations and find good agreement with experiment. Finally, these results demonstrate a crucial step towards a new generation of hybrid superconducting quantum circuits.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Capping layer influence and isotropic in-plane upper critical field of the superconductivity at the FeSe / SrTiO 3 interface

Understanding the superconductivity at the interface of FeSe/SrTiO 3 is a problem of great contemporary interest due to the significant increase in critical temperature (T c ) compared to that of bulk FeSe, as well as the possibility of an unconventional pairing mechanism and topological superconductivity. We report a study of the influence of a capping layer on superconductivity in thin films of FeSe grown on SrTiO 3 using molecular beam epitaxy. We used in vacuo four-probe electrical resistance measurements and ex situ magnetotransport measurements to examine the effect of three capping layers that provide distinct charge transfer into FeSe: insulating FeTe, nonmetallic Te, and metallic Zr. Our results show that FeTe provides an optimal cap that barely influences the inherent T c found in pristine FeSe/SrTiO 3 , while the transfer of holes from a nonmetallic Te cap completely suppresses superconductivity and leads to insulating behavior. Finally, we used ex situ magnetoresistance measurements in FeTe capped FeSe films to extract the angular dependence of the in-plane upper critical magnetic field. Our observations reveal an almost isotropic in-plane upper critical field, providing insight into the symmetry and pairing mechanism of high-temperature superconductivity in FeSe.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Superconductivity by alloying the topological insulator SnBi 2 Te 4

Alloying indium into the topological insulator SnBi 2 Te 4 induces bulk superconductivity with critical temperatures T c up to 1.85 K and upper critical fields up to about 14 kOe. This is confirmed by electrical resistivity, heat capacity, and magnetic susceptibility measurements. The heat capacity shows a discontinuity at T c and temperature dependence below T c consistent with weak coupling BCS theory, and suggests a superconducting gap near 0.25 meV. The superconductivity is type-II and the topological surface states have been verified by photoemission. Here, a simple picture suggests analogies with the isostructural magnetic topological insulator MnBi 2 Te 4 , in which a natural heterostructure hosts complementary properties on different sublattices, and motivates new interest in this large family of compounds. The existence of both topological surface states and superconductivity in Sn 1-x In x Bi 2 Te 4 identifies these materials as promising candidates for the study of topological superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Absence of hydrogen insertion into highly crystalline superconducting infinite layer nickelates

Here, the discovery of superconductivity in the infinite layer nickelates introduced a materials system analogous to the cuprates for the study of unconventional superconductivity. The synthesis of infinite layer nickelates, (RNiO 2 , R = lanthanide) often uses calcium hydride (CaH 2 ) to facilitate the deintercalation of apical site oxygen atoms from a precursor perovskite (RNiO 3 ) phase via topotactic reduction. However, it remains uncertain whether the use of CaH 2 results in the insertion of hydrogen into the infinite layer structure, and if it does, what the implications are for superconductivity. To quantify the hydrogen composition of highly crystalline infinite layer nickelates, we synthesized Nd 1-x⁢ Sr x ⁢NiO 2 thin films on LSAT substrates and conducted time-of-flight secondary ion mass spectroscopy measurements to generate hydrogen depth profiles. We compare the hydrogen density of nickelates prepared with and without a SrTiO 3 capping layer. Additionally, we measure the hydrogen content in nickelate samples at various doping levels spanning the superconducting phase space, including the underdoped, optimally doped, and overdoped regime. We report no significant increase in hydrogen density between the perovskite and infinite layer phases in any of the measured samples. Furthermore, we put an upperbound on the hydrogen concentration of our nickelate samples to Nd 1-x Sr x ⁢NiO 2 ⁢H 0.05 . Our results imply that hydrogen is not responsible for the emergence of superconductivity in the infinite layer nickelates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Light-Induced Melting of Competing Stripe Orders without Introducing Superconductivity in La 2 − x Ba x CuO 4

The ultrafast manipulation of quantum material has led to many novel and significant discoveries. Among them, the light-induced transient superconductivity in cuprates achieved by melting competing stripe orders represents a highly appealing accomplishment. However, recent investigations have shown that the notion of photoinduced superconductivity remains a topic of controversy, and its elucidation solely through c -axis time-resolved terahertz spectroscopy remains an arduous task. Here, we measure the in-plane and out-of-plane transient terahertz responses simultaneously in the stripe-ordered nonsuperconducting La 2 − x Ba x CuO 4 after near-infrared excitations. We find that although a pump-induced reflectivity edge appears in the c -axis reflectance spectrum, the reflectivity along the CuO 2 planes decreases simultaneously, indicating an enhancement in the scattering rate of quasiparticles. This in-plane transient response is clearly distinct from the features associated with superconducting condensation. Therefore, we conclude the out-of-plane transient responses cannot be explained by an equivalent of Josephson tunneling. Notably, those pump-induced terahertz responses remain consistent even when we vary the near-infrared optical pump wavelengths and hole concentrations. Our results provide critical evidence that transient three-dimensional superconductivity cannot be induced by melting the competing stripe orders with pump pulses whose photon energy is much higher than the superconducting gap of cuprates. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2025

Superconductivity in the Parent Infinite-Layer Nickelate NdNiO 2

We report evidence for superconductivity with onset temperatures up to 11 K in thin films of the infinite-layer nickelate parent compound NdNiO 2 . A combination of oxide molecular beam epitaxy and atomic hydrogen reduction yields samples with high crystallinity and low residual resistivities, a substantial fraction of which exhibit superconducting transitions. We survey a large series of samples with a variety of techniques, including electrical transport, scanning transmission electron microscopy, x-ray absorption spectroscopy, and resonant inelastic x-ray scattering, to investigate the possible origins of superconductivity. We propose that superconductivity could be intrinsic to the undoped infinite-layer nickelates but suppressed by disorder due to a possibly sign-changing order parameter, a finding which would necessitate a reconsideration of the nickelate phase diagram. Another possible hypothesis is that the parent materials can be hole doped from randomly dispersed apical oxygen atoms, which would suggest an alternative pathway for achieving superconductivity. Published by the American Physical Society 2025

36 MATERIALS SCIENCE↗