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Schneeloch, J.

Publications and source records attributed to Schneeloch, J..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Twofold symmetry of proximity-induced superconductivity in Bi 2 Te 3 / Bi 2 Sr 2 CaCu 2 O 8 + δ heterostructures revealed by scanning tunneling microscopy

We observe proximity-induced superconductivity in in situ prepared heterostructures constructed by topological insulator Bi 2 Te 3 thin films and high-temperature cuprate superconductors Bi 2 Sr 2 CaCu 2 O 8+δ . The superconducting gap maximum is about 7.6 meV on the surface of Bi 2 Te 3 thin films with a thickness of two quintuple layers, and the gap value decreases with an increase in the film thickness. Moreover, the quasiparticle interference data show clear evidence of a twofold symmetric superconducting gap with gap minima along one pair of the principal crystalline axes of Bi 2 Te 3 . This gap form is consistent with the Δ 4y notation of the topological superconductivity proposed in such systems. Our results provide fruitful information on the possible topological superconductivity induced by the proximity effect in high-temperature superconducting cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nematic fluctuations in the cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ

Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate Bi 2 Sr 2 CaCu 2 O 8+δ , we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superconducting proximity effect in a topological insulator using Fe(Te, Se)

Interest in the superconducting proximity effect has recently been reignited by theoretical predictions that it could be used to achieve topological superconductivity. Low- T c superconductors have predominantly been used in this effort, but small energy scales of ~1 meV have hindered the characterization of the emergent electronic phase, limiting it to extremely low temperatures. In this work, we use molecular beam epitaxy to grow topological insulator Bi 2 Te 3 in a range of thicknesses on top of a high- T c superconductor Fe(Te,Se). Using scanning tunneling microscopy and spectroscopy, we detect Δ ind as high as ~3.5 meV, which is the largest reported gap induced by proximity to an s -wave superconductor to date. We find that Δ ind decays with Bi 2 Te 3 thickness, but remains finite even after the topological surface states have been formed. Finally, by imaging the scattering and interference of surface state electrons, we provide a microscopic visualization of the fully gapped Bi 2 Te 3 surface state due to Cooper pairing. Lastly, our results establish Fe-based high- T c superconductors as a promising new platform for realizing high- T c topological superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Raman and ARPES combined study on the connection between the existence of the pseudogap and the topology of the Fermi surface in Bi 2 Sr 2 CaCu 2 O 8 + δ

Here, we study the behavior of the pseudogap in overdoped Bi 2 Sr 2 CaCu 2 O 8+δ by electronic Raman scattering (ERS) and angle-resolved photoemission spectroscopy (ARPES) on the same single crystals. Using both techniques we find that, unlike the superconducting gap, the pseudogap related to the antibonding band vanishes above the critical doping p c = 0.22 . Concomitantly, we show from ARPES measurements that the Fermi surface of the antibonding band is holelike below p c and becomes electronlike above p c . This reveals that the existence of the pseudogap depends on the Fermi surface topology in Bi 2 Sr 2 CaCu 2 O 8+δ , and more generally, puts strong constraint on theories of the pseudogap phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Anomalous density fluctuations in a strange metal

Significance The strange metal is a poorly understood state of matter found in a variety of quantum materials, notably both Cu- and Fe-based high-temperature superconductors. Strange metals exhibit a nonsaturating, T-linear electrical resistivity, seemingly indicating the absence of electron quasiparticles. Using inelastic electron scattering, we report a momentum-resolved measurement of the dynamic charge susceptibility of a strange metal, optimally doped Bi 2.1 Sr 1.9 CaCu 2 O 8+x . We find that it does not exhibit propagating collective modes, such as the plasmon excitation of normal metals, but instead exhibits a featureless continuum lacking either temperature or momentum dependence. Our study suggests the defining characteristic of the strange metal is a singular type of charge dynamics of a new kind for which there is no generally accepted theory.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Collapse of superconductivity in cuprates via ultrafast quenching of phase coherence

The possibility of driving phase transitions in low-density condensates through the loss of phase coherence alone has far-reaching implications for the study of quantum phases of matter. This has inspired the development of tools to control and explore the collective properties of condensate phases via phase fluctuations. Electrically gated oxide interfaces, ultracold Fermi atoms and cuprate superconductors, which are characterized by an intrinsically small phase stiffness, are paradigmatic examples where these tools are having a dramatic impact. In this study, we use light pulses shorter than the internal thermalization time to drive and probe the phase fragility of the Bi 2 Sr 2 CaCu 2 O 8+δ cuprate superconductor, completely melting the superconducting condensate without affecting the pairing strength. The resulting ultrafast dynamics of phase fluctuations and charge excitations are captured and disentangled by time-resolved photoemission spectroscopy. This work demonstrates the dominant role of phase coherence in the superconductor-to-normal state phase transition and offers a benchmark for non-equilibrium spectroscopic investigations of the cuprate phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superconductivity, Pairing Symmetry, and Disorder in the Doped Topological Insulator Sn 1-x In x Te for x >= 0.10.

The temperature dependence of the London penetration depth Delta lambda(T) in the superconducting doped topological crystalline insulator Sn1-xInxTe was measured down to 450 mK for two different doping levels, x approximate to 0.45 (optimally doped) and x approximate to 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance T-c, indicating that ferroelectric interactions do not compete with superconductivity.

Smylie, M. P.↗
DOE OSTI2017

Vertical temperature boundary of the pseudogap under the superconducting dome in the phase diagram of Bi 2 Sr 2 CaCu 2 O 8 + δ

We combine electronic Raman scattering experiments with cellular dynamical mean field theory and present evidence of the pseudogap in the superconducting state of various hole-doped cuprates. In Bi 2 Sr 2 CaCu 2 O 8 + δ we also track the superconducting pseudogap hallmark, a peak-dip feature, as a function of temperature T and doping p , well beyond the optimal one. We show that, at all temperatures under the superconducting dome, the pseudogap disappears at the doping p c , between 0.222 and 0.226, where also the normal-state pseudogap collapses at a Lifshitz transition. This demonstrates that the superconducting pseudogap boundary forms a vertical line in the T - p phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Energy dissipation from a correlated system driven out of equilibrium

We report that in complex materials various interactions have important roles in determining electronic properties. Angle-resolved photoelectron spectroscopy (ARPES) is used to study these processes by resolving the complex single-particle self-energy and quantifying how quantum interactions modify bare electronic states. However, ambiguities in the measurement of the real part of the self-energy and an intrinsic inability to disentangle various contributions to the imaginary part of the self-energy can leave the implications of such measurements open to debate. Here we employ a combined theoretical and experimental treatment of femtosecond time-resolved ARPES (tr-ARPES) show how population dynamics measured using tr-ARPES can be used to separate electron–boson interactions from electron–electron interactions. In conclusion, we demonstrate a quantitative analysis of a well-defined electron–boson interaction in the unoccupied spectrum of the cuprate Bi 2 Sr 2 CaCu 2 O 8+x characterized by an excited population decay time that maps directly to a discrete component of the equilibrium self-energy not readily isolated by static ARPES experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Low vibration high numerical aperture automated variable temperature Raman microscope

Raman micro-spectroscopy is well suited for studying a variety of properties and has been applied to wide- ranging areas. Combined with tuneable temperature, Raman spectra can offer even more insights into the properties of materials. However, previous designs of variable temperature Raman microscopes have made it extremely challenging to measure samples with low signal levels due to thermal and positional instability as well as low collection efficiencies. Thus, contemporary Raman microscope has found limited applicability to probing the subtle physics involved in phase transitions and hysteresis. This paper describes a new design of a closed-cycle, Raman microscope with full polarization rotation. High collection efficiency, thermal and mechanical stability are ensured by both deliberate optical, cryogenic, and mechanical design. Measurements on two samples, Bi 2 Se 3 and V 2 O 3 , which are known as challenging due to low thermal conductivities, low signal levels and/or hysteretic effects, are measured with previously undemonstrated temperature resolution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Phonon anomalies in some iron telluride materials

In this paper, the detailed temperature dependence of the infrared-active mode in Fe 1.03 Te (T N ≃ 68 K) and Fe 1.13 Te (T N ≃ 56 K) has been examined, and the position, width, strength, and asymmetry parameter have been determined using an asymmetric Fano profile superimposed on an electronic background. In both materials the frequency of the mode increases as the temperature is reduced; however, there is also a slight asymmetry in the line shape, indicating that the mode is coupled to either spin or charge excitations. Below T N there is an anomalous decrease in frequency, and the mode shows little temperature dependence, at the same time becoming more symmetric, suggesting a reduction in spin- or electron-phonon coupling. The frequency of the infrared-active mode and the magnitude of the shift below T N are predicted reasonably well by first-principles calculations; however, the predicted splitting of the mode is not observed. In superconducting FeTe 0.55 Se 0.45 (T c ≃ 14 K) the infrared-active E u mode displays asymmetric line shape at all temperatures, which is most pronounced between 100 – 200 K, indicating the presence of either spin- or electron-phonon coupling, which may be a necessary prerequisite for superconductivity in this class of materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Surface collective modes in the topological insulators Bi 2 Se 3 and Bi 0.5 Sb 1.5 Te 3-x Se x

In this study, we used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi 2 Se 3 and Bi 0.5 Sb 1.5 Te 3-x Se x . Our goal was to identify the “spin plasmon” predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ''(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

We explore by electronic Raman scattering the superconducting state of the Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) crystal by performing a fine-tuned doping study. We find three distinct energy scales in A 1g , B 1g , and B 2g symmetries which show three distinct doping dependencies. Above p=0.22, the three energies merge; below p=0.12, the A 1g scale is no longer detectable, while the B 1g and B 2g scales become constant in energy. In between, the A 1g and B 1g scales increase monotonically with underdoping, while the B 2g one exhibits a maximum at p=0.16. The three superconducting energy scales appear to be a universal feature of hole-doped cuprates. Furthermore, we propose that the nontrivial doping dependencies of the three scales originate from the Fermi-surface changes and reveal competing orders inside the superconducting dome.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Fully gapped superconductivity in In-doped topological crystalline insulator Pb 0.5 Sn 0.5 Te

In this study, superconductors derived from topological insulators and topological crystalline insulators by chemical doping have long been considered to be candidates as topological superconductors. Pb 0.5 Sn 0.5 Te is a topological crystalline insulator with mirror symmetry protected surface states on (001)-, (011)-, and (111)-oriented surfaces. The superconductor (Pb 0.5 Sn 0.5 ) 0.7 In 0.3 Te is produced by In doping in Pb 0.5 Sn 0.5 Te, and is thought to be a topological superconductor. Here we report scanning tunneling spectroscopy measurements of the superconducting state as well as the superconducting energy gap in (Pb 0.5 Sn 0.5 ) 0.7 In 0.3 Te on a (001)-oriented surface. The spectrum can be well fitted by an anisotropic s-wave gap function of Δ = 0.72 + 0.18cos4θ meV using Dynes model. The results show that the superconductor seems to be a fully gapped one without any in-gap states, in contradiction with the expectation of a topological superconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗