Showing 1–50 of 60 results for author: Schmidt, A

Perturbative aspects of analogue FLRW spacetime Jellium models

Authors: Matheus E. Pereira, Hermano Velten, Francisco B. Lustosa, Alexandre G. M. Schmidt

Abstract: We study electro-acoustic perturbative modes in homogeneous, isotropic and expanding -- dubbed as Friedmann-Lemaitre-Robertson-Walker (FLRW) -- Jellium models, thereby mimicking density perturbations in analogous Newtonian cosmological expansions. We present both novel analytic solutions for linear perturbations in specific analogue cosmological expansions and full numerical evaluations that chara… ▽ More We study electro-acoustic perturbative modes in homogeneous, isotropic and expanding -- dubbed as Friedmann-Lemaitre-Robertson-Walker (FLRW) -- Jellium models, thereby mimicking density perturbations in analogous Newtonian cosmological expansions. We present both novel analytic solutions for linear perturbations in specific analogue cosmological expansions and full numerical evaluations that characterize the temporal evolution of the electro-acoustic modes capturing their full dynamical behavior across the linear and the nonlinear regimes. For both the case of pressure supported evolution or modes sourced by nonadiabatic contributions, we also characterize the temporal evolution of such perturbations by introducing their scale dependent particle number fluctuation power spectrum which can act as a tool to connect theory and experiments. The dependence of the latter on the physical parameters of the model is demonstrated in detail. △ Less

Submitted 10 July, 2026; originally announced July 2026.

Comments: 09 pages

Two-Photon-Induced Direct 3D Printing of Freeform High-Index Phase-Change Sb2S3 Nanostructures

Authors: Abhrodeep Dey, Andrea Dellith, Anne Sauer, Uwe Hübner, Henrik Schneidewind, Markus A Schmidt, Astrid Bingel, Volker Deckert, Jer-Shing Huang, Wei Wang

Abstract: Chalcogenides have recently emerged as an important class of phase-change materials (PCMs) for nanophotonics, owing to their very high refractive index (RI) and low optical loss in the visible to near-infrared range. They exhibit an ultralarge RI change (> 0.7) upon phase transition, which can be triggered by multiple stimuli such as electrical bias, laser illumination or thermal heating. These pr… ▽ More Chalcogenides have recently emerged as an important class of phase-change materials (PCMs) for nanophotonics, owing to their very high refractive index (RI) and low optical loss in the visible to near-infrared range. They exhibit an ultralarge RI change (> 0.7) upon phase transition, which can be triggered by multiple stimuli such as electrical bias, laser illumination or thermal heating. These properties make them highly appealing materials for flat optics and metasurface applications. Current nanophotonic implementations of chalcogenide PCMs mostly rely on two-dimensional (2D) or quasi three-dimensional (3D) thin film patterning based on the coating of chalcogenide materials from a solid-state target. This limits fast prototyping of 3D freeform micro- and nanostructures, thus restricting geometric design freedom and device functionality. Here, we demonstrate a solution-phase direct printing of chalcogenide PCMs into functional structures. The method is based on dip in two photon-induced solidification (DITPS) of a specially synthesized antimony trisulfide (Sb2S3) precursor solution. Direct printing with DITPS is simple, maskless, fast and cost effective, enabling true freeform 3D printing of photonic devices with sub micron resolution. We show direct writing of Sb2S3 helices with different wire cross section profiles on gold and ITO substrates, as well as functional planar Fresnel zone plates (FZPs) and computer generated hologram metasurfaces (CGHMs) in a single printing step. This freeform DITPS approach thus enables rapid 3D prototyping of high index metasurfaces and opens a route to integrating high-index PCMs into existing photonic architectures and device platforms. △ Less

Submitted 1 May, 2026; originally announced May 2026.

Comments: 29 pages,6 figures

Proximitized Topological Insulator Charge Island Fabricated via In Situ Multi-Angle Stencil Lithography

Authors: Benedikt Frohn, Tobias Schmitt, Vanessa Serrano, Anne Schmidt, Michael Schleenvoigt, Albert Hertel, Benjamin Bennemann, Abdur Rehman Jalil, Detlev Grützmacher, Peter Schüffelgen

Abstract: Hybrid superconductor-topological insulator (TI) nanostructures constitute a promising materials platform for exploring proximity-induced superconductivity in systems with topologically protected surface states. A key obstacle has been the realization of clean and well-controlled superconductor-TI interfaces, as TI surfaces rapidly degrade under ambient conditions. Here, we introduce a fully in si… ▽ More Hybrid superconductor-topological insulator (TI) nanostructures constitute a promising materials platform for exploring proximity-induced superconductivity in systems with topologically protected surface states. A key obstacle has been the realization of clean and well-controlled superconductor-TI interfaces, as TI surfaces rapidly degrade under ambient conditions. Here, we introduce a fully in situ, multi-angle stencil lithography technique that enables the fabrication of proximitized charge islands in TIs. The approach combines selective-area growth of (Bi,Sb)$_2$Te$_3$ nanoribbons with angle-controlled deposition of diffusion barriers, superconducting Al, and ultrathin oxide tunnel barriers, allowing scalable fabrication of hybrid nanostructures without post-growth processing. Low-temperature transport measurements reveal robust Coulomb blockade and a pronounced suppression of low-energy conductance which vanishes with magnetic field, consistent with proximity-induced superconductivity in the island. These results establish a versatile nanofabrication platform that enables access to previously unexplored TI-based hybrid quantum devices and opens new routes for investigating superconductivity in topological nanostructures. △ Less

Submitted 20 April, 2026; originally announced April 2026.

Comments: 6 pages, 4 figures (supplement: 1 page, 2 figures)

Structural modulation, physical properties, and electronic band structure of the kagome metal UCr$_6$Ge$_6$

Authors: Z. W. Riedel, P. A. E. Murgatroyd, C. S. Kengle, P. M. T. Vianez, A. Schmidt, X. Du, K. Allen, T. K. Kim, C. Lane, Ying Wai Li, Jian-Xin Zhu, J. D. Thompson, F. Ronning, S. M. Thomas, P. F. S. Rosa, E. D. Bauer

Abstract: The chemical flexibility of the $RM_6X_6$ stoichiometry, where an $f$-block element is intercalated in the CoSn structure type, allows for the tuning of flatbands associated with kagome lattices to the Fermi level and for emergent phenomena due to interactions between the $f$- and $d$-electron lattices. Yet, 5$f$ members of the ``166" compounds are underrepresented compared with 4$f$ members. Here… ▽ More The chemical flexibility of the $RM_6X_6$ stoichiometry, where an $f$-block element is intercalated in the CoSn structure type, allows for the tuning of flatbands associated with kagome lattices to the Fermi level and for emergent phenomena due to interactions between the $f$- and $d$-electron lattices. Yet, 5$f$ members of the ``166" compounds are underrepresented compared with 4$f$ members. Here, we report single-crystal growth of UCr$_6$Ge$_6$, which crystallizes in a monoclinically distorted Y$_{0.5}$Co$_3$Ge$_3$-type structure. The real-space character of the modulation, which is unique within the $RM_6X_6$ family, is approximated by a 3$\times$1$\times$2 supercell of the average monoclinic cell. The compound has kagome-lattice flatbands near the Fermi level and a moderately enhanced electronic heat capacity, as evidenced by its low-temperature Sommerfeld coefficient ($γ=86.5$~mJ~mol$^{-1}$~K$^{-2}$) paired with band structure calculations. The small, isotropic magnetization and featureless resistivity of UCr$_6$Ge$_6$ suggest itinerant uranium 5$f$ electrons and Pauli paramagnetism. Angle-resolved photoemission spectroscopy results provide evidence for uranium 5$f$ weight at the Fermi level and for a flatband near the Fermi level associated with the chromium $3d$ kagome lattice. The isotropic magnetic behavior of the uranium 5$f$ electrons starkly contrasts with localized behavior in other uranium 166 compounds, highlighting the high tunability of the magnetic ground state across the material family. △ Less

Submitted 4 March, 2026; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: 20 pages, 18 figures; updates include the addition of ARPES and Hall resistivity data

Magnetomechanical Coupling in Ferronematic Phases: Influence of Spindle-Shaped Nanodopants on Liquid Crystalline Order

Authors: Karin Koch, Joachim Landers, Damian Günzing, Hajnalka Nádasi, Heiko Wende, Alexey Eremin, Annette M. Schmidt

Abstract: Ferronematic phases, composed of liquid crystals doped with magnetic nanoparticles, exhibit unique magnetomechanical coupling effects that are of interest for responsive materials. In this study, we investigate the influence of spindle-shaped α-Fe_2O_3 nanoparticles functionalized with a mesogen-decorated polymer brush on the phase behavior and field-induced transitions of a nematic host (5CB). Di… ▽ More Ferronematic phases, composed of liquid crystals doped with magnetic nanoparticles, exhibit unique magnetomechanical coupling effects that are of interest for responsive materials. In this study, we investigate the influence of spindle-shaped α-Fe_2O_3 nanoparticles functionalized with a mesogen-decorated polymer brush on the phase behavior and field-induced transitions of a nematic host (5CB). Differential scanning calorimetry (DSC), refractometry, and dielectric spectroscopy reveal a non-monotonic dependence of the nematic-isotropic transition temperature on particle concentration, indicating a competition between stabilizing and destabilizing effects. The order parameter increases with increasing nanoparticle content, in contrast to non-magnetic reference systems, suggesting an alignment effect induced by the magnetic rather than the geometric anisotropy axis of the dopants. Capacitance measurements of the Freedericksz transition show a pronounced shift in threshold fields, with a critical concentration marking a transition to enhanced magnetic responsiveness. Additional information on nanospindle diffusion correlated to the direction-dependent flow of the nematic host was inferred from comparison of Moessbauer spectroscopy and rheology data. Our findings provide insights into the interplay of magnetic and geometric anisotropy in ferronematic systems and highlight their potential for applications in tunable soft matter devices. △ Less

Submitted 15 October, 2025; originally announced October 2025.

Room-temperature spin-lifetime anisotropy exceeding 60 in bilayer graphene spin valves proximity coupled to WSe$_2$

Authors: Timo Bisswanger, Anne Schmidt, Frank Volmer, Christoph Stampfer, Bernd Beschoten

Abstract: A spin lifetime anisotropy between in-plane and out-of-plane spins in bilayer graphene (BLG) can be achieved by spin-orbit proximity coupling of graphene to transition metal dichalcogenides. This coupling reduces the in-plane spin lifetime due to proximity-induced spin scattering, while the out-of-plane spin lifetime remains largely unaffected. We show that at room temperature spin lifetime anisot… ▽ More A spin lifetime anisotropy between in-plane and out-of-plane spins in bilayer graphene (BLG) can be achieved by spin-orbit proximity coupling of graphene to transition metal dichalcogenides. This coupling reduces the in-plane spin lifetime due to proximity-induced spin scattering, while the out-of-plane spin lifetime remains largely unaffected. We show that at room temperature spin lifetime anisotropy exceeds 60 in a bilayer graphene lateral spin valve proximity coupled to WSe$_2$. The out-of-plane spin lifetime of about 250 ps closely matches that of a BLG reference region not in contact with WSe$_2$. In contrast, the estimated in-plane spin lifetime of less than 4 ps leads to a complete suppression of the in-plane spin signal at the ferromagnetic Co/MgO spin detector. The proximity coupling of WSe$_2$ to BLG is particularly promising, as it does not compromise the charge carrier mobility within the graphene channel. △ Less

Submitted 5 February, 2026; v1 submitted 25 May, 2025; originally announced May 2025.

Comments: 7 pages, 4 figures

Journal ref: 2D Materials 13, 015025 (2026)

Insight into the Correlation of Shape and Magnetism of Hematite Nanospindles

Authors: Juri Kopp, Gerald Richwien, Markus Heidelmann, Soma Salamon, Benoît Rhein, Annette M. Schmidt, Joachim Landers

Abstract: It is established that the Morin transition, a spin reorientation in hematite, is shifted to lower temperatures with decreasing nanoparticle volume. However, our findings indicate an opposite effect in a series of hematite nanospindles: The particles, synthesized by hydrothermal decomposition of iron(III) chloride solution, with aspect ratios $p$ between $1.0$ and $5.2$ (long axis ca. $70$--$290$… ▽ More It is established that the Morin transition, a spin reorientation in hematite, is shifted to lower temperatures with decreasing nanoparticle volume. However, our findings indicate an opposite effect in a series of hematite nanospindles: The particles, synthesized by hydrothermal decomposition of iron(III) chloride solution, with aspect ratios $p$ between $1.0$ and $5.2$ (long axis ca. $70$--$290$ nm) display decreasing Morin transition temperatures $T_{\text{Morin}}$ upon increasing $p$, despite the volume increase. Their inner morphology, determined via (HR)STEM and XRD, shows that they are formed by the epitactical fusion of primary particles, perfectly aligned in terms of crystallographic orientation. Combining magnetometry and Mössbauer spectroscopy, we uncover the correlation between particle shape, magnetic properties, and in particular the Morin transition: While more spherical particles undergo said transition at about $200$ K, $T_{\text{Morin}}$ decreases upon higher nanospindle elongation, while also being broadened and showing a wider thermal hysteresis. Our measurements reveal complete suppression of the Morin transition beyond a critical threshold $p \gtrapprox 1.5$, indicating stabilization of the weak ferromagnetic (WFM) state with net particle magnetic moment within the hematite basal plane, despite such behavior being unexpected based on shape anisotropy considerations. For the correlated, magnetic field-dependent spin-flop transition, a comparable trend in particle aspect ratio is detected. We have demonstrated the presence of intermediate spin alignment states that deviate both from the low-temperature antiferromagnetic (AFM) and high-temperature WFM spin structure for slightly elongated particles, likely being connected to the suppression of the Morin transition observed for $p \gtrapprox 1.5$. △ Less

Submitted 16 October, 2025; v1 submitted 20 May, 2025; originally announced May 2025.

Comments: 45 pages, 10 figures in main text, 10 figures in supplementary information, submitted in The Journal of Physical Chemistry

High-Quality Ultra-Fast Total Scattering and Pair Distribution Function Data using an X-ray Free Electron Laser

Authors: Adam F. Sapnik, Philip A. Chater, Dean S. Keeble, John S. O. Evans, Federica Bertolotti, Antonietta Guagliardi, Lise J. Støckler, Elodie A. Harbourne, Anders B. Borup, Rebecca S. Silberg, Adrien Descamps, Clemens Prescher, Benjamin D. Klee, Axel Phelipeau, Imran Ullah, Kárel G. Medina, Tobias A. Bird, Viktoria Kaznelson, William Lynn, Andrew L. Goodwin, Bo B. Iversen, Celine Crepisson, Emil S. Bozin, Kirsten M. Ø. Jensen, Emma E. McBride , et al. (26 additional authors not shown)

Abstract: High-quality total scattering data, a key tool for understanding atomic-scale structure in disordered materials, require stable instrumentation and access to high momentum transfers. This is now routine at dedicated synchrotron instrumentation using high-energy X-ray beams, but it is very challenging to measure a total scattering dataset in less than a few microseconds. This limits their effective… ▽ More High-quality total scattering data, a key tool for understanding atomic-scale structure in disordered materials, require stable instrumentation and access to high momentum transfers. This is now routine at dedicated synchrotron instrumentation using high-energy X-ray beams, but it is very challenging to measure a total scattering dataset in less than a few microseconds. This limits their effectiveness for capturing structural changes that occur at the much faster timescales of atomic motion. Current X-ray free-electron lasers (XFELs) provide femtosecond-pulsed X-ray beams with maximum energies of approximately 24 keV, giving the potential to measure total scattering and the attendant pair distribution functions (PDFs) on femtosecond timescales. Here, we show that this potential has been realised using the HED scientific instrument at the European XFEL and present normalised total scattering data for 0.35 Å-1 < Q < 16.6 Å-1 and their PDFs from a broad spectrum of materials, including crystalline, nanocrystalline and amorphous solids, liquids, and clusters in solution. We analyse the data using a variety of methods, including Rietveld refinement, small-box PDF refinement, joint reciprocal-real space refinement, cluster refinement, and Debye scattering analysis. The resolution function of the setup is also characterised. We conclusively show that high-quality data can be obtained from a single approximately 30 fs XFEL pulse. Our efforts not only significantly increase the existing maximum reported Q-range for an S(Q) measured at an XFEL but also mean that XFELs are now a viable X-ray source for the broad community of people using reciprocal space total scattering and PDF methods in their research. △ Less

Submitted 13 June, 2025; v1 submitted 30 April, 2025; originally announced April 2025.

Positive-tone Nanolithography of Antimony Trisulfide with Femtosecond Laser Wet-etching

Authors: Abhrodeep Dey, Uwe Hübner, Albane Benardais, Xiaofei Wu, Andrea Dellith, Jan Dellith, Torsten Wieduwilt, Henrik Schneidewind, Markus A Schmidt, Virginie Nazabal, Volker Deckert, Jer-Shing Huang, Wei Wang

Abstract: Antimony trisulfide ($Sb_{2}S_{3}$), as an emerging material for integrated photonic devices, has attracted significant attention due to its high index, low loss, and phase-changing property in the optical regime. However, conventional lithography-based fabrication methods involve complex, time-consuming, multistep processes, rendering the photonic application of $Sb_{2}S_{3}$ challenging. Here, w… ▽ More Antimony trisulfide ($Sb_{2}S_{3}$), as an emerging material for integrated photonic devices, has attracted significant attention due to its high index, low loss, and phase-changing property in the optical regime. However, conventional lithography-based fabrication methods involve complex, time-consuming, multistep processes, rendering the photonic application of $Sb_{2}S_{3}$ challenging. Here, we demonstrate that positive-tone fabrication of $Sb_{2}S_{3}$ nanostructures using wet-etch femtosecond laser processing, a straightforward technique for the engraving of micro- and nanoscale structures, can address major fabrication challenges. The patterning mechanism and factors influencing resolution of $Sb_{2}S_{3}$ thin film structures deposited on quartz (transmissive) and gold (reflective) substrates are experimentally investigated and supported by theoretical modelling. Using this approach, the smallest linewidth fabricated is measured at 178 nm. Consequently, multiple test patterns are demonstrated showing versatile functionalities. Functional Fresnel Zone Plates (FZPs) with varying focal length are fabricated and characterized. This study provides a significantly simplified approach for realizing $Sb_{2}S_{3}$ based integrated photonic devices. △ Less

Submitted 22 April, 2025; originally announced April 2025.

Comments: Main text: 10 pages, 4 figures. Supplementary information: 11 pages, 8 figures, 1 table

Plasma and Thermal Processing Leading to Spatial and Temporal Variability of the Trapped O2 at Europa and Ganymede

Authors: Apurva V. Oza, Robert E. Johnson, Carl A. Schmidt, Wendy M. Calvin, Yuk L. Yung

Abstract: We describe the physical processes that affect the formation, trapping, and outgassing of O2 at Europa and Ganymede. Following Voyager measurements of their ambient magnetospheric plasmas, laboratory data indicated that observed ions, mostly ejected from volcanic Io, would in turn impact and sputtering their surfaces, decomposing the ice producing thin oxygen atmospheres. Subsequently, Europa and… ▽ More We describe the physical processes that affect the formation, trapping, and outgassing of O2 at Europa and Ganymede. Following Voyager measurements of their ambient magnetospheric plasmas, laboratory data indicated that observed ions, mostly ejected from volcanic Io, would in turn impact and sputtering their surfaces, decomposing the ice producing thin oxygen atmospheres. Subsequently, Europa and Ganymede's O2 atmospheres were inferred from O aurora, condensed O2 bands identified at 5773 and 6225 Angstroms, and their atmospheres were shown to have a dusk/dawn enhancement, confirmed by recent Juno data. Although plasma produces these observables, processes that occur within the topmost surface are not well understood. Here, we note that the incident plasma particles produce nonequilibrium defect density locally in the surface ice grains. Defect diffusion within these grains leads to the formation of voids and molecular products, some of which are volatile. Although some volatiles are released into the satellite atmospheres, others are trapped at defect sites or trapped in voids, creating bubbles whose lifetimes are limited by the plasma-induced destruction rate. We discuss how trapping competes with annealing of the radiation damage, and how hemispheric differences at Europa and Ganymede, roughly determine the observed trend with latitude of O2 bands. We discuss the relative importance of condensed O2 and O2 adsorbed on regolith grains as atmospheric sources, accounting for dusk/dawn enhancements and temporal variability reported in condensed O2 band depths. Since plasma-induced damage and thermal annealing timescales drive oxidant variability on icy moons (likely also Callisto, Dione, and Rhea), they can help determine volatile downwelling, a potentially metabolic source for their oceans, and upwelling of other trapped oxidants (e.g. CO2) suggestive of ongoing geologic activity. △ Less

Submitted 15 July, 2026; v1 submitted 5 April, 2025; originally announced April 2025.

Comments: 14 pages, 3 figures, 2 tables, accepted for publication in Astrobiology

Journal ref: Astrobiology, Volume 26, Issue 6, 1 June 2026, Pages 472-484

UV$_6$Sn$_6$: a new kagome material with unusual $5f$ magnetism

Authors: S. M. Thomas, C. S. Kengle, W. Simeth, Chan-young Lim, Z. W. Riedel, K. Allen, A. Schmidt, M. Ruf, Seonggeon Gim, J. D. Thompson, F. Ronning, A. O. Scheie, C. Lane, J. D. Denlinger, S. Blanco-Canosa, Jian-Xin Zhu, E. D. Bauer, P. F. S. Rosa

Abstract: Materials in the family $R$V$_{6}$Sn$_{6}$ ($R=$ rare earth) provide a unique platform to investigate the interplay between local moments from $R$ layers and nonmagnetic vanadium kagome layers. Yet, the investigation of actinide members remains scarce. Here we report the synthesis of UV$_{6}$Sn$_{6}$ single crystals through the self-flux technique. Magnetic susceptibility, specific heat, electrica… ▽ More Materials in the family $R$V$_{6}$Sn$_{6}$ ($R=$ rare earth) provide a unique platform to investigate the interplay between local moments from $R$ layers and nonmagnetic vanadium kagome layers. Yet, the investigation of actinide members remains scarce. Here we report the synthesis of UV$_{6}$Sn$_{6}$ single crystals through the self-flux technique. Magnetic susceptibility, specific heat, electrical resistivity, and thermal expansion measurements reveal two uranium-driven antiferromagnetic transitions at $T_{N1}=29$~K and $T_{N2}=24$~K, a complex field-temperature phase diagram, and unusual negative domain wall magnetoresistance. Specific heat measurements unveil a modest Sommerfeld coefficient of $γ= 40$~mJ/mol.K$^{2}$, consistent with angle-resolved photoemission spectroscopy measurements that show a moderate $f$-electron enhancement at the Fermi level ($E_{F}$). Our experiments support a modest contribution from \textit{5f} flat bands to the density of states at $E_{F}$, whereas our band structure calculations place the vanadium flat bands 0.25~eV above $E_{F}$. Our findings point to a materials opportunity to expand the uranium 166 family with the goal of enhancing correlations by tuning $5f$ and $3d$ flat bands to $E_{F}$. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: 9 pages, 7 figures

Categorising current-voltage curves in single-molecule junctions and their comparison to Single-Level Model

Authors: Giovanna Angelis Schmidt

Abstract: This thesis investigates the mechanically controlled break junctions, with a particular emphasis on elucidating the behaviour of molecular currents at room temperature. The core of this experimental investigation involves a detailed analysis of conductance, examining how it varies over time and with changes in the gap between electrodes. Additionally, this study thoroughly evaluates transmission p… ▽ More This thesis investigates the mechanically controlled break junctions, with a particular emphasis on elucidating the behaviour of molecular currents at room temperature. The core of this experimental investigation involves a detailed analysis of conductance, examining how it varies over time and with changes in the gap between electrodes. Additionally, this study thoroughly evaluates transmission properties, coupling effects, and current characteristics. A pivotal aspect of the research was the meticulous current measurement, followed by carefully selecting optimal data sets. This process set the stage for an in-depth analysis of resonant tunnelling phenomena observed through a single channel. Notably, these experiments were conducted under open atmospheric conditions at room temperature. A significant finding from this study is the recognition that our current model requires refinement. This adjustment is necessary to encapsulate a broader spectrum of molecular transport mechanisms more accurately. Furthermore, this work significantly advances our comprehension of quantum effects in single-molecule junctions, particularly concerning similar molecules to Corannulene extending to some organometallics. One of the essential disclosures is the identification of deviations in the transport model, primarily attributable to electron-electron interactions. This insight is crucial as it paves the way for developing a more comprehensive and precise model, enhancing our understanding of molecular-scale electronic transport. △ Less

Submitted 30 August, 2024; originally announced September 2024.

Comments: Master's thesis, 129 pages, c.a. 90 figures, Thesis, urn:nbn:de:bsz:14-qucosa2-933444, full text first version on URL: https://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa2-933444

Real-Time Detection and Control of Correlated Charge Tunneling in a Quantum Dot

Authors: Johannes C. Bayer, Fredrik Brange, Adrian Schmidt, Timo Wagner, Eddy P. Rugeramigabo, Christian Flindt, Rolf J. Haug

Abstract: We experimentally demonstrate the real-time detection and control of correlated charge tunneling in a dynamically driven quantum dot. Specifically, we measure the joint distribution of waiting times between tunneling charges and show that the waiting times for holes may be strongly correlated due to the periodic drive and the Coulomb interactions on the dot, although the electron waiting times are… ▽ More We experimentally demonstrate the real-time detection and control of correlated charge tunneling in a dynamically driven quantum dot. Specifically, we measure the joint distribution of waiting times between tunneling charges and show that the waiting times for holes may be strongly correlated due to the periodic drive and the Coulomb interactions on the dot, although the electron waiting times are not. Our measurements are in excellent agreement with a theoretical model that allows us to develop a detailed understanding of the correlated tunneling events. We also demonstrate that the degree of correlations can be controlled by the drive. Our experiment paves the way for systematic real-time investigations of correlated electron transport in low-dimensional nanostructures. △ Less

Submitted 2 February, 2025; v1 submitted 26 May, 2024; originally announced May 2024.

Comments: 7 pages, 5 figures

Journal ref: Phys. Rev. Lett. 134, 046303 (2025)

On the GREM approximation of TAP free energies

Authors: Giulia Sebastiani, Marius Alexander Schmidt

Abstract: We establish both a Boltzmann-Gibbs principle and a Parisi formula for the limiting free energy of an abstract GREM (Generalized Random Energy Model) which provides an approximation of the TAP (Thouless-Anderson-Palmer) free energies associated to the Sherrington-Kirkpatrick (SK) model. We establish both a Boltzmann-Gibbs principle and a Parisi formula for the limiting free energy of an abstract GREM (Generalized Random Energy Model) which provides an approximation of the TAP (Thouless-Anderson-Palmer) free energies associated to the Sherrington-Kirkpatrick (SK) model. △ Less

Submitted 24 January, 2024; originally announced January 2024.

Comments: 17 pages

MSC Class: 60J80; 60G70; 82B44

Grayscale Electron Beam Lithography Direct Patterned Antimony Sulfide

Authors: Wei Wang, Uwe Hübner, Tao Chen, Anne Gärtner, Joseph Köbel, Franka Jahn, Henrik Schneidwind, Andrea Dellith, Jan Dellith, Torsten Wieduwilt, Matthias Zeisberger, Tanveer Ahmed Shaik, Astrid Bingel, Markus A Schmidt, Jer-Shing Huang, Volker Deckert

Abstract: The rise of micro/nanooptics and lab-on-chip devices demands the fabrication of three-dimensional structures with decent resolution. Here, we demonstrate the combination of grayscale electron beam lithography and direct forming methodology to fabricate antimony sulfide structures with free form for the first time. The refractive index of the electron beam patterned structure was calculated based o… ▽ More The rise of micro/nanooptics and lab-on-chip devices demands the fabrication of three-dimensional structures with decent resolution. Here, we demonstrate the combination of grayscale electron beam lithography and direct forming methodology to fabricate antimony sulfide structures with free form for the first time. The refractive index of the electron beam patterned structure was calculated based on an optimization algorithm that is combined with genetic algorithm and transfer matrix method. By adopting electron irradiation with variable doses, 4-level Fresnel Zone Plates and metalens were produced and characterized. This method can be used for the fabrication of three-dimensional diffractive optical elements and metasurfaces in a single step manner. △ Less

Submitted 24 January, 2024; originally announced January 2024.

Comments: 17 pages, 4 figures, 1 table, 1 scheme. The Supplement Information will be given in a second Arxiv submission or the published journal

Microfluidic Filling and Spectroscopy of Colloidal CdSe/CdS Nanoplatelets in Liquid Core Fibers

Authors: Simon Spelthann, Dan Huy Chau, Lars F. Klepzig, Dominik A. Rudolph, Mario Chemnitz, Saher Junaid, Detlev Ristau, Markus A. Schmidt, Jannika Lauth, Michael Steinke

Abstract: Colloidal 2D semiconductor nanoplatelets are highly efficient light emitters, which exhibit large absorption and emission cross sections, and constitute promising laser gain media. However, if dispersed in solutions, such nanoplatelets lack a suitable optical platform for scalable and application-oriented integration into optical setups such as lasers. Here, we demonstrate the first successful int… ▽ More Colloidal 2D semiconductor nanoplatelets are highly efficient light emitters, which exhibit large absorption and emission cross sections, and constitute promising laser gain media. However, if dispersed in solutions, such nanoplatelets lack a suitable optical platform for scalable and application-oriented integration into optical setups such as lasers. Here, we demonstrate the first successful integration of solution-processed 2D CdSe/CdS Core/Crown nanoplatelets in m-scale liquid core optical fibers. We compare the nanoplatelets' spectroscopic properties before and after filling them into the fibers and find that spontaneous emission is shifted and broadened. We even observe a first evidence of stimulated emission at high excitation energies. In conclusion, liquid core fibers constitute a novel and scalable platform for optical integration of nanoplatelets for applications as novel, highly reconfigurable laser gain medium. △ Less

Submitted 16 March, 2023; originally announced March 2023.

Comments: 4 Pages, 3 Figures

On the REM approximation of TAP free energies

Authors: Nicola Kistler, Marius Alexander Schmidt, Giulia Sebastiani

Abstract: The free energy of TAP-solutions for the SK-model of mean field spin glasses can be expressed as a nonlinear functional of local terms: we exploit this feature in order to contrive abstract REM-like models which we then solve by a classical large deviations treatment. This allows to identify the origin of the physically unsettling quadratic (in the inverse of temperature) correction to the Parisi… ▽ More The free energy of TAP-solutions for the SK-model of mean field spin glasses can be expressed as a nonlinear functional of local terms: we exploit this feature in order to contrive abstract REM-like models which we then solve by a classical large deviations treatment. This allows to identify the origin of the physically unsettling quadratic (in the inverse of temperature) correction to the Parisi free energy for the SK-model, and formalizes the $\textit{true}$ cavity dynamics which acts on TAP-space, i.e. on the space of TAP-solutions. From a non-spin glass point of view, this work is the first in a series of refinements which addresses the stability of hierarchical structures in models of evolving populations. △ Less

Submitted 22 December, 2022; originally announced December 2022.

MSC Class: 60J80; 60G70; 82B44

Phase diagram for the tap energy of the $p$-spin spherical mean field spin glass model

Authors: David Belius, Marius A. Schmidt

Abstract: We solve the Thouless-Anderson-Palmer (TAP) variational principle associated to the spherical pure $p$-spin mean field spin glass Hamiltonian and present a detailed phase diagram. In the high temperature phase the maximum of variational principle is the annealed free energy of the model. In the low temperature phase the maximum, for which we give a formula, is strictly smaller. The high temper… ▽ More We solve the Thouless-Anderson-Palmer (TAP) variational principle associated to the spherical pure $p$-spin mean field spin glass Hamiltonian and present a detailed phase diagram. In the high temperature phase the maximum of variational principle is the annealed free energy of the model. In the low temperature phase the maximum, for which we give a formula, is strictly smaller. The high temperature phase consists of three subphases. (1) In the first phase $m=0$ is the unique relevant TAP maximizer. (2) In the second phase there are exponentially many TAP maximizers, but $m=0$ remains dominant. (3) In the third phase, after the so called dynamic phase transition, $m=0$ is no longer a relevant TAP maximizer, and exponentially many non-zero relevant TAP solutions add up to give the annealed free energy. Finally in the low temperature phase a subexponential number of TAP maximizers of near-maximal TAP energy dominate. △ Less

Submitted 6 July, 2022; originally announced July 2022.

Comments: 42 pages, 4 figures

MSC Class: 60D05; 60F10; 82B26; 82B27; 82B31; 82B44

Charge-induced artifacts in non-local spin transport measurements: How to prevent spurious voltage signals

Authors: F. Volmer, T. Bisswanger, A. Schmidt, C. Stampfer, B. Beschoten

Abstract: To conduct spin-sensitive transport measurements, a non-local device geometry is often used to avoid spurious voltages that are caused by the flow of charges. However, in the vast majority of reported non-local spin valve, Hanle spin precession, or spin Hall measurements background signals have been observed that are not related to spins. We discuss seven different types of these charge-induced si… ▽ More To conduct spin-sensitive transport measurements, a non-local device geometry is often used to avoid spurious voltages that are caused by the flow of charges. However, in the vast majority of reported non-local spin valve, Hanle spin precession, or spin Hall measurements background signals have been observed that are not related to spins. We discuss seven different types of these charge-induced signals and explain how these artifacts can result in erroneous or misleading conclusions when falsely attributed to spin transport. The charge-driven signals can be divided into two groups: Signals that are inherent to the device structure and/or the measurement setup and signals that depend on a common-mode voltage. We designed and built a voltage-controlled current source that significantly diminishes all spurious voltage signals of the latter group in both DC and AC measurements by creating a virtual ground within the non-local detection circuit. This is especially important for lock-in-based measurement techniques, where a common-mode voltage can create a phase-shifted, frequency-dependent signal with an amplitude several orders of magnitude larger than the actual spin signal. Measurements performed on graphene-based non-local spin valve devices demonstrate how all spurious voltage signals that are caused by a common-mode voltage can be completely suppressed by such a current source. △ Less

Submitted 16 May, 2022; v1 submitted 3 December, 2021; originally announced December 2021.

Comments: 35 pages, 19 figures

Journal ref: Phys. Rev. Appl. 18, 014028 (2022)

In-fiber second-harmonic generation with embedded two-dimensional materials

Authors: Gia Quyet Ngo, Emad Najafidehaghani, Ziyang Gan, Sara Khazaee, Antony George, Erik P. Schartner, Heike Ebendorff-Heidepriem, Thomas Pertsch, Alessandro Tuniz, Markus A. Schmidt, Ulf Peschel, Andrey Turchanin, Falk Eilenberger

Abstract: Silica-based optical fibers are a workhorse of nonlinear optics. They have been used to demonstrate nonlinear phenomena such as solitons and self-phase modulation. Since the introduction of the photonic crystal fiber, they have found many exciting applications, such as supercontinuum white light sources and third-harmonic generation, among others. They stand out by their low loss, large interactio… ▽ More Silica-based optical fibers are a workhorse of nonlinear optics. They have been used to demonstrate nonlinear phenomena such as solitons and self-phase modulation. Since the introduction of the photonic crystal fiber, they have found many exciting applications, such as supercontinuum white light sources and third-harmonic generation, among others. They stand out by their low loss, large interaction length, and the ability to engineer its dispersive properties, which compensate for the small chi(3) nonlinear coefficient. However, they have one fundamental limitation: due to the amorphous nature of silica, they do not exhibit second-order nonlinearity, except for minor contributions from surfaces. Here, we demonstrate significant second-harmonic generation in functionalized optical fibers with a monolayer of highly nonlinear MoS2 deposited on the fiber guiding core. The demonstration is carried out in a 3.5 mm short piece of exposed core fiber, which was functionalized in a scalable process CVD-based process, without a manual transfer step. This approach is scalable and can be generalized to other transition metal dichalcogenides and other waveguide systems. We achieve an enhancement of more than 1000x over a reference sample of equal length. Our simple proof-of-principle demonstration does not rely on either phase matching to fundamental modes, or ordered growth of monolayer crystals, suggesting that pathways for further improvement are within reach. Our results do not just demonstrate a new path towards efficient in-fiber SHG-sources, instead, they establish a platform with a new route to chi(2)-based nonlinear fiber optics, optoelectronics, and photonics platforms, integrated optical architectures, and active fiber networks. △ Less

Submitted 11 August, 2021; originally announced August 2021.

Comments: 22 pages, 11 figures

CVD bilayer graphene spin valves with 26 $μ$m spin diffusion length at room temperature

Authors: T. Bisswanger, Z. Winter, A. Schmidt, F. Volmer, K. Watanabe, T. Taniguchi, C. Stampfer, B. Beschoten

Abstract: We present inverted spin-valves fabricated from CVD-grown bilayer graphene (BLG) that show more than a doubling in device performance at room temperature compared to state-of-the art bilayer graphene spin-valves. This is made possible by a PDMS droplet-assisted full-dry transfer technique that compensates for previous process drawbacks in device fabrication. Gate-dependent Hanle measurements show… ▽ More We present inverted spin-valves fabricated from CVD-grown bilayer graphene (BLG) that show more than a doubling in device performance at room temperature compared to state-of-the art bilayer graphene spin-valves. This is made possible by a PDMS droplet-assisted full-dry transfer technique that compensates for previous process drawbacks in device fabrication. Gate-dependent Hanle measurements show spin lifetimes of up to 5.8 ns and a spin diffusion length of up to 26 $μ$m at room temperature combined with a charge carrier mobility of $\approx$ 24 000 cm$^{2}$(Vs)$^{-1}$ for the best device. Our results demonstrate that CVD-grown BLG shows equally good room temperature spin transport properties as both CVD-graphene and even exfoliated single-layer graphene. △ Less

Submitted 17 March, 2022; v1 submitted 13 May, 2021; originally announced May 2021.

Comments: 14 pages, 8 figure

Journal ref: Nano Lett. 22, 4949 (2022)

Visualizing the multifractal wavefunctions of a disordered two-dimensional electron gas

Authors: Berthold Jäck, Fabian Zinser, Elio J. K\" onig, Sune N. P. Wissing, Anke B. Schmidt, Markus Donath, Klaus Kern, Christian R. Ast

Abstract: The wavefunctions of a disordered two-dimensional electron gas at the quantum-critical Anderson transition are predicted to exhibit multifractal scaling in their real space amplitude. We experimentally investigate the appearance of these characteristics in the spatially resolved local density of states of a two-dimensional mixed surface alloy Bi_xPb_{1-x}/Ag(111), by combining high-resolution scan… ▽ More The wavefunctions of a disordered two-dimensional electron gas at the quantum-critical Anderson transition are predicted to exhibit multifractal scaling in their real space amplitude. We experimentally investigate the appearance of these characteristics in the spatially resolved local density of states of a two-dimensional mixed surface alloy Bi_xPb_{1-x}/Ag(111), by combining high-resolution scanning tunneling microscopy with spin and angle-resolved inverse-photoemission experiments. Our detailed knowledge of the surface alloy electronic band structure, the exact lattice structure and the atomically resolved local density of states enables us to construct a realistic Anderson tight binding model of the mixed surface alloy, and to directly compare the measured local density of states characteristics with those from our model calculations. The statistical analyses of these two-dimensional local density of states maps reveal their log-normal distributions and multifractal scaling characteristics of the underlying wavefunctions with a finite anomalous scaling exponent. Finally, our experimental results confirm theoretical predictions of an exact scaling symmetry for Anderson quantum phase transitions in the Wigner-Dyson classes. △ Less

Submitted 15 October, 2020; originally announced October 2020.

Comments: 10 pages, 7 figures

Journal ref: Phys. Rev. Research 3, 013022 (2021)

Controlled emission time statistics of a dynamic single-electron transistor

Authors: Fredrik Brange, Adrian Schmidt, Johannes C. Bayer, Timo Wagner, Christian Flindt, Rolf J. Haug

Abstract: Quantum technologies involving qubit measurements based on electronic interferometers rely critically on accurate single-particle emission. However, achieving precisely timed operations requires exquisite control of the single-particle sources in the time domain. Here, we demonstrate accurate control of the emission time statistics of a dynamic single-electron transistor by measuring the waiting t… ▽ More Quantum technologies involving qubit measurements based on electronic interferometers rely critically on accurate single-particle emission. However, achieving precisely timed operations requires exquisite control of the single-particle sources in the time domain. Here, we demonstrate accurate control of the emission time statistics of a dynamic single-electron transistor by measuring the waiting times between emitted electrons. By ramping up the modulation frequency, we controllably drive the system through a crossover from adiabatic to nonadiabatic dynamics, which we visualize by measuring the temporal fluctuations at the single-electron level and explain using detailed theory. Our work paves the way for future technologies based on the ability to control, transmit, and detect single quanta of charge or heat in the form of electrons, photons, or phonons. △ Less

Submitted 7 January, 2021; v1 submitted 13 May, 2020; originally announced May 2020.

Comments: 5+2 pages, 3 figures, published in Science Advances

Journal ref: Sci. Adv. 7, eabe0793 (2021)

Scalable functionalization of optical fibers using atomically thin semiconductors

Authors: Gia Quyet Ngo, Antony George, Robin Tristan Klaus Schock, Alessandro Tuniz, Emad Najafidehaghani, Ziyang Gan, Nils C. Geib, Tobias Bucher, Heiko Knopf, Christof Neumann, Tilman Lühder, Stephen Warren-Smith, Heike Ebendorff-Heidepriem, Thomas Pertsch, Markus A. Schmidt, Andrey Turchanin, Falk Eilenberger

Abstract: Atomically thin transition metal dichalcogenides are highly promising for integrated optoelectronic and photonic systems due to their exciton-driven linear and nonlinear interaction with light. Integrating them into optical fibers yields novel opportunities in optical communication, remote sensing, and all-fiber optoelectronics. However, scalable and reproducible deposition of high quality monolay… ▽ More Atomically thin transition metal dichalcogenides are highly promising for integrated optoelectronic and photonic systems due to their exciton-driven linear and nonlinear interaction with light. Integrating them into optical fibers yields novel opportunities in optical communication, remote sensing, and all-fiber optoelectronics. However, scalable and reproducible deposition of high quality monolayers on optical fibers is a challenge. Here, we report the chemical vapor deposition of monolayer MoS2 and WS2 crystals on the core of microstructured exposed core optical fibers and their interaction with the fibers' guided modes. We demonstrate two distinct application possibilities of 2D-functionalized waveguides to exemplify their potential. First, we simultaneously excite and collect excitonic 2D material photoluminescence with the fiber modes, opening a novel route to remote sensing. Then we show that third harmonic generation is modified by the highly localized nonlinear polarization of the monolayers, yielding a new avenue to tailor nonlinear optical processes in fibers. We anticipate that our results may lead to significant advances in optical fiber based technologies. △ Less

Submitted 2 September, 2020; v1 submitted 8 May, 2020; originally announced May 2020.

Journal ref: Adv. Mater. 2020, 2003826

Diffusion of single active-dipolar cubes in applied fields

Authors: Martin Kaiser, Yeimy Martinez, Annette M. Schmidt, Pedro A. Sánchez, Sofia S. Kantorovich

Abstract: "Active matter" refers to a class of out-of-equilibrium systems whose ability to transform environmental energy to kinetic energy is sought after in multiple fields of science and at very different length scales. At microscopic scales, an important challenge lies in overpowering the particles reorientation due to thermal fluctuations, especially in nano-sized systems, to create non-random, directe… ▽ More "Active matter" refers to a class of out-of-equilibrium systems whose ability to transform environmental energy to kinetic energy is sought after in multiple fields of science and at very different length scales. At microscopic scales, an important challenge lies in overpowering the particles reorientation due to thermal fluctuations, especially in nano-sized systems, to create non-random, directed motion, needed for a wide range of possible applications. In this article, we employ molecular dynamics simulations to show that the diffusion of a self-propelling dipolar nanocube can be enhanced in a pre-defined direction with the help of a moderately strong applied magnetic field, overruling the effect of the thermal fluctuations. Furthermore, we show that the direction of diffusion is given by the orientation of the net internal magnetisation of the cube. This can be used to determine experimentally the latter in synthetically crafted active cobalt ferrite nanocubes. △ Less

Submitted 12 February, 2020; v1 submitted 11 February, 2020; originally announced February 2020.

Comments: 10 pages, 7 Figures, 1 Table

Liquid metal intercalation of epitaxial graphene: large-area gallenene layer fabrication through gallium self-propagation at ambient conditions

Authors: S. Wundrack, D. Momeni Pakdehi, W. Dempwolf, N. Schmidt, K. Pierz, L. Michaliszyn, H. Spende, A. Schmidt, H. W. Schumacher, R. Stosch, A. Bakin

Abstract: We demonstrate the fabrication of an ultra thin gallium film, also known as gallenene, beneath epitaxial graphene on 6H-SiC under ambient conditions triggered by liquid gallium intercalation. Gallenene has been fabricated using the liquid metal intercalation, achieving lateral intercalation and diffusion of Ga atoms at room temperature on square centimeter areas limited only by the graphene sample… ▽ More We demonstrate the fabrication of an ultra thin gallium film, also known as gallenene, beneath epitaxial graphene on 6H-SiC under ambient conditions triggered by liquid gallium intercalation. Gallenene has been fabricated using the liquid metal intercalation, achieving lateral intercalation and diffusion of Ga atoms at room temperature on square centimeter areas limited only by the graphene samples' size. The stepwise self-propagation of the gallenene film below the epitaxial graphene surface on the macroscopic scale was observed by optical microscopy shortly after the initial processing without further physical or chemical treatment. Directional Ga diffusion of gallenene occurs on SiC terraces since the terrace steps form an energetic barrier (Ehrlich-Schwoebel barrier),retarding the gallenene propagation. The subsequent conversion of the epitaxial graphene into quasi free-standing bilayer graphene (QFBLG) and the graphene-gallenene heterostack interactions have been analyzed by XPS and Raman measurements. The results reveal a novel approach for controlled fabrication of wafer-scale gallenene as well as for two-dimensional heterostructures and stacks based on the interaction between liquid metal and epitaxial graphene. Please note, this work was also titled as Graphene meets gallenene -- A straightforward approach to developing large-area heterostacks by gallium self-propagation https://www.researchgate.net/publication/333451130_Graphene_meets_gallenene_-_A_straightforward_approach_to_developing_large-area_heterostacks_by_gallium_self-propagation △ Less

Submitted 16 July, 2020; v1 submitted 29 May, 2019; originally announced May 2019.

Comments: A copy of the video can be requested via the following email address: stefan.wundrack@ptb.de

Journal ref: Phys. Rev. Materials 5, 024006 (2021)

Fragility of Fermi arcs in Dirac semimetals

Authors: Yun Wu, Na Hyun Jo, Lin-Lin Wang, Connor A. Schmidt, Kathryn M. Neilson, Benjamin Schrunk, Przemyslaw Swatek, Andrew Eaton, S. L. Bud'ko, P. C. Canfield, Adam Kaminski

Abstract: We use tunable, vacuum ultraviolet laser-based angle-resolved photoemission spectroscopy and density functional theory calculations to study the electronic properties of Dirac semimetal candidate cubic PtBi${}_{2}$. In addition to bulk electronic states we also find surface states in PtBi${}_{2}$ which is expected as PtBi${}_{2}$ was theoretical predicated to be a candidate Dirac semimetal. The su… ▽ More We use tunable, vacuum ultraviolet laser-based angle-resolved photoemission spectroscopy and density functional theory calculations to study the electronic properties of Dirac semimetal candidate cubic PtBi${}_{2}$. In addition to bulk electronic states we also find surface states in PtBi${}_{2}$ which is expected as PtBi${}_{2}$ was theoretical predicated to be a candidate Dirac semimetal. The surface states are also well reproduced from DFT band calculations. Interestingly, the topological surface states form Fermi contours rather than double Fermi arcs that were observed in Na$_3$Bi. The surface bands forming the Fermi contours merge with bulk bands in proximity of the Dirac points projections, as expected. Our data confirms existence of Dirac states in PtBi${}_{2}$ and reveals the fragility of the Fermi arcs in Dirac semimetals. Because the Fermi arcs are not topologically protected in general, they can be deformed into Fermi contours, as proposed by [Kargarian {\it et al.}, PNAS \textbf{113}, 8648 (2016)]. Our results demonstrate validity of this theory in PtBi${}_{2}$. △ Less

Submitted 5 April, 2019; originally announced April 2019.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. B 99, 161113(R) 2019

From Parisi to Boltzmann

Authors: Goetz Kersting, Nicola Kistler, Adrien Schertzer, Marius A. Schmidt

Abstract: We sketch a new framework for the analysis of disordered systems, in particular mean field spin glasses, which is variational in nature and within the formalism of classical thermodynamics. For concreteness, only the Sherrington-Kirkpatrick model is considered here. For this we show how the Parisi solution (replica symmetric, or when replica symmetry is broken) emerges, in large but finite volumes… ▽ More We sketch a new framework for the analysis of disordered systems, in particular mean field spin glasses, which is variational in nature and within the formalism of classical thermodynamics. For concreteness, only the Sherrington-Kirkpatrick model is considered here. For this we show how the Parisi solution (replica symmetric, or when replica symmetry is broken) emerges, in large but finite volumes, from a high temperature expansion to second order of the Gibbs potential with respect to order parameters encoding the law of the effective fields. In contrast with classical systems where convexity in the order parameters is the default situation, the functionals employed here are, at infinite temperature, concave: this feature is eventually due to the Gaussian nature of the interaction and implies, in particular, that the canonical Boltzmann-Gibbs variational principles must be reversed. The considerations suggest that thermodynamical phase transitions are intimately related to the divergence of the infinite expansions. △ Less

Submitted 25 February, 2019; v1 submitted 3 February, 2019; originally announced February 2019.

Comments: 19 pages, 6 figures. Amended, revised and extended version. In particular, both high and low temperature regimes are addressed: for the latter we sketch how the RSB-formula also emerges, from finite volumes, via high temperature (second order) expansions of the Gibbs potential

Short-range correlations and the charge density

Authors: Ronen Weiss, Axel Schmidt, Gerald A. Miller, Nir Barnea

Abstract: Sophisticated high-energy and large momentum-transfer scattering experiments combined with ab-initio calculations can reveal the short-distance behavior of nucleon pairs in nuclei. On an opposite energy and resolution scale, elastic electron scattering experiments are used to extract the charge density and charge radius of different nuclei. We show that even though the charge density has no obviou… ▽ More Sophisticated high-energy and large momentum-transfer scattering experiments combined with ab-initio calculations can reveal the short-distance behavior of nucleon pairs in nuclei. On an opposite energy and resolution scale, elastic electron scattering experiments are used to extract the charge density and charge radius of different nuclei. We show that even though the charge density has no obvious connection with nuclear short-range correlations, it can be used to extract properties of such correlations. This is accomplished by using the nuclear contact formalism to derive a relation between the charge density and the proton-proton nuclear contacts that describe the probability of two protons being at close proximity. With this relation, the values of the proton-proton contacts are extracted for various nuclei using only the nuclear charge density and a solution of the two-nucleon Schroedinger equation as inputs. For symmetric nuclei, the proton-neutron contacts can also be extracted from the charge density. Good agreement is obtained with previous extractions of the nuclear contacts. These results imply that one can predict (with reasonably good accuracy) the results of high-energy and large momentum-transfer electron-scattering experiments and ab-initio calculations of high momentum tails using only experimental data of elastic scattering experiments. △ Less

Submitted 17 February, 2019; v1 submitted 23 July, 2018; originally announced July 2018.

Report number: NT@UW-18-07

Topological Crystalline Transition Metals: Strained W, Ta, Mo, and Nb

Authors: Danny Thonig, Tomáš Rauch, Hossein Mirhosseini, Jügen Henk, Ingrid Mertig, Henry Wortelen, Bernd Engelkamp, Anke B. Schmidt, Markus Donath

Abstract: In a joint theoretical and experimental investigation we show that a series of transition metals with strained body-centered cubic lattice ---W, Ta, Nb, and Mo--- host surface states that are topologically protected by mirror symmetry. Our finding extends the class of topologically nontrivial systems by topological crystalline transition metals. The investigation is based on independent calculatio… ▽ More In a joint theoretical and experimental investigation we show that a series of transition metals with strained body-centered cubic lattice ---W, Ta, Nb, and Mo--- host surface states that are topologically protected by mirror symmetry. Our finding extends the class of topologically nontrivial systems by topological crystalline transition metals. The investigation is based on independent calculations of the electronic structures and of topological invariants, the results of which agree with established properties of the Dirac-type surface state in W(110). To further support our prediction, we investigate both experimentally by spin-resolved inverse photoemission and theoretically an unoccupied topologically nontrivial surface state in Ta(110). △ Less

Submitted 12 May, 2016; originally announced May 2016.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. B 94, 155132 (2016)

Specific heat and entropy of fractional quantum Hall states in the second Landau level

Authors: B. A. Schmidt, K. Bennaceur, S. Gaucher, G. Gervais, L. N. Pfeiffer, K. W. West

Abstract: Specific heat has had an important role in the study of superfluidity and superconductivity, and could provide important information about the fractional quantum Hall effect as well. However, traditional measurements of the specific heat of a two-dimensional electron gas are difficult due to the large background contribution of the phonon bath, even at very low temperatures. Here, we report measur… ▽ More Specific heat has had an important role in the study of superfluidity and superconductivity, and could provide important information about the fractional quantum Hall effect as well. However, traditional measurements of the specific heat of a two-dimensional electron gas are difficult due to the large background contribution of the phonon bath, even at very low temperatures. Here, we report measurements of the specific heat per electron in the second Landau level by measuring the thermalization time between the electrons and phonons. We observe activated behaviour of the specific heat of the 5/2 and 7/3 fractional quantum Hall states, and extract the entropy by integrating over temperature. Our results are in excellent agreement with previous measurements of the entropy via longitudinal thermopower. Extending the technique to lower temperatures could lead to detection of the non-Abelian entropy predicted for bulk quasiparticles at 5/2 filling △ Less

Submitted 7 June, 2017; v1 submitted 8 May, 2016; originally announced May 2016.

Journal ref: Phys. Rev. B 95, 201306 (2017)

Immune response to functionalized mesoporous silica nanoparticles for targeted drug delivery

Authors: S. Heidegger, S. Niedermayer, A. Schmidt, D. Gößl, C. Argyo, S. Endres, T. Bein, C. Bourquin

Abstract: Multifunctional mesoporous silica nanoparticles (MSN) have attracted substantial attention with regard to their high potential for targeted drug delivery. For future clinical applications it is crucial to address safety concerns and understand the potential immunotoxicity of these nanoparticles. In this study, we assess the biocompatibility and functionality of multifunctional MSN in freshly isola… ▽ More Multifunctional mesoporous silica nanoparticles (MSN) have attracted substantial attention with regard to their high potential for targeted drug delivery. For future clinical applications it is crucial to address safety concerns and understand the potential immunotoxicity of these nanoparticles. In this study, we assess the biocompatibility and functionality of multifunctional MSN in freshly isolated, primary murine immune cells. We show that the functionalized silica nanoparticles are rapidly and efficiently taken up into the endosomal compartment by specialized antigen-presenting cells such as dendritic cells. The silica nanoparticles showed a favorable toxicity profile and did not affect the viability of primary immune cells from the spleen in relevant concentrations. Cargo-free MSN induced only very low immune responses in primary cells as determined by surface expression of activation markers and release of pro-inflammatory cytokines such as Interleukin-6, -12 and -1β. In contrast, when surface-functionalized MSN with a pH-responsive polymer capping were loaded with an immune-activating drug, the synthetic Toll-like receptor 7 agonist R848, a strong immune response was provoked. We thus demonstrate that MSN represent an efficient drug delivery vehicle to primary immune cells that is both non-toxic and non-inflammagenic, which is a prerequisite for the use of these particles in biomedical applications. △ Less

Submitted 3 September, 2015; originally announced September 2015.

Comments: The manuscript includes 23 pages, 6 figures, 1 table

Fast, label-free tracking of single viruses and weakly scattering nanoparticles in a nano-fluidic optical fiber

Authors: Sanli Faez, Yoav Lahini, Stefan Weidlich, Rees F. Garmann, Katrin Wondraczek, Matthias Zeisberger, Markus A. Schmidt, Michel Orrit, Vinothan N. Manoharan

Abstract: High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limi… ▽ More High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber containing a sub-wavelength, nano-fluidic channel and illuminate them using the fiber's strongly confined optical mode. The diffusing particles in this cylinderical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions - 4.6 megadaltons in size - at rates of over 2 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems. △ Less

Submitted 18 July, 2015; v1 submitted 22 June, 2015; originally announced June 2015.

Comments: 12 pages, 4 figures, updated references

Journal ref: ACS Nano, 2015, 9(12), pp 12349-12357

Second Landau Level Fractional Quantum Hall Effects in the Corbino Geometry

Authors: B. A. Schmidt, K. Bennaceur, S. Bilodeau, G. Gervais, L. N. Pfeiffer, K. W. West

Abstract: For certain measurements, the Corbino geometry has a distinct advantage over the Hall and van der Pauw geometries, in that it provides a direct probe of the bulk 2DEG without complications due to edge effects. This may be important in enabling detection of the non-Abelian entropy of the 5/2 fractional quantum Hall state via bulk thermodynamic measurements. We report the successful fabrication and… ▽ More For certain measurements, the Corbino geometry has a distinct advantage over the Hall and van der Pauw geometries, in that it provides a direct probe of the bulk 2DEG without complications due to edge effects. This may be important in enabling detection of the non-Abelian entropy of the 5/2 fractional quantum Hall state via bulk thermodynamic measurements. We report the successful fabrication and measurement of a Corbino-geometry sample in an ultra-high mobility GaAs heterostructure, with a focus on transport in the second and higher Landau levels. In particular, we report activation energy gaps of fractional quantum Hall states, with all edge effects ruled out, and extrapolate the conductivity prefactor from the Arrhenius fits. Our results show that activated transport in the second Landau level remains poorly understood. The development of this Corbino device opens the possibility to study the bulk of the 5/2 state using techniques not possible in other geometries. △ Less

Submitted 18 June, 2015; v1 submitted 26 March, 2015; originally announced March 2015.

Journal ref: Solid State Communications 217, 1 (2015)

Mechanical Flip-Chip for Ultra-High Electron Mobility Devices

Authors: K. Bennaceur, B. A. Schmidt, S. Gaucher, D. Laroche, M. P. Lilly, J. L. Reno, K. W. West, L. N. Pfeiffer, G. Gervais

Abstract: Electrostatic gates are of paramount importance for the physics of devices based on high-mobility two-dimensional electron gas (2DEG) since they allow depletion of electrons in selected areas. This field-effect gating enables the fabrication of a wide range of devices such as, for example, quantum point contacts (QPC), electron interferometers and quantum dots. To fabricate these gates, processing… ▽ More Electrostatic gates are of paramount importance for the physics of devices based on high-mobility two-dimensional electron gas (2DEG) since they allow depletion of electrons in selected areas. This field-effect gating enables the fabrication of a wide range of devices such as, for example, quantum point contacts (QPC), electron interferometers and quantum dots. To fabricate these gates, processing is usually performed on the 2DEG material, which is in many cases detrimental to its electron mobility. Here we propose an alternative process which does not require any processing of the 2DEG material other than for the ohmic contacts. This approach relies on processing a separate wafer that is then mechanically mounted on the 2DEG material in a flip-chip fashion. This technique proved successful to fabricate quantum point contacts on both GaAs/AlGaAs materials with both moderate and ultra-high electron mobility. △ Less

Submitted 17 March, 2015; originally announced March 2015.

Comments: 5 pages, 3 figures

Journal ref: Scientific Reports 5, Article number: 13494 (2015)

Micro- and Nano-scale Measurement Methods for Phase Change Heat Transfer on Planar and Structured Surfaces

Authors: Jacopo Buongiorno, David G. Cahill, Carlos H. Hidrovo, Saeed Moghaddam, Aaron J. Schmidt, Li Shi

Abstract: In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fie… ▽ More In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fields, as well as measurements at the single bubble level. Finally, we discuss techniques to probe the kinetics of vapor formation within a few molecular layers of the interface. We conclude with our outlook for future progress in experimental methods for phase change heat transfer. △ Less

Submitted 1 August, 2014; originally announced August 2014.

Journal ref: J. Buongiorno, D. G. Cahill, C. H. Hidrovo, S. Moghaddam, A.J. Schmidt, L. Shi, Nanoscale and Microscale Thermophysical Engineering, vol. 18, p. 270-287 (2014)

Using thermal boundary conditions to engineer the quantum state of a bulk magnet

Authors: M. A. Schmidt, D. M. Silevitch, G. Aeppli, T. F. Rosenbaum

Abstract: The degree of contact between a system and the external environment can alter dramatically its proclivity to quantum mechanical modes of relaxation. We show that controlling the thermal coupling of cubic centimeter-sized crystals of the Ising magnet $LiHo_xY_{1-x}F_4$ to a heat bath can be used to tune the system between a glassy state dominated by thermal excitations over energy barriers and a st… ▽ More The degree of contact between a system and the external environment can alter dramatically its proclivity to quantum mechanical modes of relaxation. We show that controlling the thermal coupling of cubic centimeter-sized crystals of the Ising magnet $LiHo_xY_{1-x}F_4$ to a heat bath can be used to tune the system between a glassy state dominated by thermal excitations over energy barriers and a state with the hallmarks of a quantum spin liquid. Application of a magnetic field transverse to the Ising axis introduces both random magnetic fields and quantum fluctuations, which can retard and speed the annealing process, respectively, thereby providing a mechanism for continuous tuning between the destination states. The non-linear response of the system explicitly demonstrates quantum interference between internal and external relaxation pathways. △ Less

Submitted 13 February, 2014; originally announced February 2014.

Comments: 23 pages, 4 figures. Accepted for publication in PNAS

Journal ref: PNAS v111 p3689-3694 (2014)

Worm Algorithm for Abelian Gauge-Higgs Models

Authors: Ydalia Delgado, Alexander Schmidt

Abstract: We present the surface worm algorithm (SWA) which is a generalization of the Prokof'ev Svistunov worm algorithm to perform the simulation of the dual representation (surfaces and loops) of Abelian gauge-Higgs models on a lattice. We compare the SWA to a local Metropolis update in the dual representation and show that the SWA outperforms the local update for a wide range of parameters. We present the surface worm algorithm (SWA) which is a generalization of the Prokof'ev Svistunov worm algorithm to perform the simulation of the dual representation (surfaces and loops) of Abelian gauge-Higgs models on a lattice. We compare the SWA to a local Metropolis update in the dual representation and show that the SWA outperforms the local update for a wide range of parameters. △ Less

Submitted 11 April, 2013; originally announced April 2013.

Comments: 6 pages, 6 figures. Proceedings for "Excited QCD 2013", Sarajevo, 03-09 Feb, 2013

Surface worm algorithm for abelian Gauge-Higgs systems on the lattice

Authors: Ydalia Delgado, Christof Gattringer, Alexander Schmidt

Abstract: The Prokof'ev Svistunov worm algorithm was originally developed for models with nearest neighbor interactions that in a high temperature expansion are mapped to systems of closed loops. In this work we present the surface worm algorithm (SWA) which is a generalization of the worm algorithm concept to abelian Gauge-Higgs models on a lattice which can be mapped to systems of surfaces and loops (dual… ▽ More The Prokof'ev Svistunov worm algorithm was originally developed for models with nearest neighbor interactions that in a high temperature expansion are mapped to systems of closed loops. In this work we present the surface worm algorithm (SWA) which is a generalization of the worm algorithm concept to abelian Gauge-Higgs models on a lattice which can be mapped to systems of surfaces and loops (dual representation). Using Gauge-Higgs models with gauge groups Z(3) and U(1) we compare the SWA to the conventional approach and to a local update in the dual representation. For the Z(3) case we also consider finite chemical potential where the conventional representation has a sign problem which is overcome in the dual representation. For a wide range of parameters we find that the SWA clearly outperforms the local update. △ Less

Submitted 12 February, 2013; v1 submitted 14 November, 2012; originally announced November 2012.

Comments: 32 pages; appendix added; revised version published in Comput.Phys.Commun

Journal ref: Comput. Phys. Commun. 184 (2013) 1535

Monte Carlo simulation of abelian gauge-Higgs lattice models using dual representation

Authors: Alexander Schmidt, Ydalia Delgado Mercado, Christof Gattringer

Abstract: We study abelian gauge-Higgs models on the lattice and consider gauge groups Z(3) and U(1). For both cases the partition sums are mapped exactly to a dual representation where the degrees of freedom are surfaces for the gauge fields and loops of flux that may serve as boundaries for the surfaces represent the matter fields. Also at finite chemical potential the dual partition sums have only real a… ▽ More We study abelian gauge-Higgs models on the lattice and consider gauge groups Z(3) and U(1). For both cases the partition sums are mapped exactly to a dual representation where the degrees of freedom are surfaces for the gauge fields and loops of flux that may serve as boundaries for the surfaces represent the matter fields. Also at finite chemical potential the dual partition sums have only real and positive contributions and the complex action problem of the conventional representation is overcome in the dual approach. We apply a local Metropolis update for the dual degrees of freedom, as well as a generalization of the worm algorithm to bounded surfaces. Results that illustrate condensation phenomena as a function of chemical potential are discussed. △ Less

Submitted 7 November, 2012; originally announced November 2012.

Journal ref: PoS(Lattice 2012)098

Simulation of impact and fragmentation with the material point method

Authors: Biswajit Banerjee, James E. Guilkey, Todd B. Harman, John A. Schmidt, Patrick A. McMurtry

Abstract: The simulation of high-rate deformation and failure of metals is has traditionally been performed using Lagrangian finite element methods or Eulerian hydrocodes. Lagrangian mesh-based methods are limited by issues involving mesh entanglement under large deformation and considerable complexity in handling contact. On the other hand, Eulerian hydrocodes are prone to material diffusion. In the Materi… ▽ More The simulation of high-rate deformation and failure of metals is has traditionally been performed using Lagrangian finite element methods or Eulerian hydrocodes. Lagrangian mesh-based methods are limited by issues involving mesh entanglement under large deformation and considerable complexity in handling contact. On the other hand, Eulerian hydrocodes are prone to material diffusion. In the Material Point Method (MPM), the material state is defined on solid Lagrangian particles. The particles interact with other particles in the same body, with other solid bodies, or with fluids through a background mesh. Thus, some of the problems associated with finite element codes and hydrocodes are alleviated. Another attractive feature of the material point method is the ease with which large deformation, fully coupled, fluid-structure interaction problems can be handled. In this work, we present MPM simulations that involve large plastic deformations, contact, material failure and fragmentation, and fluid-structure interaction. △ Less

Submitted 11 January, 2012; originally announced January 2012.

Comments: 6 pages, 4 figures, Proceedings of 11th International Conference on Fracture, March 2005, Turin, Italy

Spectroscopic Imaging STM Studies of Electronic Structure in the Superconducting and Pseudogap Phases of Cuprate High-Tc Superconductors

Authors: Kazuhiro Fujita, Andrew R. Schmidt, Eun-Ah Kim, Michael J. Lawler, Dung Hai Lee, J. C. Davis, Hiroshi Eisaki, Shin-ichi Uchida

Abstract: One of the key motivations for the development of atomically resolved spectroscopic imaging STM (SI-STM) has been to probe the electronic structure of cuprate high temperature superconductors. In both the d-wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates, two distinct classes of electronic states are observed using SI-STM. The first class consists of the dispersive… ▽ More One of the key motivations for the development of atomically resolved spectroscopic imaging STM (SI-STM) has been to probe the electronic structure of cuprate high temperature superconductors. In both the d-wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates, two distinct classes of electronic states are observed using SI-STM. The first class consists of the dispersive Bogoliubov quasiparticles of a homogeneous d-wave superconductor. These are detected below a lower energy scale |E|=Δ0 and only upon a momentum space (k-space) arc which terminates near the lines connecting k=\pm(π/a0,0) to k=\pm(0, π/a0). In both the dSC and PG phases, the only broken symmetries detected in the |E|\leq Δ0 states are those of a d-wave superconductor. The second class of states occurs at energies near the pseudogap energy scale |E| Δ1 which is associated conventionally with the 'antinodal' states near k=\pm(π/a0,0) and k=\pm(0, π/a0). We find that these states break the 90o-rotational (C4) symmetry of electronic structure within CuO2 unit cells, at least down to 180o rotational (C2) symmetry (nematic) but in a spatially disordered fashion. This intra-unit-cell C4 symmetry breaking coexists at |E| Δ1 with incommensurate conductance modulations locally breaking both rotational and translational symmetries (smectic). The properties of these two classes of |E| Δ1 states are indistinguishable in the dSC and PG phases. To explain this segregation of k-space into the two regimes distinguished by the symmetries of their electronic states and their energy scales |E| Δ1 and |E|\leqΔ0, and to understand how this impacts the electronic phase diagram and the mechanism of high-Tc superconductivity, represents one of a key challenges for cuprate studies. △ Less

Submitted 26 December, 2011; originally announced December 2011.

Comments: 45 pages, 12 figures

Journal ref: J. Phys. Soc. Jpn. 81 (2012) 011005

How Kondo Holes Create Intense Nanoscale Heavy-Fermion Hybridization Disorder

Authors: Mohammad H. Hamidian, Andrew R. Schmidt, Inês A. Firmo, Milan P. Allan, Phelim Bradley, Jim D. Garrett, Travis J. Williams, Graeme M. Luke, Yonatan Dubi, Alexander V. Balatsky, J. C. Séamus Davis

Abstract: Replacing a magnetic atom by a spinless atom in a heavy fermion compound generates a quantum state often referred to as a 'Kondo-hole'. No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact (Lawrence JM, et al. (1996) Kondo hole behavior in Ce0. 97La0. 03Pd3. Phys Rev B 53:12559-12562; Bauer ED, et al. (2011) Electronic i… ▽ More Replacing a magnetic atom by a spinless atom in a heavy fermion compound generates a quantum state often referred to as a 'Kondo-hole'. No experimental imaging has been achieved of the atomic-scale electronic structure of a Kondo-hole, or of their destructive impact (Lawrence JM, et al. (1996) Kondo hole behavior in Ce0. 97La0. 03Pd3. Phys Rev B 53:12559-12562; Bauer ED, et al. (2011) Electronic inhomogeneity in a Kondo lattice. Proc Natl Acad Sci. 108:6857-6861) on the hybridization process between conduction and localized electrons which generates the heavy fermion state. Here we report visualization of the electronic structure at Kondo-holes created by substituting spinless Thorium atoms for magnetic Uranium atoms in the heavy-fermion system URu2Si2. At each Thorium atom, an electronic bound state is observed. Moreover, surrounding each Thorium atom we find the unusual modulations of hybridization strength recently predicted to occur at Kondo-holes (Figgins J, Morr DK (2011) Defects in heavy-fermion materials: unveiling strong correlations in real space. Phys Rev Lett 107:066401). Then, by introducing the 'hybridization gapmap' technique to heavy fermion studies, we discover intense nanoscale heterogeneity of hybridization due to a combination of the randomness of Kondo-hole sites and the long-range nature of the hybridization oscillations. These observations provide direct insight into both the microscopic processes of heavy-fermion forming hybridization and the macroscopic effects of Kondo-hole doping. △ Less

Submitted 18 October, 2011; originally announced October 2011.

Comments: Main Article + Figures, Supporting Information + Figures; PNAS 2011

Electronic Structure of the Cuprate Superconducting and Pseudogap Phases from Spectroscopic Imaging STM

Authors: A R Schmidt, K Fujita, E -A Kim, M J Lawler, H Eisaki, S Uchida, D-H Lee, J C Davis

Abstract: We survey the use of spectroscopic imaging STM to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E=Delta0. We… ▽ More We survey the use of spectroscopic imaging STM to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E=Delta0. We find that the Bogoliubov quasiparticle interference signatures of delocalized Cooper pairing are restricted to a k-space arc which terminates near the lines connecting k=\pm(pi/a0,0) to k=\pm(pi/a0). This arc shrinks continuously with decreasing hole density such that Luttinger's theorem could be satisfied if it represents the front side of a hole-pocket which is bounded behind by the lines between k=\pm(pi/a0,0) and k=\pm(0,pi/a0). In both phases the only broken symmetries detected for the |E|<Delta0 states are those of a d-wave superconductor. The second class of states occurs proximate to the pseudogap energy scale E=Delta1. Here the non-dispersive electronic structure breaks the expected 90o-rotational symmetry of electronic structure within each unit cell, at least down to 180o-rotational symmetry. This Q=0 electronic symmetry breaking was first detected as an electronic inequivalence at the two oxygen sites within each unit cell by using a measure of nematic (C2) symmetry. Incommensurate non-dispersive conductance modulations, locally breaking both rotational and translational symmetries, coexist with this intra-unit-cell electronic symmetry breaking at E=Delta1. Their characteristic wavevector Q is determined by the k-space points where Bogoliubov quasiparticle interference terminates and therefore changes continuously with doping. The distinct broken electronic symmetry states (Q=0 and finite Q) coexisting at E~Delta1 are found to be indistinguishable in the dSC and PG phases. △ Less

Submitted 9 February, 2011; originally announced February 2011.

Comments: 32 pages with 10 figures

Two-bands superconductivity with intra- and interband pairing for synthetic superlattices

Authors: Alex A. Schmidt, Jose J. Rodríguez-Núñez, Antonio Bianconi, Andrea Perali

Abstract: We consider a model for superconductivity in a two-band superconductor, having an anisotropic electronic structure made of two partially overlapping bands with a first hole-like and a second electron-like fermi surface. In this pairing scenario, driven by the interplay between interband $V_{i,j}$ and intraband $V_{i,i}$ pairing terms, we have solved the two gap equations at the critical temperatur… ▽ More We consider a model for superconductivity in a two-band superconductor, having an anisotropic electronic structure made of two partially overlapping bands with a first hole-like and a second electron-like fermi surface. In this pairing scenario, driven by the interplay between interband $V_{i,j}$ and intraband $V_{i,i}$ pairing terms, we have solved the two gap equations at the critical temperature $T = T_c$ and calculate $T_c$ and the chemical potential $μ$ as a function of the number of carriers $n$ for various values of pairing interactions, $V_{1,1}$, $V_{2,2}$, and $V_{1,2}$. The results show the complexity of the physics of condensates with multiple order parameters with the chemical potential near band edges. △ Less

Submitted 15 December, 2010; originally announced December 2010.

Comments: 6 pages, 2 figures

Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states

Authors: M. J. Lawler, K. Fujita, Jhinhwan Lee, A. R. Schmidt, Y. Kohsaka, Chung Koo Kim, H. Eisaki, S. Uchida, J. C. Davis, J. P. Sethna, Eun-Ah Kim

Abstract: In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced1. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a qua… ▽ More In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced1. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within CuO2 unit cell. We analyze spectroscopic-imaging scanning tunneling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8+δ and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90o -rotational symmetry within every CuO2 unit cell. △ Less

Submitted 19 July, 2010; originally announced July 2010.

Comments: See the Nature website for the published version. High-resolution version of figures, supplementary information and supplementary movies are available at http://eunahkim.ccmr.cornell.edu/KimGroup/highlights.html

Journal ref: Nature 466, 347, (2010)

Imaging the Fano Lattice to 'Hidden Order' Transition in URu2Si2

Authors: Andrew R. Schmidt, Mohammad H. Hamidian, Peter Wahl, Focko Meier, Alexander V. Balatsky, James D. Garret, Travis J. Williams, Graeme M. Luke, J. C. Séamus Davis

Abstract: Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called 'heavy fermions'. In URu2Si2 these effects begin at temperatures around 55K but they are suddenly altered by an unidentified electronic phase transition at To = 17.5 K. Whether this is conventional ordering… ▽ More Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called 'heavy fermions'. In URu2Si2 these effects begin at temperatures around 55K but they are suddenly altered by an unidentified electronic phase transition at To = 17.5 K. Whether this is conventional ordering of the k-space states, or a change in the hybridization of the r-space states at each U atom, is unknown. Here we use spectroscopic imaging scanning tunnelling microscopy (SI-STM) to image the evolution of URuSi2 electronic structure simultaneously in r-space and k-space. Above To, the 'Fano lattice' electronic structure predicted for Kondo screening of a magnetic lattice is revealed. Below To, a partial energy gap without any associated density-wave signatures emerges from this Fano lattice. Heavy-quasiparticle interference imaging within this gap reveals its cause as the rapid splitting below To of a light k-space band into two new heavy fermion bands. Thus, the URu2Si2 'hidden order' state emerges directly from the Fano lattice electronic structure and exhibits characteristics, not of a conventional density wave, but of sudden alterations in both the hybridization at each U atom and the associated heavy fermion states. △ Less

Submitted 28 June, 2010; originally announced June 2010.

Comments: Main Article + Supplementary Information

Journal ref: Nature 465, 570 (2010)

Spectroscopic Fingerprint of Phase-Incoherent Superconductivity in the Cuprate Pseudogap State

Authors: Jhinhwan Lee, K. Fujita, A. R. Schmidt, Chung Koo Kim, H. Eisaki, S. Uchida, J. C. Davis

Abstract: A possible explanation for the existence of the cuprate "pseudogap" state is that it is a d-wave superconductor without quantum phase rigidity. Transport and thermodynamic studies provide compelling evidence that supports this proposal, but few spectroscopic explorations of it have been made. One spectroscopic signature of d-wave superconductivity is the particle-hole symmetric "octet" of disper… ▽ More A possible explanation for the existence of the cuprate "pseudogap" state is that it is a d-wave superconductor without quantum phase rigidity. Transport and thermodynamic studies provide compelling evidence that supports this proposal, but few spectroscopic explorations of it have been made. One spectroscopic signature of d-wave superconductivity is the particle-hole symmetric "octet" of dispersive Bogoliubov quasiparticle interference modulations. Here we report on this octet's evolution from low temperatures to well into the underdoped pseudogap regime. No pronounced changes occur in the octet phenomenology at the superconductor's critical temperature Tc, and it survives up to at least temperature T ~ 1.5Tc. In the pseudogap regime, we observe the detailed phenomenology that was theoretically predicted for quasiparticle interference in a phase-incoherent d-wave superconductor. Thus, our results not only provide spectroscopic evidence to confirm and extend the transport and thermodynamics studies, but they also open the way for spectroscopic explorations of phase fluctuation rates, their effects on the Fermi arc, and the fundamental source of the phase fluctuations that suppress superconductivity in underdoped cuprates. △ Less

Submitted 19 November, 2009; originally announced November 2009.

Comments: 27 pages, 12 figures

Journal ref: Science 325, 1099-1103 (2009)

How Cooper pairs vanish approaching the Mott insulator in Bi2Sr2CaCu2O8+d

Authors: Y. Kohsaka, C. Taylor, P. Wahl, A. Schmidt, Jhinhwan Lee, K. Fujita, J. W. Alldredge, Jinho Lee, K. McElroy, H. Eisaki, S. Uchida, D. -H. Lee, J. C. Davis

Abstract: The antiferromagnetic ground state of copper oxide Mott insulators is achieved by localizing an electron at each copper atom in real space (r-space). Removing a small fraction of these electrons (hole doping) transforms this system into a superconducting fluid of delocalized Cooper pairs in momentum space (k-space). During this transformation, two distinctive classes of electronic excitations ap… ▽ More The antiferromagnetic ground state of copper oxide Mott insulators is achieved by localizing an electron at each copper atom in real space (r-space). Removing a small fraction of these electrons (hole doping) transforms this system into a superconducting fluid of delocalized Cooper pairs in momentum space (k-space). During this transformation, two distinctive classes of electronic excitations appear. At high energies, the enigmatic 'pseudogap' excitations are found, whereas, at lower energies, Bogoliubov quasi-particles -- the excitations resulting from the breaking of Cooper pairs -- should exist. To explore this transformation, and to identify the two excitation types, we have imaged the electronic structure of Bi2Sr2CaCu2O8+d in r-space and k-space simultaneously. We find that although the low energy excitations are indeed Bogoliubov quasi-particles, they occupy only a restricted region of k-space that shrinks rapidly with diminishing hole density. Concomitantly, spectral weight is transferred to higher energy r-space states that lack the characteristics of excitations from delocalized Cooper pairs. Instead, these states break translational and rotational symmetries locally at the atomic scale in an energy independent fashion. We demonstrate that these unusual r-space excitations are, in fact, the pseudogap states. Thus, as the Mott insulating state is approached by decreasing the hole density, the delocalized Cooper pairs vanish from k-space, to be replaced by locally translational- and rotational-symmetry-breaking pseudogap states in r-space. △ Less

Submitted 27 August, 2008; originally announced August 2008.

Comments: This is author's version. See the Nature website for the published version

Journal ref: Nature 454, 1072 (2008)

An Intrinsic Bond-Centered Electronic Glass with Unidirectional Domains in Underdoped Cuprates

Authors: Y. Kohsaka, C. Taylor, K. Fujita, A. Schmidt, C. Lupien, T. Hanaguri, M. Azuma, M. Takano, H. Eisaki, H. Takagi, S. Uchida, J. C. Davis

Abstract: Removing electrons from the CuO2 plane of cuprates alters the electronic correlations sufficiently to produce high-temperature superconductivity. Associated with these changes are spectral weight transfers from the high energy states of the insulator to low energies. In theory, these should be detectable as an imbalance between the tunneling rate for electron injection and extraction - a tunneli… ▽ More Removing electrons from the CuO2 plane of cuprates alters the electronic correlations sufficiently to produce high-temperature superconductivity. Associated with these changes are spectral weight transfers from the high energy states of the insulator to low energies. In theory, these should be detectable as an imbalance between the tunneling rate for electron injection and extraction - a tunneling asymmetry. We introduce atomic-resolution tunneling-asymmetry imaging, finding virtually identical phenomena in two lightly hole-doped cuprates: Ca1.88Na0.12CuO2Cl2 and Bi2Sr2Dy0.2Ca0.8Cu2O8+d. Intense spatial variations in tunneling asymmetry occur primarily at the planar oxygen sites; their spatial arrangement forms a Cu-O-Cu bond centered electronic pattern without long range order but with 4a0-wide unidirectional electronic domains dispersed throughout (a0: the Cu-O-Cu distance). The emerging picture is then of a partial hole-localization within an intrinsic electronic glass evolving, at higher hole-densities, into complete delocalization and highest temperature superconductivity. △ Less

Submitted 12 March, 2007; originally announced March 2007.

Comments: 28 pages, 9 figures, published version is available at http://people.ccmr.cornell.edu/~jcdavis/mK_stm/publications/domains/index.htm

Journal ref: Science 315, 1380 (2007)