arXiv subjects

Reinhold Kleiner

Publications and source records attributed to Reinhold Kleiner.

At least 37 records · Page 2Linked to original sources

arXiv2024

Extracting the current-phase-relation of a monolithic three-dimensional nano-constriction using a DC-current-tunable superconducting microwave cavity

Superconducting circuits with nonlinear elements such as Josephson tunnel junctions or kinetic inductance nanowires are the workhorse for microwave quantum and superconducting sensing technologies. For devices, which can be operated at high temperatures and large magnetic fields, nano-constrictions as nonlinear elements are recently under intense investigation. Constrictions, however, are far less understood than conventional Josephson tunnel junctions, and their current-phase-relationships (CPRs) -- although highly important for device design -- are hard to predict. Here, we present a niobium microwave cavity with a monolithically integrated, neon-ion-beam patterned three-dimensional (3D) nano-constriction. By design, we obtain a DC-current-tunable microwave circuit and characterize how the bias-current-dependent constriction properties impact the cavity resonance. Based on the results of these experiments, we reconstruct the CPR of the nanoconstriction. Finally, we discuss the Kerr nonlinearity of the device, a parameter important for many high-dynamic-range applications and an experimental probe for the second and third derivatives of the CPR. Our platform provides a useful method to comprehensively characterize nonlinear elements integrated in microwave circuits and could be of interest for current sensors, hybrid quantum systems and parametric amplifiers. Our findings furthermore contribute to a better understanding of nano-fabricated 3D constrictions.

cond-mat.mes-hall↗

arXiv2024

Laser-induced quenching of metastability at the Mott-insulator to metal transition

There is growing interest in strongly correlated insulator thin films because the intricate interplay of their intrinsic and extrinsic state variables causes memristive behavior that might be used for bio-mimetic devices in the emerging field of neuromorphic computing. In this study we find that laser irradiation tends to drive V$_2$O$_3$ from supercooled/superheated metastable states towards thermodynamic equilibrium, most likely in a non-thermal way. We study thin films of the prototypical Mott-insulator V$_2$O$_3$, which show spontaneous phase separation into metal-insulator herringbone domains during the Mott transition. Here, we use low-temperature microscopy to investigate how these metal-insulator domains can be modified by scanning a focused laser beam across the thin film surface. We find that the response depends on the thermal history: When the thin film is heated from below the Mott transition temperature, the laser beam predominantly induces metallic domains. On the contrary, when the thin film is cooled from a temperature above the transition, the laser beam predominantly induces insulating domains. Very likely, the V$_2$O$_3$ thin film is in a superheated or supercooled state, respectively, during the first-order phase transition, and the perturbation by a laser beam drives these metastable states into stable ones. This way, the thermal history is locally erased. Our findings are supported by a phenomenological model with a laser-induced lowering of the energy barrier between the metastable and equilibrium states.

cond-mat.str-el↗

arXiv2023

High-Q magnetic levitation and control of superconducting microspheres at millikelvin temperatures

We report the levitation of a superconducting lead-tin sphere with 100 micrometer diameter (corresponding to a mass of 5.6 micrograms) in a static magnetic trap formed by two coils in an anti-Helmholtz configuration, with adjustable resonance frequencies up to 240 hertz. The center-of-mass motion of the sphere is monitored magnetically using a dc superconducting quantum interference device as well as optically and exhibits quality factors of up to 2.6e7. We also demonstrate 3D magnetic feedback control of the sphere's motion. The setup is housed in a dilution refrigerator operating at 15 millikelvin. By implementing a cryogenic vibration isolation system we can attenuate environmental vibrations at 200 hertz by approximately seven orders of magnitude. The combination of low temperature, large mass and high quality factor as well as adjustable resonance frequencies provides a promising platform for testing quantum physics in previously unexplored regimes with high mass and long coherence times.

quant-ph↗

arXiv2023

Niobium Quantum Interference Microwave Circuits with Monolithic Three-Dimensional (3D) Nanobridge Junctions

Nonlinear microwave circuits are key elements for many groundbreaking research directions and technologies, such as quantum computation and quantum sensing. The majority of microwave circuits with Josephson nonlinearities to date is based on aluminum thin films, and therefore they are severely restricted in their operation range regarding temperatures and external magnetic fields. Here, we present the realization of superconducting niobium microwave resonators with integrated, three-dimensional (3D) nanobridge-based superconducting quantum interference devices. The 3D nanobridges (constriction weak links) are monolithically patterned into pre-fabricated microwave LC circuits using neon ion beam milling, and the resulting quantum interference circuits show frequency tunabilities, flux responsivities and Kerr nonlinearities on par with comparable aluminum nanobridge devices, but with the perspective of a much larger operation parameter regime. Our results reveal great potential for application of these circuits in hybrid systems with e.g. magnons and spin ensembles or in flux-mediated optomechanics.

quant-ph↗

arXiv2023

Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin Films with a Periodic Pinning~Lattice

The competition between intrinsic disorder in superconducting YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage-current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature ($T_g$) vs. applied magnetic field ($B_a$) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase.

cond-mat.supr-con↗

arXiv2023

Characteristic lengthscales of the electrically-induced insulator-to-metal transition

Some correlated materials display an insulator-to-metal transition as the temperature is increased. In most cases this transition can also be induced electrically, resulting in volatile resistive switching due to the formation of a conducting filament. While this phenomenon has attracted much attention due to potential applications, many fundamental questions remain unaddressed. One of them is its characteristic lengths: what sets the size of these filaments, and how does this impact resistive switching properties. Here we use a combination of wide-field and scattering-type scanning near-field optical microscopies to characterize filament formation in NdNiO3 and SmNiO3 thin films. We find a clear trend: smaller filaments increase the current density, yielding sharper switching and a larger resistive drop. With the aid of numerical simulations, we discuss the parameters controlling the filament width and, hence, the switching properties.

cond-mat.mtrl-sci↗

arXiv2022

Ordered Bose Glass of Vortices in Superconducting YBa$_{2}$Cu$_{3}$O$_{7-δ}$ Thin Films with a Periodic Pin Lattice Created by Focused Helium Ion Irradiation

The defect-rich morphology of YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) thin films leads to a glass-like arrangement of Abrikosov vortices which causes the resistance to disappear in vanishing current densities. This vortex glass consists of entangled vortex lines and is identified by a characteristic scaling of the voltage-current isotherms. Randomly distributed columnar defects stratify the vortex lines and lead to a Bose glass. Here, we report on the observation of an ordered Bose glass in a YBCO thin film with a hexagonal array of columnar defects with 30 nm spacings. The periodic pinning landscape was engineered by a focused beam of 30 keV He$^+$ ions in a helium-ion microscope.

cond-mat.supr-con↗

arXiv2021

Combining Electron Spin Resonance Spectroscopy with Scanning Tunneling Microscopy at High Magnetic Fields

Magnetic media remain a key in information storage and processing. The continuous increase of storage densities and the desire for quantum memories and computers pushes the limits of magnetic characterisation techniques. Ultimately, a tool which is capable of coherently manipulating and detecting individual quantum spins is needed. The scanning tunnelling microscope (STM) is the only technique which unites the prerequisites of high spatial and energy resolution, low temperature and high magnetic fields to achieve this goal. Limitations in the available frequency range for electron spin resonance STM (ESR-STM) mean that many instruments operate in the thermal noise regime. We resolve challenges in signal delivery to extend the operational frequency range of ESR-STM by more than a factor of two and up to 100GHz, making the Zeeman energy the dominant energy scale at achievable cryogenic temperatures of a few hundred millikelvin. We present a general method for augmenting existing instruments into ESR-STMs to investigate spin dynamics in the high-field limit. We demonstrate the performance of the instrument by analysing inelastic tunnelling in a junction driven by a microwave signal and provide proof of principle measurements for ESR-STM.

cond-mat.mes-hall↗

arXiv2021

Space-time crystalline order of a high-critical-temperature superconductor with intrinsic Josephson junctions

We theoretically demonstrate that the high-critical-temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (BSCCO) is a natural candidate for the recently envisioned classical space-time crystal. BSCCO intrinsically forms a stack of Josephson junctions. Under a periodic parametric modulation of the Josephson critical current density, the Josephson currents develop coupled space-time crystalline order, breaking the continuous translational symmetry in both space and time. The modulation frequency and amplitude span a (nonequilibrium) phase diagram for a so-defined spatiotemporal order parameter, which displays rigid pattern formation within a particular region of the phase diagram. Based on our calculations using representative material properties, we propose a laser-modulation experiment to realize the predicted space-time crystalline behavior. Our findings bring new insight into the nature of space-time crystals and, more generally, into nonequilibrium driven condensed matter systems.

cond-mat.mes-hall↗

arXiv2021

Optical imaging of strain-mediated phase coexistence during electrothermal switching in a Mott insulator

Resistive-switching -- the current-/voltage-induced electrical resistance change -- is at the core of memristive devices, which play an essential role in the emerging field of neuromorphic computing. This study is about resistive switching in a Mott-insulator, which undergoes a thermally driven metal-to-insulator transition. Two distinct switching mechanisms were reported for such a system: electric-field-driven resistive switching and electrothermal resistive switching. The latter results from an instability caused by Joule heating. Here, we present the visualization of the reversible resistive switching in a planar V$_2$O$_3$ thin-film device using high-resolution wide-field microscopy in combination with electric transport measurements. We investigate the interaction of the electrothermal instability with the strain-induced spontaneous phase-separation in the V$_2$O$_3$ thin film at the Mott-transition. The photomicrographs show the formation of a narrow metallic filament with a minimum width $\lesssim$ 500\,nm. Although the filament formation and the overall shape of the current-voltage characteristics (IVCs) are typical of an electrothermal breakdown, we also observe atypical effects like oblique filaments, filament splitting, and hysteretic IVCs with sawtooth-like jumps at high currents in the low-resistance regime. We were able to reproduce the experimental results in a numerical model based on a two-dimensional resistor network. This model demonstrates that resistive switching, in this case, is indeed electrothermal and that the intrinsic heterogeneity is responsible for the atypical effects. This heterogeneity is strongly influenced by strain, thereby establishing a link between switching dynamics and structural properties.

cond-mat.mtrl-sci↗

arXiv2021

Cavity driven Rabi oscillations between Rydberg states of atoms trapped on a superconducting atom chip

Hybrid quantum systems involving cold atoms and microwave resonators can enable cavity-mediated infinite-range interactions between atomic spin systems and realize atomic quantum memories and transducers for microwave to optical conversion. To achieve strong coupling of atoms to on-chip microwave resonators, it was suggested to use atomic Rydberg states with strong electric dipole transitions. Here we report on the realization of coherent coupling of a Rydberg transition of ultracold atoms trapped on an integrated superconducting atom chip to the microwave field of an on-chip coplanar waveguide resonator. We observe and characterize the cavity driven Rabi oscillations between a pair of Rydberg states of atoms in an inhomogeneous electric field near the chip surface. Our studies demonstrate the feasibility, but also reveal the challenges, of coherent state manipulation of Rydberg atoms interacting with superconducting circuits.

quant-ph↗

arXiv2020

Angular magnetic-field dependence of vortex matching in pinning lattices fabricated by focused or masked helium ion beam irradiation of superconducting YBa$_2$Cu$_3$O$_{7-δ}$ thin films

The angular dependence of magnetic-field commensurability effects in thin films of the cuprate high-critical-temperature superconductor YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO) with an artificial pinning landscape is investigated. Columns of point defects are fabricated by two different methods of ion irradiation -- scanning the focused 30 keV ion beam in a helium ion microscope or employing the wide-field 75 keV He$^+$ beam of an ion implanter through a stencil mask. Simulations of the ion-target interactions and the resulting collision cascades reveal that with both methods square arrays of defect columns with sub-$μ$m spacings can be created. They consist of dense point-defect clusters, which act as pinning centers for Abrikosov vortices. This is verified by the measurement of commensurable peaks of the critical current and related minima of the flux-flow resistance vs magnetic field at the matching fields. In oblique magnetic fields the matching features are exclusively governed by the component of the magnetic field parallel to the axes of the columnar defects, which confirms that the magnetic flux is penetrated along the defect columns. We demonstrate that the latter dominate the pinning landscape despite of the strong intrinsic pinning in thin YBCO films.

cond-mat.supr-con↗

arXiv2020

On-chip sensing of hotspots in superconducting terahertz emitters

Intrinsic Josephson junctions in high-temperature superconductor Bi2Sr2CaCu2O8 are known for their capability to emit high-power terahertz photons with widely tunable frequencies. Hotspots, as inhomogeneous temperature distributions across the junctions, are believed to play a critical role in synchronizing the gauge-invariant phase difference among the junctions, so as to achieve coherent strong emission. Previous optical imaging techniques have indirectly suggested that the hotspot temperature can go higher than the superconductor critical temperature. However, such optical approaches often disturb the local temperature profile and are too slow for device applications. In this paper, we demonstrate an on-chip in situ sensing technique that can precisely quantify the local temperature profile. This is achieved by fabricating a series of micro "sensor" junctions on top of an "emitter" junction and measuring the critical current on the sensors versus the bias current applied to the emitter. This fully electronic on-chip design could enable efficient close-loop control of hotspots in BSCCO junctions and significantly enhance the functionality of superconducting terahertz emitters.

cond-mat.supr-con↗

arXiv2019

Characterizing dielectric properties of ultra-thin films using superconducting coplanar microwave resonators

We present an experimental approach for cryogenic dielectric measurements on ultra-thin insulating films. Based on a coplanar microwave waveguide design we implement superconducting quarter-wave resonators with inductive coupling, which allows us to determine the real part $\varepsilon_1$ of the dielectric function at GHz frequencies and for sample thicknesses down to a few nm. We perform simulations to optimize resonator coupling and sensitivity, and we demonstrate the possibility to quantify $\varepsilon_1$ with a conformal mapping technique in a wide sample-thickness and $\varepsilon_1$-regime. Experimentally we determine $\varepsilon_1$ for various thin-film samples (photoresist, MgF$_2$, and SiO$_2$) in the thickness regime of nm up to $μm$. We find good correspondence with nominative values and we identify the precision of the film thickness as our predominant error source. Additionally we present a temperature-dependent measurement for a SrTiO$_3$ bulk sample, using an in-situ reference method to compensate for the temperature dependence of the superconducting resonator properties.

cond-mat.mtrl-sci↗

arXiv2019

Ultradense Tailored Vortex Pinning Arrays in Superconducting YBa$_2$Cu$_3$O$_{7-δ}$ Thin Films Created by Focused He Ion Beam Irradiation for Fluxonics Applications

Magnetic fields penetrate a type-II superconductor as magnetic flux quanta, called vortices. In a clean superconductor they arrange in a hexagonal lattice, while by adding periodic artificial pinning centers many other arrangements can be realized. Using the focused beam of a helium ion microscope we have fabricated periodic patterns of dense pinning centers with spacings as small as 70 nm in thin films of the cuprate superconductor YBa$_{2}$Cu$_{3}$O$_{7-δ}$. In these ultradense kagomé-like patterns, the voids lead to magnetic caging of vortices, resulting in unconventional commensurability effects that manifest themselves as peaks in the critical current and minima in the resistance versus applied magnetic field up to $\sim 0.4\,$T. The various vortex patterns at different magnetic fields are analyzed by molecular dynamics simulations of vortex motion, and the magnetic field dependence of the critical current is confirmed. These findings open the way for a controlled manipulation of vortices in cuprate superconductors by artificial sub-100 nm pinning landscapes.

cond-mat.supr-con↗

arXiv2018

Superconducting coplanar microwave resonators with operating frequencies up to 50 GHz

We demonstrate the operation of superconducting coplanar microwave resonators in a very large frequency range up to 50 GHz. The resonators are fabricated from niobium thin films on sapphire substrates and optimized for these high frequencies by small chip sizes. We study numerous harmonics of the resonators at temperatures between 1.5 K and 6 K, and we determine quality factors of up to 25000 at 1.5 K. As an example for spectroscopy applications of such resonators we detect the superconducting transition of a bulk tin sample at multiple probing frequencies.

cond-mat.supr-con↗

arXiv2018

Tunable superconducting two-chip lumped element resonator

We have fabricated and investigated a stacked two-chip device, consisting of a lumped element resonator on one chip, which is side-coupled to a coplanar waveguide transmission line on a second chip. We present a full model to predict the behavior of the device dependent on the position of the lumped element resonator with respect to the transmission line. We identify different regimes, in which the device can be operated. One of them can be used to tune the coupling between the two subsystems. Another regime enables frequency tunability of the device, without leaving the over-coupled limit for internal quality factors of about $10^4$, while in the last regime the resonator properties are insensitive against small variations of the position. Finally, we have measured the transmission characteristics of the resonator for different positions, demonstrating a good agreement with the model.

cond-mat.supr-con↗

arXiv2017

A High-Resolution Combined Scanning Laser- and Widefield Polarizing Microscope for Imaging at Temperatures from 4 K to 300 K

Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as for example birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved. The sample is mounted on a $^4$He continuous flow cryostat providing a temperature range between 4 K and 300 K, and electromagnets are used to apply magnetic fields of up to 800 mT with variable in-plane orientation and 20 mT with out-of-plane orientation. Typical applications of the polarizing microscope are the imaging of the in-plane and out-of-plane magnetization via the longitudinal and polar MOKE, imaging of magnetic flux structures in superconductors covered with a magneto-optical indicator film via Faraday effect or imaging of structural features, such as twin-walls in tetragonal SrTiO$_3$. The scanning laser microscope furthermore offers the possibility to gain local information on electric transport properties of a sample by detecting the beam-induced voltage change across a current-biased sample. This combination of magnetic, structural and electric imaging capabilities makes the microscope a viable tool for research in the fields of oxide electronics, spintronics, magnetism and superconductivity.

physics.ins-det↗