arXiv subjects

Steven M. Anlage

Publications and source records attributed to Steven M. Anlage.

At least 55 records · Page 3Linked to original sources

arXiv2019

Tunable Superconducting Josephson Dielectric Metamaterial

We demonstrate a low-dissipation dielectric metamaterial with tunable properties based on the Josephson effect. Superconducting wires loaded with regularly spaced Josephson junctions ($I_c \approx 0.25$ $μ$A) spanning a K-band waveguide and aligned with the microwave electric fields create a superconducting dielectric metamaterial. Applied dc current tunes the cutoff frequency and effective permittivity of this unique electric metamaterial. The results are in agreement with an analytical model for microwave transmission through the artificial dielectric medium.

cond-mat.supr-con↗

arXiv2019

Microwave Meissner Screening of Proximity coupled Topological Insulator / Superconductor Bilayers

The proximity coupled topological insulator / superconductor (TI/SC) bilayer system is a representative system to realize topological superconductivity. In order to better understand this unique state and design devices from the TI/SC bilayer, a comprehensive understanding of the microscopic properties of the bilayer is required. In this work, a microwave Meissner screening study, which exploits a high-precision microwave resonator technique, is conducted on the SmB6/YB6 thin film bilayers as an example TI/SC system. The study reveals spatially dependent electrodynamic screening response of the TI/SC system that is not accessible to other techniques, from which the corresponding microscopic properties of a TI/SC bilayer can be obtained. The TI thickness dependence of the effective penetration depth suggests the existence of a bulk insulating region in the TI layer. The spatially dependent electrodynamic screening model analysis provides an estimate for the characteristic lengths of the TI/SC bilayer: normal penetration depth, normal coherence length, and the thickness of the surface states. We also discuss implications of these characteristic lengths on the design of a vortex Majorana device such as the radius of the vortex core, the energy splitting due to intervortex tunneling, and the minimum thickness required for a device.

cond-mat.supr-con↗

arXiv2019

Wave scattering properties of multiple weakly-coupled complex systems

The statistics of scattering of waves inside single ray-chaotic enclosures have been successfully described by the Random Coupling Model (RCM). We expand the RCM to systems consisting of multiple complex ray-chaotic enclosures with variable coupling scenarios. The statistical properties of the model-generated quantities are tested against measured data of electrically large multi-cavity systems of various designs. The statistics of model-generated trans-impedance and induced voltages on a load impedance agree well with the experimental results. The RCM coupled chaotic enclosure model is general and can be applied to other physical systems including coupled quantum dots, disordered nanowires, and short-wavelength electromagnetic propagation through rooms in buildings, aircraft and ships.

physics.class-ph↗

arXiv2019

Topologically Protected Photonic Modes in Composite Quantum Hall/Quantum Spin Hall Waveguides

Photonic topological systems, the electromagnetic analog of the topological materials in condensed matter physics, create many opportunities to design optical devices with novel properties. We present an experimental realization of the bi-anisotropic meta waveguide photonic system replicating both quantum Hall (QH) and quantum spin-Hall (QSH) topological insulating phases. With careful design, a composite QH-QSH photonic topological material is created and experimentally shown to support reflection-free edgemodes, a heterogeneous topological structure that is unprecedented in condensed matter physics. The effective spin degree of freedom of such topologically protected modes determines their unique pathways through these systems, free from backscattering and able to travel around sharp corners. {As an example of their novel properties, we experimentally demonstrate reflection-less photonic devices including a 2-port isolator, a unique 3-port topological device, and a full 4-port circulator based on composite QH and QSH structures

cond-mat.mes-hall↗

arXiv2019

High Frequency Nonlinear Response of Superconducting Cavity-Grade Nb surfaces

Nb Superconducting Radio-Frequency (SRF) cavities are observed to break down and lose their high-Q superconducting properties at accelerating gradients below the limits imposed by theory. The microscopic origins of SRF cavity breakdown are still a matter of some debate. To investigate these microscopic issues temperature and power dependent local third harmonic response was measured on bulk Nb and Nb thin film samples using a novel near-field magnetic microwave microscope between 2.9K-10K and 2GHz-6GHz. Both periodic and non-periodic response as a function of applied RF field amplitude are observed. We attribute these features to extrinsic and intrinsic nonlinear responses of the sample. The RF-current-biased Resistively Shunted Junction (RSJ) model can account for the periodic response and fits very well to the data using reasonable parameters. The non-periodic response is consistent with vortex semi-loops penetrating into the bulk of the sample once sufficiently high RF magnetic field is applied, and the data can be fit to a Time-Dependent Ginzburg-Landau (TDGL) model of this process. The fact that these responses are measured on a wide variety of Nb samples suggests that we have captured the generic nonlinear response of air-exposed Nb surfaces.

cond-mat.supr-con↗

arXiv2019

Dielectric Resonator Method For Determining Gap Symmetry Of Superconductors Through Anisotropic Nonlinear Meissner Effect

We present a new measurement method which can be used to image gap nodal structure of superconductors whose pairing symmetry is under debate. This technique utilizes a high quality factor microwave resonance involving the sample of interest. While supporting a circularly symmetric standing wave current pattern, the sample is perturbed by a scanned laser beam, creating a photoresponse that was previously shown to reveal the superconducting gap anisotropy. Simulation and the measurement of the photoresponse of an unpatterned Nb film show less than 8\% anisotropy, as expected for a superconductor with nearly isotropic energy gap along with expected systematic uncertainty. On the other hand, measurement of a YBa$_2$Cu$_3$O$_{7-δ}$ thin film shows a clear 4-fold symmetric image with $\mathtt{\sim}12.5$\% anisotropy, indicating the well-known 4-fold symmetric $d_{x^2-y^2}$ gap nodal structure in the $ab$-plane. The deduced gap nodal structure can be further cross-checked by low temperature surface impedance data, which is simultaneously measured. The important advantage of the presented method over the previous spiral resonator method is that it does not require a complicated lithographic patterning process which limits one from testing various kinds of materials due to photoresponse arising from patterning defects. This advantage of the presented technique, and the ability to measure unpatterned samples such as planar thin films and single crystals, enables one to survey the pairing symmetry of a wide variety of unconventional superconductors.

cond-mat.supr-con↗

arXiv2019

Imaging collective behavior in an rf-SQUID metamaterial tuned by DC and RF magnetic fields

We examine the collective behavior of two-dimensional nonlinear superconducting metamaterials using a non-contact spatially resolved imaging technique. The metamaterial is made up of sub-wavelength nonlinear oscillators in a strongly coupled 27x27 planar array of radio-frequency Superconducting QUantum Interference Devices (rf SQUIDs). By using low-temperature laser scanning microscopy we image microwave currents in the driven SQUIDs while in non-radiating dark modes and identify the clustering and uniformity of like-oscillating meta-atoms. We follow the rearrangement of coherent patterns due to meta-atom resonant frequency tuning as a function of external dc and rf magnetic flux bias. We find that the rf current distribution across the SQUID array at zero dc flux and small rf flux reveals a low degree of coherence. By contrast, the spatial coherence improves dramatically upon increasing of rf flux amplitude, in agreement with simulation.

cond-mat.supr-con↗

arXiv2018

Scattering Statistics in Nonlinear Wave Chaotic Systems

The Random Coupling Model (RCM) is a statistical approach for studying the scattering properties of linear wave chaotic systems in the semi-classical regime. Its success has been experimentally verified in various over-moded wave settings, including both microwave and acoustic systems. It is of great interest to extend its use to nonlinear systems. This paper studies the impact of a nonlinear port on the measured statistical electromagnetic properties of a ray-chaotic complex enclosure in the short wavelength limit. A Vector Network Analyzer is upgraded with a high power option which enables calibrated scattering (S) parameter measurements up to +43 dBm. By attaching a diode to the excitation antenna, amplitude-dependent S-parameters are observed. We have systematically studied how the key components in the RCM are affected by this nonlinear port, including the radiation impedance, short ray orbit corrections, and statistical properties. By applying the newly developed radiation efficiency extension to the RCM, we find that the diode admittance increases with excitation amplitude. This reduces the amount of power entering the cavity through the port, so that the diode effectively acts as a protection element.

physics.class-ph↗

arXiv2018

Uncovering Universal Wave Fluctuations In a Scaled Ray-Chaotic Cavity With Remote Injection

The Random Coupling Model (RCM), introduced by Zheng, Antonsen and Ott, predicts the statistical properties of waves inside a ray-chaotic enclosure in the semi-classical regime by using Random Matrix Theory, combined with system-specific information. Experiments on single cavities are in general agreement with the predictions of the RCM. It is now desired to test the RCM on more complex structures, such as a cascade or network of coupled cavities, that represent realistic situations, but which are difficult to test due to the large size of the structures of interest. This paper presents a novel experimental setup that replaces a cubic-meter-scale microwave cavity with a miniaturized cavity, scaled down by a factor of 20 in each dimension, operated at a frequency scaled up by a factor of 20 and having wall conductivity appropriately scaled up by a factor of 20. We demonstrate experimentally that the miniaturized cavity maintains the statistical wave properties of the larger cavity. This scaled setup opens the opportunity to study wave properties in large structures such as the floor of an office building, a ship, or an aircraft, in a controlled laboratory setting.

physics.class-ph↗

arXiv2017

Imaging the paramagnetic nonlinear Meissner effect in nodal gap superconductor

Boundary surfaces of nodal gap superconductors can host Andreev bound states (ABS) which develop a paramagnetic response under external RF field in contrast to the bulk diamagnetic response of the bulk superconductor. At low temperature this surface paramagnetic response dominates and enhances the nonlinear RF response of the sample. With a recently developed photoresponse imaging technique, the anisotropy of this "paramagnetic" nonlinear Meissner response, and its current direction (angular) and RF power dependence has been systematically studied. A theoretical model describing the current flow in the surface paramagnetic Andreev bound state, the bulk diamagnetic Meissner state, and their response to optical illumination is proposed and it shows good agreement with the experimental results.

cond-mat.supr-con↗

arXiv2017

Nonlinear Wave Chaos: Statistics of Second Harmonic Fields

Concepts from the field of wave chaos have been shown to successfully predict the statistical properties of linear electromagnetic fields in electrically large enclosures. The Random Coupling Model (RCM) describes these properties by incorporating both universal features described by Random Matrix Theory and the system-specific features of particular system realizations. In an effort to extend this approach to the nonlinear domain, we add an active nonlinear frequency-doubling circuit to an otherwise linear wave chaotic system, and we measure the statistical properties of the resulting second harmonic fields. We develop an RCM-based model of this system as two linear chaotic cavities coupled by means of a nonlinear transfer function. The harmonic field strengths are predicted to be the product of two statistical quantities and the nonlinearity characteristics. Statistical results from measurement-based calculation, RCM-based simulation, and direct experimental measurements are compared and show good agreement over many decades of power.

nlin.CD↗

arXiv2017

Coherent Oscillations of Driven rf SQUID Metamaterials

Through experiments and numerical simulations we explore the behavior of rf SQUID (radio frequency superconducting quantum interference device) metamaterials, which show extreme tunability and nonlinearity. The emergent electromagnetic properties of this metamaterial are sensitive to the degree of coherent response of the driven interacting SQUIDs. Coherence suffers in the presence of disorder, which is experimentally found to be mainly due to a dc flux gradient. We demonstrate methods to recover the coherence, specifically by varying the coupling between the SQUID meta-atoms and increasing the temperature or the amplitude of the applied rf flux.

cond-mat.supr-con↗

arXiv2016

Exciting Reflectionless Unidirectional Edge Modes in a Reciprocal Photonic Topological Insulator Medium

Photonic topological insulators are an interesting class of materials whose photonic band structure can have a bandgap in the bulk while supporting topologically protected unidirectional edge modes. Recent studies [1-6] on bianisotropic metamaterials that emulate the electronic quantum spin Hall effect using its electromagnetic analog are examples of such systems with relatively simple and elegant design. In this paper, we present a rotating magnetic dipole antenna, composed of two perpendicularly oriented coils, that can efficiently excite the unidirectional topologically protected surface waves in the bianisotropic metawaveguide (BMW) structure recently realized by Ma, et al. [1], despite the fact that the BMW medium does not break time-reversal invariance. In addition to achieving high directivity, the antenna can be tuned continuously to excite reflectionless edge modes to the two opposite directions with various amplitude ratios. We demonstrate its performance through experiment and compare to simulation results.

cond-mat.mes-hall↗

arXiv2016

Intermodulation in Nonlinear SQUID Metamaterials: Experiment and Theory

The response of nonlinear metamaterials and superconducting electronics to two-tone excitation is critical for understanding their use as low-noise amplifiers and tunable filters. A new setting for such studies is that of metamaterials made of radio frequency superconducting quantum interference devices (rf-SQUIDs). The two-tone response of self-resonant rf-SQUID meta-atoms and metamaterials is studied here via intermodulation (IM) measurement over a broad range of tone frequencies and tone powers. A sharp onset followed by a surprising strongly suppressed IM region near the resonance is observed. Using a two time scale analysis technique, we present an analytical theory that successfully explains our experimental observations. The theory predicts that the IM can be manipulated with tone power, center frequency, frequency difference between the two tones, and temperature. This quantitative understanding potentially allows for the design of rf-SQUID metamaterials with either very low or very high IM response.

cond-mat.supr-con↗

arXiv2016

Focusing Waves at Arbitrary Locations in a Ray-Chaotic Enclosure Using Time-Reversed Synthetic Sonas

Time reversal methods are widely used to achieve wave focusing in acoustics and electromagnetics. A typical time reversal experiment requires that a transmitter be initially present at the target focusing point, which limits the application of this technique. In this paper, we propose a method to focus waves at an arbitary location inside a complex enclosure using a numerically calculated wave excitation signal. We use a semi-classical ray algorithm to calculate the signal that would be received at a transceiver port resulting from the injection of a short pulse at the desired target location. The time-reversed version of this signal is then injected into the transceiver port and an approximate reconstruction of the short pulse is created at the target. The quaility of the pulse reconstruction is quantified in three different ways and the values of these metrics are predicted by the statistics of the scattering-parameter $|S_{21}|^2$ between the transceiver and target points in the enclosure. We experimentally demonstrate the method using a flat microwave billiard and quantify the reconstruction quality as a function of enclosure loss, port coupling and other considerations.

nlin.CD↗

arXiv2015

Localized High Frequency Electrodynamic Behavior of Optimally-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ Single Crystal films

Localized high frequency (several GHz) electrodynamic properties of a high quality epitaxial, single-crystal Iron-Pnicitde Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ thin film near optimal doping (x=0.08) are measured under a localized and strong RF magnetic field, created by a near-field microwave microscope. Two reflection electrodynamic measurements, including linear and the third harmonic responses, are performed to understand the electromagnetic properties of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Our measurement results show that Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ has have a wide superconducting transition width and may have a multi-gap nature. In addition, based on the $1/T^2$ dependence of the third harmonics signal at lower temperature, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ shows the possibility of nodal behavior.

cond-mat.supr-con↗

arXiv2015

Nanoscale Nonlinear Radio Frequency Properties of Bulk Nb : Origins of Extrinsic Nonlinear Effects

The performance of Niobium-based Superconducting Radio Frequency (SRF) particle accelerator cavities can be sensitive to localized defects that give rise to quenches at high accelerating gradients. In order to identify these material defects on bulk Nb surfaces at their operating frequency and temperature, a wide bandwidth microwave microscope with localized and strong RF magnetic fields is developed by integrating a magnetic write head into the near-field microwave microscope to enable mapping of the local electrodynamic response in the multi-GHz frequency regime at cryogenic temperatures. This magnetic writer demonstrates a localized and strong RF magnetic field on bulk Nb surface with $B_{surface}$ > 102 mT and sub-micron resolution. By measuring the nonlinear response of the superconductor, nonlinearity coming from the nano-scale weak link Josephson junctions due to the contaminated surface in the cavity fabrication process is demonstrated.

cond-mat.supr-con↗

arXiv2015

Tunable negative permeability in a three-dimensional superconducting metamaterial

We report on highly tunable radio frequency (rf) characteristics of a low-loss and compact three dimensional (3D) metamaterial made of superconducting thin film spiral resonators. The rf transmission spectrum of a single element of the metamaterial shows a fundamental resonance peak at $\sim$24.95 MHz that shifts to a 25$\%$ smaller frequency and becomes degenerate when a 3D array of such elements is created. The metamaterial shows an $\emph{in-situ}$ tunable narrow frequency band in which the real part of the effective permeability is negative over a wide range of temperature, which reverts to gradually near-zero and positive values as the superconducting critical temperature is approached. This metamaterial can be used for increasing power transfer efficiency and tunability of electrically small rf-antennas.

cond-mat.supr-con↗