arXiv subjects

Alexey Bezryadin

Publications and source records attributed to Alexey Bezryadin.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry of the critical current function in superconducting nanodevices

We study a variety of nano-scale superconducting devices containing more than one weak link. Even in devices with multiple weak links the IB symmetry is usually obeyed, which means that if we reverse both the bias current direction and the magnetic field direction at the same time, the superconducting response, namely the critical current, remains unchanged. We also provide a detailed analysis of the situations in which such symmetry is violated.

cond-mat.supr-con↗

arXiv2026

Competition for Survival and the Maximum Entropy Production Principle in Self-Organized Silver Particle Chains

The maximum entropy production (MEP) principle is a hypothetical law of physics which dictates that complex systems, far from equilibrium, evolve into an ordered dissipative structure (DS) which generates as much entropy per second as possible. An important problem is whether the natural competition for resources, limits the ability of DS to achieve the maximum of the entropy production rate (EPR). We investigate this competition between DS by performing high precision electrical measurements on suspensions of silver particles under electric fields. To establish the impact of competition on MEP principle, precise electrical measurements are performed on two Ag suspension samples connected in parallel. The samples are able to self-organize, dissipate energy, generate entropy, and compete with each other for resources, i.e., electrical current. Our findings are as follows: (1) There is a competition between the two samples, which prevents both systems from achieving their maximum possible contribution to the global entropy production rate. (2) Due to this competition, we find that only one out of two samples can self-organize, while the other deteriorates and approaches zero EPR. (3) The global EPR, i.e., the entropy produced by the samples and the energy supply circuit, is also reduced from its possible maximum due to the competition between the sub-systems. Based on these observations, we propose that the competition effect constitutes an essential constraint that must be incorporated into formulations of the MEP. This principle parallels real-world phenomena, reflecting the competition for resources observed among species and individual organisms in natural systems. We also examine the global implications of the MEP and propose that it serves as a driving mechanism propelling the hypothetical ascent of civilizations along the Kardashev scale.

cond-mat.stat-mech↗

arXiv2026

Comparison of Two-Level System Microwave Losses in Pure Bulk Microcrystalline Nb2O5 and NbO2 Oxide Samples

Losses from two-level systems (TLS) associated with amorphous oxides remain one of the primary limitations to the performance of superconducting qubits and microwave cavities. Niobium resonators are widely used in quantum science experiments, yet niobium's natural oxide layer contains various types of oxides whose relative contributions to TLS loss have not been clearly distinguished. Here, we use a superconducting 3D microwave cavity to measure commercial 99.9\% trace metal pure, microcrystalline oxide powders \ch{Nb2O5} and \ch{NbO2} in bulk amounts. Using this approach, we directly compare the loss characteristics of \ch{Nb2O5} and \ch{NbO2}. Our measurements show that the nominal \ch{Nb2O5} bulk oxide powder samples exhibit losses which have the power and temperature behavior expected for TLS. Moreover, the measurements agree with existing theoretical models. Analogous measurements performed on \ch{NbO2} bulk powder samples do not show any detectable TLS loss signatures. Based on our results we propose that the TLS losses might be reduced if a high quality microcrystalline \ch{NbO2} oxide dominates the \ch{Nb2O5} oxide in practical Nb cavities. These results establish a materials based strategy for isolating oxide specific TLS losses and provide a reference measurement for niobium oxide phases relevant to superconducting quantum devices.

cond-mat.supr-con↗

arXiv2026

A Dayem Loop Qubit Based on Interfering Superconducting Nanowires

We propose a qubit design based on two parallel superconducting nanowires (i.e., a "Dayem loop qubit"). The inclusion of two nanowires instead of one leads to the Little-Parks effect, which provides an oscillator behavior for the qubit frequency as well as anharmonicity. Our key result is that even if the nanowires have an increasingly linear CPR at low supercurrents, the quantum interference between two condensates, induced by a magnetic field, leads to a restoration of cubic nonlinearity, which is predicted to be sufficient to create a functional transmon qubit based on thin superconducting wires. We consider both generic (cubic) current-phase relationships (CPR) as well as more realistic microscopic CPR, having higher-order nonlinearities. For higher-order CPRs, we propose a simple power-law phenomenological approximation valid at very low temperatures, at which superconducting qubits normally operate.

cond-mat.supr-con↗

arXiv2025

Perfect Superconducting Diode and Supercurrent Range Controller

Diodes have a nonreciprocal voltage versus current relationship, produced by breaking the space and time reversal symmetry. However, developing high-end superconducting computers requires a superconducting analogue of the traditional semiconductor diode. Such a superconducting diode exhibits non-reciprocity, or a high asymmetry in its critical currents. We present a model of a perfect superconducting diode based on a superconducting quantum interference device made with multiple superconducting nanowires. The diode predicted by our model has a large positive critical current, while the negative critical current can be exactly zero. This 100\% diode efficiency ($η= 1$) remains stable against small changes of the magnetic field. Another important result is that under certain and quite broad conditions such devices can act as supercurrent range controllers. In such device a supercurrent can flow with zero voltage applied, but only if the supercurrent is contained in some narrow, adjustable range, which excludes zero current.

cond-mat.supr-con↗

arXiv2025

Multiple-Nanowire Superconducting Quantum Interference Devices: Critical Currents, Symmetries, and Vorticity Stability Regions

An ordinary superconducting quantum interference device (SQUID) contains two weak links connected in parallel. We model a multiple-wire SQUID (MW-SQUID), generalized in two ways. First, the number of weak links, which are provided by parallel superconducting nanowires, is larger than two. Second, the current-phase relationship of each nanowire is assumed linear, which is typical for a homogeneous superconducting thin wire. For such MW-SQUIDs, our model predicts that the critical current ($I_c$) is a multi-valued function of the magnetic field. We also calculate vorticity stability regions (VSR), i.e., regions in the current-magnetic field plane in which, for a given distribution of vortices, the currents in all wires are below their critical values, so the vortices do not move between the cells. The VSRs have rhombic shapes in the case of two-wire SQUIDS and have more complicated shapes in the case of many nanowires. We present a classification of such VSRs and determine conditions under which VSR is disjoint, leading to 100\% supercurrent modulation and quantum phase transitions. According to the model, the maximum critical current curves obey $IB$ symmetry, while each VSR obeys $IBV$ symmetry. The model predicts conditions at which MW-SQUID exhibits a perfect diode effect in which the critical current of one polarity is zero while it is not zero for the opposite polarity of the bias current. We also provide a classification of the stability regions produced by (1) completely symmetric, (2) phase disordered, (3) position disordered, (4) critical current disordered, and (5) completely disordered multi-wire SQUIDs.

cond-mat.supr-con↗

arXiv2022

Interference, diffraction, and diode effects in superconducting array based on Bi0.8Sb1.2Te3 topological insulator

It is a well known phenomenon in optics that spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in the Young's famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator (TI) film Bi0.8Sb1.2Te3. In the limit of extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Because of this, such arrays can be used as sensitive absolute magnetic field sensors. An important finding is that, due to the inherent asymmetry of such arrays, the device also acts as a superconducting diode.

cond-mat.supr-con↗

arXiv2020

Nanoscale detection of metastable states in porous and granular media

Microseismicity in subsurface geologic environments, such as sandstone gas reservoirs, is expected in the presence of liquid or gas injection. Although difficult to predict, the potential for microseismic events is important to field-scale projects, such as geologic storage of CO2 whereby the gas is injected into natural sandstone formations. We conjecture that a primary factor causing microseismicity is the existence of metastable states in granular porous medium and provide experimental evidence for its validity. External perturbation trigger abrupt relaxation events, which, with a certain probability, can grow into macroscopic microseismic events. Here the triggering perturbation is produced by cooling to a cryogenic temperature. As the "sensor" for the abrupt relaxation events we use thin Al films deposited on the sandstone surface. We show that as the temperature is varied, the films' resistance exhibits sharp jumps, which we attribute to mechanical restructuring or microfractures in the fabric of the sandstone. We checked the superconducting characteristics of the Al thin films on the sandstone and found microwave-induced Shapiro steps on the voltage-current diagrams. Such quantized steps provide indicates that the film is made of a network of nanobridges, which makes it ever more sensitive to abrupt relaxation events occurring in the substrate, i.e., in the underlying sandstone.

physics.app-ph↗

arXiv2020

Nanometer-Scale Deformations of Berea Sandstone under Moisture Content Variations

Sandstone mechanical stability is of key concern in projects involving injections of CO2 in sandstone geological reservoirs, for the purpose of long-term storage. We developed a method to measure nanometer-scale deformations of sandstones in real time. We demonstrate that Berea sandstone, when hydrated, changes dimensions with a relative deformation of the order of 10^(-4). If the moisture content increases, sandstone samples exhibit an extension and if the moisture content decreases then the samples shrink. We also discover that, immediately after exposure to water, the sandstone temporarily shrinks, just for a few seconds, after which a slow extension begins, and continues until about half of the fluid evaporates. Such shrinkage followed by an extension has been observed also when the sample was exposed to acetone, Mineral Spirits or Vacuum Oil. The results are obtained using a high-resolution nano-positioner technique and, in independent experiments, confirmed using the technique of coda wave interferometry.

physics.app-ph↗

arXiv2020

Supercurrent-Controlled Kinetic Inductance Superconducting Memory

We report superconducting kinetic inductance memory (SKIM) element, which can be controlled exclusively by the bias supercurrent, without involving magnetic fields and heating elements. The SKIM is non-volatile memory. The device is made of Nb and it can operate reliable up to 2.8 K. The achieved error rate is as low as one in 100000 operations.

cond-mat.supr-con↗

arXiv2020

Giant energy storage effect in nanolayer capacitors charged by the field emission tunneling

We fabricate nanolayer alumina capacitor and apply high electric fields, close to 1 GV/m, to inject charges in the dielectric. Asymmetric charge distributions have been achieved due to the selectivity of the quantum tunneling process. Namely, the electrons cannot tunnel to a region near cathode, where the total energy would be less than the potential energy. This mechanism exhibits a strong tendency to populate charge traps located near the anode, i.e., the regions where their potential energy is the lowest. This charge injection allows a permanent storage of the bulk charge even if the capacitor plates are short-circuited, provided that the temperature is sufficiently low so that the conductivity of the dielectric is negligible. In our experiments, the total charge stored in the dielectric was up to seven and a half times higher than the charge stored on the capacitor plates. Also, measurements of the breakdown voltage show that the breakdown electric field, i.e., the dielectric strength, is independent of the thickness of the dielectric.

cond-mat.mes-hall↗

arXiv2020

Coulomb barrier creation by means of electronic field emission in nanolayer capacitors

The main mechanism of energy loss in capacitors with nanoscale dielectric films is leakage currents. Using the example of Al-Al2O3-Al, we show that there are two main contributions, namely the cold field emission effect and the hopping conductivity through the dielectric. Our main finding is that an application of a high electric field, ~0.6-0.7 GV/m, causes electrons to penetrate the dielectric. If the temperature is sufficiently low, such electrons become permanently trapped in the dielectric. To achieve a strong charging of the dielectric, the voltage needs to be high enough, so that a field emission occurs from the cathode into the dielectric. Such a strongly charged dielectric layer generates a Coulomb barrier and leads to a suppression of the leakage current. Thus, after the dielectric nanolayer of the capacitor is charged, the field emission and the hopping conductivity are both suppressed, and the hysteresis of the I-V curve disappears. The phenomenon is observed at temperatures up to ~225 K. It would be advantageous to identify insulators in which the phenomenon of the Coulomb barriers persists even up to the room temperature, but at this time it is not known whether such dielectrics exist and/or can be designed.

physics.app-ph↗

arXiv2020

Superconducting phase transition in inhomogeneous chains of superconducting islands

We study one dimensional chains of superconducting islands with a particular emphasis on the regime in which every second island is switched into its normal state, thus forming a superconductor-insulator-normal metal (S-I-N) repetition pattern. As is known since Giaever tunneling experiments, tunneling charge transport between a superconductor and a normal metal becomes exponentially suppressed, and zero-bias resistance diverges, as the temperature is reduced and the energy gap of the superconductor grows larger than the thermal energy. Here we demonstrate that this physical phenomenon strongly impacts transport properties of inhomogeneous superconductors made of weakly coupled islands with fluctuating values of the critical temperature. We observe a non-monotonous dependence of the chain resistance on both temperature and magnetic field, with a pronounced resistance peak at temperatures at which some but not all islands are superconducting. We explain this phenomenon by the inhomogeneity of the chains, in which neighboring superconducting islands have slightly different critical temperatures. We argue that the Giaever's resistance divergence can also occur in the zero-temperature limit. Such quantum transition can occur if the magnetic field is tuned such that it suppresses superconductivity in the islands with the weaker critical field, while the islands with stronger energy gap remain superconducting. In such a field, the system acts as a chain of S-I-N junctions.

cond-mat.supr-con↗

arXiv2017

Nanoscale superconducting memory based on the kinetic inductance of asymmetric nanowire loops

The demand for low-dissipation nanoscale memory devices is as strong as ever. As Moore's Law is staggering, and the demand for a low-power-consuming supercomputer is high, the goal of making information processing circuits out of superconductors is one of the central goals of modern technology and physics. So far, digital superconducting circuits could not demonstrate their immense potential. One important reason for this is that a dense superconducting memory technology is not yet available. Miniaturization of traditional superconducting quantum interference devices is difficult below a few micrometers because their operation relies on the geometric inductance of the superconducting loop. Magnetic memories do allow nanometer-scale miniaturization, but they are not purely superconducting (Baek et al 2014 Nat. Commun. 5 3888). Our approach is to make nanometer scale memory cells based on the kinetic inductance (and not geometric inductance) of superconducting nanowire loops, which have already shown many fascinating properties (Aprili 2006 Nat. Nanotechnol. 1 15; Hopkins et al 2005 Science 308 1762). This allows much smaller devices and naturally eliminates magnetic-field cross-talk. We demonstrate that the vorticity, i.e., the winding number of the order parameter, of a closed superconducting loop can be used for realizing a nanoscale nonvolatile memory device. We demonstrate how to alter the vorticity in a controlled fashion by applying calibrated current pulses. A reliable read-out of the memory is also demonstrated. We present arguments that such memory can be developed to operate without energy dissipation.

cond-mat.supr-con↗

arXiv2017

Asymmetric nanowire SQUID: linear CPR, stochastic switching, and symmetries

We study nanodevices based on ultrathin superconducting nanowires connected in parallel to form nanowire SQUIDs. The function of the critical current versus magnetic field, $I_{C}(B)$, is multivalued, asymmetric and its maxima and minima are shifted from the usual integer and half integer flux quantum points. The nanowire interference device is qualitatively distinct from conventional SQUIDs because nanowires do not obey the same current-phase relationship (CPR) as Josephson junctions. We demonstrate that the results can be explained assuming that (i) the CPR is linear and (ii) that each wire is characterized by a sample-specific critical phase, which is usually much larger than $π/2$. Our proposed model offers accurate fits to $I_{C}(B)$. It explains the single-valuedness regions where only one vorticity (i.e., the order parameter winding number) is stable as well as regions where multiple vorticity values are allowed for the SQUIDs. We also observe and explain regions in which the standard deviation of the switching current is independent of the magnetic field. We develop a technique that allows a reliable detection of hidden phase-slips. Using this technique we find that our model correctly predicts the boundaries of vorticity regions, even at low currents where $I_C(B)$ is not directly measurable.

cond-mat.supr-con↗

arXiv2015

Formation of Quantum Phase Slip Pairs in Superconducting Nanowires

Macroscopic quantum tunneling (MQT) is a fundamental phenomenon of quantum mechanics related to the actively debated topic of quantum-to-classical transition. The ability to realize MQT affects implementation of qubit-based quantum computing schemes and their protection against decoherence. Decoherence in qubits can be reduced by means of topological protection, e.g. by exploiting various parity effects. In particular, paired phase slips can provide such protection for superconducting qubits. Here, we report on the direct observation of quantum paired phase slips in thin-wire superconducting loops. We show that in addition to conventional single phase slips that change superconducting order parameter phase by $2π$, there are quantum transitions changing the phase by $4π$. Quantum paired phase slips represent a synchronized occurrence of two macroscopic quantum tunneling events, i.e. cotunneling. We demonstrate the existence of a remarkable regime in which paired phase slips are exponentially more probable than single ones.

cond-mat.supr-con↗

arXiv2015

Meissner transmon qubit - architecture and characterization

We present a new type of transmon split-junction qubit which can be tuned by Meissner screening currents in the adjacent superconducting film electrodes. The best detected relaxation time ($T_1$) was of the order of 50 $μ$s and the dephasing time ($T_2$) about 40 $μ$s. The achieved period of oscillation with magnetic field was much smaller than in usual SQUID-based transmon qubits, thus a strong effective field amplification has been realized. This Meissner qubit allows an efficient coupling to superconducting vortices. We present a quantitative analysis of the radiation-free energy relaxation in qubits coupled to Abrikosov vortices. The observation of coherent quantum oscillations provides strong evidence that vortices can exist in coherent quantum superpositions of different position states. According to our suggested model, the wave function collapse is defined by Caldeira-Leggett dissipation associated with viscous motion of the vortex cores.

cond-mat.mes-hall↗

arXiv2014

Measuring the superconducting coherence length in thin films using a two-coil experiment

We present measurements of the superconducting coherence length ξ in thin (d < 100 Å) films of MoGe alloy and Nb using a combination of linear and nonlinear mutual inductance techniques. As the alternating current in the drive coil is increased at fixed temperature, we see a crossover from linear to nonlinear coupling to the pickup coil, consistent with the unbinding of vortex-antivortex pairs as the peak pair momentum nears \hbar\/ξ and the unbinding barrier vanishes. We compare measurements of ξ made by this mutual inductance technique to values determined from the films' upper critical fields, thereby confirming the applicability of a recent calculation of the upper limit on a vortex-free state in our experiment.

cond-mat.supr-con↗