arXiv subjects

M. E. Gershenson

Publications and source records attributed to M. E. Gershenson.

At least 19 recordsLinked to original sources

arXiv2021

Magnetic-field-driven redistribution between extended and localized electronic states in high-mobility Si MOSFETs at low temperatures

In the study of oscillatory electron transport in high-mobility Si MOSFETs at low temperatures we observed two correlated effects in weak in-plane magnetic fields: a steep decrease of the renormalized magnetic susceptibility $χ^*(H)$ and an increase of the concentration of mobile carriers $n(H)$. We suggest a phenomenological model of the magnetic field driven redistribution between the extended and localized electronic states that qualitatively explains both effects. We argue that the redistribution is mainly caused by magnetization of the large-spin localized states with energies close to the Fermi energy $E_F$, coexisting with the majority Fermi liquid state. Our findings also resolve a long-standing disagreement between the experimental data on $χ^*$ obtained in weak ($H \sim k_BT/μ_B$) and strong ($H \sim E_F/gμ_B$) magnetic fields.

cond-mat.str-el↗

arXiv2020

A Parity-Protected Superconductor-Semiconductor Qubit

Coherence of superconducting qubits can be improved by implementing designs that protect the parity of Cooper pairs on superconducting islands. Here, we introduce a parity-protected qubit based on voltage-controlled semiconductor nanowire Josephson junctions, taking advantage of the higher harmonic content in the energy-phase relation of few-channel junctions. A symmetric interferometer formed by two such junctions, gate-tuned into balance and frustrated by a half-quantum of applied flux, yields a cos(2ϕ) Josephson element, reflecting coherent transport of pairs of Cooper pairs. We demonstrate that relaxation of the qubit can be suppressed tenfold by tuning into the protected regime.

cond-mat.mes-hall↗

arXiv2018

Josephson Ladders as a Model System for 1D Quantum Phase Transitions

We propose a novel platform for the study of quantum phase transitions in one dimension (1D QPT). The system consists of a specially designed chain of asymmetric SQUIDs; each SQUID contains several Josephson junctions with one junction shared between the nearest-neighbor SQUIDs.We develop the theoretical description of the low energy part of the spectrum. In particular, we show that the system exhibits the quantum phase transition of Ising type. In the vicinity of the transition the low energy excitations of the system can be described by Majorana fermions. This allow us to compute the matrix elements of the physical perturbations in the low energy sector. In the microwave experiments with this system, we explored the phase boundaries between the ordered and disordered phases and the critical behavior of the system's low-energy modes close to the transition. Due to the flexible chain design and control of the parameters of individual Josephson junctions, future experiments will be able to address the effects of non-integrability and disorder on the 1D QPT.

cond-mat.str-el↗

arXiv2018

Probing spin susceptibility of a correlated two-dimensional electron system by transport and magnetization measurements

We report temperature and density dependences of the spin susceptibility of strongly interacting electrons in Si inversion layers. We measured (i) the itinerant electron susceptibility $χ^*$ from the Shubnikov-de Haas oscillations in crossed magnetic fields and (ii) thermodynamic susceptibility $χ_{\rm T}$ sensitive to all the electrons in the layer. Both $χ^*$ and $χ_{\rm T}$ are strongly enhanced with lowering the electron density in the metallic phase. However, there is no sign of divergency of either quantity at the density of the metal-insulator transition $n_c$. Moreover, the value of $χ_{\rm T}$, which can be measured across the transition down to very low densities deep in the insulating phase, increases with density at $n<n_c$, as expected. In the absence of magnetic field, we found the temperature dependence of $χ^*$ to be consistent with Fermi-liquid-based predictions, and to be much weaker than the power-law, predicted by non-Fermi-liquid models. We attribute a much stronger temperature dependence of $χ_{\rm T}$ to localized spin droplets. In strong enough in-plane magnetic field, we found the temperature dependence of $χ^*$ to be stronger than that expected for the Fermi liquid interaction corrections.

cond-mat.str-el↗

arXiv2018

Microresonators fabricated from high-kinetic-inductance Aluminum films

We have studied superconducting coplanar-waveguide (CPW) resonators fabricated from disordered (granular) films of Aluminum. Very high kinetic inductance of these films, inherent to disordered materials, allows us to implement ultra-short (200 $μ$m at a 5GHz resonance frequency) and high-impedance (up to 5 k$Ω$) half-wavelength resonators. We have shown that the intrinsic losses in these resonators at temperatures $\lesssim 250$ mK are limited by resonator coupling to two-level systems in the environment. The demonstrated internal quality factors are comparable with those for CPW resonators made of conventional superconductors. High kinetic inductance and well-understood losses make these disordered Aluminum resonators promising for a wide range of microwave applications which include kinetic inductance photon detectors and superconducting quantum circuits.

cond-mat.supr-con↗

arXiv2017

Josephson Metamaterial with a widely tunable positive/negative Kerr constant

We report on the microwave characterization of a novel one-dimensional Josephson metamaterial composed of a chain of asymmetric superconducting quantum interference devices (SQUIDs) with nearest-neighbor coupling through common Josephson junctions. This metamaterial demonstrates a strong Kerr nonlinearity, with a Kerr constant tunable over a wide range, from positive to negative values, by a magnetic flux threading the SQUIDs. The experimental results are in good agreement with the theory of nonlinear effects in Josephson chains. The metamaterial is very promising as an active medium for Josephson traveling-wave parametric amplifiers; its use facilitates phase matching in a four-wave mixing process for efficient parametric gain.

cond-mat.supr-con↗

arXiv2016

Spectroscopic Evidence of the Aharonov-Casher effect in a Cooper Pair Box

We have observed the effect of the Aharonov-Casher (AC) interference on the spectrum of a superconducting system containing a symmetric Cooper pair box (CPB) and a large inductance. By varying the charge $n_{g}$ induced on the CPB island, we observed oscillations of the device spectrum with the period $Δn_{g}=2e$. These oscillations are attributed to the charge-controlled AC interference between the fluxon tunneling processes in the CPB Josephson junctions. Total suppression of the tunneling (complete destructive interference) has been observed for the charge $n_{g}=e(2n+1)$. The CPB in this regime represents the $4π$-periodic Josephson element, which can be used for the development of the parity-protected superconducting qubits.

cond-mat.mes-hall↗

arXiv2014

Probing Electron Interactions in a Two-Dimensional System by Quantum Magneto-Oscillations

We have experimentally studied the renormalized effective mass m* and Dingle temperature T_D in two spin subbands with essentially different electron populations. Firstly, we found that the product (m*T_D) that determines damping of quantum oscillations, to the first approximation, is the same in the majority and minority subbands even at the spin polarization degree as high as 66\%. This result confirms the theoretical predictions that the interaction takes place at high energies ~ E_F rather than within a narrow strip of energies E_F\pm k_BT. Secondly, to the next approximation, we revealed a difference in the damping factor of the two spin subbands, which causes skewness of the oscillation lineshape. In the absence of the in-plane magnetic field, the damping factor (m*T_D) is systematically smaller in the spin-majority subband. The difference, quantified with the skew factor γ= (T_{D\downarrow}-T_{D\uparrow})/2T_{D0} can be as large as 20%. The skew factor tends to decrease as B_\parallel or temperature grow, or perpendicular field decreases; for low electron densities and high in-plane fields the skew factor even changes sign. Finally, we compared the temperature and magnetic field dependencies of the magneto-oscillations amplitude with predictions of the interaction correction theory, and found, besides some qualitative similarities, several quantitative and qualitative differences. To explain qualitatively our results, we suggested an empirical model that assumes the existence of easily magnetized triplet scatterers on the Si/SiO_2 interface.

cond-mat.str-el↗

arXiv2012

Quantum Superinductor with Tunable Non-Linearity

We report on the realization of a superinductor, a dissipationless element whose microwave impedance greatly exceeds the resistance quantum. The design of the superinductor, implemented as a ladder of nanoscale Josephson junctions, enables tuning of the inductance and its nonlinearity by a weak magnetic field. The Rabi decay time of the superinductor-based qubit exceeds 1 microsecond. The high kinetic inductance and strong nonlinearity offer new types of functionality, including the development of qubits protected from both flux and charge noises, fault tolerant quantum computing, and high-impedance isolation for electrical current standards based on Bloch oscillations.

cond-mat.supr-con↗

arXiv2011

Magnetic Field Driven Quantum Phase Transitions in Josephson Arrays

We have studied the magnetic-field-driven quantum phase transitions in Josephson junction arrays with a large coordination number. The characteristic energies were extracted in both the superconducting and insulating phases by integrating the current-voltage characteristics over a voltage range 2eV\leqk_B T. For the arrays with a relatively strong Josephson coupling, we observed duality between the energies in the superconducting and insulating phases. The arrays with a weaker Josephson coupling demonstrate an intermediate, "bad metal" regime in weak magnetic fields; this observation underlines the importance of vortex pinning at large scales and, presumably, emergent inhomogeneity in the presence of strong offset charge disorder.

cond-mat.dis-nn↗

arXiv2010

Energy resolution of terahertz single-photon-sensitive bolometric detectors

We report measurements of the energy resolution of ultra-sensitive superconducting bolometric detectors. The device is a superconducting titanium nanobridge with niobium contacts. A fast microwave pulse is used to simulate a single higher-frequency photon, where the absorbed energy of the pulse is equal to the photon energy. This technique allows precise calibration of the input coupling and avoids problems with unwanted background photons. Present devices have an intrinsic full-width at half-maximum energy resolution of approximately 23 terahertz, near the predicted value due to intrinsic thermal fluctuation noise.

cond-mat.supr-con↗

arXiv2008

Interaction Effects in Conductivity of a Two-Valley Electron System in High-Mobility Si Inversion Layers

We have measured the conductivity of high-mobility (001) Si metal-oxide-semiconductor field effect transistors (MOSFETs) over wide ranges of electron densities n=(1.8-15)x10^11cm^2, temperatures T=30mK-4.2K, and in-plane magnetic fields B=0-5T. The experimental data have been analyzed using the theory of interaction effects in the conductivity of disordered 2D systems. The parameters essential for comparison with the theory, such as the intervalley scattering time and valley splitting, have been measured or evaluated in independent experiments. The observed behavior of the conductivity, including its quasi-linear increase with decreasing T down to ~0.4K and its downturn at lower temperatures, is in agreement with the theory. The values of the Fermi- liquid parameter obtained from the comparison agree with the corresponding values extracted from the analysis of Shubnikov-de Haas oscillations based on the theory of magnetooscillations in interacting 2D systems.

cond-mat.dis-nn↗

arXiv2007

Electronic functionalization of the surface of organic semiconductors with self-assembled monolayers

Molecular self-assembly has been extensively used for surface modification of metals and oxides for a variety of applications, including molecular and organic electronics. One of the goals of this research is to learn how the electronic properties of these surfaces can be modified by self-assembled monolayers (SAM). Here, we demonstrate a new type of molecular self-assembly: the growth of organosilane SAMs at the surface of organic semiconductors, which results in a dramatic increase of the surface conductivity of organic materials. For organosilane molecules with a large dipole moment, SAM-induced surface conductivity of organic molecular crystals approaches 10^-5 S per square, which is comparable to the highest conductivity realized in organic field-effect transistors (OFETs) at ultra-high densities of charge carriers. SAM-functionalized organic surfaces are fully accessible to the environment which makes them very attractive for sensing applications. We have observed that the interaction of vapors of polar molecules with SAM-functionalized organic semiconductors results in a fast and reversible change of the conductivity, proportional to the pressure of an analyte vapor.

cond-mat.mtrl-sci↗

arXiv2007

Light Quasiparticles Dominate Electronic Transport in Molecular Crystal Field-Effect Transistors

We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m* comparable to free electron mass. Furthermore, the m* values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

cond-mat.mtrl-sci↗

arXiv2007

Intervalley scattering and weak localization in Si-based two-dimensional structures

We have measured the weak localization magnetoresistance in (001)-oriented Si MOS structures with a wide range of mobilities. For the quantitative analysis of the data, we have extended the theory of weak-localization corrections in the ballistic regime to the system with two equivalent valleys in electron spectrum. This theory describes the observed magnetoresistance and allows the extraction of the phase breaking time tau_phi and the intervalley scattering time tau_v. The temperature dependences tau_phi(T) for all studied structures are in good agreement with the theory of electron-electron interaction effects in two-dimensional systems. The intervalley scattering is elastic and rather strong: tau_v is typically only an order of magnitude greater than the transport time, tau. It is found that the intervalley scattering rate is temperature-independent and the ratio tau_v/tau decreases with increasing the electron density. These observations suggest that the roughness of the Si-SiO2 interface plays the major role in intervalley scattering.

cond-mat.dis-nn↗

arXiv2006

Microwave-Induced Dephasing in One-Dimensional Metal Wires

We report on the effect of monochromatic microwave (MW) radiation on the weak localization corrections to the conductivity of quasi-one-dimensional (1D) silver wires. Due to the improved electron cooling in the wires, the MW-induced dephasing was observed without a concomitant overheating of electrons over wide ranges of the MW power $P_{MW}$ and frequency $f$. The observed dependences of the conductivity and MW-induced dephasing rate on $P_{MW}$ and $f$ are in agreement with the theory by Altshuler, Aronov, and Khmelnitsky \cite{Alt81}. Our results suggest that in the low-temperature experiments with 1D wires, saturation of the temperature dependence of the dephasing time can be caused by an MW electromagnetic noise with a sub-pW power.

cond-mat.mes-hall↗

arXiv2005

Hall effect in the accumulation layers on the surface of organic semiconductors

We have observed the Hall effect in the field-induced accumulation layer on the surface of small-molecule organic semiconductor. The Hall mobility mu_H increases with decreasing temperature in both the intrinsic (high-temperature) and trap-dominated (low-temperature) conduction regimes. In the intrinsic regime, the density of mobile field-induced charge carriers extracted from the Hall measurements, n_H, coincides with the density n calculated using the gate-channel capacitance, and becomes smaller than n in the trap-dominated regime. The Hall data are consistent with the diffusive band-like motion of field-induced charge carriers between the trapping events.

cond-mat.mtrl-sci↗

arXiv2005

Interaction of Organic Surfaces with Active Species in the High-Vacuum Environment

Using single-crystal organic field-effect transistors with the conduction channel exposed to environmental agents we have observed generation of electronic defects at the organic surface in the high-vacuum environment. Rapid decrease of the source-drain current of an operating device is observed upon exposure of the channel to the species generated by high-vacuum gauges. We attribute this effect to interaction of the organic surface with electrically neutral free radicals produced in the process of hydrocarbon cracking on hot filaments with a relatively low activation energy Ea ~ 2.5 eV (240 kJ/mol). The reported results might be important for optimizing the high-vacuum processes of fabrication and characterization of a wide range of organic and molecular electronic devices.

cond-mat.mtrl-sci↗