arXiv subjects

A. T. Hatke

Publications and source records attributed to A. T. Hatke.

At least 19 recordsLinked to original sources

arXiv2019

Relating Andreev Bound States and Supercurrents in Hybrid Josephson Junctions

We investigate superconducting quantum interference devices consisting of two highly transmissive Josephson junctions coupled by a superconducting loop, all defined in an epitaxial InAs/Al heterostructure. A novel device design allows for independent measurements of the Andreev bound state spectrum within the normal region of a junction and the resulting current-phase relation. We show that knowledge of the Andreev bound state spectrum alone is enough to derive the independently measured phase dependent supercurrent. On the other hand, the opposite relation does not generally hold true as details of the energy spectrum are averaged out in a critical current measurement. Finally, quantitative understanding of field dependent spectrum and supercurrent require taking into account the second junction in the loop and the kinetic inductance of the epitaxial Al film.

cond-mat.mes-hall↗

arXiv2018

Wigner solids of wide quantum wells near Landau filling $ν=1$

Microwave spectroscopy within the Landau filling ($ν$) range of the integer quantum Hall effect (IQHE) has revealed pinning mode resonances signifying Wigner solids (WSs) composed of quasi-particles or -holes. We study pinning modes of WSs in wide quantum wells (WQWs) for $ 0.8\leν\le1.2$, varying the density, $n$, and tilting the sample by angle $θ$ in the magnetic field. Three distinct WS phases are accessed. One phase, S1, is phenomenologically the same as the WS observed in the IQHEs of narrow QWs. The second phase, S2, exists at $ν$ further from $ν=1$ than S1, and requires a sufficiently large $n$ or $θ$, implying S2 is stabilized by the Zeeman energy. The melting temperatures of S1 and S2, estimated from the disappearance of the pinning mode, show different behavior vs $ν$. At the largest $n$ or $θ$, S2 disappears and the third phase, S1A, replaces S1, also exhibiting a pinning mode. This occurs as the WQW $ν=1$ IQHE becomes a two-component, Halperin-Laughlin $\pone$ state. We interpret S1A as a WS of the excitations of $\pone$, which has not been previously observed.

cond-mat.mes-hall↗

arXiv2018

Wigner solid pinning modes tuned by fractional quantum Hall states of a nearby layer

We study a bilayer system hosting exotic many-body states of two-dimensional electron systems (2DESs) in close proximity but isolated from one another by a thin barrier. One 2DES has low electron density and forms a Wigner solid (WS) at high magnetic fields. The other has much higher density and, in the same field exhibits fractional quantum Hall states (FQHSs). The WS manifests microwave resonances which are understood as pinning modes, collective oscillations of the WS within the small but finite ubiquitous disorder. Our measurements reveal a striking evolution of the pinning mode frequencies of the WS layer with the formation of the FQHSs in the nearby layer, evincing a strong coupling between the WS pinning modes and the state of the 2DES in the adjacent layer, mediated by screening.

cond-mat.mes-hall↗

arXiv2018

High mobility InAs 2DEGs on GaSb substrates: a platform for mesoscopic quantum transport

High mobility, strong spin-orbit coupling, and large Landé g-factor make the two-dimensional electron gas (2DEG) in InAs quantum wells grown on nearly-lattice-matched GaSb substrates an attractive platform for mesoscopic quantum transport experiments. Successful operation of mesoscopic devices relies on three key properties: electrical isolation from the substrate; ability to fully deplete the 2DEG and control residual sidewall conduction with lithographic gates; and high mobility to ensure ballistic transport over mesoscopic length scales. Simultaneous demonstration of these properties has remained elusive for InAs 2DEGs on GaSb substrates. Here we report on heterostructure design, molecular beam epitaxy growth, and device fabrication that result in high carrier mobility and full 2DEG depletion with minimal residual edge conduction. Our results provide a pathway to fully-controlled 2DEG-based InAs mesoscopic devices.

cond-mat.mes-hall↗

arXiv2017

Bloch-Grüneisen nonlinearity of electron transport in GaAs/AlGaAs heterostructures

We report on nonlinear transport measurements in a two-dimensional electron gas hosted in GaAs/AlGaAs heterostructures. Upon application of direct current, the low-temperature differential resistivity acquires a positive correction, which exhibits a pronounced maximum followed by a plateau. With increasing temperature, the nonlinearity diminishes and disappears. These observations can be understood in terms of a crossover from the Bloch-Grüneisen regime to the quasielastic scattering regime as the electrons are heated by direct current. Calculations considering the interaction of electrons with acoustic phonons provide a reasonable description of our experimental findings.

cond-mat.mes-hall↗

arXiv2017

Mobility in excess of $10^{6}$ cm$^2$/Vs in InAs quantum wells grown on lattice mismatched InP substrates

InAs-based two-dimensional electron systems grown on lattice mismatched InP substrates offer a robust platform for the pursuit of topologically protected quantum computing. We investigated strained composite quantum wells of In$_{0.75}$Ga$_{0.25}$As/InAs/In$_{0.75}$Ga$_{0.25}$As with In$_{0.75}$Al$_{0.25}$As barriers. By optimizing the widths of the In$_{0.75}$Ga$_{0.25}$As layers, the In$_{0.75}$Al$_{0.25}$As barrier, and the InAs quantum well we demonstrate mobility in excess of $1 \times 10^{6}\,$cm$^{2}/$Vs. Mobility vs. density data indicates that scattering is dominated by a residual three dimensional distribution of charged impurities. We extract the Rashba parameter and spin-orbit length as important material parameters for investigations involving Majorana zero modes.

cond-mat.mtrl-sci↗

arXiv2016

Microwave spectroscopic observation of a Wigner solid within the 1/2 fractional quantum Hall effect

The fractional quantum Hall effect (FQHE) states at half integer Landau fillings ($ν$) have long been of great interest, since they have correlations that differ from those of the fundamental Laughlin states found at odd denominators. At $ν=1/2$ the FQHE has been observed in wide or double quantum wells, and is ascribed to the two-component Halperin-Laughlin $Ψ_{331}$ state. $Ψ_{331}$ excitations carry charge $\pm e/4$, like the carriers of $ν=5/2$ states which are of interest in quantum computation. Further, such an excitation (quasiparticle or -hole) of $Ψ_{331}$ has unequal, opposite charge in the top and bottom layers, and hence an up or down dipole moment. Here we report evidence for a Wigner solid (WS) of such dipolar quasiholes from a quantitative study of the microwave spectra of a wide quantum well (WQW) at $ν$ close to 1/2.

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arXiv2015

Shubnikov-de Haas oscillations in two-dimensional electron gas under subterahertz radiation

We report on magnetotransport measurements in a two-dimensional (2D) electron gas subject to subterahertz radiation in the regime where Shubnikov-de Haas oscillations (SdHO) and microwave-induced resistance oscillations (MIRO) coexist over a wide magnetic field range, spanning several harmonics of the cyclotron resonance. Surprisingly, we find that the SdHO amplitude is modified by the radiation in a non-trivial way owing to the oscillatory correction which has the same period and phase as MIRO. This finding challenges our current understanding of microwave photoresistance in 2D electron gas, calling for future investigations.

cond-mat.mes-hall↗

arXiv2014

Microwave spectroscopic studies of the bilayer electron solid states at low Landau filling in a wide quantum well

At the low Landau filling factor $(ν)$ termination of the fractional quantum Hall effect (FQHE) series, two-dimensional electron systems (2DESs) exhibit an insulating phase that is understood as a form of pinned Wigner solid. Here we use microwave spectroscopy to probe the transition to the insulator for a wide quantum well (WQW) sample that can support single-layer or bilayer states depending on its overall carrier density, $n$. We find the insulator exhibits a resonance, which is characteristic of a bilayer solid. The resonance also reveals a pair of transitions within the solid, which are not accessible to dc transport measurements. As $n$ is biased deeper into the bilayer solid regime, the resonance grows in specific intensity, and the transitions within the insulator disappear. These behaviors are suggestive of a picture of the insulating phase as an emulsion of liquid and solid components.

cond-mat.mes-hall↗

arXiv2014

Multiphoton processes at cyclotron resonance subharmonics in a 2D electron system under DC and microwave excitation

We investigate a two-dimensional electron system (2DES) under microwave illumination at cyclotron resonance subharmonics. The 2DES carries sufficient direct current, $I$, that the differential resistivity oscillates as $I$ is swept. At magnetic fields sufficient to resolve individual Landau levels, we find the number of oscillations within an $I$ range systematically changes with increasing microwave power. Microwave absorption and emission of $N$ photons, where $N$ is controlled by the microwave power, describes our observations in the framework of the displacement mechanism of impurity scattering between Hall-field tilted Landau levels.

cond-mat.mes-hall↗

arXiv2013

Microwave spectroscopic observation of distinct electron solid phases in wide quantum wells

In high magnetic fields ($B$), two dimensional electron systems (2DESs) can form a number of phases in which interelectron repulsion plays the central role, since the kinetic energy is frozen out by Landau quantization. These phases include the well-known liquids of the fractional quantum Hall effect (FQHE), as well as solid phases with broken spatial symmetry and crystalline order. Solids can occur at the low Landau filling ($ν$) termination of the FQHE series, but also within integer quantum Hall effects (IQHEs). Here, we present microwave spectroscopy studies of wide quantum wells (WQWs). The spectra clearly reveal two distinct solid phases, hidden within what in dc transport would be the zero diagonal conductivity of an integer quantum Hall effect state. Explanation of these solids is not possible with the simple picture of a Wigner solid (WS) of ordinary (quasi) electrons or holes.

cond-mat.mes-hall↗

arXiv2013

Evidence for effective mass reduction in GaAs/AlGaAs quantum wells

We have performed microwave photoresistance measurements in high mobility GaAs/AlGaAs quantum wells and investigated the value of the effective mass. Surprisingly, the effective mass, obtained from the period of microwave-induced resistance oscillations, is found to be about 12% lower than the band mass in GaAs, $\mb$. This finding provides strong evidence for electron-electron interactions which can be probed by microwave photoresistance in very high Landau levels. In contrast, the measured magnetoplasmon dispersion revealed an effective mass which is close to $\mb$, in accord with previous studies.

cond-mat.mes-hall↗

arXiv2012

Microwave-induced resistance oscillations in tilted magnetic fields

We have studied the effect of an in-plane magnetic field on microwave-induced resistance oscillations in a high mobility two-dimensional electron system. We have found that the oscillation amplitude decays exponentially with an in-plane component of the magnetic field $B_\parallel$. While these findings cannot be accounted for by existing theories, our analysis suggests that the decay can be explained by a $B_\parallel$-induced correction to the quantum scattering rate, which is quadratic in $B_\parallel$.

cond-mat.mes-hall↗

arXiv2012

Nonlinear response in overlapping and separated Landau levels of GaAs quantum wells

We have studied magnetotransport properties of a high-mobility two-dimensional electron system subject to weak electric fields. At low magnetic field $B$, the differential resistivity acquires a correction $δr \propto -λ^2 j^2/B^2$, where $λ$ is the Dingle factor and $j$ is the current density, in agreement with theoretical predictions. At higher magnetic fields, however, $δr$ becomes $B$-independent, $δr \propto -j^2$. While the observed change in behavior can be attributed to a crossover from overlapping to separated Landau levels, full understanding of this behavior remains a subject of future theories.

cond-mat.mes-hall↗

arXiv2012

Shubnikov-de Haas oscillations in GaAs quantum wells in tilted magnetic fields

We report on quantum magneto-oscillations in an ultra-high mobility GaAs/AlGaAs quantum well at very high tilt angles. Unlike previous studies, we find that the spin and cyclotron splittings become equal over a continuous range of angles, but only near certain, angle-dependent filling factors. At high enough tilt angles, Shubnikov-de Haas oscillations reveal a prominent beating pattern, indicative of consecutive level crossings, all occurring at the same angle. We explain these unusual observations by an in-plane field-induced increase of the carrier mass, which leads to accelerated, filling factor-driven crossings of spin sublevels in tilted magnetic fields.

cond-mat.mes-hall↗

arXiv2012

Magnetoplasmon resonance in 2D electron system driven into a zero-resistance state

We report on a remarkably strong, and a rather sharp, photoresistance peak originating from a dimensional magnetoplasmon resonance (MPR) in a high mobility GaAs/AlGaAs quantum well driven by microwave radiation into a zero-resistance state (ZRS). The analysis of the MPR signalreveals a negative background providing experimental evidence for the concept of absolute negative resistance associated with the ZRS. When a system is further subject to a dc field, the maxima of microwave-induced resistance oscillations decay away and a system reveals a state with close-to-zero differential resistance. The MPR peak, on the other hand, remains essentially unchanged, indicating surprisingly robust Ohmic behavior under the MPR conditions.

cond-mat.mes-hall↗

arXiv2012

Giant negative magnetoresistance in high-mobility 2D electron systems

We report on a giant negative magnetoresistance in very high mobility GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at $B \simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T \lesssim 2$ K. Unlike the zero-field resistivity which saturates at $T \simeq 2 $ K, the resistivity at this minimum continues to drop at an accelerated rate to much lower temperatures and becomes several times smaller than the zero-field resistivity. Unexpectedly, we also find that the effect is destroyed not only by increasing temperature but also by modest in-plane magnetic fields. The analysis shows that giant negative magnetoresistance cannot be explained by existing theories considering interaction-induced or disorder-induced corrections.

cond-mat.mes-hall↗

arXiv2011

Phase of phonon-induced resistance oscillations in a high-mobility two-dimensional electron gas

We report on experimental studies of magnetoresistance oscillations that originate from the resonant interaction of two-dimensional electrons with thermal transverse-acoustic phonons in very high-mobility GaAs/AlGaAs quantum wells. We find that the oscillation maxima consistently occur when a frequency of a phonon with twice the Fermi momentum exceeds an integer multiple of the cyclotron frequency. This observation is in contrast to to all previous experiments associating resistance maxima with magnetophonon resonance and its harmonics. Our experimentally obtained resonant condition is in excellent quantitative agreement with recent theoretical proposals.

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