We report an experimental study of proximity induced superconductivity in planar Josephson junction devices made from free-standing InAs nanosheets. The nanosheets are grown by molecular beam ...epitaxy, and the Josephson junction devices are fabricated by directly contacting the nanosheets with superconductor Al electrodes. The fabricated devices are explored by low-temperature carrier transport measurements. The measurements show that the devices exhibit a gate-tunable supercurrent, multiple Andreev reflections, and a good quality superconductor-semiconductor interface. The superconducting characteristics of the Josephson junctions are investigated at different magnetic fields and temperatures and are analyzed based on the Bardeen–Cooper–Schrieffer (BCS) theory. The measurements of the ac Josephson effect are also conducted under microwave radiations with different radiation powers and frequencies, and integer Shapiro steps are observed. Our work demonstrates that InAs nanosheet based hybrid devices are desired systems for investigating the forefront of physics, such as two-dimensional topological superconductivity.
Appl. Phys. Lett. 120, 233102 (2022) A thin, narrow-bandgap semiconductor Bi$_2$O$_2$Te nanosheet is obtained via
mechanical exfoliation and a Hall-bar device is fabricated from it on a heavily
doped ...Si/SiO$_2$ substrate and studied at low temperatures. Gate transfer
characteristic measurements show that the transport carriers in the nanosheet
are of $n$-type. The carrier density, mobility, and mean free path in the
nanosheet are determined by measurements of the Hall resistance and the
longitudinal resistance of the Hall-bar device and it is found that the
electron transport in the nanosheet is in a quasi-two-dimensional (2D),
strongly disordered regime. Magnetotransport measurements for the device at
magnetic fields applied perpendicular to the nanosheet plane show dominantly
weak antilocalization (WAL) characteristics at low fields and a linear
magnetoresistance (LMR) behavior at large fields. We attribute the WAL
characteristics to strong spin-orbit interaction (SOI) and the LMR to the
classical origin of strong disorder in the nanosheet. Low-field
magnetoconductivity measurements are also performed and are analyzed based on
the multi-channel Hikami-Larkin-Nagaoka theory with the LMR correction being
taken into account. The phase coherence length, spin relaxation length,
effective 2D conduction channel number and coefficient in the linear term due
to the LMR in the nanosheet are extracted. It is found that the spin relaxation
length in the Bi$_2$O$_2$Te nanosheet is several times smaller than it in its
counterpart Bi$_2$O$_2$Se nanosheet and thus an ultra-strong SOI is present in
the Bi$_2$O$_2$Te nanosheet. Our results reported in this study would greatly
encourage further studies and applications of this emerging narrow-bandgap
semiconductor 2D material.
The absence of odd-order Shapiro steps is one of the predicted signatures for topological superconductors. Experimentally, the missing first-order Shapiro step has been reported in several ...superconducting systems presumably to be topologically non-trivial, as well as in the topologically trivial regime of superconductor-semiconductor Josephson junctions. In this work, we revisit the missing first Shapiro step signature in the topologically trivial regime of Al-InSb nanosheet Josephson junctions under microwave irradiation. The missing first Shapiro step is found to be accompanied by a sharp voltage jump during the superconducting switching and reappears when the jump is softened by increasing temperature or magnetic field. The missing first Shapiro step also reappears with an increased microwave frequency. The sharp switching jump, existing without microwave irradiation, deviates from the relation given by the standard resistively shunted junction (RSJ) model. Missing Shapiro step signatures are qualitatively captured by introducing the sharp voltage jump into the RSJ model. This work reveals a common, yet overlooked, phenomenon that leads to the missing first Shapiro step, providing a new perspective on fractional Josephson experiments.
A thin, narrow-bandgap semiconductor Bi\(_2\)O\(_2\)Te nanosheet is obtained via mechanical exfoliation and a Hall-bar device is fabricated from it on a heavily doped Si/SiO\(_2\) substrate and ...studied at low temperatures. Gate transfer characteristic measurements show that the transport carriers in the nanosheet are of \(n\)-type. The carrier density, mobility, and mean free path in the nanosheet are determined by measurements of the Hall resistance and the longitudinal resistance of the Hall-bar device and it is found that the electron transport in the nanosheet is in a quasi-two-dimensional (2D), strongly disordered regime. Magnetotransport measurements for the device at magnetic fields applied perpendicular to the nanosheet plane show dominantly weak antilocalization (WAL) characteristics at low fields and a linear magnetoresistance (LMR) behavior at large fields. We attribute the WAL characteristics to strong spin-orbit interaction (SOI) and the LMR to the classical origin of strong disorder in the nanosheet. Low-field magnetoconductivity measurements are also performed and are analyzed based on the multi-channel Hikami-Larkin-Nagaoka theory with the LMR correction being taken into account. The phase coherence length, spin relaxation length, effective 2D conduction channel number and coefficient in the linear term due to the LMR in the nanosheet are extracted. It is found that the spin relaxation length in the Bi\(_2\)O\(_2\)Te nanosheet is several times smaller than it in its counterpart Bi\(_2\)O\(_2\)Se nanosheet and thus an ultra-strong SOI is present in the Bi\(_2\)O\(_2\)Te nanosheet. Our results reported in this study would greatly encourage further studies and applications of this emerging narrow-bandgap semiconductor 2D material.
Under certain symmetry-breaking conditions, a superconducting system exhibits asymmetric critical currents, dubbed the ``superconducting diode effect". Recently, systems with the ideal ...superconducting diode efficiency or unidirectional superconductivity have received considerable interest. In this work, we report the study of Al-InAs nanowire-Al Josephson junctions under microwave irradiation and magnetic fields. We observe an enhancement of superconducting diode effect under microwave driving, featured by a horizontal offset of the zero-voltage step in the voltage-current characteristic that increases with microwave power. Devices reach the unidirectional superconductivity regime at sufficiently high driving amplitudes. The offset changes sign with the reversal of the magnetic field direction. Meanwhile, the offset magnitude exhibits a roughly linear response to the microwave power in dBm when both the power and the magnetic field are large. The signatures observed are reminiscent of a recent theoretical proposal using the resistively shunted junction (RSJ) model. However, the experimental results are not fully explained by the RSJ model, indicating a new mechanism for unidirectional superconductivity that is possibly related to non-equilibrium dynamics or dissipation in periodically driven superconducting systems.
We report an experimental study of quantum point contacts defined in a high-quality strained germanium quantum well with layered electric gates. At zero magnetic field, we observe quantized ...conductance plateaus in units of 2\(e^2/h\). Bias-spectroscopy measurements reveal that the energy spacing between successive one-dimensional subbands ranges from 1.5 to 5\,meV as a consequence of the small effective mass of the holes and the narrow gate constrictions. At finite magnetic fields perpendicular to the device plane, the edges of the conductance plateaus get splitted due to the Zeeman effect and Land\'{e} \(g\) factors are estimated to be \(\sim6.6\) for the holes in the germanium quantum well. We demonstrate that all quantum point contacts in the same device have comparable performances, indicating a reliable and reproducible device fabrication process. Thus, our work lays a foundation for investigating multiple forefronts of physics in germanium-based quantum devices that require quantum point contacts as a building block.
High-quality free-standing InAs nanosheets are emerging layered semiconductor materials with potentials in designing planar Josephson junction devices for novel physics studies due to their unique ...properties including strong spin-orbit couplings, large Landé g-factors and the two dimensional nature. Here, we report an experimental study of proximity induced superconductivity in planar Josephson junction devices made from free-standing InAs nanosheets. The nanosheets are grown by molecular beam epitaxy and the Josephson junction devices are fabricated by directly contacting the nanosheets with superconductor Al electrodes. The fabricated devices are explored by low-temperature carrier transport measurements. The measurements show that the devices exhibit a gate-tunable supercurrent, multiple Andreev reflections, and a good quality superconductor-semiconductor interface. The superconducting characteristics of the Josephson junctions are investigated at different magnetic fields and temperatures, and are analyzed based on the Bardeen-Cooper-Schrieffer (BCS) theory. The measurements of ac Josephson effect are also conducted under microwave radiations with different radiation powers and frequencies, and integer Shapiro steps are observed. Our work demonstrates that InAs nanosheet based hybrid devices are desired systems for investigating forefront physics, such as the two-dimensional topological superconductivity.
Organic field-effect transistor nonvolatile memory (OFET-NVM) is an indispensable element for flexible and wearable electronics. The emerging multi-bit OFET-NVMs propose an effective strategy to ...further multiply the storage capacity. However, they have still suffered serious bottleneck issues of high programming/erasing (P/E) voltage and slow P/E speed. In this letter, we demonstrate a facile method to resolve the both bottlenecks, and investigate the relevant mechanisms. Our flexible OFET-NVMs exhibit excellent 2-bit memory features, with a fast P/E speed of Formula Omitted, low P/E voltages of ±15 V, highly reliable endurance, highly stable retention, and good mechanical durability. This work paves the way toward the development of next-generation high-speed, high-capacity flexible memory.
Organic field-effect transistor nonvolatile memory (OFET-NVM) is an indispensable element for flexible and wearable electronics. The emerging multi-bit OFET-NVMs propose an effective strategy to ...further multiply the storage capacity. However, they have still suffered serious bottleneck issues of high programming/erasing (P/E) voltage and slow P/E speed. In this letter, we demonstrate a facile method to resolve the both bottlenecks, and investigate the relevant mechanisms. Our flexible OFET-NVMs exhibit excellent 2-bit memory features, with a fast P/E speed of 5 μs, low P/E voltages of ±15 V, highly reliable endurance, highly stable retention, and good mechanical durability. This work paves the way toward the development of next-generation high-speed, high-capacity flexible memory.
