1,161 research outputs found
Probing spin-charge separation in a Tomonaga-Luttinger liquid
In a one-dimensional (1D) system of interacting electrons, excitations of
spin and charge travel at different speeds, according to the theory of a
Tomonaga-Luttinger Liquid (TLL) at low energies. However, the clear observation
of this spin-charge separation is an ongoing challenge experimentally. We have
fabricated an electrostatically-gated 1D system in which we observe spin-charge
separation and also the predicted power-law suppression of tunnelling into the
1D system. The spin-charge separation persists even beyond the low-energy
regime where the TLL approximation should hold. TLL effects should therefore
also be important in similar, but shorter, electrostatically gated wires, where
interaction effects are being studied extensively worldwide.Comment: 11 pages, 4 PDF figures, uses scicite.sty, Science.bs
Effects of Zeeman spin splitting on the modular symmetry in the quantum Hall effect
Magnetic-field-induced phase transitions in the integer quantum Hall effect
are studied under the formation of paired Landau bands arising from Zeeman spin
splitting. By investigating features of modular symmetry, we showed that
modifications to the particle-hole transformation should be considered under
the coupling between the paired Landau bands. Our study indicates that such a
transformation should be modified either when the Zeeman gap is much smaller
than the cyclotron gap, or when these two gaps are comparable.Comment: 8 pages, 4 figure
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Soil Microbial Networks Shift Across a High-Elevation Successional Gradient.
While it is well established that microbial composition and diversity shift along environmental gradients, how interactions among microbes change is poorly understood. Here, we tested how community structure and species interactions among diverse groups of soil microbes (bacteria, fungi, non-fungal eukaryotes) change across a fundamental ecological gradient, succession. Our study system is a high-elevation alpine ecosystem that exhibits variability in successional stage due to topography and harsh environmental conditions. We used hierarchical Bayesian joint distribution modeling to remove the influence of environmental covariates on species distributions and generated interaction networks using the residual species-to-species variance-covariance matrix. We hypothesized that as ecological succession proceeds, diversity will increase, species composition will change, and soil microbial networks will become more complex. As expected, we found that diversity of most taxonomic groups increased over succession, and species composition changed considerably. Interestingly, and contrary to our hypothesis, interaction networks became less complex over succession (fewer interactions per taxon). Interactions between photosynthetic microbes and any other organism became less frequent over the gradient, whereas interactions between plants or soil microfauna and any other organism were more abundant in late succession. Results demonstrate that patterns in diversity and composition do not necessarily relate to patterns in network complexity and suggest that network analyses provide new insight into the ecology of highly diverse, microscopic communities
Probing the Sensitivity of Electron Wave Interference to Disorder-Induced Scattering in Solid-State Devices
The study of electron motion in semiconductor billiards has elucidated our
understanding of quantum interference and quantum chaos. The central assumption
is that ionized donors generate only minor perturbations to the electron
trajectories, which are determined by scattering from billiard walls. We use
magnetoconductance fluctuations as a probe of the quantum interference and show
that these fluctuations change radically when the scattering landscape is
modified by thermally-induced charge displacement between donor sites. Our
results challenge the accepted understanding of quantum interference effects in
nanostructures.Comment: 8 pages, 5 figures, Submitted to Physical Review
Proximity induced superconductivity in indium gallium arsenide quantum wells
We report on the experimental observation of the proximity induced superconductivity in an indium gallium arsenide (In0.75Ga0.25As) quantum well. The Josephson junction was fabricated by several photo-lithographic processes on an InGaAs heterojunction and Niobium (Nb) was used as superconducting electrodes. Owing to the Andreev reflections and Andreev bound states at the Nb-In0.75Ga0.25As quantum well-Nb interfaces, the subharmonic energy gap structures (SGS) are observed at the differential conductance (dI/dV) versus voltage (V) plots when the applied source-drain bias voltages satisfy the expression VSD = 2Δ/ne. The dI/dV as a function of applied magnetic field B shows a maximum at zero B which decreases by increasing B. When decreasing B to below ±0.4 T, a hysteresis and shift of the conductance maxima close to B = 0 T are observed. Our results help to pave the way to the development of integrated coherent quantum circuitry.Authors acknowledge financial support from EPSRC grant numbers EP/M009505/1 and EP/J017671/1. K. Delfanazari is grateful to Dr. H. Asai for helpful discussions
On-Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In0.75Ga0.25AsQuantum-Well–Nb Josephson Junctions
A superconducting hard gap in hybrid superconductor–semiconductor devices has been found to be necessary to access topological superconductivity that hosts Majorana modes (non-Abelian excitation). This requires the formation of homogeneous and barrier-free interfaces between the superconductor and semiconductor. Here, a new platform is reported for topological superconductivity based on hybrid Nb–InGaAs-quantum-well–Nb that results in hard superconducting gap detection in symmetric, planar, and ballistic Josephson junctions. It is shown that with careful etching, sputtered Nb films can make high-quality and transparent contacts to the InGaAs quantum well, and the differential resistance and critical current measurements of these devices are discussed as a function of temperature and magnetic field. It is demonstrated that proximity-induced superconductivity in the InGaAs-quantum-well 2D electron gas results in the detection of a hard gap in four out of seven junctions on a chip with critical current values of up to 0.2 µA and transmission probabilities of >0.96. The results, together with the large g-factor and Rashba spin–orbit coupling in InGaAs quantum wells, which indeed can be tuned by the indium composition, suggest that the Nb–InGaAs–Nb system can be an excellent candidate to achieve topological phase and to realize hybrid topological superconducting devices.Authors acknowledge financial support from EPSRC grant numbers EP/M009505/1 and EP/J017671/1
Imaging Fractal Conductance Fluctuations and Scarred Wave Functions in a Quantum Billiard
We present scanning-probe images and magnetic-field plots which reveal
fractal conductance fluctuations in a quantum billiard. The quantum billiard is
drawn and tuned using erasable electrostatic lithography, where the scanning
probe draws patterns of surface charge in the same environment used for
measurements. A periodicity in magnetic field, which is observed in both the
images and plots, suggests the presence of classical orbits. Subsequent
high-pass filtered high-resolution images resemble the predicted probability
density of scarred wave functions, which describe the classical orbits.Comment: 5 pages, 4 figures To be published in PR
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