Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers

We have investigated the electrical transport through strained p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement shift for diodes with different well width, the shift due to a central potential spike in a well, and magnetotunnelling spectroscopy demonstrate that the first two resonances are due to tunnelling through heavy hole levels, whereas there is no sign of tunnelling through the first light hole state. This demonstrates for the first time the conservation of the total angular momentum in valence band resonant tunnelling. It is also shown that conduction through light hole states is possible in many structures due to tunnelling of carriers from bulk emitter states.Comment: 4 pages, 4 figure

Tuning decoherence with a voltage probe

We present an experiment where we tune the decoherence in a quantum interferometer using one of the simplest object available in the physic of quantum conductors : an ohmic contact. For that purpose, we designed an electronic Mach-Zehnder interferometer which has one of its two arms connected to an ohmic contact through a quantum point contact. At low temperature, we observe quantum interference patterns with a visibility up to 57%. Increasing the connection between one arm of the interferometer to the floating ohmic contact, the voltage probe, reduces quantum interferences as it probes the electron trajectory. This unique experimental realization of a voltage probe works as a trivial which-path detector whose efficiency can be simply tuned by a gate voltage

Tomonaga-Luttinger physics in electronic quantum circuits

In one-dimensional conductors, interactions result in correlated electronic systems. At low energy, a hallmark signature of the so-called Tomonaga-Luttinger liquids (TLL) is the universal conductance curve predicted in presence of an impurity. A seemingly different topic is the quantum laws of electricity, when distinct quantum conductors are assembled in a circuit. In particular, the conductances are suppressed at low energy, a phenomenon called dynamical Coulomb blockade (DCB). Here we investigate the conductance of mesoscopic circuits constituted by a short single-channel quantum conductor in series with a resistance, and demonstrate a proposed link to TLL physics. We reformulate and establish experimentally a recently derived phenomenological expression for the conductance using a wide range of circuits, including carbon nanotube data obtained elsewhere. By confronting both conductance data and phenomenological expression with the universal TLL curve, we demonstrate experimentally the predicted mapping between DCB and the transport across a TLL with an impurity.Comment: 9p,6fig+SI; to be published in nature comm; v2: mapping extended to finite range interactions, added discussion and SI material, added reference

Electrically injected cavity polaritons

We have realised a semiconductor quantum structure that produces electroluminescence while operating in the light-matter strong coupling regime. The mid-infrared light emitting device is composed of a quantum cascade structure embedded in a planar microcavity, based on the GaAs/AlGaAs material system. At zero bias, the structure is characterised using reflectivity measurements which show, up to room temperature, a wide polariton anticrossing between an intersubband transition and the resonant cavity photon mode. Under electrical injection the spectral features of the emitted light change drastically, as electrons are resonantly injected in a reduced part of the polariton branches. Our experiment demonstrates that electrons can be selectively injected into polariton states up to room temperature.Comment: 10 pages, 4 figure

Experimental Test of the Dynamical Coulomb Blockade Theory for Short Coherent Conductors

We observed the recently predicted quantum suppression of dynamical Coulomb blockade on short coherent conductors by measuring the conductance of a quantum point contact embedded in a tunable on-chip circuit. Taking advantage of the circuit modularity we measured most parameters used by the theory. This allowed us to perform a reliable and quantitative experimental test of the theory. Dynamical Coulomb blockade corrections, probed up to the second conductance plateau of the quantum point contact, are found to be accurately normalized by the same Fano factor as quantum shot noise, in excellent agreement with the theoretical predictions.Comment: 4 pages, 4 figures, accepted for publication in Physical Review Letter

Sensing domain wall pinning in the longitudinal magnetoresistance of a two-dimensional electron gas

We investigate the sensing of domain wall pinning in thin Co wires positioned on top of a two-dimensional electron gas (2DEG) heterostructure by measuring the longitudinal resistance of the 2DEG as the magnetic field is swept, in an analogy to the Barkhausen effect. For comparison, we also measure the magnetoresistance of the ferromagnetic film in the same device in a subsequent sweep. Compared to the Hall measurements, the longitudinal measurement has the advantage of sensing magnetic activity over longer lengths, while compared to the measurement of the magnetoresistance in the ferromagnetic wire, it offers complementary information related to the pinning and unpinning of the domain wall, due to its sensitivity only to the out-of-plane magnetic field component.Fil: Kazazis, D.. No especifíca;Fil: Schüler, B.. Heinrich Heine University; AlemaniaFil: Granada, Mara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Gennser, U.. No especifíca;Fil: Faini, G.. No especifíca;Fil: Cerchez, M.. Heinrich Heine University; AlemaniaFil: Heinzel, T.. Heinrich Heine University; Alemani

Wigner and Kondo physics in quantum point contacts revealed by scanning gate microscopy

Quantum point contacts exhibit mysterious conductance anomalies in addition to well known conductance plateaus at multiples of 2e^2/h. These 0.7 and zero-bias anomalies have been intensively studied, but their microscopic origin in terms of many-body effects is still highly debated. Here we use the charged tip of a scanning gate microscope to tune in situ the electrostatic potential of the point contact. While sweeping the tip distance, we observe repetitive splittings of the zero-bias anomaly, correlated with simultaneous appearances of the 0.7 anomaly. We interpret this behaviour in terms of alternating equilibrium and non-equilibrium Kondo screenings of different spin states localized in the channel. These alternating Kondo effects point towards the presence of a Wigner crystal containing several charges with different parities. Indeed, simulations show that the electron density in the channel is low enough to reach one-dimensional Wigner crystallization over a size controlled by the tip position

Influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors

In a recent paper [B. A. Piot et al., Phys. Rev. B 72, 245325 (2005)], we have shown that the lifting of the electron spin degeneracy in the integer quantum Hall effect at high filling factors should be interpreted as a magnetic-field-induced Stoner transition. In this work, we extend the analysis to investigate the influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors. The single-particle Zeeman energy is tuned through the application of an additional in-plane magnetic field. Both the evolution of the spin polarization of the system and the critical magnetic field for spin splitting are well described as a function of the tilt angle of the sample in the magnetic field.Comment: Published in Phys. Rev.

Biomarkers of neuronal damage in saturation diving-a controlled observational study

PURPOSE: A prospective and controlled observational study was performed to determine if the central nervous system injury markers glial fibrillary acidic protein (GFAp), neurofilament light (NfL) and tau concentrations changed in response to a saturation dive. METHODS: The intervention group consisted of 14 submariners compressed to 401 kPa in a dry hyperbaric chamber. They remained pressurized for 36 h and were then decompressed over 70 h. A control group of 12 individuals was used. Blood samples were obtained from both groups before, during and after hyperbaric exposure, and from the intervention group after a further 25-26 h. RESULTS: There were no statistically significant changes in the concentrations of GFAp, NfL and tau in the intervention group. During hyperbaric exposure, GFAp decreased in the control group (mean/median - 15.1/ - 8.9 pg·mL-1, p < 0.01) and there was a significant difference in absolute change of GFAp and NfL between the groups (17.7 pg·mL-1, p = 0.02 and 2.34 pg·mL-1, p = 0.02, respectively). Albumin decreased in the control group (mean/median - 2.74 g/L/ - 0.95 g/L, p = 0.02), but there was no statistically significant difference in albumin levels between the groups. In the intervention group, haematocrit and mean haemoglobin values were slightly increased after hyperbaric exposure (mean/median 2.3%/1.5%, p = 0.02 and 4.9 g/L, p = 0.06, respectively). CONCLUSION: Hyperbaric exposure to 401 kPa for 36 h was not associated with significant increases in GFAp, NfL or tau concentrations. Albumin levels, changes in hydration or diurnal variation were unlikely to have confounded the results. Saturation exposure to 401 kPa seems to be a procedure not harmful to the central nervous system. TRIAL REGISTRATION: ClinicalTrials.gov NCT03192930