Quantum tunnelling

About: Quantum tunnelling is a research topic. Over the lifetime, 24431 publications have been published within this topic receiving 579635 citations. The topic is also known as: tunneling effect & tunnel effect.

The physics of low-dimensional semiconductors : an introduction

Abstract: Preface Introduction 1. Foundations 2. Electrons and phonons in crystals 3. Heterostructures 4. Quantum wells and low-dimensional systems 5. Tunnelling transport 6. Electric and magnetic fields 7. Approximate methods 8. Scattering rates: the Golden Rule 9. The two-dimensional electron gas 10. Optical properties of quantum wells Appendix 1. Table of physical constants Appendix 2. Properties of important semiconductors Appendix 3. Properties of GaAs-AlAs alloys at room temperature Appendix 4. Hermite's equation: harmonic oscillator Appendix 5. Airy functions: triangular well Appendix 6. Kramers-Kronig relations and response functions Bibliography.

Conductance and exchange coupling of two ferromagnets separated by a tunneling barrier.

Abstract: A theory is given for three closely related effects involving a nonmagnetic electron-tunneling barrier separating two ferromagnetic conductors. The first is Julliere's magnetic valve effect, in which the tunnel conductance depends on the angle \ensuremath{\theta} between the moments of the two ferromagnets. One finds that discontinuous change of the potential at the electrode-barrier interface diminishes the spin-polarization factor governing this effect and is capable of changing its sign. The second is an effective interfacial exchange coupling -J cos\ensuremath{\theta} between the ferromagnets. One finds that the magnitude and sign of J depend on the height of the barrier and the Stoner splitting in the ferromagnets. The third is a new, irreversible exchange term in the coupled dynamics of the ferromagnets. For one sign of external voltage V, this term describes relaxation of the Landau-Lifshitz type. For the opposite sign of V, it describes a pumping action which can cause spontaneous growth of magnetic oscillations. All of these effects were investigated consistently by analyzing the transmission of charge and spin currents flowing through a rectangular barrier separating free-electron metals. In application to Fe-C-Fe junctions, the theory predicts that the valve effect is weak and that the coupling is antiferromagnetic (Jl0). Relations connecting the three effects suggest experiments involving small spatial dimensions.

Carrier tunneling and device characteristics in polymer light‐emitting diodes

Abstract: In this paper it is demonstrated that the characteristics of light‐emitting diodes based upon MEH‐PPV [more fully known as poly(2‐methoxy,5‐(2’‐ethyl‐hexoxy)‐1,4‐phenylene‐ vinylene)] are determined by tunneling of both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes. It is shown that manipulating these offsets can control the useful operating voltage of the device as well as its efficiency. A model is developed that clearly explains the device characteristics of a wide range of diodes based upon MEH‐PPV. The turn‐on voltage for an ideal device is shown to be equal to the band gap, i.e., 2.1 eV for MEH‐PPV, and is slightly lower at 1.8 eV for an indium‐tin oxide/MEH‐PPV/Ca device. If there is a significant difference in the barrier height, the smaller of the two barriers controls the I–V characteristics, while the larger barrier determines the device efficiency. In indium‐tin‐oxide/MEH‐PPV/Ca devices, the barrier to hole injection is ...

Anomalous Zero-Bias Conductance Peak in a Nb-InSb Nanowire-Nb Hybrid Device.

Abstract: Semiconductor InSb nanowires are expected to provide an excellent material platform for the study of Majorana fermions in solid state systems. Here, we report on the realization of a Nb-InSb nanowire-Nb hybrid quantum device and the observation of a zero-bias conductance peak structure in the device. An InSb nanowire quantum dot is formed in the device between the two Nb contacts. Due to the proximity effect, the InSb nanowire segments covered by the superconductor Nb contacts turn to superconductors with a superconducting energy gap Δ(InSb) ∼ 0.25 meV. A tunable critical supercurrent is observed in the device in high back gate voltage regions in which the Fermi level in the InSb nanowire is located above the tunneling barriers of the quantum dot and the device is open to conduction. When a perpendicular magnetic field is applied to the devices, the critical supercurrent is seen to decrease as the magnetic field increases. However, at sufficiently low back gate voltages, the device shows the quasi-particle Coulomb blockade characteristics and the supercurrent is strongly suppressed even at zero magnetic field. This transport characteristic changes when a perpendicular magnetic field stronger than a critical value, at which the Zeeman energy in the InSb nanowire is E(z) ∼ Δ(InSb), is applied to the device. In this case, the transport measurements show a conductance peak at the zero bias voltage and the entire InSb nanowire in the device behaves as in a topological superconductor phase. We also show that this zero-bias conductance peak structure can persist over a large range of applied magnetic fields and could be interpreted as a transport signature of Majorana fermions in the InSb nanowire.

Confinement of electrons to quantum corrals on a metal surface.

Abstract: A method for confining electrons to artificial structures at the nanometer lengthscale is presented. Surface state electrons on a copper(111) surface were confined to closed structures (corrals) defined by barriers built from iron adatoms. The barriers were assembled by individually positioning iron adatoms with the tip of a 4-kelvin scanning tunneling microscope (STM). A circular corral of radius 71.3 A was constructed in this way out of 48 iron adatoms. Tunneling spectroscopy performed inside of the corral revealed a series of discrete resonances, providing evidence for size quantization. STM images show that the corral's interior local density of states is dominated by the eigenstate density expected for an electron trapped in a round two-dimensional box.