Helical Hole State in Multiple Conduction Modes in Ge/Si Core/Shell Nanowire

Abstract

Helical states, a prerequisite for the engineering of Majorana zero modes in solid-state systems, have recently been reported in the conduction band of III-V nanowires (NWs) subject to strong Rashba spin-orbit interaction. We report the observation of re-entrant conductance features consistent with the presence of helical hole states in multiple conduction modes of a Ge/Si core/shell NW. The Ge/Si system has several potential advantages over electron systems such as longer spin coherence time due to weaker coupling to nuclear spins and the possibility of isotope-purified materials for nuclear spin-free devices. We derive the Landé g factor of 3.6 from magneto-transport measurements, comparable to theoretical predictions and significantly larger when compared with that in strongly confined quantum dots. The spin-orbit energy is evaluated as ∼2.1 meV, on par with values in III-V NWs, showing good agreement with previous theoretical predictions and weak antilocalization measurements.

The germanium quantum information route

“…The DRSOI requires HH-LH mixing and can be switched on and off via gate electrodes in the experimental setup. In contrast to the well-known case of conduction-band electrons in Rashba NWs, the effective DRSOI coefficient does not rely on couplings between the conduction-band and valence-band states and can therefore be exceptionally large, in agreement with experiments [69][70][71][72][73][74] . For example, spin-orbit energies of a few meV were recently measured for holes in Ge/Si NWs 72,73 .…”

“…In contrast to the well-known case of conduction-band electrons in Rashba NWs, the effective DRSOI coefficient does not rely on couplings between the conduction-band and valence-band states and can therefore be exceptionally large, in agreement with experiments [69][70][71][72][73][74] . For example, spin-orbit energies of a few meV were recently measured for holes in Ge/Si NWs 72,73 . According to theoretical studies, a moderate electric field in the Ge core is sufficient for such high spin-orbit energies 49,50 and, e.g., allows for efficient hole-spin qubit rotations 53 via electric dipole spin resonance (EDSR) 75 .…”

“…3c). More recently, detailed measurements of spin-orbit energies in 1DHGs Ge/Si NWs 72,73 confirmed the large values expected by the DRSOI 49,50 . In ref 72 highly tunable 1DHG FET devices with a dual-gate architecture were fabricated and a very large and tunable spin-orbit energy was evaluated in the range 1-6 meV, almost one order of magnitude larger than that reported for NWs in III-Vs semiconductors.…”

Exchange interaction of hole-spin qubits in double quantum dots in highly anisotropic semiconductors

“…These systems benefit from an even stronger Rashba type of SOI that relies on the HH-LH mixing and is not suppressed by the fundamental band gap [32,33]. In agreement with recent experiments [15,17,[34][35][36][37][38][39][40][41], Si and Ge/Si core/shell nanowires (NWs) are particularly promising platforms for such low-dimensional hole systems. Remarkably, these NWs and QDs therein can be formed with a complementary metal-oxide-semiconductor compatible fabrication process [17,36,38,42,43], which indicates an exceptional scalability.…”

Ambipolar MoS2 Field‐Effect Transistor by Spatially Controlled Chemical Doping

“…Here, we utilized mechanically exfoliated h‐BN flake as the mask and transferred it using the dry van der Waals technique onto the targeting MoS 2 . Good alignment within 0.1 μm can be guaranteed using a home‐made mechanical manipulator . Figure a shows three FETs fabricated on the same MoS 2 flake with a transferred h‐BN covering half of the flake, resulting in three distinct FETs having a fully covered channel, “serially” half covered channel, and a fully exposed channel, respectively.…”