Ultralong spin lifetimes in one-dimensional semiconductor nanowires

Abstract

We experimentally demonstrate ultralong spin lifetimes of electrons in the one-dimensional (1D) quantum limit of semiconductor nanowires. Optically probing single wires of different diameters reveals an increase in the spin relaxation time by orders of magnitude as the electrons become increasingly confined until only a single 1D subband is populated after thermalization. We find the observed spin lifetimes of more than 200 ns to result from the robustness of 1D electrons against major spin relaxation mechanisms, highlighting the promising potential of these wires for long-range transport of coherent spin information.Nanowires (NWs) present three key assets: their unique shape, an exceptional surface-to-volume ratio and a high level of control during the epitaxial crystal growth. These features have established NWs in a cornerstone role for an impressively diverse area of nanoscale concepts, ranging from custom-tailored light-matter interaction 1-3 , energy harvesting and sensing 4,5 to ballistic quantum transport 6 . By controlling the diameter at the nanoscale, NWs can for instance be tailored to a specific application by matching them with the length scale of a particular (quasi-) particle. Introducing radial spatial quantum confinement for electrons in semiconductor NWs, thus leaving only one direction of free motion, opens an experimental route to fascinating new phenomena such as Majorana-bound states 7 , the unique Coulomb interactions in Tomonaga-Luttinger liquids 8 , unusual dispersion effects in spin-orbit coupled 1D systems 9 or long-range, coherent spin transport. Promising groundwork towards long-range spin transport has been demonstrated in wirelike, but yet diffusive systems [10][11][12][13][14][15][16][17][18][19] . While these studies highlight a correlation between the wire width and the spin relaxation, going beyond diffusive systems by pushing experiments into the one-dimensional (1D) quantum limit should give access to a new realm of spin coherence.In this Letter, we present a series of GaAs NWs with different diameters to investigate how spin relaxation evolves in the transition from a continuous threedimensional (3D) dispersion to the electronic 1D quantum limit, where only a single 1D subband is occupied. Our optical approach allows us to investigate single, freestanding NWs. In our NW system, spatially confining electrons to 1D is expected to completely remove the usually very efficient mechanism of Dyakonov-Perel spin relaxation 20 . We indeed experimentally observe extraordinarily long spin relaxation times of more than 200 ns for the thinnest NWs: an increase by a factor ∼ 500 for the transition from 3D to 1D. We demonstrate that the spin a) Electronic mail: *dominique.bougeard@ur.de relaxation in our experiment is a result of the electronhole (e-h) exchange interaction. Our analysis shows that the confinement of e-h pairs to increasingly smaller length scales very efficiently suppresses this exchangedriven spin relaxation in our NWs, causing the strong increase observed in our experim...

Proximity exchange effects in MoSe2 and WSe2 heterostructures with CrI3 : Twist angle, layer, and gate dependence

“…Especially interesting are the proximity exchange parameters, being roughly 2 meV in magnitude, translating into about 10 T exchange field [46][47][48][49] , in agreement with recent experiments 54,61 . The calculation of the atomic magnetic moments reveals, that the magnetization direction of the TMDC is the same as in the I atoms, opposite to the Cr atoms, therefore giving negative proximity exchange parameters for a net CrI 3 magnetization pointing along positive z-direction towards the TMDC.…”

“…Recently, photoinduced magnetization switching of the CrI 3 layer underneath a TMDC 7 was shown, by tuning the laser excitation power. The optical induced carrier density n o depends on the laser power, the excitation energy, the absorption coefficient and the area of the laser spot, as reported for semiconductor nanowires 46 . The electrical gate induced magnetization switching occurs for threshold densities of n t ≈ 2 × 10 13 cm −245 .…”

“…The interplay of the two couplings, exchange and valley Zeeman, motivates explorations of stacked TMDCs and 2D ferromagnets. Certainly, one can introduce Zeeman coupling by applying an external magnetic field pointing out of the plane, but such fields produce modest valley splittings, about 0.1 -0.2 meV per tesla [46][47][48][49] . Proximity exchange fields can induce much stronger effects, perhaps up to hundreds of meVs, without significantly altering the band structure of TMDCs.…”

Persistent spin textures and currents in wurtzite nanowire-based quantum structures

“…20 If the size reduction structurally confines the carriers to one dimension (1D), the momentum is fixed to a single axis which avoids the spin decoherence and produces extraordinarily long spin lifetimes. 21 However, in the strict 1D limit, the high relevance of many-body interactions and disorder presents additional challenges for the utilization for spintronic devices. [22][23][24][25] Nanowires constitute a building block for future generation spintronic and electronic devices with novel functionalities and far-reaching applications.…”

Electric Field Modulation of Spin Transport

“…A large SOC, however, leads to short spin lifetime and diffusion lengths, representing a severe limitation for the development of spintronic devices. Conversely, the small SOC in light semiconductors yields to longer electron spin lifetimes, as observed in both lightly-doped bulk [4] and low-dimensional materials [5,6]. Among semiconductors, Si and Ge possess the longest lifetimes, since, at variance from GaAs, the Dyakonov-Perel mechanism of spin relaxation is totally suppressed in a centrosymmetric lattice [7].…”