Spin–orbit interaction in Pt or Bi2Te3 nanoparticle-decorated graphene realized by a nanoneedle method

Abstract

The introduction of spin-orbit interactions (SOIs) and the subsequent appearance of a twodimensional (2D) topological phase are crucial for voltage-controlled and zero-emission energy spintronic devices. In contrast, graphene basically lacks SOIs due to the small mass of the carbon atom, and appropriate experimental reports for SOIs are rare. Here, we control small-amount (cover ratios < 8%) random decoration of heavy nanoparticles [platinum (Pt) or bismuth telluride (Bi2Te3)] onto mono-layer graphene by developing an original nanoneedle method. Xray photoelectron spectra support low-damage and low-contamination decoration of the nanoparticles, suggesting the presence of Bi-C and Te-C coupling orbitals. In the samples, we find particle-density-dependent non-local resistance (RNL) peaks, which are attributed to the (inverse) spin Hall effect (SHE) arising from SOI with energies as large as 30 meV. This is a larger value than in previous reports and supported by scanning tunneling spectroscopy. The present observation should lead to topological phases of graphene, which can be introduced by random decoration with controlled small amounts of heavy nanoparticles, and their applications.

Room-temperature quantum spin Hall phase in laser-patterned few-layer 1T′- MoS2

“…2d, where a well-developed plateau with a value of R Q /4 appears. The R Q /4 value becomes even more well-defined at T = 1.5 K. This value has been reported in H-letter like patterns also using four electrode probes on HgTe/(Hg, Cd)Te quantum wells 3 , our Bi 2 Te 3 -nanoparticle decorated graphene 8,9 , and in our previous high-power laser-irradiated thin 1T′ MoS 2 17 . A straightforward calculation based on the Landauer-Büttiker formalism confirms the measured value for this contact geometry (see Supplementary Note 10).…”

“…The prototypical QSH insulator was, however, predicted to be graphene 7 , but graphene lacks a sizable spin-orbit coupling (SOC) and various efforts have been made to enhance SOC and facilitate the observation of its QSH phase. Indeed, we realized QSH phases in graphene by decorating it with Bi 2 Te 3 nanoparticles at very small coverage (∼3%) 8,9 . However, the operating temperature for the QSH phase was still low (<∼20 K) and the Δ values were small (<∼20 meV).…”

Evidence for a quantum spin Hall phase in graphene decorated with Bi 2 Te 3 nanoparticles

“…We further deposit Bi 2 Te 3 nanoparticles with diameters of ~1 to 30 nm (Sigma-Aldrich Inc.) onto the graphene surface following our previous nanoneedle method [section S2 and ( 26 )]. Specifically, for the present experiment, we repeatedly drop and then absorb a small acetone droplet containing the nanoparticles using the narrow tip of the needle (Saito Medical Instruments Inc.), which has an inner pore diameter of ~50 μm, allowing precise control of the low nanoparticle density D within the small graphene Hall bar (section S2 and movie S1).…”

“…Specifically, we explore graphene decorated with dilute, randomly positioned Bi 2 Te 3 nanoparticles. These nanoparticles carry giant spin-orbit coupling via tunneling current and can thus significantly modify graphene’s electronic structure even at very low coverages ( 26 ); they can also be inserted into the graphene lattice in a minimally invasive manner. As theoretically demonstrated on heavy adatom/graphene systems (e.g., Os atom) in our previous study ( 20 ), topological bulk gaps open due to the hybridization between the graphene’s π states (Dirac state) and the spin-orbit split d xz and d yz Os-atom orbitals in the case of Os adatom.…”

Quantum Spin Hall Materials

“…Recently, a study on Bi 2 Te 3 decorated graphene reports resistivity peak values qualitatively agree with helical edge transport result . The authors attribute this behavior to spin–orbit coupling induced by Bi 2 Te 3 . QSH effect is also predicted in graphene interacting with single crystal WS 2 or WSe 2 .…”