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Kim, Jinwoong,Kim, Jeongwoo,Song, Young-Sun,Wu, Ruqian,Jhi, Seung-Hoon,Kioussis, Nicholas American Physical Society 2017 Physical review. B Vol.96 No.23
<P>The interfacial phase-change memory (iPCM) GeTe/Sb2Te3, a promising candidate for the next generation nonvolatile random-accessmemories, exhibits fascinating topological properties. Depending on the atomic-layerstacking sequence of the GeTe block, the iPCM can be either in the SET (Ge-Te-Ge-Te) or RESET (Te-Ge-Ge-Te) states, where the former exhibits ferroelectric polarization and electrical conductivity two orders of magnitude larger than that of the RESET state. Yet, its microscopic origin remains elusive. Here, we predict the emergence of a Weyl semimetal phase in the SET state induced by the ferroelectric polarization which breaks the crystal inversion symmetry. We show that the giant conductivity enhancement of the SET phase is due to the appearance of gapless Weyl nodes. The Ge-Te-or Sb-Te-terminated surfaces of Weyl semimetal iPCM exhibit surface states with completely distinctive topology, where the former consists solely of Fermi arcs while the latter consists of both closed Fermi surface and open Fermi arcs. The iPCM with van der Waals interfaces offers an ideal platform for exploiting the exotic Weyl properties as well as for future memory device applications.</P>
Giant enhancement of the intrinsic spin Hall conductivity in β -tungsten via substitutional doping
Sui, Xuelei,Wang, Chong,Kim, Jinwoong,Wang, Jianfeng,Rhim, S. H.,Duan, Wenhui,Kioussis, Nicholas American Physical Society 2017 Physical Review B Vol.96 No.24
<P>A key challenge in manipulating the magnetization in heavy-metal/ferromagnetic bilayers via the spin-orbit torque is to identify materials that exhibit an efficient charge-to-spin current conversion. Ab initio electronic structure calculations reveal that the intrinsic spin Hall conductivity (SHC) for pristine beta-W is about 60% larger than that of alpha-W. More importantly, we demonstrate that the SHC of beta-W can be enhanced via Ta alloying. This is corroborated by spin Berry curvature calculations of W1-x Ta-x (x similar to 12.5%) alloys which show a giant enhancement of the spin Hall angle of up to approximate to-0.5. The underlying mechanism is the synergistic behavior of the SHC and longitudinal conductivity with the Fermi level position. These findings not only pave the way for enhancing the intrinsic spin Hall effect in beta-W, but also provide guidelines to exploit substitutional alloying to tailor the spin Hall effect in various materials.</P>
Lee, Paengro,Kim, Jinwoong,Kim, Jin Gul,Ryu, Min-tae,Park, Hee-min,Kim, Namdong,Kim, Yongsam,Lee, Nam-Suk,Kioussis, Nicholas,Jhi, Seung-Hoon,Chung, Jinwook IOP 2016 Journal of physics, an Institute of Physics journa Vol.28 No.8
<P>We observe the modified surface states of an epitaxial thin film of a homologous series of (Bi<SUB>2</SUB>)<SUB>m</SUB>(Bi<SUB>2</SUB>Se<SUB>3</SUB>)<SUB>n</SUB>, as a topological insulator (TI), by angle-resolved photoemission spectroscopy measurements. A thin film with <I>m</I> : <I>n</I> = 1 : 3 (Bi<SUB>8</SUB>Se<SUB>9</SUB>) has been grown with Bi<SUB>2</SUB> bilayers embedded every other three quintuple layers (QLs) of Bi<SUB>2</SUB>Se<SUB>3</SUB>. Despite the reduced dimension of continuous QLs due to the Bi<SUB>2</SUB> heterolayers, we find that the topological surface states stem from the inverted Bi and Se states and the topologically nontrivial structures are mainly based on the prototype of 3D TI Bi<SUB>2</SUB>Se<SUB>3</SUB> without affecting the overall topological order.</P>