75 research outputs found
Excited quantum Hall effect: enantiomorphic flat bands in a Yin-Yang Kagome lattice
Quantum Hall effect (QHE) is one of the most fruitful research topics in
condensed-matter physics. Ordinarily, the QHE manifests in a ground state with
time-reversal symmetry broken by magnetization to carry a quantized chiral edge
conductivity around a two-dimensional insulating bulk. We propose a theoretical
concept and model of non-equilibrium excited-state QHE (EQHE) without intrinsic
magnetization. It arises from circularly polarized photoexcitation between two
enantiomorphic flat bands of opposite chirality, each supporting originally a
helical topological insulating state hosted in a Yin-Yang Kagome lattice. The
chirality of its edge state can be reversed by the handedness of light, instead
of the direction of magnetization as in the conventional quantum (anomalous)
Hall effect, offering a simple switching mechanism for quantum devices.
Implications and realization of EQHE in real materials are discussed
Higher-dimensional spin selectivity in chiral crystals
This study aims to investigate the interplay between chiral-induced
spin-orbit coupling along the screw axis and antisymmetric spin-orbit coupling
(ASOC) in the normal plane within a chiral crystal, using both general model
analysis and first-principles simulations of InSeI, a chiral van der Waals
crystal. While chiral molecules of light atoms typically exhibit spin
selectivity only along the screw axis, chiral crystals with heavier atoms can
have strong ASOC effects that influence spin-momentum locking in all
directions. The resulting phase diagram of spin texture shows the potential for
controlling phase transition and flipping spin by reducing symmetry through
surface cleavage, thickness reduction or strain. We also experimentally
synthesized high-quality InSeI crystals of the thermodynamically stable achiral
analogue which showed exposed (110) facets corresponding to single-handed
helices to demonstrate the potential of material realization for
higher-dimensional spin selectivity in the development of spintronic devices
Higher-order Topological and Nodal Superconductors MS (M = Nb and Ta) Transition-metal Sulfides
Intrinsic topological superconducting materials are exotic and vital to
develop the next-generation topological superconducting devices, topological
quantum calculations, and quantum information technologies. Here, we predict
the topological and nodal superconductivity of MS (M = Nb and Ta)
transition-metal sulfides by using the density functional theory for
superconductors combining with the symmetry indicators. We reveal their
higher-order topology nature with an index of Z4 = 2. These materials have a
higher Tc than the Nb or Ta metal superconductors due to their flat-band and
strong electron-phonon coupling nature. Electron doping and lighter isotopes
can effectively enhance the Tc. Our findings show that the MS (M = Nb and Ta)
systems can be new platforms to study exotic physics in the higher-order
topological superconductors, and provide a theoretical support to utilize them
as the topological superconducting devices in the field of advanced topological
quantum calculations and information technologies.Comment: 5 pages, 3 figure
Controllable Strain-driven Topological Phase Transition and Dominant Surface State Transport in High-Quality HfTe5 Samples
Controlling materials to create and tune topological phases of matter could
potentially be used to explore new phases of topological quantum matter and to
create novel devices where the carriers are topologically protected. It has
been demonstrated that a trivial insulator can be converted into a topological
state by modulating the spin-orbit interaction or the crystal lattice. However,
there are limited methods to controllably and efficiently tune the crystal
lattice and at the same time perform electronic measurements at cryogenic
temperatures. Here, we use large controllable strain to demonstrate the
topological phase transition from a weak topological insulator phase to a
strong topological insulator phase in high-quality HfTe5 samples. After
applying high strain to HfTe5 and converting it into a strong topological
insulator, we found that the sample's resistivity increased by more than two
orders of magnitude (24,000%) and that the electronic transport is dominated by
the topological surface states at cryogenic temperatures. Our findings show
that HfTe5 is an ideal material for engineering topological properties, and it
could be generalized to study topological phase transitions in van der Waals
materials and heterostructures. These results can pave the way to create novel
devices with applications ranging from spintronics to fault-tolerant
topologically protected quantum computers
Exceptional electronic transport and quantum oscillations in thin bismuth crystals grown inside van der Waals materials
Confining materials to two-dimensional forms changes the behavior of
electrons and enables new devices. However, most materials are challenging to
produce as uniform thin crystals. Here, we present a new synthesis approach
where crystals are grown in a nanoscale mold defined by atomically-flat van der
Waals (vdW) materials. By heating and compressing bismuth in a vdW mold made of
hexagonal boron nitride (hBN), we grow ultraflat bismuth crystals less than 10
nanometers thick. Due to quantum confinement, the bismuth bulk states are
gapped, isolating intrinsic Rashba surface states for transport studies. The
vdW-molded bismuth shows exceptional electronic transport, enabling the
observation of Shubnikov-de Haas quantum oscillations originating from the
(111) surface state Landau levels, which have eluded previous studies. By
measuring the gate-dependent magnetoresistance, we observe multi-carrier
quantum oscillations and Landau level splitting, with features originating from
both the top and bottom surfaces. Our vdW-mold growth technique establishes a
platform for electronic studies and control of bismuth's Rashba surface states
and topological boundary modes. Beyond bismuth, the vdW-molding approach
provides a low-cost way to synthesize ultrathin crystals and directly integrate
them into a vdW heterostructure
Enhanced electrical and thermal conductivities of 3D-SiC(rGO, G x ) PDCs based on polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO) precursor containing graphene fillers
Abstract(#br)Lightweight 3D-SiC(rGO, G x ) PDCs were fabricated from polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO) precursor added by different amounts of graphene fillers via direct cold molding and pyrolysis at 1400 °C in an easy manner. Results reveal that SiC(rGO, G x ) PDCs consist of β-SiC nanocrystals homogeneously embedded within amorphous SiO x C y /C free , and graphene is well compatible with SiO x C y /C free for void-free bonded interface, efficiently delaying decomposition of SiO x C y phase into β-SiC. The nanocomposite structure provides an ingenious strategy for constructing complexes with good integrity, high ceramic yield, excellent thermal stability, high electrical and thermal conductivities. This improvement is primarily attributed to the presence of graphene with considerably increasing electric-charge carriers and wider phonon-channel. Such 3D-SiC(rGO, G 20% ) PDCs possess satisfying hardness (12.02 GPa), high electrical conductivity (23.82 S cm −1 ) and thermal conductivity (7.47 W m −1 K −1 ), which make them attractive candidates for microelectromechanical systems (MEMS) devices, energy storage/conversion systems and high precision components, etc
Remembering the City: Changing Conceptions of Community in Urban China
Adopting complimentary integrative research methodologies, this article examines changing conceptions of community amongst urban residents within the city of Suzhou, Jiangsu province, China. Whilst the impact of urban transformation from a macro-perspective, deploying large scale quantitative measures to capture resident perceptions within China’s mega-cities, has been addressed, there is something of a scholarly lacuna that adopts a micro-perspective to explore the
nation-state’s smaller developing cities. Thus, through local residents’ past memories, ‘everyday’ experiences of (former) urban communities, and reflections on a particular way of life, we focus upon the subjective/affective meanings and memories attached to processes of urban change. We place emphasis on the manner in which residents make sense of socio-spatial transformations in relation to the (re)making of community, local social interaction, and a sense of belonging. Discussion centres on the affective and embodied notions of a particular way of life in (older) communities; sensory performances that were deemed difficult to replicate within modern development zones and the broader field of contemporary Chinese society
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