1,440 research outputs found
Quantum spin Hall density wave insulator of correlated fermions
We present the theory of a new type of topological quantum order which is
driven by the spin-orbit density wave order parameter, and distinguished by
topological invariant. We show that when two oppositely polarized chiral
bands [resulting from the Rashba-type spin-orbit coupling , is
crystal momentum] are significantly nested by a special wavevector , it induces a spatially modulated inversion of the
chirality () between different sublattices. The
resulting quantum order parameters break translational symmetry, but preserve
time-reversal symmetry. It is inherently associated with a -topological
invariant along each density wave propagation direction. Hence it gives a weak
topological insulator in two dimensions, with even number of spin-polarized
boundary states. This phase is analogous to the quantum spin-Hall state, except
here the time-reversal polarization is spatially modulated, and thus it is
dubbed quantum spin-Hall density wave (QSHDW) state. This order parameter can
be realized or engineered in quantum wires, or quasi-2D systems, by tuning the
spin-orbit couping strength and chemical potential to achieve the special
nesting condition.Comment: 8 pages, 4 figure
Ultrafast and low-energy switching in voltage-controlled elliptical pMTJ
Switching magnetization in a perpendicular magnetic tunnel junction (pMTJ)
via voltage controlled magnetic anisotropy (VCMA) has shown the potential to
markedly reduce the switching energy. However, the requirement of an external
magnetic field poses a critical bottleneck for its practical applications. In
this work, we propose an elliptical-shaped pMTJ to eliminate the requirement of
providing an external field by an additional circuit. We demonstrate that a 10
nm thick in-plane magnetized bias layer (BL) separated by a metallic spacer of
3 nm from the free layer (FL) can be engineered within the MTJ stack to provide
the 50 mT bias magnetic field for switching. By conducting macrospin
simulation, we find that a fast switching in 0.38 ns with energy consumption as
low as 0.3 fJ at a voltage of 1.6 V can be achieved. Furthermore, we study the
phase diagram of switching probability, showing that a pulse duration margin of
0.15 ns is obtained and a low-voltage operation (~ 1 V) is favored. Finally,
the MTJ scalability is considered, and it is found that scaling-down may not be
appealing in terms of both the energy consumption and the switching time for
the precession based VCMA switching.Comment: There are 28 pages and 5 figure
Rise of Fifth Estate: Challenges and the Way Ahead
From news to social media, from net banking to e-commerce, online gaming to ordering food at home, technology has paved its way into our lives. Technology has become our nervous system and any disruption to it can cause paralysis in an individual's life. The individual's personal information, which one never shares in physical space, has moved to the cloud and is sold for a few bucks in the market. Technical gadgets have become so advanced that one can get a real feel of a war zone, a robbery scene, a terrorist attack, or a high-speed jet inside a room wearing suitable gaming kits. The physical meetings have moved to virtual space. Technology is virtually 24x7 with us knowingly or unknowingly. Technology is an enabler and at the same time, it has enhanced the potential of lawbreakers. The biggest challenge, as the technology advances, remains that of security and legality in virtual space, because in virtual space there are no boundaries, limited laws can be applied and illegal activities continue through the dark web, albeit in a legal way
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