61 research outputs found
Generation of single skyrmions by picosecond magnetic field pulses
We numerically demonstrate an ultrafast method to create
skyrmions in a ferromagnetic sample by applying a
picosecond (effective) magnetic field pulse in the presence of
Dzyaloshinskii-Moriya interaction. For small samples the applied magnetic field
pulse could be either spatially uniform or nonuniform while for large samples a
nonuniform and localized field is more effective. We examine the phase diagram
of pulse width and amplitude for the nucleation. Our finding could ultimately
be used to design future skyrmion-based devices.Comment: 4.5 pages+Supplemental Materia
Second-order topological superconductor via noncollinear magnetic texture
We put forth a theoretical framework for engineering a two-dimensional (2D)
second-order topological superconductor (SOTSC) by utilizing a heterostructure:
incorporating noncollinear magnetic textures between an s-wave superconductor
and a 2D quantum spin Hall insulator. It stabilizes the higher order
topological superconducting phase, resulting in Majorana corner modes (MCMs) at
four corners of a 2D domain. The calculated non-zero quadrupole moment
characterizes the bulk topology. Subsequently, through a unitary
transformation, an effective low-energy Hamiltonian reveals the effects of
magnetic textures, resulting in an effective in-plane Zeeman field and
spin-orbit coupling. This approach provides a qualitative depiction of the
topological phase, substantiated by numerical validation within exact
real-space model. Analytically calculated effective pairings in the bulk
illuminate the microscopic behavior of the SOTSC. The comprehension of MCM
emergence is aided by a low-energy edge theory, which is attributed to the
interplay between effective pairings of (px + py )-type and (px + ipy )-type.
Our extensive study paves the way for practically attaining the SOTSC phase by
integrating noncollinear magnetic textures
Observation of anisotropic Dirac cones in the topological material Ti2Te2P
Anisotropic bulk Dirac (or Weyl) cones in three dimensional systems have
recently gained intense research interest as they are examples of materials
with tilted Dirac (or Weyl) cones indicatig the violation of Lorentz
invariance. In contrast, the studies on anisotropic surface Dirac cones in
topological materials which contribute to anisotropic carrier mobility have
been limited. By employing angle-resolved photoemission spectroscopy and
first-principles calculations, we reveal the anisotropic surface Dirac
dispersion in a tetradymite material Ti2Te2P on the (001) plane of the
Brillioun zone. We observe the quasi-elliptical Fermi pockets at the M -point
of the Brillouin zone forming the anisotropic surface Dirac cones. Our
calculations of the Z2 indices confirm that the system is topologically
non-trivial with multiple topological phases in the same material. In addition,
the observed nodal-line like feature formed by bulk bands makes this system
topologically rich.Comment: 21 pages, 17 figures, Supplementary Information include
"The fruits of independence": Satyajit Ray, Indian nationhood and the spectre of empire
Challenging the longstanding consensus that Satyajit Ray's work is largely free of ideological concerns and notable only for its humanistic richness, this article shows with reference to representations of British colonialism and Indian nationhood that Ray's films and stories are marked deeply and consistently by a distinctively Bengali variety of liberalism. Drawn from an ongoing biographical project, it commences with an overview of the nationalist milieu in which Ray grew up and emphasizes the preoccupation with colonialism and nationalism that marked his earliest unfilmed scripts. It then shows with case studies of Kanchanjangha (1962), Charulata (1964), First Class Kamra (First-Class Compartment, 1981), Pratidwandi (The Adversary, 1970), Shatranj ke Khilari (The Chess Players, 1977), Agantuk (The Stranger, 1991) and Robertsoner Ruby (Robertson's Ruby, 1992) how Ray's mature work continued to combine a strongly anti-colonial viewpoint with a shifting perspective on Indian nationhood and an unequivocal commitment to cultural cosmopolitanism. Analysing how Ray articulated his ideological positions through the quintessentially liberal device of complexly staged debates that were apparently free, but in fact closed by the scenarist/director on ideologically specific notes, this article concludes that Ray's reputation as an all-forgiving, ‘everybody-has-his-reasons’ humanist is based on simplistic or even tendentious readings of his work
Tailoring phase transition from topological superconductor to trivial superconductor induced by magnetic textures of a spin-chain on a -wave superconductor
We theoretically investigate the phase transition from a non-trivial
topological -wave superconductor to a trivial -wave like superconducting
phase through a gapless phase, driven by different magnetic textures as an
one-dimensional spin-chain impurity, Bloch-type, in-plane and
out-of-plane N\'eel-type spin-chains etc. In our proposal, the chain of
magnetic impurities is placed on a spin-triplet -wave superconductor where
we obtain numerically as well as analytically an effective -wave like
pairing due to spin rotation, resulting in gradual destruction of the Majorana
zero modes present in the topological superconducting phase. In particular,
when the impurity spins are antiferromagnetically aligned spiral wave
vector , the system becomes an effective -wave superconductor
without Majorana zero modes in the local density of states. The Shiba bands, on
the other hand, formed due to the overlapping of Yu-Shiba-Rusinov states play a
crucial role in this topological to trivial superconductor phase transition,
confirmed by the sign change in the minigap within the Shiba bands. Moreover,
interference of the Shiba bands exhibiting oscillatory behavior within the
superconducting gap, to , as a function of ,
also reflects an important evidence for the formation of an effective -wave
pairing. Such oscillation is absent in the -wave regime. Our study paves the
way to foresee the stability and tunability of topological superconducting
phase via controlled manipulation of the spin spiral configurations of the
magnetic impurity chain.Comment: 13 pages, 7 figure
- …