66,992 research outputs found
Higgs amplitude mode in massless Dirac fermion systems
The Higgs amplitude mode in superconductors is the condensed matter analogy
of Higgs bosons in particle physics. We investigate the time evolution of Higgs
amplitude mode in massless Dirac systems, induced by a weak quench of an
attractive interaction. We find that the Higgs amplitude mode in the
half-filling honeycomb lattice has a logarithmic decaying behaviour,
qualitatively different from the decay in the normal
superconductors. Our study is also extended to the doped cases in honeycomb
lattice. As for the 3D Dirac semimetal at half filling, we obtain an undamped
oscillation of the amplitude mode. Our finding is not only an important
supplement to the previous theoretical studies on normal fermion systems, but
also provide an experimental signature to characterize the superconductivity in
2D or 3D Dirac systems.Comment: 6 pages, 8 figure
Bulk Rotational Symmetry Breaking in Kondo Insulator SmB6
Kondo insulator samarium hexaboride (SmB6) has been intensely studied in
recent years as a potential candidate of a strongly correlated topological
insulator. One of the most exciting phenomena observed in SmB6 is the clear
quantum oscillations appearing in magnetic torque at a low temperature despite
the insulating behavior in resistance. These quantum oscillations show multiple
frequencies and varied effective masses. The origin of quantum oscillation is,
however, still under debate with evidence of both two-dimensional Fermi
surfaces and three-dimensional Fermi surfaces. Here, we carry out
angle-resolved torque magnetometry measurements in a magnetic field up to 45 T
and a temperature range down to 40 mK. With the magnetic field rotated in the
(010) plane, the quantum oscillation frequency of the strongest oscillation
branch shows a four-fold rotational symmetry. However, in the angular
dependence of the amplitude of the same branch, this four-fold symmetry is
broken and, instead, a twofold symmetry shows up, which is consistent with the
prediction of a two-dimensional Lifshitz-Kosevich model. No deviation of
Lifshitz-Kosevich behavior is observed down to 40 mK. Our results suggest the
existence of multiple light-mass surface states in SmB6, with their mobility
significantly depending on the surface disorder level.Comment: 15 pages, 9 figure
Recommended from our members
Studies on Temperature and Strain Sensitivities of a Few-mode Critical Wavelength Fiber Optic Sensor
This paper studied the relationship between the temperature/strain wavelength sensitivity of a fiber optic in-line Mach-Zehnder Interferometer (MZI) sensor and the wavelength separation of the measured wavelength to the critical wavelength (CWL) in a CWL-existed interference spectrum formed by interference between LP01 and LP02 modes. The in-line MZI fiber optic sensor has been constructed by splicing a section of specially designed few-mode fiber (FMF), which support LP01 and LP02 modes propagating in the fiber, between two pieces of single mode fiber. The propagation constant difference, Δβ, between the LP01 and LP02 modes, changes non-monotonously with wavelength and reaches a maximum at the CWL. As a result, in sensor operation, peaks on the different sides of the CWL then shift in opposite directions, and the associated temperature/strain sensitivities increase significantly when the measured wavelength points become close to the CWL, from both sides of the CWL. A theoretical analysis carried out has predicted that with this specified FMF sensor approach, the temperature/strain wavelength sensitivities are governed by the wavelength difference between the measured wavelength and the CWL. This conclusion was seen to agree well with the experimental results obtained. Combining the wavelength shifts of the peaks and the CWL in the transmission spectrum of the SFS structure, this study has shown that this approach forms the basis of effective designs of high sensitivity sensors for multi-parameter detection and offering a large measurement range to satisfy the requirements needed for better industrial measurements
3D quantum Hall effect of Fermi arcs in topological semimetals
The quantum Hall effect is usually observed in 2D systems. We show that the
Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological
semimetals. Because of the topological constraint, the Fermi arc at a single
surface has an open Fermi surface, which cannot host the quantum Hall effect.
Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at
opposite surfaces can form a complete Fermi loop and support the quantum Hall
effect. The edge states of the Fermi arcs show a unique 3D distribution, giving
an example of (d-2)-dimensional boundary states. This is distinctly different
from the surface-state quantum Hall effect from a single surface of topological
insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall
conductivity evolves from the 1/B dependence to quantized plateaus at the Weyl
nodes. This behavior can be realized by tuning gate voltages in a slab of
topological semimetal, such as the TaAs family, CdAs, or NaBi. This
work will be instructive not only for searching transport signatures of the
Fermi arcs but also for exploring novel electron gases in other topological
phases of matter.Comment: 5 pages, 3 figure
Euler equation of the optimal trajectory for the fastest magnetization reversal of nano-magnetic structures
Based on the modified Landau-Lifshitz-Gilbert equation for an arbitrary
Stoner particle under an external magnetic field and a spin-polarized electric
current, differential equations for the optimal reversal trajectory, along
which the magnetization reversal is the fastest one among all possible reversal
routes, are obtained. We show that this is a Euler-Lagrange problem with
constrains. The Euler equation of the optimal trajectory is useful in designing
a magnetic field pulse and/or a polarized electric current pulse in
magnetization reversal for two reasons. 1) It is straightforward to obtain the
solution of the Euler equation, at least numerically, for a given magnetic
nano-structure characterized by its magnetic anisotropy energy. 2) After
obtaining the optimal reversal trajectory for a given magnetic nano-structure,
finding a proper field/current pulse is an algebraic problem instead of the
original nonlinear differential equation
- …