1,896 research outputs found
Picovoltmeter for probing vortex dynamics in a single weak-pinning Corbino channel
We have developed a picovoltmeter using a Nb dc Superconducting QUantum
Interference Device (SQUID) for measuring the flux-flow voltage from a small
number of vortices moving through a submicron weak-pinning superconducting
channel. We have applied this picovoltmeter to measure the vortex response in a
single channel arranged in a circle on a Corbino disk geometry. The circular
channel allows the vortices to follow closed orbits without encountering any
sample edges, thus eliminating the influence of entry barriers.Comment: 4 pages, 3 figures, submitted to Review of Scientific Instrument
Shell structure and electron-electron interaction in self-assembled InAs quantum dots
Using far-infrared spectroscopy, we investigate the excitations of
self-organized InAs quantum dots as a function of the electron number per dot,
1<n<6, which is monitored in situ by capacitance spectroscopy. Whereas the
well-known two-mode spectrum is observed when the lowest s - states are filled,
we find a rich excitation spectrum for n=3, which reflects the importance of
electron-electron interaction in the present, strongly non-parabolic confining
potential. From capacitance spectroscopy we find that the electronic shell
structure in our dots gives rise to a distinct pattern in the charging energies
which strongly deviates from the monotonic behavior of the Coulomb blockade
found in mesoscopic or metallic structures.Comment: 4 pages, 3 PostScript figure
Ba{1-x}KxMn2As2: An Antiferromagnetic Local-Moment Metal
The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a
local-moment antiferromagnetic insulator with a Neel temperature TN = 625 K and
a large ordered moment mu = 3.9 mu_B/Mn. We demonstrate that this compound can
be driven metallic by partial substitution of Ba by K, while retaining the same
crystal and antiferromagnetic structures together with nearly the same high TN
and large mu. Ba_{1-x}K_xMn2As2 is thus the first metallic ThCr2Si2-type
MAs-based system containing local 3d transition metal M magnetic moments, with
consequences for the ongoing debate about the local moment versus itinerant
pictures of the FeAs-based superconductors and parent compounds. The
Ba_{1-x}K_xMn2As2 class of compounds also forms a bridge between the layered
iron pnictides and cuprates and may be useful to test theories of high Tc
superconductivity.Comment: 5 two-column typeset pages, 5 figures, 20 references; v2: minor
revisions, 4 new references, published versio
Coulombically Interacting Electrons in a One-dimensional Quantum Dot
The spectral properties of up to four interacting electrons confined within a
quasi one--dimensional system of finite length are determined by numerical
diagonalization including the spin degree of freedom. The ground state energy
is investigated as a function of the electron number and of the system length.
The limitations of a description in terms of a capacitance are demonstrated.
The energetically lowest lying excitations are physically explained as
vibrational and tunneling modes. The limits of a dilute, Wigner-type
arrangement of the electrons, and a dense, more homogeneous charge distribution
are discussed.Comment: 10 pages (excl. Figures), Figures added in POSTSCRIPT, LaTe
NiSi: New venue for antiferromagnetic spintronics
Envisaging antiferromagnetic spintronics pivots on two key criteria of high
transition temperature and tuning of underlying magnetic order using
straightforward application of magnetic field or electric current. Here, we
show that NiSi metal can provide suitable new platform in this quest. First,
our study unveils high temperature antiferromagnetism in single crystal NiSi
with K. Antiferromagnetic order in NiSi is accompanied by the
non-centrosymmetric magnetic character with small ferromagnetic component in
a-c plane. Second, we find that NiSi manifests distinct magnetic and electronic
hysteresis responses to field applications due to the disparity in two moment
directions. While magnetic hysteresis is characterized by one-step switching
between ferromagnetic states of uncompensated moment, electronic behavior is
ascribed to metamagnetic switching phenomena between non-collinear spin
configurations. Importantly, the switching behaviors persist to high
temperature. The properties underscore the importance of NiSi in the pursuit of
antiferromagnetic spintronics.Comment: 8 pages, 6 figure
Helmholtz theorem and the v-gauge in the problem of superluminal and instantaneous signals in classical electrodynamics
In this work we substantiate the applying of the Helmholtz vector
decomposition theorem (H-theorem) to vector fields in classical
electrodynamics. Using the H-theorem, within the framework of the two-parameter
Lorentz-like gauge (so called v-gauge), we show that two kinds of magnetic
vector potentials exist: one of them (solenoidal) can act exclusively with the
velocity of light c and the other one (irrotational) with an arbitrary finite
velocity (including a velocity more than c . We show also that the
irrotational component of the electric field has a physical meaning and can
propagate exclusively instantaneously.Comment: This variant has been accepted for publication in Found. Phys.
Letter
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