325 research outputs found
Fluctuating charge density waves in a cuprate superconductor
Cuprate materials hosting high-temperature superconductivity (HTS) also
exhibit various forms of charge and/or spin ordering whose significance is not
fully understood. To date, static charge-density waves (CDWs) have been
detected by diffraction probes only at special doping or in an applied external
field. However, dynamic CDWs may also be present more broadly and their
detection, characterization and relationship with HTS remain open problems.
Here, we present a new method, based on ultrafast spectroscopy, to detect the
presence and measure the lifetimes of CDW fluctuations in cuprates. In an
underdoped La1.9Sr0.1CuO4 film (Tc = 26 K), we observe collective excitations
of CDW that persist up to 100 K. This dynamic CDW fluctuates with a
characteristic lifetime of 2 ps at T = 5 K which decreases to 0.5 ps at T = 100
K. In contrast, in an optimally doped La1.84Sr0.16CuO4 film (Tc = 38.5 K), we
detect no signatures of fluctuating CDWs at any temperature, favoring the
competition scenario. This work forges a path for studying fluctuating order
parameters in various superconductors and other materials.Comment: 16 pages, 4 figures, accepted to Nature Material
Metal nanoring and tube formation on carbon nanotubes
The structural and electronic properties of aluminum covered single wall
carbon nanotubes (SWNT) are studied from first-principles for a large number of
coverage. Aluminum-aluminum interaction that is stronger than aluminum-tube
interaction, prevents uniform metal coverage, and hence gives rise to the
clustering. However, a stable aluminum ring and aluminum nanotube with well
defined patterns can also form around the semiconducting SWNT and lead to
metallization. The persistent current in the Al nanoring is discussed to show
that a high magnetic field can be induced at the center of SWNT.Comment: Submitted to Physical Review
Invariant quantum discord in qubit-qutrit systems under local dephasing
We investigate the dynamics of quantum discord and entanglement for a
class of mixed qubit-qutrit states assuming that only the qutrit is under the action of a dephasing channel. We demonstrate that even though the entanglement in the qubit-qutrit state disappears in a finite time interval, partial coherence left in the system enables quantum discord to remain invariant throughout the whole time evolution
Examination of forest products trade between Turkey and European Union countries with gravity model approach
The success of getting in the foreign trade forms one of the basic stones of economic development for countries. The current and potential trading volume among countries and determining the main factors affecting trade are quite important. The trade currents of the European Union (EU) countries and Turkey in the forest products industry field were analyzed by the gravity model in this study. For this reason, the panel data method was used for 2000 - 2006 periods. The results show the existence of a high degree of trade integration between Turkey and EU. The estimated gravity models explained 63% of the variation regarding the volume of bilateral trade flows in the EU and Turkey. Furthermore, it was determined that GDP had a positive effect on the amount of foreign trade while distance had a negativeeffect; and Turkey has lower trading volume with the EU countries than its potential regarding the forest products industry field
Quantum correlations in a few-atom spin-1 Bose-Hubbard model
We study the thermal quantum correlations and entanglement in spin-1 Bose-Hubbard model with two and three particles. While we use negativity to calculate entanglement, more general non-classical correlations are quantified using a new measure based on a necessary and sufficient condition for zero-discord state. We demonstrate that the energy level crossings in the ground state of the system are signalled by both the behavior of thermal quantum correlations and entanglement
Second harmonic generation as a probe of broken mirror symmetry
The notion of spontaneous symmetry breaking has been used to describe phase
transitions in a variety of physical systems. In crystalline solids, the
breaking of certain symmetries, such as mirror symmetry, is difficult to detect
unambiguously. Using 1-TaS, we demonstrate here that
rotational-anisotropy second harmonic generation (RA-SHG) is not only a
sensitive technique for the detection of broken mirror symmetry, but also that
it can differentiate between mirror symmetry-broken structures of opposite
planar chirality. We also show that our analysis is applicable to a wide class
of different materials with mirror symmetry-breaking transitions. Lastly, we
find evidence for bulk mirror symmetry-breaking in the incommensurate charge
density wave phase of 1-TaS. Our results pave the way for RA-SHG to
probe candidate materials where broken mirror symmetry may play a pivotal role
Second harmonic generation as a probe of broken mirror symmetry
The notion of spontaneous symmetry breaking has been used to describe phase
transitions in a variety of physical systems. In crystalline solids, the
breaking of certain symmetries, such as mirror symmetry, is difficult to detect
unambiguously. Using 1-TaS, we demonstrate here that
rotational-anisotropy second harmonic generation (RA-SHG) is not only a
sensitive technique for the detection of broken mirror symmetry, but also that
it can differentiate between mirror symmetry-broken structures of opposite
planar chirality. We also show that our analysis is applicable to a wide class
of different materials with mirror symmetry-breaking transitions. Lastly, we
find evidence for bulk mirror symmetry-breaking in the incommensurate charge
density wave phase of 1-TaS. Our results pave the way for RA-SHG to
probe candidate materials where broken mirror symmetry may play a pivotal role.Comment: 13 pages, 10 figures. Edited (v2) to include Bilal G\"okce in the
authors list who was mistakenly excluded. Edited again (v3) to incorporate
modifications recommended by referees. Replaced (v4) with version published
in Physical Review
Nodal quasiparticle meltdown in ultra-high resolution pump-probe angle-resolved photoemission
High- cuprate superconductors are characterized by a strong
momentum-dependent anisotropy between the low energy excitations along the
Brillouin zone diagonal (nodal direction) and those along the Brillouin zone
face (antinodal direction). Most obvious is the d-wave superconducting gap,
with the largest magnitude found in the antinodal direction and no gap in the
nodal direction. Additionally, while antinodal quasiparticle excitations appear
only below , superconductivity is thought to be indifferent to nodal
excitations as they are regarded robust and insensitive to . Here we
reveal an unexpected tie between nodal quasiparticles and superconductivity
using high resolution time- and angle-resolved photoemission on optimally doped
BiSrCaCuO. We observe a suppression of the nodal
quasiparticle spectral weight following pump laser excitation and measure its
recovery dynamics. This suppression is dramatically enhanced in the
superconducting state. These results reduce the nodal-antinodal dichotomy and
challenge the conventional view of nodal excitation neutrality in
superconductivity.Comment: 7 pages, 3 figure. To be published in Nature Physic
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