66 research outputs found
Amplitude dynamics of charge density wave in LaTe: theoretical description of pump-probe experiments
We formulate a dynamical model to describe a photo-induced charge density
wave (CDW) quench transition and apply it to recent multi-probe experiments on
LaTe [A. Zong et al., Nat. Phys. 15, 27 (2019)]. Our approach relies on
coupled time-dependent Ginzburg-Landau equations tracking two order parameters
that represent the modulations of the electronic density and the ionic
positions. We aim at describing the amplitude of the order parameters under the
assumption that they are homogeneous in space. This description is supplemented
by a three-temperature model, which treats separately the electronic
temperature, temperature of the lattice phonons with stronger couplings to the
electronic subsystem, and temperature of all other phonons. The broad scope of
available data for LaTe and similar materials as well as the synergy
between different time-resolved spectroscopies allow us to extract model
parameters. The resulting calculations are in good agreement with ultra-fast
electron diffraction experiments, reproducing qualitative and quantitative
features of the CDW amplitude evolution during the initial few picoseconds
after photoexcitation.Comment: 21 pages, 14 figures; this version is almost identical to the
published version; comparing to the earlier arXiv submission, current version
contains a new figure (Fig.10), and a broader discussion of theoretical
results and approximation
Self-similar dynamics of order parameter fluctuations in pump-probe experiments
Upon excitation by a laser pulse, broken-symmetry phases of a wide variety of
solids demonstrate similar order parameter dynamics characterized by a dramatic
slowing down of relaxation for stronger pump fluences. Motivated by this
recurrent phenomenology, we develop a simple non-perturbative effective model
of dynamics of collective bosonic excitations in pump-probe experiments. We
find that as the system recovers after photoexcitation, it shows universal
prethermalized dynamics manifesting a power-law, as opposed to exponential,
relaxation, explaining the slowing down of the recovery process. For strong
quenches, long-wavelength over-populated transverse modes dominate the
long-time dynamics; their distribution function exhibits universal scaling in
time and space, whose universal exponents can be computed analytically. Our
model offers a unifying description of order parameter fluctuations in a regime
far from equilibrium, and our predictions can be tested with available
time-resolved techniques
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Amplitude dynamics of the charge density wave in LaTe3: Theoretical description of pump-probe experiments
We formulate a dynamical model to describe a photo-induced charge density
wave (CDW) quench transition and apply it to recent multi-probe experiments on
LaTe [A. Zong et al., Nat. Phys. 15, 27 (2019)]. Our approach relies on
coupled time-dependent Ginzburg-Landau equations tracking two order parameters
that represent the modulations of the electronic density and the ionic
positions. We aim at describing the amplitude of the order parameters under the
assumption that they are homogeneous in space. This description is supplemented
by a three-temperature model, which treats separately the electronic
temperature, temperature of the lattice phonons with stronger couplings to the
electronic subsystem, and temperature of all other phonons. The broad scope of
available data for LaTe and similar materials as well as the synergy
between different time-resolved spectroscopies allow us to extract model
parameters. The resulting calculations are in good agreement with ultra-fast
electron diffraction experiments, reproducing qualitative and quantitative
features of the CDW amplitude evolution during the initial few picoseconds
after photoexcitation
Ultrafast manipulation of mirror domain walls in a charge density wave
Domain walls (DWs) are singularities in an ordered medium that often host
exotic phenomena such as charge ordering, insulator-metal transition, or
superconductivity. The ability to locally write and erase DWs is highly
desirable, as it allows one to design material functionality by patterning DWs
in specific configurations. We demonstrate such capability at room temperature
in a charge density wave (CDW), a macroscopic condensate of electrons and
phonons, in ultrathin 1T-TaS. A single femtosecond light pulse is shown to
locally inject or remove mirror DWs in the CDW condensate, with probabilities
tunable by pulse energy and temperature. Using time-resolved electron
diffraction, we are able to simultaneously track anti-synchronized CDW
amplitude oscillations from both the lattice and the condensate, where
photo-injected DWs lead to a red-shifted frequency. Our demonstration of
reversible DW manipulation may pave new ways for engineering correlated
material systems with light
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
Periodic dynamics in superconductors induced by an impulsive optical quench
A number of experiments have evidenced signatures of enhanced superconducting correlations after photoexcitation. Initially, these experiments were interpreted as resulting from quasi-static changes in the Hamiltonian parameters, for example, due to lattice deformations or melting of competing phases. Yet, several recent observations indicate that these conjectures are either incorrect or do not capture all the observed phenomena, which include reflectivity exceeding unity, large shifts of Josephson plasmon edges, and appearance of new peaks in terahertz reflectivity. These observations can be explained from the perspective of a Floquet theory involving a periodic drive of system parameters, but the origin of the underlying oscillations remains unclear. In this paper, we demonstrate that following incoherent photoexcitation, long-lived oscillations are generally expected in superconductors with low-energy Josephson plasmons, such as in cuprates or fullerene superconductor K3C60. These oscillations arise from the parametric generation of plasmon pairs due to pump-induced perturbation of the superconducting order parameter. We show that this bi-plasmon response can persist even above the transition temperature as long as strong superconducting fluctuations are present. Our analysis offers a robust framework to understand light-induced superconducting behavior, and the predicted bi-plasmon oscillations can be directly detected using available experimental techniques
A solid-state high harmonic generation spectrometer with cryogenic cooling
Solid-state high harmonic generation spectroscopy (sHHG) is a promising
technique for studying electronic structure, symmetry, and dynamics in
condensed matter systems. Here, we report on the implementation of an advanced
sHHG spectrometer based on a vacuum chamber and closed-cycle helium cryostat.
Using an in situ temperature probe, it is demonstrated that the sample
interaction region retains cryogenic temperature during the application of
high-intensity femtosecond laser pulses that generate high harmonics. The
presented implementation opens the door for temperature-dependent sHHG
measurements down to few Kelvin, which makes sHHG spectroscopy a new tool for
studying phases of matter that emerge at low temperatures, which is
particularly interesting for highly correlated materials
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Impact of water uptake and mixing state on submicron particle deposition in the human respiratory tract (HRT) based on explicit hygroscopicity measurements at HRT-like conditions
Particle hygroscopicity plays a key role in determining the particle deposition in the human respiratory tract (HRT). In this study, the effects of hygroscopicity and mixing state on regional and total deposition doses on the basis of the particle number concentration for children, adults, and the elderly were quantified using the Multiple-Path Particle Dosimetry model, based on the size-resolved particle hygroscopicity measurements at HRT-like conditions (relative humidity = 98 %) performed in the North China Plain. The measured particle population with an external mixing state was dominated by hygroscopic particles (number fraction = (91.5 ± 5.7) %, mean ± standard deviation (SD); the same below). Particle hygroscopic growth in the HRT led to a reduction by around 24 % in the total doses of submicron particles for all age groups. Such a reduction was mainly caused by the growth of hygroscopic particles and was more pronounced in the pulmonary and tracheobronchial regions. Regardless of hygroscopicity, the elderly group of people had the highest total dose among three age groups, while children received the maximum total deposition rate. With 270 nm in diameter as the boundary, the total deposition doses of particles smaller than this diameter were overestimated, and those of larger particles were underestimated, assuming no particle hygroscopic growth in the HRT. From the perspective of the daily variation, the deposition rates of hygroscopic particles with an average of (2.88 ± 0.81) × 109 particles h-1 during the daytime were larger than those at night ((2.32 ± 0.24) × 109 particles h-1). On the contrary, hydrophobic particles interpreted as freshly emitted soot and primary organic aerosols exhibited higher deposition rates at nighttime ((3.39 ± 1.34) × 108 particles h-1) than those in the day ((2.58 ± 0.76) × 108 particles h-1). The traffic emissions during the rush hours enhanced the deposition rate of hydrophobic particles. This work provides a more explicit assessment of the impact of hygroscopicity and mixing state on the deposition pattern of submicron particles in the HRT. Copyright
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