13 research outputs found
Photo-induced phase-transitions in complex solids
Photo-induced phase-transitions (PIPTs) driven by highly cooperative
interactions are of fundamental interest as they offer a way to tune and
control material properties on ultrafast timescales. Due to strong correlations
and interactions, complex quantum materials host several fascinating PIPTs such
as light-induced charge density waves and ferroelectricity and have become a
desirable setting for studying these PIPTs. A central issue in this field is
the proper understanding of the underlying mechanisms driving the PIPTs. As
these PIPTs are highly nonlinear processes and often involve multiple time and
length scales, different theoretical approaches are often needed to understand
the underlying mechanisms. In this review, we present a brief overview of PIPTs
realized in complex materials, followed by a discussion of the available
theoretical methods with selected examples of recent progress in understanding
of the nonequilibrium pathways of PIPTs.Comment: 13 pages, 6 figure
Ultrafast spin-nematic and ferroelectric phase transitions induced by femto-second light pulses
Optically-induced phase transitions of the manganite have been simulated using a model Hamiltonian, that
captures the dynamics of strongly correlated charge, orbital, lattice, and spin
degrees of freedom. Its parameters have been extracted from first-principles
calculations. Beyond a critical intensity of a femto-second light pulse, the
material undergoes ultra-fast and non-thermal magnetic phase transition from a
non-collinear to collinear antiferromagnetic phases. The light-pulse excites
selectively either a spin-nematic or a ferroelectric phase depending on the
light-polarization. The behavior can be traced to an optically induced
ferromagnetic coupling between Mn-trimers, i.e. polarons which are delocalized
over three Mn-sites. The polarization guides the polymerization of the
polaronic crystal into distinct patterns of ferromagnetic chains determining
the target phase.Comment: 6 pages, 4 figure
A non-perturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition
Solid systems with strong correlations and interactions under light
illumination have the potential for exhibiting interesting bulk photovoltaic
behavior in the non-perturbative regime, which has remained largely unexplored
in the past theoretical studies. We investigate the bulk photovoltaic response
of a perovskite manganite with strongly coupled electron-spin-lattice dynamics,
using real-time simulations performed with a tight-binding model. The transient
changes in the band structure and the photoinduced phase transitions, emerging
from spin and phonon dynamics, result in a nonlinear current versus intensity
behavior beyond the perturbative limit. The current rises sharply across a
photoinduced magnetic phase transition, which later saturates at higher light
intensities due to excited phonon and spin modes. The predicted peak
photoresponsivity is orders of magnitude higher than other known ferroelectric
oxides such as BiFeO. We disentangle phonon-and spin-assisted components to
the ballistic photocurrent, showing that they are comparable in magnitude. Our
results illustrate a promising alternative way for controlling and optimizing
the bulk photovoltaic response through the photoinduced phase transitions in
strongly-correlated systems
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A non-perturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition
Solid systems with strong correlations and interactions under light
illumination have the potential for exhibiting interesting bulk photovoltaic
behavior in the non-perturbative regime, which has remained largely unexplored
in the past theoretical studies. We investigate the bulk photovoltaic response
of a perovskite manganite with strongly coupled electron-spin-lattice dynamics,
using real-time simulations performed with a tight-binding model. The transient
changes in the band structure and the photoinduced phase transitions, emerging
from spin and phonon dynamics, result in a nonlinear current versus intensity
behavior beyond the perturbative limit. The current rises sharply across a
photoinduced magnetic phase transition, which later saturates at higher light
intensities due to excited phonon and spin modes. The predicted peak
photoresponsivity is orders of magnitude higher than other known ferroelectric
oxides such as BiFeO. We disentangle phonon-and spin-assisted components to
the ballistic photocurrent, showing that they are comparable in magnitude. Our
results illustrate a promising alternative way for controlling and optimizing
the bulk photovoltaic response through the photoinduced phase transitions in
strongly-correlated systems
INQ, a modern GPU-accelerated computational framework for (time-dependent) density functional theory
We present INQ, a new implementation of density functional theory (DFT) and
time-dependent DFT (TDDFT) written from scratch to work on graphical processing
units (GPUs). Besides GPU support, INQ makes use of modern code design features
and takes advantage of newly available hardware. By designing the code around
algorithms, rather than against specific implementations and numerical
libraries, we aim to provide a concise and modular code. The result is a fairly
complete DFT/TDDFT implementation in roughly 12,000 lines of open-source C++
code representing a modular platform for community-driven application
development on emerging high-performance computing architectures for the
simulation of materials