arXiv subjects

P. Rao

Publications and source records attributed to P. Rao.

4 recordsLinked to original sources

arXiv2026

Intermediate Field Spin(on) Dynamics in $\alpha$-RuCl$_3$

We present comprehensive inelastic neutron spectroscopic maps of the magnetic field-induced disordered phase of the Kitaev quantum spin liquid candidate material $\alpha$-RuCl$_3$. For fields along both in-plane high-symmetry directions we observe that the spin excitation spectrum at and above a magnetic field of 8~T is gapped. Excitation modes then sharpen for increasing field but are consistently broader than experimental resolution even at 13.5~T. The out-of-plane dispersion diminishes in the 7-10~T regime, signifying enhanced two-dimensional behavior as the in-plane liquid correlations are established. In this regime, excitations are very broad and largely flat for all accessible energy-momenta, which is kinematically at odds with a magnon-decay picture. By contrast, a continuum of fractionalized excitations naturally yields a broad continuum response, which crucially may be accompanied by sharper modes of bound states of fractionalized excitations. Their damping by the continuum accounts for the observed spectral broadening and field dependence. Our results provide strong evidence for the existence of fractionalized excitations in $\alpha$-RuCl$_3$ in a magnetic field.

cond-mat.str-el↗

arXiv2024

Imaging ultrafast electronic domain fluctuations with X-ray speckle visibility

Speckle patterns manifesting from the interaction of coherent X-rays with matter offer a glimpse into the dynamics of nanoscale domains that underpin many emergent phenomena in quantum materials. While the dynamics of the average structure can be followed with time-resolved X-ray diffraction, the ultrafast evolution of local structures in nonequilibrium conditions have thus far eluded detection due to experimental limitations, such as insufficient X-ray coherent flux. Here we demonstrate a nonequilibrium speckle visibility experiment using a split-and-delay setup at an X-ray free-electron laser. Photoinduced electronic domain fluctuations of the magnetic model material Fe$_{3}$O$_{4}$ reveal changes of the trimeron network configuration due to charge dynamics that exhibit liquid-like fluctuations, analogous to a supercooled liquid phase. This suggests that ultrafast dynamics of electronic heterogeneities under optical stimuli are fundamentally different from thermally-driven ones.

cond-mat.str-el↗

arXiv2016

Nonlinear effects in buoyancy-driven variable density turbulence

We consider the time-dependence of a hierarchy of scaled $L^{2m}$-norms $D_{m,ω}$ and $D_{m,θ}$ of the vorticity $\boldsymbol ω = \boldsymbol{\nabla} \times {\mathbf u}$ and the density gradient $\boldsymbol{\nabla} θ$, where $θ=\log (ρ^*/ρ^*_0)$, in a buoyancy-driven turbulent flow as simulated by \cite{LR2007}. $ρ^*({\mathbf x},\,t) $ is the composition density of a mixture of two incompressible miscible fluids with fluid densities $ρ^*_2 > ρ^*_1$ and $ρ^*_{0}$ is a reference normalisation density. Using data from the publicly available Johns Hopkins Turbulence Database we present evidence that the $L^{2}$-spatial average of the density gradient $\boldsymbol{\nabla} θ$ can reach extremely large values, even in flows with low Atwood number $At = (ρ^*_{2} - ρ^*_{1})/(ρ^*_{2} + ρ^*_{1}) = 0.05$, implying that very strong mixing of the density field at small scales can arise in buoyancy-driven turbulence. This large growth raises the possibility that the density gradient $\boldsymbol{\nabla} θ$ might blow up in a finite time.

physics.flu-dyn↗

arXiv2004

Radio halos in merging clusters of galaxies

We present the preliminary results of 235 MHz, 327 MHz and 610 MHz observations of the galaxy cluster A3562 in the core of the Shapley Concentration. The purpose of these observations, carried out with the Giant Metrewave Radio Telescope (GMRT, Pune, India) was to study the radio halo located at the centre of A3562 and determine the shape of its radio spectrum at low frequencies, in order to understand the origin of this source. In the framework of the re--acceleration model, the preliminary analysis of the halo spectrum suggests that we are observing a young source (few $10^8$ yrs) at the beginning of the re--acceleration phase.

astro-ph↗