arXiv subjects

Devendra Kumar

Publications and source records attributed to Devendra Kumar.

22 records · Page 2Linked to original sources

arXiv2010

Heterogeneous nucleation and metal-insulator transition in epitaxial films of NdNiO$_3$

We have investigated the temperature driven first order metal-insulator (M-I) transition in thin films of NdNiO$_3$ and have compared it with the bulk behavior. The M-I transition of thin films is sensitive to epitaxial strain and a partial relaxation of epitaxial strain creates an inhomogeneous strain field in the films which broadens the M-I transition. Both the thin film and the bulk samples exhibit non equilibrium features in the transition regime which are attributed to the presence of high temperature metallic phases in their supercooled state. The degree of supercooling in the thin films is found to be much smaller than in the bulk which suggests that the metal insulator transition in the thin film occurs through heterogeneous nucleation.

cond-mat.mes-hall↗

arXiv2009

Evidence of kinetically arrested supercooled phases in the pervoskite oxide NdNiO$_3$

We report the time and temperature dependent response of thermopower in the non-magnetic perovskite oxide NdNiO$_3$. We find that on cooling below the metal-insulator transition temperature the system evolves into a phase separated state which consists of supercooled metallic and insulating phases. This phase separated state exhibits out of equilibrium features such as cooling rate dependence and time dependence. The existence of these dynamical features is attributed to the transformation of supercooled metallic phases to the insulating state. On cooling a small fraction of supercooled phases gets kinetically arrested in a glassy state and these supercooled phases remain in that state down to low temperature. In the heating cycle the arrested states dearrest above 150 K and this results in the reappearance of time dependent features.

cond-mat.other↗

arXiv2008

Slow Dynamics in Hard Condensed Matter: A Case Study of the Phase Separating System NdNiO$_3$

We report the time dependent response of electrical resistivity in the non-magnetic perovskite oxide NdNiO$_3$ in its phase separated state and provide a physical explanation of the observations. We also model the system and do an accurate Monte Carlo simulation of the observed behavior. While cooling a phase separation takes place in this system below its metal-insulator transition temperature and in this state the material exhibits various dynamical phenomena such as relaxation of resistivity, dependence of resistivity on cooling rate and rejuvenation of the material after ageing. These phenomena signal that the phase separated state of NdNiO$_3$ is not in thermodynamic equilibrium and we conjecture that it consists of supercooled paramagnetic metallic and antiferromagnetic insulating phases. The supercooled phases are metastable and they switch over to the insulating equilibrium state stochastically and this can account for the slow dynamics observed in our system. We also verify the predictive power of our model by simulating the result of a new experiment and confirming it by actual measurements.

cond-mat.other↗

arXiv2008

Supercooling and the Metal-Insulator Phase Transition of NdNiO$_{3}$

We report the temperature and time dependence of electrical resistivity on high temperature, high oxygen pressure prepared polycrystalline samples of NdNiO_3. NdNiO_3 is metallic above 195 K and below that temperature it undergoes a transition to an insulating state. We find that on cooling NdNiO_3 below 195 K it goes into a state which is not in thermodynamic equilibrium and slowly relaxes over several hours. As we cool it further and go below about 110 K it goes into a stable insulating state. On heating the system from the insulating state towards 200 K we find that it remains stable and insulating and undergoes a rather sharp insulator to metal transition in the temperature range 185 K to 195 K. We try to make sense of these and a few other interesting observations on the basis of our current understanding of first order phase transitions, supercooling, and metal-insulator transitions.

cond-mat.other↗