arXiv subjects

Sanat Kumar Gogoi

Publications and source records attributed to Sanat Kumar Gogoi.

3 recordsLinked to original sources

arXiv2024

Quantum fluctuations lead to glassy electron dynamics in the good metal regime of electron doped KTaO3

One of the central challenges in condensed matter physics is to comprehend systems that have strong disorder and strong interactions. In the strongly localized regime, their subtle competition leads to glassy electron dynamics which ceases to exist well before the insulator-to-metal transition is approached as a function of doping. Here, we report on the discovery of glassy electron dynamics deep inside the good metal regime of an electron-doped quantum paraelectric system: KTaO$_3$. We reveal that upon excitation of electrons from defect states to the conduction band, the excess injected carriers in the conduction band relax in a stretched exponential manner with a large relaxation time, and the system evinces simple aging phenomena - a telltale sign of glassy dynamics. Most significantly, we observe a critical slowing down of carrier dynamics below 35 K, concomitant with the onset of quantum paraelectricity in the undoped KTaO$_3$. Our combined investigation using second harmonic generation technique, density functional theory and phenomenological modeling demonstrates quantum fluctuation-stabilized soft polar modes as the impetus for the glassy behavior. This study addresses one of the most fundamental questions regarding the potential promotion of glassiness by quantum fluctuations and opens a route for exploring glassy dynamics of electrons in a well-delocalized regime.

cond-mat.str-el↗

arXiv2020

Oxygen Vacancy-Induced Topological Hall effect in a Nonmagnetic Band Insulator

The discovery of skyrmions has sparked tremendous interests about topologically nontrivial spin textures in recent times. The signature of noncoplanar nature of magnetic moments can be observed as topological Hall effect (THE) in electrical measurement. Realization of such nontrivial spin textures in new materials and through new routes is an ongoing endeavour due to their huge potential for future ultra-dense low-power memory applications. In this work, we report oxygen vacancy (OV) induced THE and anomalous Hall effect (AHE) in a 5$d^0$ system KTaO$_3$. The observation of weak antilocalization behavior and THE in the same temperature range strongly implies the crucial role of spin-orbit coupling (SOC) behind the origin of THE. Ab initio calculations reveal the formation of the magnetic moment on Ta atoms around the OV and Rashba-type spin texturing of conduction electrons. In the presence of Rashba SOC, the local moments around vacancy can form bound magnetic polarons (BMP) with noncollinear spin texture, resulting THE. Scaling analysis between transverse and longitudinal resistance establishes skew scattering driven AHE in present case. Our study opens a route to realize topological phenomena through defect engineering.

cond-mat.mtrl-sci↗

arXiv2020

Oxygen vacancy induced electronic structure modification of KTaO$_3$

The observation of metallic interface between band insulators LaAlO$_3$ and SrTiO$_3$ has led to massive efforts to understand the origin of the phenomenon as well as to search for other systems hosting such two dimensional electron gases (2-DEG). However, the understanding of the origin of the 2-DEG is very often hindered as several possible mechanisms such as polar catastrophe, cationic intermixing and oxygen vacancy (OV) etc. can be operative simultaneously. The presence of a heavy element makes KTaO$_3$ (KTO) based 2-DEG a potential platform to investigate spin orbit coupling driven novel electronic and magnetic phenomena. In this work, we investigate the sole effect of the OV, which makes KTO metallic. Our detailed \textit{ab initio} calculations not only find partially filled conduction bands in the presence of an OV but also predict a highly localized mid-gap state due to the linear clustering of OVs around Ta. Photoluminescence measurements indeed reveal the existence of such mid-gap state and O $K$-edge X-ray absorption spectroscopy finds electron doping in Ta $t_{2g}^*$ antibonding states. This present work suggests that one should be cautious about the possible presence of OVs within KTO substrate in interpreting metallic behavior of KTO based 2-DEG.

cond-mat.mtrl-sci↗