Showing 1–24 of 24 results for author: Rana, A

Spin bath mediated long-lived coherent oscillations of NV centers in diamond

Authors: Akshat Rana, Pooja Lamba, Basanta Mistri, Dieter Suter, Siddharth Dhomkar, Rama K. Kamineni

Abstract: Decoherence is the biggest bottleneck in all quantum technologies. For nitrogen-vacancy (NV) centers in diamond, the loss of coherence is caused by the electron and nuclear spin bath of the diamond lattice. Here, we demonstrate that the spin bath - that typically causes decoherence - entangles the spin states of the NV electron and the host $^{14}$N nucleus. The many-body interaction between the… ▽ More Decoherence is the biggest bottleneck in all quantum technologies. For nitrogen-vacancy (NV) centers in diamond, the loss of coherence is caused by the electron and nuclear spin bath of the diamond lattice. Here, we demonstrate that the spin bath - that typically causes decoherence - entangles the spin states of the NV electron and the host $^{14}$N nucleus. The many-body interaction between the $^{14}$N nucleus - electron - bath spins at an energy level anti-crossing occurring for an applied magnetic field orientation perpendicular to the NV axis is responsible for this effect. This is observed experimentally in NV ensembles via electron spin-echo measurements, where the echo envelope is modulated at the frequency of a $^{14}$N nuclear spin transition. Using numerical simulations, we show that the spin bath coupling to the NV centers is essential for observing this modulation. Due to the zero first-order Zeeman effect at the anti-crossing, the observed oscillations have long spin-echo coherence times, 2--3 times those at the parallel magnetic field orientation. The oscillation frequency is highly stable and robust against environmental fluctuations. These findings provide new opportunities for fundamental studies of many-body physics and quantum sensing. △ Less

Submitted 25 August, 2026; v1 submitted 29 June, 2026; originally announced June 2026.

Comments: 17 pages, 9 figures

Thermodynamic Driving Force Activated Phonon Scattering in InN

Authors: Zaheer Ahmad, Osama A. Rana, Shakeel Ahmad, Mark Vernon, Brendan Cross, Alexander Kozhanov

Abstract: Defect related disorder during InN growth is a major challenge for making high performance electronic and optoelectronic devices. This is partly because film quality is often described using reactor specific settings instead of general physical variables. In this study, we show that plasma assisted MOCVD growth of InN can be described using a single thermodynamic driving force coordinate. This coo… ▽ More Defect related disorder during InN growth is a major challenge for making high performance electronic and optoelectronic devices. This is partly because film quality is often described using reactor specific settings instead of general physical variables. In this study, we show that plasma assisted MOCVD growth of InN can be described using a single thermodynamic driving force coordinate. This coordinate brings together growth kinetics, defect sensitive Raman response and structural coherence across different process conditions. When we use this coordinate, the incorporation rate follows a universal activated trend with a kinetic scale of about 0.08 eV. Raman measurements show a clear crossover between a defect sparse and a defect rich regime, a disorder activated Raman metric increases quickly after the crossover, while an A1-LO control metric stays mostly the same. This suggests that short range lattice disorder, not long range polar coupling, dominates the defect activation process. X-ray diffraction shows that the out of plane coherence length stays the same for samples with the same driving force, even if reactor settings are very different. This supports the idea that structural coherence is organized by thermodynamics in this growth window. Finally, a simple kinetic Monte Carlo model using driving force biased incorporation and defect activation events matches the observed exponential trends and the two regimes, supporting the driving force approach. These results show that a transferable driving force coordinate can be used for plasma assisted InN growth and offer a quantitative way to achieve defect sparse growth conditions. △ Less

Submitted 12 January, 2026; originally announced January 2026.

Imaging of microwave magnetic field orientation using continuous-wave experiments on nitrogen-vacancy centers in diamond

Authors: Akshat Rana, Pooja Lamba, Atanu Ghosh, Siddharth Dhomkar, Rama K. Kamineni

Abstract: Imaging of microwave magnetic fields with nano-scale resolution has interesting applications. Specifically, detecting the orientation of the microwave fields is useful in condensed matter physics and quantum control. However, most of the existing methods for microwave field imaging are limited to detecting the magnitude of the fields. Due to their small sensor size and favorable optical and spin p… ▽ More Imaging of microwave magnetic fields with nano-scale resolution has interesting applications. Specifically, detecting the orientation of the microwave fields is useful in condensed matter physics and quantum control. However, most of the existing methods for microwave field imaging are limited to detecting the magnitude of the fields. Due to their small sensor size and favorable optical and spin properties, nitrogen-vacancy (NV) centers in diamond are highly suitable for imaging dc and ac magnetic fields. The reported methods for detecting the orientation of microwave magnetic fields use pulsed Rabi frequency measurements. Here, we demonstrate imaging of the orientation of microwave magnetic fields by only using continuous-wave experiments on NV centers. This simplifies the sensor apparatus and is particularly advantageous in applications where pulsing of the target microwave field is not possible. The method requires static bias magnetic field oriented perpendicular to the quantization axis of NV centers. We detect the direction of an arbitrary microwave magnetic field using NV centers of two different orientations. Moreover, we demonstrate that the projection of the microwave fields onto a plane can be imaged using NV centers of single orientation. It can be straightforwardly implemented using a single NV center. △ Less

Submitted 21 June, 2025; originally announced June 2025.

Comments: 7 pages, 4 figures

Journal ref: Journal of Physics D: Applied Physics 58, 435302 (2025)

Electrotaxis of self-propelling artificial swimmers in microchannels

Authors: Carola M. Buness, Avi Rana, Corinna C. Maass, Ranabir Dey

Abstract: Ciliated microswimmers and flagellated bacteria alter their swimming trajectories to follow the direction of an applied electric field exhibiting electrotaxis. Both for matters of application and physical modelling, it is instructive to study such behaviour in synthetic swimmers. We show here that under an external electric field, self-propelling active droplets autonomously modify their swimming… ▽ More Ciliated microswimmers and flagellated bacteria alter their swimming trajectories to follow the direction of an applied electric field exhibiting electrotaxis. Both for matters of application and physical modelling, it is instructive to study such behaviour in synthetic swimmers. We show here that under an external electric field, self-propelling active droplets autonomously modify their swimming trajectories in microchannels, even undergoing `U-turns', to exhibit robust electrotaxis. Depending on the relative initial orientations of the microswimmer and the external electric field, the active droplet can also navigate upstream of an external flow following a centre-line motion, instead of the oscillatory upstream trajectory observed in absence of electric field. Using a hydrodynamic theory model, we show that the electrically induced angular velocity and electrophoretic effects, along with the microswimmer motility and its hydrodynamic interactions with the microchannel walls, play crucial roles in dictating the electrotactic trajectories and dynamics. Specifically, the transformation in the trajectories during upstream swimming against an external flow under an electric field can be understood as a reverse Hopf bifurcation for a dynamical system. Our study provides a simple methodology and a systematic understanding of manoeuvring active droplets in microconfinements for micro-robotic applications especially in biotechnology. △ Less

Submitted 25 January, 2024; originally announced January 2024.

Visualizing Magnetic Order in Self-Assembly of Superparamagnetic Nanoparticles

Authors: Xingyuan Lu, Ji Zou, Minh Pham, Arjun Rana, Chen-Ting Liao, Emma Cating Subramanian, Xuefei Wu, Yuan Hung Lo, Charles S. Bevis, Robert M. Karl Jr, Serban Lepadatu, Young-Sang Yu, Yaroslav Tserkovnyak, Thomas P. Russell, David A. Shapiro, Henry C. Kapteyn, Margaret M. Murnane, Robert Streubel, Jianwei Miao

Abstract: We use soft x-ray vector-ptychographic tomography to determine the three-dimensional magnetization field in superparamagnetic nanoparticles self-assembled at the liquid-liquid interface and reveal the magnetic order induced by layered structure. The spins in individual nanoparticles become more aligned with increasing number of layers, resulting in a larger net magnetization. Our experimental resu… ▽ More We use soft x-ray vector-ptychographic tomography to determine the three-dimensional magnetization field in superparamagnetic nanoparticles self-assembled at the liquid-liquid interface and reveal the magnetic order induced by layered structure. The spins in individual nanoparticles become more aligned with increasing number of layers, resulting in a larger net magnetization. Our experimental results show a magnetic short-range order in the monolayer due to the proliferation of thermally induced magnetic vortices and a magnetic long-range order in the bilayer and trilayer, stemming from the strengthened dipolar interactions that effectively suppress thermal fluctuations. We also observe a screening effect of magnetic vortices and the attractive interaction between the magnetic vortices with opposite topological charges. Our work demonstrates the crucial role of layered structure in shaping the magnetization of nanoparticle assemblies, providing new opportunities to modulate these properties through strategic layer engineering. △ Less

Submitted 2 January, 2024; originally announced January 2024.

Vector detection of AC magnetic fields by Nitrogen-Vacancy centers of single orientation in diamond

Authors: Pooja Lamba, Akshat Rana, Sougata Halder, Siddharth Dhomkar, Dieter Suter, Rama K. Kamineni

Abstract: Nitrogen-Vacancy (NV) centers in diamond have useful properties for detecting both AC and DC magnetic fields with high sensitivity at nano-scale resolution. Vector detection of AC magnetic fields can be achieved by using NV centers having three different orientations. Here, we propose a method to achieve this by using NV centers of single orientation. In this method, a static magnetic field is app… ▽ More Nitrogen-Vacancy (NV) centers in diamond have useful properties for detecting both AC and DC magnetic fields with high sensitivity at nano-scale resolution. Vector detection of AC magnetic fields can be achieved by using NV centers having three different orientations. Here, we propose a method to achieve this by using NV centers of single orientation. In this method, a static magnetic field is applied perpendicular to the NV axis, leading to strong mixing of the $m_{s}=-1$ and $1$ electron spin states. As a result, all three electron spin transitions of the triplet ground state have non-zero dipole moments, with each transition coupling to a single component of the magnetic field. This can be used to measure both strength and orientation of the applied AC field. To validate the technique, we perform a proof of principle experiment using a subset of ensemble NV centers in diamond, all having the same orientation. △ Less

Submitted 18 August, 2023; originally announced August 2023.

Comments: 7 pages, 5 figures

Journal ref: Physical Review B 109, 195424 (2024)

Nanomechanical inhomogeneities in CVA-deposited titanium nitride thin films: Nanoindentation and Finite Element Method Investigations

Authors: Neeraj Kumar Sharma, Anchal Rana, O. S. Panwar, Abhimanyu Singh Rana

Abstract: Refractory metals that can withstand at high temperatures and harsh conditions are of utmost importance for solar-thermal and energy storage applications. Thin films of TiN have been deposited using cathodic vacuum arc deposition (CVA) at relatively low temperatures ~ 300 oC using the substrate bias ~ -60V. The nanomechanical properties of these films were investigated using nanoindentation and th… ▽ More Refractory metals that can withstand at high temperatures and harsh conditions are of utmost importance for solar-thermal and energy storage applications. Thin films of TiN have been deposited using cathodic vacuum arc deposition (CVA) at relatively low temperatures ~ 300 oC using the substrate bias ~ -60V. The nanomechanical properties of these films were investigated using nanoindentation and the spatial fluctuations were observed. The nanoindentation results were simulated using finite element method (FEM) through Johnson-Cook model. We have found the local nitridation plays an important role on nanomechanical properties of TiN thin films and confirms that the nitrogen deficient regions are ductile with low yield stress and hardening modulus. This study further opens the opportunities of modelling the nanoscale system using FEM analysis. △ Less

Submitted 15 August, 2023; v1 submitted 14 August, 2023; originally announced August 2023.

Anisotropic Inflation in Dipolar Bose-Einstein Condensates

Authors: Arun Rana, Abhijit Pendse, Sebastian Wüster, Sukanta Panda

Abstract: Early during the era of cosmic inflation, rotational invariance may have been broken, only later emerging as a feature of low-energy physics. This motivates ongoing searches for residual signatures of anisotropic space-time, for example in the power spectrum of the cosmic microwave background. We propose that dipolar Bose-Einstein condensates (BECs) furnish a laboratory quantum simulation platform… ▽ More Early during the era of cosmic inflation, rotational invariance may have been broken, only later emerging as a feature of low-energy physics. This motivates ongoing searches for residual signatures of anisotropic space-time, for example in the power spectrum of the cosmic microwave background. We propose that dipolar Bose-Einstein condensates (BECs) furnish a laboratory quantum simulation platform for the anisotropy evolution of fluctuation spectra during inflation, exploiting the fact that the speed of dipolar condensate sound waves depends on direction. We construct the anisotropic analogue space-time metric governing sound, by linking the time-varying strength of dipolar and contact interactions in the BEC to the scale factors in different coordinate directions. Based on these, we calculate the dynamics of phonon power spectra during an inflation that renders the initially anisotropic universe isotropic. We find that the expansion speed provides an experimental handle to control and study the degree of final residual anisotropy. Gravity analogues using dipolar condensates can thus provide tuneable experiments for a field of cosmology that was until now confined to a single experiment, our universe. △ Less

Submitted 7 August, 2023; v1 submitted 5 July, 2023; originally announced July 2023.

Comments: Updated Format, More References Added

On the resistance minimum in LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ heterostructures

Authors: N. Lebedev, Y. Huang, A. Rana, D. Jannis, N. Gauquelin, J. Verbeeck, J. Aarts

Abstract: In this paper we study LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ structures with nominally x = 0, 0.1 and different thicknesses of the Eu$_{1-x}$La$_x$TiO$_3$ layer. We observe that both systems have many properties similar to previously studied LaAlO$_3$/EuTiO$_3$/SrTiO$_3$ and other oxide interfaces, such as the formation of a 2D electron liquid for 1 or 2 unit cells of Eu$_{1-x}$La$_x$TiO… ▽ More In this paper we study LaAlO$_3$/Eu$_{1-x}$La$_x$TiO$_3$/SrTiO$_3$ structures with nominally x = 0, 0.1 and different thicknesses of the Eu$_{1-x}$La$_x$TiO$_3$ layer. We observe that both systems have many properties similar to previously studied LaAlO$_3$/EuTiO$_3$/SrTiO$_3$ and other oxide interfaces, such as the formation of a 2D electron liquid for 1 or 2 unit cells of Eu$_{1-x}$La$_x$TiO$_3$; a metal-insulator transition driven by the thickness increase of Eu$_{1-x}$La$_x$TiO$_3$ layer; the presence of an Anomalous Hall effect (AHE) when driving the systems above the Lifshitz point with a backgate voltage; and a minimum in the temperature dependence of the sheet resistance below the Lifshitz point in the one-band regime, which becomes more pronounced with increasing gate voltage. However, and notwithstanding the likely presence of magnetism in the system, we do not attribute that minimum to the Kondo effect, but rather to the properties of SrTiO$_3$ crystal and the inevitable effects of charge trapping when using back gates. △ Less

Submitted 1 September, 2021; originally announced September 2021.

Comments: 9 pages, 6 figures

Quantum oscillations in an optically-illuminated two-dimensional electron system at the LaAlO$_3$/SrTiO$_3$ interface

Authors: I. Leermakers, K. Rubi, M. Yang, B. Kerdi, M. Goiran, W. Escoffier, A. S. Rana, A. E. M. Smink, A. Brinkman, H. Hilgenkamp, J. C. Maan, U. Zeitler

Abstract: We have investigated the illumination effect on the magnetotransport properties of a two-dimensional electron system at the LaAlO$_3$/SrTiO$_3$ interface. The illumination significantly reduces the zero-field sheet resistance, eliminates the Kondo effect at low-temperature, and switches the negative magnetoresistance into the positive one. A large increase in the density of high-mobility carriers… ▽ More We have investigated the illumination effect on the magnetotransport properties of a two-dimensional electron system at the LaAlO$_3$/SrTiO$_3$ interface. The illumination significantly reduces the zero-field sheet resistance, eliminates the Kondo effect at low-temperature, and switches the negative magnetoresistance into the positive one. A large increase in the density of high-mobility carriers after illumination leads to quantum oscillations in the magnetoresistance originating from the Landau quantization. The carrier density ($\sim 2 \times 10^{12}$ cm$^{-2}$) and effective mass ($\sim 1.7 ~m_e$) estimated from the oscillations suggest that the high-mobility electrons occupy the d$_{xz/yz}$ subbands of Ti:t$_{2g}$ orbital extending deep within the conducting sheet of SrTiO$_3$. Our results demonstrate that the illumination which induces additional carriers at the interface can pave the way to control the Kondo-like scattering and study the quantum transport in the complex oxide heterostructures. △ Less

Submitted 20 August, 2021; originally announced August 2021.

Direct observation of 3D topological spin textures and their interactions using soft x-ray vector ptychography

Authors: Arjun Rana, Chen-Ting Liao, Ezio Iacocca, Ji Zou, Minh Pham, Emma-Elizabeth Cating Subramanian, Yuan Hung Lo, Sinéad A. Ryan, Xingyuan Lu, Charles S. Bevis, Robert M. Karl Jr, Andrew J. Glaid, Young-Sang Yu, Pratibha Mahale, David A. Shapiro, Sadegh Yazdi, Thomas E. Mallouk, Stanley J. Osher, Henry C. Kapteyn, Vincent H. Crespi, John V. Badding, Yaroslav Tserkovnyak, Margaret M. Murnane, Jianwei Miao

Abstract: Magnetic topological defects are energetically stable spin configurations characterized by symmetry breaking. Vortices and skyrmions are two well-known examples of 2D spin textures that have been actively studied for both fundamental interest and practical applications. However, experimental evidence of the 3D spin textures has been largely indirect or qualitative to date, due to the difficulty of… ▽ More Magnetic topological defects are energetically stable spin configurations characterized by symmetry breaking. Vortices and skyrmions are two well-known examples of 2D spin textures that have been actively studied for both fundamental interest and practical applications. However, experimental evidence of the 3D spin textures has been largely indirect or qualitative to date, due to the difficulty of quantitively characterizing them within nanoscale volumes. Here, we develop soft x-ray vector ptychography to quantitatively image the 3D magnetization vector field in a frustrated superlattice with 10 nm spatial resolution. By applying homotopy theory to the experimental data, we quantify the topological charge of hedgehogs and anti-hedgehogs as emergent magnetic monopoles and probe their interactions inside the frustrated superlattice. We also directly observe virtual hedgehogs and anti-hedgehogs created by magnetically inert voids. We expect that this new quantitative imaging method will open the door to study 3D topological spin textures in a broad class of magnetic materials. Our work also demonstrates that magnetically frustrated superlattices could be used as a new platform to investigate hedgehog interactions and dynamics and to exploit optimized geometries for information storage and transport applications. △ Less

Submitted 26 April, 2021; originally announced April 2021.

X-ray linear dichroic ptychography

Authors: Yuan Hung Lo, Jihan Zhou, Arjun Rana, Drew Morrill, Christian Gentry, Bjoern Enders, Young-Sang Yu, Chang-Yu Sun, David Shapiro, Roger Falcone, Henry Kapteyn, Margaret Murnane, Pupa U. P. A. Gilbert, Jianwei Miao

Abstract: Biominerals such as seashells, corals skeletons, bone, and enamel are optically anisotropic crystalline materials with unique nano- and micro-scale organization that translates into exceptional macroscopic mechanical properties, providing inspiration for engineering new and superior biomimetic structures. Here we use particles of Seriatopora aculeata coral skeleton as a model and demonstrate, for… ▽ More Biominerals such as seashells, corals skeletons, bone, and enamel are optically anisotropic crystalline materials with unique nano- and micro-scale organization that translates into exceptional macroscopic mechanical properties, providing inspiration for engineering new and superior biomimetic structures. Here we use particles of Seriatopora aculeata coral skeleton as a model and demonstrate, for the first time, x-ray linear dichroic ptychography. We map the aragonite (CaCO3) crystal c-axis orientations in coral skeleton with 35 nm spatial resolution. Linear dichroic phase imaging at the O K-edge energy shows strong polarization-dependent contrast and reveals the presence of both narrow (< 35°) and wide (> 35°) c-axis angular spread in sub-micrometer coral particles. These x-ray ptychography results were corroborated using 4D scanning transmission electron nano-diffraction on the same particles. Evidence of co-oriented but disconnected corallite sub-domains indicates jagged crystal boundaries consistent with formation by amorphous nanoparticle attachment. Looking forward, we anticipate that x-ray linear dichroic ptychography can be applied to study nano-crystallites, interfaces, nucleation and mineral growth of optically anisotropic materials with sub-ten nanometers spatial resolution in three dimensions. △ Less

Submitted 2 September, 2020; originally announced September 2020.

Inhomogeneous superconductivity and quasilinear magnetoresistance at amorphous LaTiO3/SrTiO3 interfaces

Authors: N. Lebedev, M. Stehno, A. Rana, N. Gauquelin, J. Verbeeck, A. Brinkman, J. Aarts

Abstract: We have studied the transport properties of LaTiO3/SrTiO3 (LTO/STO) heterostructures. In spite of 2D growth observed in reflection high energy electron diffraction, Transmission Electron Microscopy images revealed that the samples tend to amorphize. Still, we observe that the structures are conducting, and some of them exhibit high conductance and/or superconductivity. We established that conducti… ▽ More We have studied the transport properties of LaTiO3/SrTiO3 (LTO/STO) heterostructures. In spite of 2D growth observed in reflection high energy electron diffraction, Transmission Electron Microscopy images revealed that the samples tend to amorphize. Still, we observe that the structures are conducting, and some of them exhibit high conductance and/or superconductivity. We established that conductivity arises mainly on the STO side of the interface, and shows all the signs of the 2-dimensional electron gas usually observed at interfaces between SrTiO3 and LaTiO3 or LaAlO3, including the presence of two electron bands and tunability with a gate voltage. Analysis of magnetoresistance (MR) and superconductivity indicates presence of a spatial fluctuations of the electronic properties in our samples. That can explain the observed quasilinear out-of-plane MR, as well as various features of the in-plane MR and the observed superconductivity. △ Less

Submitted 7 August, 2020; originally announced August 2020.

Comments: 10 pages, 6 figures, plus Supplementary Information

Determining the three-dimensional atomic structure of a metallic glass

Authors: Yao Yang, Jihan Zhou, Fan Zhu, Yakun Yuan, Dillan Chang, Dennis S. Kim, Minh Pham, Arjun Rana, Xuezeng Tian, Yonggang Yao, Stanley Osher, Andreas K. Schmid, Liangbing Hu, Peter Ercius, Jianwei Miao

Abstract: Amorphous solids such as glass are ubiquitous in our daily life and have found broad applications ranging from window glass and solar cells to telecommunications and transformer cores. However, due to the lack of long-range order, the three-dimensional (3D) atomic structure of amorphous solids have thus far defied any direct experimental determination without model fitting. Here, using a multi-com… ▽ More Amorphous solids such as glass are ubiquitous in our daily life and have found broad applications ranging from window glass and solar cells to telecommunications and transformer cores. However, due to the lack of long-range order, the three-dimensional (3D) atomic structure of amorphous solids have thus far defied any direct experimental determination without model fitting. Here, using a multi-component metallic glass as a proof-of-principle, we advance atomic electron tomography to determine the 3D atomic positions in an amorphous solid for the first time. We quantitatively characterize the short-range order (SRO) and medium-range order (MRO) of the 3D atomic arrangement. We find that although the 3D atomic packing of the SRO is geometrically disordered, some SRO connect with each other to form crystal-like networks and give rise to MRO. We identify four crystal-like MRO networks - face-centred cubic, hexagonal close-packed, body-centered cubic and simple cubic - coexisting in the sample, which show translational but no orientational order. These observations confirm that the 3D atomic structure in some parts of the sample is consistent with the efficient cluster packing model. Looking forward, we anticipate this experiment will open the door to determining the 3D atomic coordinates of various amorphous solids, whose impact on non-crystalline solids may be comparable to the first 3D crystal structure solved by x-ray crystallography over a century ago. △ Less

Submitted 17 October, 2020; v1 submitted 5 April, 2020; originally announced April 2020.

Journal ref: Nature 592, 60-64 (2021)

Gate-tuned Anomalous Hall Effect Driven by Rashba Splitting in Intermixed LaAlO3/GdTiO3/SrTiO3

Authors: N. Lebedev, M. Stehno, A. Rana, P. Reith, N. Gauquelin, J. Verbeeck, H. Hilgenkamp, A. Brinkman, J. Aarts

Abstract: The Anomalous Hall Effect (AHE) is an important quantity in determining the properties and understanding the behavior of the two-dimensional electron system forming at the interface of SrTiO3-based oxide heterostructures. The occurrence of AHE is often interpreted as a signature of ferromagnetism, but it is becoming more and more clear that also paramagnets may contribute to AHE. We studied the in… ▽ More The Anomalous Hall Effect (AHE) is an important quantity in determining the properties and understanding the behavior of the two-dimensional electron system forming at the interface of SrTiO3-based oxide heterostructures. The occurrence of AHE is often interpreted as a signature of ferromagnetism, but it is becoming more and more clear that also paramagnets may contribute to AHE. We studied the influence of magnetic ions by measuring intermixed LaAlO3/GdTiO3/SrTiO3 at temperatures below 10 K. We find that, as function of gate voltage, the system undergoes a Lifshitz transition, while at the same time an onset of AHE is observed. However, we do not observe clear signs of ferromagnetism. We argue the AHE to be due to the change in Rashba spin-orbit coupling at the Lifshitz transition and conclude that also paramagnetic moments which are easily polarizable at low temperatures and high magnetic filds lead to the presence of AHE, which needs to be taken into account when extracting carrier densities and mobilities. △ Less

Submitted 26 February, 2020; originally announced February 2020.

Comments: 11 pages, 8 figures; and supplement

Tailoring Vanadium Dioxide Film Orientation using Nanosheets: A Combined Microscopy, Diffraction, Transport and Soft X-ray in Transmission Study

Authors: Phu Tran Phong Le, Kevin Hofhuis, Abhi Rana, Mark Huijben, Hans Hilgenkamp, G. Rijnders, A. ten Elshof, Gertjan Koster, Nicolas Gauquelin, Gunnar Lumbeeck, Christian Schlüßler-Langeheine, Horia Popescu, F. Fortuna, Steef Smit, Xanthe H. Verbeek, Georgios Araizi-Kanoutas, Shrawan Mishra, Igor Vakivskyi, Hermann A. Durr, Mark S. Golden

Abstract: VO2 is a much-discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of vanadium dioxide (VO2) was realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X-ray transparent silicon nitride membranes. The out-of-plane orientation of the VO2 thin films was controlled at will between (011)M1/(110)R… ▽ More VO2 is a much-discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of vanadium dioxide (VO2) was realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X-ray transparent silicon nitride membranes. The out-of-plane orientation of the VO2 thin films was controlled at will between (011)M1/(110)R and (-402)M1/(002)R by coating the bulk substrates with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth. Temperature dependent X-ray diffraction and automated crystal orientation mapping in microprobe TEM mode (ACOM-TEM) characterized the high phase purity, the crystallographic and orientational properties of the VO2 films. Transport measurements and soft X-ray absorption in transmission are used to probe the VO2 metal-insulator transition, showing results of a quality equal to those from epitaxial films on bulk single-crystal substrates. Successful local manipulation of two different VO2 orientations on a single substrate is demonstrated using VO2 grown on lithographically-patterned lines of Ti0.87O2 and NbWO6 nanosheets investigated by electron backscatter diffraction. Finally, the excellent suitability of these nanosheet-templated VO2 films for advanced lensless imaging of the metal-insulator transition using coherent soft X-rays is discussed. △ Less

Submitted 25 January, 2019; originally announced January 2019.

Search for Origin of Room Temperature Ferromagnetism Properties in Ni doped ZnO Nanostructure

Authors: Amit Kumar Rana, Yogendra Kumar, Parasmani Rajput, S. N. Jha, D. Bhattacharyya, Parasharam M. Shirage

Abstract: The origin of room temperature (RT) ferromagnetism (FM) in Ni doped ZnO samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means… ▽ More The origin of room temperature (RT) ferromagnetism (FM) in Ni doped ZnO samples are systematically investigated through physical, optical, and magnetic properties of nanostructure, prepared by simple low-temperature wet chemical method. Reitveld refinement of X-ray diffraction pattern displays an increase in lattice parameters with strain relaxation and contraction in Zn/O occupancy ratio by means of Ni-doping. Similarly scanning electron microscope demonstrates modification in the morphology from nanorods to nanoflakes with Ni doping, suggests incorporation of Ni ions in ZnO. More interestingly, XANES (X-ray absorption near edge spectroscopy) measurements confirm that Ni is being incorporated in ZnO as Ni2+. EXAFS (Extended X-ray Absorption Fine Structure) analysis reveals that structural disorders near the Zn sites in the ZnO samples upsurges with increasing Ni concentration. Raman spectroscopy exhibits additional defect driven vibrational mode at 275 cm-1, appeared with Ni-doped sample only and the shift with broadening in 580 cm-1 peak, which manifests the presence of the oxygen vacancy (VO) related defects. Moreover, in photoluminescence (PL) spectra we observed peak appears at 524 nm, indicates the presence of singly ionized VO+, which may activate bound magnetic polarons (BMPs) in dilute magnetic semiconductors (DMSs). Magnetization measurements indicate weak ferromagnetism at RT, which rises with increasing Ni consolidation. It is therefore proposed that effect of the Ni-ions as well as the inherent exchange interactions rising from VO+ assist to produce BMPs, which are accountable for the RT-FM in Zn1-xNixO (0<x<0.125) system. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: ACS Applied Materials & Interfaces 9 (8), 7691-7700 (2017)

Growth of transparent Zn1-xSrxO films by facile wet chemical method: Effect of Sr doping on the structural, optical and sensing properties

Authors: Amit Kumar Rana, Rajasree Das, Yogendra Kumar, Somaditya Sen, Parasharam M. Shirage

Abstract: Sr doped ZnO nanorods thin films are prepared using wet chemical technique on transparent flexible substrate. Effect of Sr doping on structural and optical properties of ZnO is systematically investigated. The sensing property of the ZnO is enhanced by Sr doping and imitates as a promising material for future toxic and flammable gas sensor applications as well as for optoelectronic devices. Sr doped ZnO nanorods thin films are prepared using wet chemical technique on transparent flexible substrate. Effect of Sr doping on structural and optical properties of ZnO is systematically investigated. The sensing property of the ZnO is enhanced by Sr doping and imitates as a promising material for future toxic and flammable gas sensor applications as well as for optoelectronic devices. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: Applied Surface Science 379, 23-32 (2016)

Sr- and Ni-doping in ZnO nanorods synthesized by simple wet chemical method as excellent materials for CO and CO2 gas sensing

Authors: Parasharam M. Shirage, Amit Kumar Rana, Yogendra Kumar, Somaditya Sen, S. G. Leonardi, G. Neri

Abstract: In this study, the effect of Sr- and Ni-doping on microstructural, morphological and sensing properties of ZnO nanorods has been investigated. Nanorods with different Sr and Ni loadings were prepared using a simple wet chemical method and characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. XRD data confirmed that Sr- and Ni-dop… ▽ More In this study, the effect of Sr- and Ni-doping on microstructural, morphological and sensing properties of ZnO nanorods has been investigated. Nanorods with different Sr and Ni loadings were prepared using a simple wet chemical method and characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. XRD data confirmed that Sr- and Ni-doped samples maintainsthe wurtzite hexagonal structure of pure ZnO. However, unlikes Sr, Ni doping modifies the nanorod morphology, increases the surface area (SA) and decreases the ratio of IUV/Igreen photoluminescence peak to a greater extent. Sensing tests were performed on thick films resistive planar devices for monitoring CO and CO2, as indicators of indoor air quality.The effect of the operating temperature, nature and loading of dopant on the sensibility and selectivity of the fabricated sensors towards these two harmful gases were investigated. The gas sensing characteristics of Ni- and Sr-doped ZnO based sensors showed a remarkable enhancement (i. e. the response increased and shifted towards lower temperature for both gases) compared to ZnO-based one, demonstrating that these ZnO nanostructures are promising to fabricate sensor devices for monitoring indoor air quality. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: RSC Advances 6 (86), 82733-82742 (2016)

Synthesis of Ni doped ZnO nanostructures by low temperature wet chemical method and their enhanced field emission properties

Authors: Amit Kumar Rana, Prashant Bankar, Yogendra Kumar, Mahendra A. More, Dattatray J. Late, Parasharam M. Shirage

Abstract: In this study, we report the enhancement in field emission (FE) properties of ZnO nanostructure by Ni doping at the base pressure of ~1 x 10-8 mbar, which were grown by the simple wet chemical process. ZnO nanostructure shows single crystalline wurtzite structure up to Ni 10% doping. FESEM represents change in the nanostructure morphology from thick nanoneedles to nanoflakes via thin nanorods with… ▽ More In this study, we report the enhancement in field emission (FE) properties of ZnO nanostructure by Ni doping at the base pressure of ~1 x 10-8 mbar, which were grown by the simple wet chemical process. ZnO nanostructure shows single crystalline wurtzite structure up to Ni 10% doping. FESEM represents change in the nanostructure morphology from thick nanoneedles to nanoflakes via thin nanorods with increase in Ni doped ZnO. The turn-on field required to draw a field emission (FE) current density at 1μA/cm2 is found to be 2.5, 2.3, 1.8 and 1.7 V/μm for ZnO(Ni0%), ZnO(Ni5%), ZnO(Ni7.5%) and ZnO(Ni10%), respectively. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: RSC Advances 6 (106), 104318-104324 (2016)

Controlling of ZnO nanostructures by solute concentrationand its effect on growth, structural and optical properties

Authors: Yogendra Kumar, Amit Kumar Rana, Prateek Bhojane, Manojit Pusty, Vivas Bagwe, Somaditya Sen, Parasharam M. Shirage

Abstract: ZnO nanostructured films were prepared by chemical bath deposition method on glass substrates without any assistance of either microwave or high pressure autoclaves. The effect of solute concentration on the pure wurtzite ZnO nanostructure morphologies is studied. The controlling of the solute concentration help to control nano-structure in the form of nano-needles, and rods. ZnO nanostructured films were prepared by chemical bath deposition method on glass substrates without any assistance of either microwave or high pressure autoclaves. The effect of solute concentration on the pure wurtzite ZnO nanostructure morphologies is studied. The controlling of the solute concentration help to control nano-structure in the form of nano-needles, and rods. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: Materials Research Express 2(10),105017 (2015)

Enhancement of Two photon absorption with Ni doping in the dilute magnetic Semiconductor ZnO Crystalline Nanorods

Authors: Amit Kumar Rana, Aneesh. J, Yogendra Kumar, Arjunan. M. S, K. V. Adarsh, Somaditya Sen, Parasharam M. Shirage

Abstract: In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient beta increases by as much as 14 times i.e. 7.6 err 0.4 to 112 err 6 cm per GW, when the Ni doping is increased from 0 to 10 percent. The substa… ▽ More In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient beta increases by as much as 14 times i.e. 7.6 err 0.4 to 112 err 6 cm per GW, when the Ni doping is increased from 0 to 10 percent. The substantial enhancement in beta is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UVVis and photo luminescence spectroscopic, continuously red shift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: Applied Physics Letters, 107(23), 231907 (2015)

Controlling of ZnO nanostructures morphology for guiding the structural and optical properties

Authors: Amit Kumar Rana, Yogendra Kumar, Niharika Saxena, Rajasree Das, Somaditya Sen, Parasharam M. Shirage

Abstract: Most of the applications of the nano structures dependent on the morphology which affects the opto electronics properties. This research article provides a pathway of guiding optical properties like band-gap and fluorescence properties by controlled growth of nano-rods, -flowers, -needles or- tubes without external chemical doping, by simple hydro thermal method by controlling over synthesis param… ▽ More Most of the applications of the nano structures dependent on the morphology which affects the opto electronics properties. This research article provides a pathway of guiding optical properties like band-gap and fluorescence properties by controlled growth of nano-rods, -flowers, -needles or- tubes without external chemical doping, by simple hydro thermal method by controlling over synthesis parameter, temperature. △ Less

Submitted 31 August, 2017; originally announced August 2017.

Journal ref: AIP Advances, 5, 097118 (2015)

Soluble `Supersymmetric' Quantum XY Model

Authors: A. E. Rana, S. M. Girvin

Abstract: We present a `supersymmetric' modification of the $d$-dimensional quantum rotor model whose ground state is exactly soluble. The model undergoes a vortex-binding transition from insulator to metal as the rotor coupling is varied. The Hamiltonian contains three-site terms which are relevant: they change the universality class of the transition from that of the ($d+1$)--- to the $d$-dimensional cl… ▽ More We present a `supersymmetric' modification of the $d$-dimensional quantum rotor model whose ground state is exactly soluble. The model undergoes a vortex-binding transition from insulator to metal as the rotor coupling is varied. The Hamiltonian contains three-site terms which are relevant: they change the universality class of the transition from that of the ($d+1$)--- to the $d$-dimensional classical XY model. The metallic phase has algebraic ODLRO but the superfluid density is identically zero. Variational wave functions for single-particle and collective excitations are presented. △ Less

Submitted 20 January, 1993; originally announced January 1993.

Comments: 12 pages, REVTEX 3.0, IUCM93-001