A5060917865- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- High-pressure geophysics and materials
- Graphene research and applications
- Iron-based superconductors research
- Boron and Carbon Nanomaterials Research
- Magnetic properties of thin films
- ZnO doping and properties
- Rare-earth and actinide compounds
- Superconducting Materials and Applications
- MXene and MAX Phase Materials
- Quantum and electron transport phenomena
- Crystal Structures and Properties
- Multiferroics and related materials
- Superconductivity in MgB2 and Alloys
- Plasmonic and Surface Plasmon Research
- Surface and Thin Film Phenomena
- Diamond and Carbon-based Materials Research
- Near-Field Optical Microscopy
- Photonic and Optical Devices
- Copper-based nanomaterials and applications
- Ferroelectric and Piezoelectric Materials
- Dielectric properties of ceramics
Yale University
2016-2024
Fairfield University
2024
Stony Brook University
2022
Columbia University
2022
Binghamton University
2022
University of New Haven
2019
Brookhaven National Laboratory
2006-2014
Port Washington Public Library
2012
Brookhaven College
2004-2009
University of Akron
2009
The question of how thin cuprate layers can be while still retaining high-temperature superconductivity (HTS) has been challenging to address, in part because experimental studies require the synthesis near-perfect ultrathin HTS and ways profile superconducting properties such as critical temperature superfluid density across interfaces with atomic resolution. We used atomic-layer molecular beam epitaxy synthesize bilayers a metal (La(1.65)Sr(0.45)CuO4) insulator (La2CuO4) which each layer...
Low energy polarized electronic Raman scattering of the electron-doped superconductor Nd2-x Ce x CuO4 ( = 0.15, T(c) 22 K) has revealed a nonmonotonic d(x(2)-y(2)) superconducting order parameter. It maximum gap 4.4k(B)T(c) at Fermi surface intersections with an antiferromagnetic Brillouin zone (the "hot spots") and smaller 3.3k(B)T(c) fermionic boundaries. The enhancement in vicinity hot spots emphasizes role fluctuations similarity origin superconductivity for electron- hole-doped cuprates.
We use resonant soft x-ray scattering (RSXS) to quantify the hole distribution in a superlattice of insulating La2CuO4 (LCO) and overdoped La2-xSrxCuO4 (LSCO). Despite its nonsuperconducting constituents, this structure is superconducting with T_{c}=38 K. found that conducting holes redistribute electronically from LSCO LCO layers. The layers were be optimally doped, suggesting they are main drivers superconductivity. Our results demonstrate utility RSXS for separating electronic structural...
Tungsten oxide and its associated bronzes (compounds of tungsten an alkali metal) are well known for their interesting optical electrical characteristics. We have modified the transport properties thin WO 3 films by electrolyte gating using both ionic liquids polymer electrolytes. able to tune resistivity gated film more than five orders magnitude, a clear insulator-to-metal transition is observed. To clarify doping mechanism, we performed series incisive operando experiments, ruling out...
Abstract Borophene, an atomically thin covalently bonded boron sheet, has attracted great attention as a novel quantum material because of its structural tunability and potential utilization in flexible transparent electronics. So far, borophene been synthesized on silver or copper single crystals, but these substrates are small, very expensive, unsuitable for study transport properties electronics applications. Here, we report synthesis nanometer-scale thick Cu(111) films grown sapphire. We...
We used transport and Raman scattering measurements to identify the insulating state of self-doped spin 1/2 two-leg ladders Sr_{14}Cu_{24}O_{41} as a weakly pinned, sliding density wave with non-linear conductivity giant dielectric response that persists remarkably high temperatures.
Polaritons are light-matter quasiparticles that govern the optical response of quantum materials at nanoscale, enabling on-chip communication and local sensing. Here, we report Landau-phonon polaritons (LPPs) in magnetized charge-neutral graphene encapsulated hexagonal boron nitride (hBN). These emerge from interaction Dirac magnetoexciton modes with hyperbolic phonon polariton hBN. Using infrared magneto-nanoscopy, reveal ability to completely halt LPP propagation real space quantized...
For ${\mathrm{CaCu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}$---an insulator that exhibits a giant dielectric response above 100 K---${\mathrm{Cu}}^{2+}$ antiferromagnetic spin ordering has been investigated by magnetic Raman scattering and magnetization measurements. Below the N\'eel temperature, ${T}_{N}=25\mathrm{K},$ excitations have identified. Above ${T}_{N}$ spectra reveal short-range fluctuations increase with cooling like ${T}^{\ensuremath{-}1}.$ No deviations from Curie-Weiss law...
Neutron diffraction was used to determine the crystal structure and magnetic ordering pattern of a ${\mathrm{La}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}$ single crystal, with without applied field. A previously unreported, subtle monoclinic distortion away from orthorhombic space group $Bmab$ detected. The is also present in lightly Sr-doped crystals. refinement shows that deviation symmetry predominantly determined drive continuous reorientation copper spins $b$ axis $c$ axis, directly confirming...
The electron-doped cuprates Pr_{2-x}Ce_xCuO_4 and Nd_{2-x}Ce_xCuO_4 have been studied by electronic Raman spectroscopy across the entire region of superconducting (SC) phase diagram. SC pairing strength is found to be consistent with a weak-coupling regime except in under-doped where we observe an in-gap collective mode at 4.5 k_{B}T_c while maximum amplitude gap ~8 k_{B}T_{c}. In normal state, doped carriers divide into coherent quasi-particles (QPs) that remain incoherent. QPs mainly...
The magnetic penetration depth (λ) in thin superconducting films is usually measured by the mutual inductance technique. accuracy of this method has been limited uncertainties geometry solenoids and film position thickness, parasitic coupling between coils, etc. Here, we present several improvements apparatus method. To ensure precise thickness layer, engineer at atomic level using atomic-layer-by-layer molecular beam epitaxy. In way, also eliminate secondary-phase precipitates, grain...
We present information on the temperature-dependent changes of complex pseudodielectric function in high-${T}_{c}$ superconductor ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8\ensuremath{-}\ensuremath{\delta}}$ by means spectroscopic ellipsometry. reveal existence three distinct spectral regions. Below 2 eV, there are dielectric associated with free-carrier response. In slightly underdoped compounds we find at around 3 eV a strong rise ${\ensuremath{\epsilon}}_{2}$...
The magnetic phase diagram of La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$ thin films grown on single-crystal LaSrAlO${}_{4}$ substrates has been determined by low-energy muon-spin rotation. shows the same features as one bulk La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$, but transition temperatures between distinct states are significantly different. In antiferromagnetic N\'eel temperature ${T}_{\mathrm{N}}$ is strongly reduced, and no hole spin freezing observed at low temperatures....
We study long wavelength magnetic excitations in lightly doped ${\mathrm{L}\mathrm{a}}_{2\ensuremath{-}x}{\mathrm{S}\mathrm{r}}_{x}{\mathrm{C}\mathrm{u}\mathrm{O}}_{4}$ ($x\ensuremath{\le}0.03$) detwinned crystals. The lowest energy anisotropy induced gap can be understood terms of the antisymmetric spin interaction inside antiferromagnetic (AF) phase. second resonance, analyzed in-plane anisotropy, shows unconventional behavior within AF state; it led to discovery collective pertaining a...
Using low-energy time-of-flight scattering and recoil spectroscopy (TOFSARS) mass of recoiled ions (MSRI) we analyze the surface structure an atomically smooth $\mathrm{Ba}\mathrm{Bi}{\mathrm{O}}_{3}$ film grown by molecular beam epitaxy. We demonstrate high sensitivity TOFSARS MSRI spectra to slight changes in orientation ion plane with respect crystallographic axes. The observed angle dependence allows us clearly identify termination layer as $\mathrm{Bi}{\mathrm{O}}_{2}$. Our data also...
The two-magnon (2M) excitation at 3000 cm(-1) in Sr14Cu24O41 two-leg ladder is studied by Raman scattering. A slight anisotropy of the superexchange coupling J(perpendicular)/J(parallel) approximately 0.8 with J(parallel) = 110+/-20 meV proposed from analysis magnetic resonant across charge transfer gap increases 2M intensity orders magnitude. scattering dependent upon energy. relaxation found to be correlated temperature electronic continuum low frequencies.
We show, by means of low-energy muon-spin rotation measurements, that few-unit-cells thick La(2)CuO(4) layers synthesized digitally molecular beam epitaxy are antiferromagnetically ordered. Below a thickness about 5 CuO(2) the long-range ordered state breaks down, and magnetic appears with enhanced quantum fluctuations reduced spin stiffness. This can exist in close proximity (few Å) to high-temperature superconducting layers, without transmitting supercurrents.
Electron density oscillations with acoustic dispersions and sustained at boundaries between different media provide information about surface interface properties of hetero-structures. In ultra-thin metallic films these plasmonic excitations are heavily damped. Superconductivity is predicted to reduce dissipation allowing detection resonances. Emerging low-loss Cooper-pair waves have been studied before, however, the observation surface-confined Josephson plasmons has remained elusive. Here,...