A5038372434- Advanced Condensed Matter Physics
- Multiferroics and related materials
- Rare-earth and actinide compounds
- Topological Materials and Phenomena
- Magnetic and transport properties of perovskites and related materials
- Nuclear materials and radiation effects
- Physics of Superconductivity and Magnetism
- High-pressure geophysics and materials
- Theoretical and Computational Physics
- Ferroelectric and Piezoelectric Materials
- Crystal Structures and Properties
- Superconducting Materials and Applications
- Magnetic Properties of Alloys
- Solidification and crystal growth phenomena
- Solid-state spectroscopy and crystallography
- Electronic and Structural Properties of Oxides
- Magnetic properties of thin films
- Iron-based superconductors research
- Geological and Geochemical Analysis
- Metallurgical Processes and Thermodynamics
- Quantum Chromodynamics and Particle Interactions
- ZnO doping and properties
- Nuclear Physics and Applications
- Quantum many-body systems
- Atomic and Subatomic Physics Research
Johns Hopkins University
2015-2024
University of Baltimore
2018
University of Birmingham
2005-2012
Multiferroics have attracted strong interest for potential applications where electric fields control magnetic order. The ultimate speed of via magnetoelectric coupling, however, remains largely unexplored. Here, we report an experiment in which drove spin dynamics multiferroic TbMnO3 with intense few-cycle terahertz (THz) light pulse tuned to resonance electromagnon, electric-dipole active excitation. We observed the resulting motion using time-resolved resonant soft x-ray diffraction. Our...
Optical reflectivity experiments on Cd${}_{3}$As${}_{2}$ indicate the presence of Kane electrons rather than Dirac fermions in this material. The results contradict those from recent ARPES experiments, but agree with STM results.
Inelastic neutron scattering reveals a broad continuum of excitations in ${\mathrm{Pr}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$, the temperature and magnetic field dependence which indicate continuous distribution quenched transverse fields ($\mathrm{\ensuremath{\Delta}}$) acting on non-Kramers ${\mathrm{Pr}}^{3+}$ crystal ground state doublets. Spin-ice correlations are apparent within 0.2 meV Zeeman energy. A random phase approximation provides an excellent account data with...
Using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator ${\mathrm{SmB}}_{6}$ and describe its relation to low energy insulating band structure. The intensity is confined $X$ $R$ high symmetry points, repeating outside first Brillouin zone dispersing less than 2 meV, with $5d$-like magnetic form factor. We present slave-boson treatment of Anderson Hamiltonian third neighbor dominated hybridized This approach produces spin exciton below...
Kink bound states in the one-dimensional ferromagnetic Ising chain compound CoNb2O6 have been studied using high-resolution time-domain terahertz spectroscopy zero applied magnetic field. When order develops at low temperature, nine of kinks become visible. Their energies can be modeled exceedingly well by Airy function solutions to a 1D Schrödinger equation with linear confining potential. This sequence terminates threshold energy near 2 times lowest state. Above this scale we observe broad...
Topological insulators such as SmB${}_{6}$ have widespread uses in spintronics and quantum computation applications. New experiments suggest that the low-temperature conductivity of can be modulated via carbon doping, providing a chemical way to control resistivity.
A series of ${\mathrm{Yb}}_{2+x}{\mathrm{Ti}}_{2\ensuremath{-}x}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ doped samples demonstrates the effects off-stoichiometry on ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$'s structure, properties, and magnetic ground state via x-ray diffraction, specific heat, magnetization measurements. stoichiometric single crystal ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ grown by traveling solvent floating zone technique (solvent = 30 wt...
Abstract The transverse Ising magnet Hamiltonian describing the chain in a magnetic field is archetypal example of system that undergoes transition at quantum critical point (QCP). columbite CoNb 2 O 6 closest realization found to date. At low temperatures, neutron diffraction has observed set discrete collective spin modes near QCP. Here, we ask if there are low-lying excitations distinct from these relatively high-energy modes. Using heat capacity, show significant band gapless exists....
The Kondo insulator SmB$_6$ has long been known to display anomalous transport behavior at low temperatures, T$<5$ K. In this temperatures range, a plateau is observed in the dc resistivity, contrary exponential divergence expected for gapped system. Recent theoretical calculations suggest that may be first topological (TKI) and propose residual conductivity due surface states which reside within gap. Since TKI prediction many experiments have claimed observe high mobility perfectly...
We report a comprehensive inelastic neutron-scattering study of the frustrated pyrochlore antiferromagnet MgCr2O4 in its cooperative paramagnetic regime. Theoretical modeling yields microscopic Heisenberg model with exchange interactions up to third-nearest neighbors, which quantitatively explains all details dynamic magnetic response. Our work demonstrates that excitations are faithfully represented entire Brillouin zone by theory magnons propagating highly-correlated background. results...
We present a magnetic phase diagram of rare-earth pyrochlore ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ in $⟨111⟩$ field. Using heat capacity, magnetization, and neutron scattering data, we show an unusual field dependence first-order boundary, wherein small applied increases the ordering temperature. The zero-field ground state has ferromagnetic domains, while spins polarize along above 0.65 T. A classical Monte Carlo analysis published Hamiltonians does account for critical low...
We describe why Ising spin chains with competing interactions in $\rm SrHo_2O_4$ segregate into ordered and disordered ensembles at low temperatures ($T$). Using elastic neutron scattering, magnetization, specific heat measurements, the two distinct are inferred to have N\'eel ($\uparrow\downarrow\uparrow\downarrow$) double-N\'eel ($\uparrow\uparrow\downarrow\downarrow$) ground states respectively. Below $T_\mathrm{N}=0.68(2)$~K, develop three dimensional (3D) long range order (LRO), which...
Abstract Recent theoretical and experimental findings suggest the long-known but not well understood low temperature resistance plateau of SmB 6 may originate from protected surface states arising a topologically non-trivial bulk band structure having strong Kondo hybridization. Yet others have ascribed this feature to impurities, vacancies reconstructions. Given typical methods used prepare single crystals, flux floating-zone procedures, such ascriptions should be taken lightly. We...
We explore the stability of hybridization gap in ${\mathrm{SmB}}_{6}$ to presence a small number Sm vacancies typical for this material, and demonstrate extreme fragility Kondo insulating state. For most stoichiometric sample we detect which appears below 50 K as depressed electronic Raman intensity about 30 meV. The spectral weight that shifts higher frequencies on opening forms two maxima at 100 41 assign these excitations between hybridized $4f\ensuremath{-}5d$ bands using recent band...
We document the coexistence of ferro- and anti-ferromagnetism in pyrochlore $\rm Yb_2Ti_2O_7$ using three neutron scattering techniques on stoichiometric crystals: elastic shows a canted ferromagnetic ground state, spin wave excitations from both ferro-and an antiferro-magnetic field temperature dependent small angle reveals corresponding anisotropic magnetic domain structure. High-field $\langle 111 \rangle$ fits show that is extremely close to antiferromagnetic phase boundary. Classical...
We report the discovery of surface states in perovskite superconductor [Tl4]TlTe3 (Tl5Te3) and its nonsuperconducting tin-doped derivative [Tl4](Tl0.4Sn0.6)Te3 as observed by angle-resolved photoemission spectroscopy. Density functional theory calculations predict that are protected a Z2 topology bulk band structure. Specific heat magnetization measurements show Tl5Te3 has superconducting volume fraction excess 95%. Thus is an ideal material which to study interplay superconductivity.
The thermal conductivity of CoNb${}_{2}$O${}_{6}$ is suppressed around its quantum critical point whereas the specific heat enhanced, highlighting role frustration in determining magnetic excitations.
<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>MgCr</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>4</a:mn></a:msub></a:mrow></a:math> is one of the best-known realizations pyrochlore-lattice Heisenberg antiferromagnet. The strong antiferromagnetic exchange interactions are perturbed by small further-neighbor exchanges such that this compound may in principle realize a spiral spin liquid (SSL) phase zero-temperature limit. However,...
We performed ultrafast time-resolved near-infrared pump, resonant soft x-ray diffraction probe measurements to investigate the coupling between photoexcited electronic system and spin cycloid magnetic order in multiferroic $\mathrm{TbMn}{\mathrm{O}}_{3}$ at low temperatures. observe melting of long range antiferromagnetic excitation fluences with a decay time constant $22.3\ifmmode\pm\else\textpm\fi{}1.1\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$, which is much slower than \ensuremath{\sim}1 ps...
NiNb$_{2}$O$_{6}$ is an almost ideal realization of a 1D spin-1 ferromagnetic Heisenberg chain compound with weak unidirectional anisotropy. Using time-domain THz spectroscopy, we measure the low-energy electrodynamic response as function temperature and external magnetic field. At low temperatures, find magnon-like spin-excitation, which corresponds to lowest energy excitation at $q\sim0$. higher unexpectedly observe temperature-dependent renormalization spin-excitation energy, has strong...
The thermal conductivity $\kappa$ of the Kondo insulator SmB$_6$ was measured at low temperature, down to 70 mK, in magnetic fields up 15 T, on single crystals grown using both floating-zone and flux methods. residual linear term $\kappa_0/T$ $T \to 0$ is found be zero all samples, for fields, agreement with previous studies. There therefore no clear evidence fermionic heat carriers. In contrast some prior data, we observe a large enhancement $\kappa(T)$ increasing field. effect field...