77 research outputs found
Probing the interplay between surface and bulk states in the topological Kondo insulator SmB through conductance fluctuation spectroscopy
We present results of resistance fluctuation spectroscopy on single crystals
of the predicted Kondo topological insulator material SmB. Our measurements
show that at low temperatures, transport in this system takes place only
through surface states. The measured noise in this temperature range arises due
to Universal Conductance Fluctuations whose statistics was found to be
consistent with theoretical predictions for that of two-dimensional systems in
the Symplectic symmetry class. At higher temperatures, we find signatures of
glassy dynamics and establish that the measured noise is caused by mobility
fluctuations in the bulk. We find that, unlike the topological insulators of
the dichalcogenide family, the noise in surface and bulk conduction channels in
SmB are completely uncorrelated. Our measurements establish that at
sufficiently low temperatures, the bulk has no discernible contribution to
electrical transport in SmB making it an ideal platform for probing the
physics of topological surface states.Comment: 9 pages, 11 figure
Robust local and non-local transport in the Topological Kondo Insulator SmB in the presence of high magnetic field
SmB has been predicted to be a Kondo Topological Insulator with
topologically protected conducting surface states. We have studied
quantitatively the electrical transport through surface states in high quality
single crystals of SmB. We observe a large non-local surface signal at
temperatures lower than the bulk Kondo gap scale. Measurements and finite
element simulations allow us to distinguish unambiguously between the
contributions from different transport channels. In contrast to general
expectations, the electrical transport properties of the surface channels was
found to be insensitive to high magnetic fields. Local and non-local
magnetoresistance measurements allowed us to identify definite signatures of
helical spin states and strong inter-band scattering at the surface.Comment: 7 pages, 8 figures, 1 tabl
Structural and Magnetic Investigations of Single-Crystals of the Neodymium Zirconate Pyrochlore, Nd2Zr2O7
We report structural and magnetic properties studies of large high quality
single-crystals of the frustrated magnet, NdZrO. Powder x-ray
diffraction analysis confirms that NdZrO adopts the pyrochlore
structure. Room-temperature x-ray diffraction and time-of-flight neutron
scattering experiments show that the crystals are stoichiometric in composition
with no measurable site disorder. The temperature dependence of the magnetic
susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits
to the magnetic susceptibility data using a Curie-Weiss law reveal a
ferromagnetic coupling between the Nd moments. Magnetization versus field
measurements show a local Ising anisotropy along the axes of the
Nd ions in the ground state. Specific heat versus temperature
measurements in zero applied magnetic field indicate the presence of a thermal
anomaly below K, but no evidence of magnetic ordering is observed down
to 0.5 K. The experimental temperature dependence of the single-crystal bulk dc
susceptibility and isothermal magnetization are analyzed using crystal field
theory and the crystal field parameters and exchange coupling constants
determined.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in Physical
Review
Surface resonance of the (2×1) reconstructed lanthanum hexaboride (001)-cleavage plane : a combined STM and DFT study
We performed a combined study of the (001)-cleavage plane of lanthanum hexaboride (LaB6) using scanning tunneling microscopy and density-functional theory (DFT). Experimentally, we found a (2×1) reconstructed surface on a local scale. The reconstruction is only short-range ordered and tends to order perpendicularly to step edges. At larger distances from surface steps, the reconstruction evolves to a labyrinthlike pattern. These findings are supported by low-energy electron diffraction experiments. Slab calculations within the framework of DFT show that the atomic structure consists of parallel lanthanum chains on top of boron octahedra. Scanning tunneling spectroscopy shows a prominent spectral feature at −0.6eV. Using DFT, we identify this structure as a surface resonance of the (2×1) reconstructed LaB6 (100) surface which is dominated by boron dangling bond states and lanthanum d states
Surface analysis of the PrB6 (001) cleavage plane by scanning tunneling microscopy and spectroscopy
Scanning tunneling microscopy and spectroscopy were performed on the (001) cleavage plane of praseodymium hexaboride (PrB6). We found three different ordered morphologies, namely, a chainlike (2 × 1) reconstruction and two uniform terminations. The chainlike (2 × 1) reconstruction is rationalized as parallel Pr rows on top of a complete B6 network. The two uniform terminations are identified as complete Pr or B6 layers. Although the uniform terminations could be expected to be simply (1 × 1) reconstructed, one of them shows a rather stripelike atomic corrugation for close tip-sample distances. All morphologies share two spectral features at −0.2 and +0.2 eV around EF. In addition, one uniform termination shows an additional peak in the differential conductance at −0.7 eV. Similarly, the chainlike (2 × 1) reconstruction reveals a feature in the differential conductance at −1.1 eV when moving the tip closer to the surface. The distance dependency points towards rather localized electronic states, which we tentatively attribute to a 4 f -related feature
Observation of magnetic fragmentation in spin ice
Fractionalised excitations that emerge from a many body system have revealed
rich physics and concepts, from composite fermions in two-dimensional electron
systems, revealed through the fractional quantum Hall effect, to spinons in
antiferromagnetic chains and, more recently, fractionalisation of Dirac
electrons in graphene and magnetic monopoles in spin ice. Even more surprising
is the fragmentation of the degrees of freedom themselves, leading to
coexisting and a priori independent ground states. This puzzling phenomenon was
recently put forward in the context of spin ice, in which the magnetic moment
field can fragment, resulting in a dual ground state consisting of a
fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic
monopole crystal. Here we show, by means of neutron scattering measurements,
that such fragmentation occurs in the spin ice candidate NdZrO. We
observe the spectacular coexistence of an antiferromagnetic order induced by
the monopole crystallisation and a fluctuating state with ferromagnetic
correlations. Experimentally, this fragmentation manifests itself via the
superposition of magnetic Bragg peaks, characteristic of the ordered phase, and
a pinch point pattern, characteristic of the Coulomb phase. These results
highlight the relevance of the fragmentation concept to describe the physics of
systems that are simultaneously ordered and fluctuating.Comment: accepted in Nature Physic
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