Metamaterials exhibit numerous novel effects and operate over a large portion of the electromagnetic spectrum. Metamaterial devices based on these effects include gradient-index lenses, modulators ...for terahertz radiation and compact waveguides. The resonant nature of metamaterials results in frequency dispersion and narrow bandwidth operation where the centre frequency is fixed by the geometry and dimensions of the elements comprising the metamaterial composite. The creation of frequency-agile metamaterials would extend the spectral range over which devices function and, further, enable the manufacture of new devices such as dynamically tunable notch filters. Here, we demonstrate such frequency-agile metamaterials operating in the far-infrared by incorporating semiconductors in critical regions of metallic split-ring resonators. For this first-generation device, external optical control results in tuning of the metamaterial resonance frequency by ∼20%. Our approach is integrable with current semiconductor technologies and can be implemented in other regions of the electromagnetic spectrum.
Phase-change materials are functionally important materials that can be thermally interconverted between metallic (crystalline) and semiconducting (amorphous) phases on a very short time scale. ...Although the interconversion appears to involve a change in local atomic coordination numbers, the electronic basis for this process is still unclear. Here, we demonstrate that in a nearly vacancy-free binary GeSb system where we can drive the phase change both thermally and, as we discover, by pressure, the transformation into the amorphous phase is electronic in origin. Correlations between conductivity, total system energy, and local atomic coordination revealed by experiments and long time ab initio simulations show that the structural reorganization into the amorphous state is driven by opening of an energy gap in the electronic density of states. The electronic driving force behind the phase change has the potential to change the interconversion paradigm in this material class.
MHz conductivity, torque magnetometer, and magnetization measurements are reported on single crystals of CeOs4Sb12 and NdOs4Sb12 using temperatures down to 0.5 K and magnetic fields of up to 60 ...tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the 010 and 01¯1 directions. The results indicate that NdOs4Sb12 has a similar Fermi surface topology to that of the unusual superconductor PrOs4Sb12, but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs4Sb12. By contrast, CeOs4Sb12 undergoes a field-induced transition from an unusual semimetal into a high-field, high-temperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the band structure lead us to propose that the field-induced phase transition in CeOs4Sb12 is similar in origin to the well-known α−γ transition in Ce and its alloys.
MHz conductivity, torque magnetometer and magnetization measurements are
reported on single crystals of CeOs$_4$Sb$_{12}$ and NdOs$_4$Sb$_{12}$ using
temperatures down to 0.5~K and magnetic fields of ...up to 60~tesla. The
field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas
oscillations is deduced by rotating the samples about the $010$ and
$0\bar{1}1$ directions. The results indicate that NdOs$_4$Sb$_{12}$ has a
similar Fermi surface topology to that of the unusual superconductor
PrOs$_4$Sb$_{12}$, but with significantly smaller effective masses, supporting
the importance of local phonon modes in contributing to the low-temperature
heat capacity of NdOs$_4$Sb$_{12}$. By contrast, CeOs$_4$Sb$_{12}$ undergoes a
field-induced transition from an unusual semimetal into a high-field,
high-temperature state characterized by a single, almost spherical
Fermi-surface section. The behavior of the phase boundary and comparisons with
models of the bandstructure lead us to propose that the field-induced phase
transition in CeOs$_4$Sb$_{12}$ is similar in origin to the well-known
$\alpha-\gamma$ transition in Ce and its alloys.
A quantum spin liquid (QSL) is a state of matter in which magnetic spins interact strongly, but quantum fluctuations inhibit long-range magnetic order even at zero temperature. A QSL has been ...predicted to have a host of exotic properties, including fractionalized excitations and long-range quantum entanglement. Despite the numerous theoretical studies, experimental realization of a QSL has proved to be challenging due to the lack of candidate materials. The triangular organic salts EtMe3SbPd(dmit)22 and {\kappa}-(BEDT-TTF)2Cu2(CN)3, and kagome ZnCu3(OH)6Cl2 (Herbertsmithite) have recently emerged as promising candidates of exhibiting a QSL state, but the nature of their ground states is still elusive. Here we studied a large-area high-quality single crystal of Herbertsmithite by means of time-domain terahertz (THz) spectroscopy. We observed in the low-frequency (0.6-2.2 THz) optical conductivity evidence for the nature of the spin system. In particular, the in-plane absorption spectrum exhibits a unique frequency dependence that can be described by a power-law with an exponent of approximately 1.4, in sharp contrast with the {\omega}^4 dependence expected for an ordered Mott insulator. The absorption is also found to increase as the temperature decreases, a behavior unexpected for conventional insulators. Such features are consistent with recent theory based on the interactions between the charge and spin degrees of freedom in a QSL system.
MHz conductivity, torque magnetometer and magnetization measurements are reported on single crystals of CeOs\(_4\)Sb\(_{12}\) and NdOs\(_4\)Sb\(_{12}\) using temperatures down to 0.5~K and magnetic ...fields of up to 60~tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the \(010\) and \(0\bar{1}1\) directions. The results indicate that NdOs\(_4\)Sb\(_{12}\) has a similar Fermi surface topology to that of the unusual superconductor PrOs\(_4\)Sb\(_{12}\), but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs\(_4\)Sb\(_{12}\). By contrast, CeOs\(_4\)Sb\(_{12}\) undergoes a field-induced transition from an unusual semimetal into a high-field, high-temperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the bandstructure lead us to propose that the field-induced phase transition in CeOs\(_4\)Sb\(_{12}\) is similar in origin to the well-known \(\alpha-\gamma\) transition in Ce and its alloys.
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