Low-energy phonons and superconductivity in Sn0.8In0.2Te

We present neutron scattering measurements on low-energy phonons from a superconducting (Tc=2.7K) Sn0.8In0.2Te single-crystal sample. The longitudinal acoustic phonon mode and one transverse acoustic branch have been mapped out around the (002) Bragg peak for temperatures of 1.7 and 4.2 K. We observe a substantial energy width of the transverse phonons at energies comparable to twice the superconducting gap; however, there is no change in this width between the superconducting and normal states, and the precise origin of this energy width anomaly is not entirely clear. We also confirm that the compound is well ordered, with no indications of structural instability

Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

We report neutron inelastic scattering experiments on single-crystal PbMg1/3Nb2/3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4≤ω≤9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropic field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E. Our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled

Low-energy phonons and superconductivity in Sn0.8In0.2Te

We present neutron scattering measurements on low-energy phonons from a superconducting (Tc=2.7K) Sn0.8In0.2Te single-crystal sample. The longitudinal acoustic phonon mode and one transverse acoustic branch have been mapped out around the (002) Bragg peak for temperatures of 1.7 and 4.2 K. We observe a substantial energy width of the transverse phonons at energies comparable to twice the superconducting gap; however, there is no change in this width between the superconducting and normal states, and the precise origin of this energy width anomaly is not entirely clear. We also confirm that the compound is well ordered, with no indications of structural instability

Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

We report neutron inelastic scattering experiments on single-crystal PbMg1/3Nb2/3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4≤ω≤9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropic field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E. Our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled

First-order reversal curve of the magnetostructural phase transition in FeTe

We apply the first-order reversal curve (FORC) method, adapted from studies of ferromagnetic materials, to the magnetostructural phase transition of Fe1+yTe. FORC measurements reveal two features in the hysteretic phase transition, even in samples where traditional temperature measurements display only a single transition. For Fe1.13Te, the influence of magnetic field suggests that the main feature is primarily structural while a smaller, slightly higher-temperature transition is magnetic in origin. By contrast, Fe1.03Te has a single transition which shows a uniform response to magnetic field, indicating a stronger coupling of the magnetic and structural phase transitions. We also introduce uniaxial stress, which spreads the distribution width without changing the underlying energy barrier of the transformation. The work shows how FORC can help disentangle the roles of the magnetic and structural phase transitions in FeTe

First-order reversal curve of the magnetostructural phase transition in FeTe

We apply the first-order reversal curve (FORC) method, adapted from studies of ferromagnetic materials, to the magnetostructural phase transition of Fe1+yTe. FORC measurements reveal two features in the hysteretic phase transition, even in samples where traditional temperature measurements display only a single transition. For Fe1.13Te, the influence of magnetic field suggests that the main feature is primarily structural while a smaller, slightly higher-temperature transition is magnetic in origin. By contrast, Fe1.03Te has a single transition which shows a uniform response to magnetic field, indicating a stronger coupling of the magnetic and structural phase transitions. We also introduce uniaxial stress, which spreads the distribution width without changing the underlying energy barrier of the transformation. The work shows how FORC can help disentangle the roles of the magnetic and structural phase transitions in FeTe

Chiral magnetic effect in ZrTe 5

The chiral magnetic effect is the generation of an electric current induced by chirality imbalance in the presence of a magnetic field. It is a macroscopic manifestation of the quantum anomaly in relativistic field theory of chiral fermions (massless spin 1/2 particles with a definite projection of spin on momentum) - a remarkable phenomenon arising from a collective motion of particles and antiparticles in the Dirac sea. The recent discovery of Dirac semimetals with chiral quasiparticles opens a fascinating possibility to study this phenomenon in condensed matter experiments. Here we report on the measurement of magnetotransport in zirconium pentatelluride, ZrTe 5, that provides strong evidence for the chiral magnetic effect. Our angle-resolved photoemission spectroscopy experiments show that this material's electronic structure is consistent with a three-dimensional Dirac semimetal. We observe a large negative magnetoresistance when the magnetic field is parallel with the current. The measured quadratic field dependence of the magnetoconductance is a clear indication of the chiral magnetic effect. The observed phenomenon stems from the effective transmutation of a Dirac semimetal into a Weyl semimetal induced by parallel electric and magnetic fields that represent a topologically non-trivial gauge field background. We expect that the chiral magnetic effect may emerge in a wide class of materials that are near the transition between the trivial and topological insulators

Coexistence of superconductivity and short-range double-stripe spin correlations in Te-vapor annealed FeTe1-xSex (x≤0.2) COEXISTENCE of SUPERCONDUCTIVITY and SHORT- ⋯ ZHIJUN XU et al.

In as-grown bulk crystals of Fe1+yTe1-xSex with x≲0.3, excess Fe (y>0) is inevitable and correlates with a suppression of superconductivity. At the same time, there remains the question as to whether the character of the antiferromagnetic correlations associated with the enhanced anion height above the Fe planes in Te-rich samples is compatible with superconductivity. To test this, we have annealed as-grown crystals with x=0.1 and 0.2 in Te vapor, effectively reducing the excess Fe and inducing bulk superconductivity. Inelastic neutron scattering measurements reveal low-energy magnetic excitations consistent with short-range correlations of the double-stripe type; nevertheless, cooling into the superconducting state results in a spin gap and a spin resonance, with the extra signal in the resonance being short range with a mixed single-stripe/double-stripe character, which is different than other iron-based superconductors. The mixed magnetic character of these superconducting samples does not appear to be trivially explainable by inhomogeneity