Magnetic domain depinning as possible evidence for two ferromagnetic phases in LaCrGe3_3

Two ferromagnetic phases, FM1 and FM2, were first proposed to exist in LaCrGe$_3$ based on a broad maximum in the temperature derivative of resistivity resembling that of the superconducting ferromagnet UGe$_2$ where FM1 and FM2 are well-established. While evidence for two FM phases can be found in certain additional probes, corresponding anomalies in magnetization have not been recognized until now. Our spatially-resolved images of the magnetic domains show a substantial change in the domain structure between the higher temperature FM1 phase and the lower temperature FM2 phase. Furthermore, our measurements of the coercive field and virgin magnetization curves reveal an unconventional magnetic domain pinning region in the FM1 phase, followed by a depinning region at lower temperatures where the system is reported to crossover into the FM2 phase. We incorporate this discovery into a simple domain magnetization model that demystifies the magnetization curve seen in all previous studies. Finally, we find that the unusual domain behavior can be explained by a change in the ferromagnetic exchange interaction and magnetic moment, both of which are consistent with the existence of two FM phases. This revelation may help explain a range of anomalous behaviors observed in LaCrGe$_3$ and rekindles the discussion about the prevalence of multiple FM phases in fragile FM systems.Comment: 7+8 pages, 4+8 figures. Revised with suggestions from refere

Topological surface states above the Fermi energy in Hf2Te2P\textrm{Hf}_{2}\textrm{Te}_2\textrm{P}

We report a detailed experimental study of the band structure of the recently discovered topological material $\textrm{Hf}_{2}\textrm{Te}_2\textrm{P}$. Using the combination of scanning tunneling spectroscopy and angle-resolved photo-emission spectroscopy with surface K-doping, we probe the band structure of $\textrm{Hf}_{2}\textrm{Te}_2\textrm{P}$ with energy and momentum resolution above the Fermi level. Our experiments show the presence of multiple surface states with a linear Dirac-like dispersion, consistent with the predictions from previously reported band structure calculations. In particular, scanning tunneling spectroscopy measurements provide the first experimental evidence for the strong topological surface state predicted at 460 meV, which stems from the band inversion between Hf-d and Te-p orbitals. This band inversion comprised of more localized d-states could result in a better surface-to-bulk conductance ratio relative to more traditional topological insulators.Comment: Supplementary materials available upon reques

Long range order and two-fluid behavior in heavy electron materials

The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we have extended Knight shift measurements to URu$_2$Si$_2$, CeIrIn$_5$ and CeRhIn$_5$. In CeRhIn$_5$ we find that the antiferromagnetic order is preceded by a relocalization of the Kondo liquid, providing independent evidence for a local moment origin of antiferromagnetism. In URu$_2$Si$_2$ the hidden order is shown to emerge directly from the Kondo liquid and so is not associated with local moment physics. Our results imply that the nature of the ground state is strongly coupled with the hybridization in the Kondo lattice in agreement with phase diagram proposed by Yang and Pines.Comment: 9 pages, 13 figure

Topological surface states above the Fermi level in Hf2Te2 P

We report a detailed experimental study of the band structure of the recently discovered topological material Hf2Te2P. Using the combination of scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy with surface K doping, we probe the band structure of Hf2Te2P with energy and momentum resolution above the Fermi level. Our experiments show the presence of multiple surface states with a linear Dirac-like dispersion, consistent with the predictions from previously reported band-structure calculations. In particular, scanning tunneling spectroscopy measurements provide experimental evidence for the strong topological surface state predicted at 460meV, which stems from the band inversion between Hf-d and Te-p orbitals. This band inversion comprised of more localized d states could result in a better surface-to-bulk conductance ratio relative to more traditional topological insulators

Magnetic structure and Kondo lattice behavior in CeVGe3_3: an NMR and neutron scattering study

We present nuclear magnetic resonance (NMR), neutron diffraction, magnetization, and transport measurements on a single crystal and powder of CeVGe$_3$. This material exhibits heavy fermion behavior at low temperature, accompanied by antiferromagnetic (AFM) order below 5.8 K. We find that the magnetic structure is incommensurate with AFM helical structure, characterized by a magnetic modulated propagation vector of $(0, 0, 0.49)$ with in-plane moments rotating around the $c$-axis. The NMR Knight shift and spin-lattice relaxation rate reveal a coherence temperature $T^*\sim 15$ K, and the presence of significant antiferromagnetic fluctuations reminiscent of the archetypical heavy fermion compound CeRhIn$_5$. We further identify a metamagnetic transition above $H_m\sim 2.5$ T for magnetic fields perpendicular to $c$. We speculate that the magnetic structure in this field-induced phase consists of a superposition with both ferromagnetic and antiferromagnetic components, which is consistent with the NMR spectrum in this region of the phase diagram. Our results thus indicate that CeVGe$_3$ is a hexagonal structure analog to tetragonal CeRhIn$_5$.Comment: 13 pages, 11 figure